Text Book Back Questions and Answers - Chapter 10 Types of Chemical Reactions 10th Science Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]
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Chapter 10 - Types of Chemical Reactions - 10th Science Guide Samacheer Kalvi Solutions
Question 1.
Calculate the $\mathrm{pH}$ of $0.01 \mathrm{M} \mathrm{HNO}_{3}$ ?
Solution:
$
\begin{aligned}
{\left[\mathrm{H}^{*}\right] } &=0.01 \\
\mathrm{pH} &=-\log _{10}\left[\mathrm{H}^{+}\right] \\
\mathrm{pH} &=-\log _{10}[0.01] \\
\mathrm{pH} &=-\log _{10}\left[1 \times 10^{-2}\right] \\
\mathrm{pH} &=-\left(\log _{10} 1-2 \log _{10} 10\right) \\
\mathrm{pH} &=0+2 \times \log _{10} 10 \\
\mathrm{pH} &=0+2 \times 1=2 \\
\mathrm{pH} &=2
\end{aligned}
$
Question 2.
The hydroxyl ion concentration of a solution is $1 \times 10^{-9} \mathrm{M}$. What is the $\mathrm{pOH}$ of the solution?
Solution:
$
\begin{aligned}
&\mathrm{pOH}=-\log _{10}\left[\mathrm{OH}^{-}\right] \\
&\mathrm{pOH}=-\log _{10}\left[1 \times 10^{-9}\right] \\
&\mathrm{pOH}=-\left(\log _{10} 1.0+\log _{10} 10^{-9}\right) \\
&\mathrm{pOH}=-\left(0-9 \log _{10} 10\right) \\
&\mathrm{pOH}=-(0-9) \\
&\mathrm{pOH}=9
\end{aligned}
$
Question $3 .$
A solution has a pOH of 11.76. What is the $\mathrm{pH}$ of this solution?
Solution:
$
\begin{aligned}
&\mathrm{pH}=14-\mathrm{pOH} \\
&\mathrm{pH}=14-11.76=2.24 .
\end{aligned}
$
Question $4 .$
Calculate the $\mathrm{pH}$ of $0.001$ molar solution of $\mathrm{HCl}$.
Solution:
$\mathrm{HCl}$ is a strong acid and is completely dissociated in its solutions according to the process:
$
\mathrm{HCl}_{(\mathrm{aq})} \rightarrow \mathrm{H}_{(\mathrm{aq})}^{+}+\mathrm{Cl}_{(\mathrm{aq})}^{-}
$
From this process it is clear that one mole of $\mathrm{HCl}$ would give one mole of $\mathrm{H}^{+}$ions.
Therefore, the concentration of $\mathrm{H}^{+}$ions would be equal to that of $\mathrm{HCl}_{\text {, i.e., }} 0.001$ molar or $1.0 \times 10^{-3} \mathrm{~mol}$ litre $^{-1}$.
Thus, $\left[\mathrm{H}^{+}\right]=1 \times 10^{-3} \mathrm{~mol} \mathrm{litre}^{-1}$
$
\begin{aligned}
\mathrm{pH} &=-\log _{10}\left[\mathrm{H}^{+}\right]=-\log _{10} 10^{-3} \\
&=-\left(-3 \times \log _{10}\right)=-(3 \times 1)=3
\end{aligned}
$
Thus, $\mathrm{pH}=3$
Question $5 .$
What would be the $\mathrm{pH}$ of an aqueous solution of sulphuric acid which is $5 \times 10^{-5} \mathrm{~mol} \mathrm{litre}^{-1}$ in concentration?
Solution:
Sulphuric acid dissociates in water as:
$
\mathrm{H}_{2} \mathrm{SO}_{4 \text { (aq) }} \rightarrow 2 \mathrm{H}_{\text {(aq) }}^{+}+\mathrm{SO}_{4}^{2-}(\mathrm{aq})
$
Each mole of sulphuric acid gives two moles of $\mathrm{H}^{+}$ions in the solution. One litre of $\mathrm{H}_{2} \mathrm{SO}_{4}$ solution contains $5 \times 10^{-5}$ moles of $\mathrm{H}_{2} \mathrm{SO}_{4}$ which would give $2 \times 5 \times 10^{-5}=10 \times 10^{-5}$ or $1.0 \times 10^{-4}$ moles of $\mathrm{H}^{+}$ion in one litre of the solution.
Therefore,
$
\begin{aligned}
{\left[\mathrm{H}^{+}\right] } &=1.0 \times 10^{-4} \mathrm{~mol} \operatorname{litre}^{-1} \\
\mathrm{pH} &=-\log _{10}\left[\mathrm{H}^{+}\right]=-\log _{10} 10^{-4}=-\left(-4 \times \log _{10} 10\right) \\
&=-(-4 \times 1)=4
\end{aligned}
$
Question $6 .$
Calculate the $\mathrm{pH}$ of $1 \times 10^{-4}$ molar solution of $\mathrm{NaOH}$.
Solution:
$\mathrm{NaOH}$ is a strong base and dissociates in its solution as:
$
\mathrm{NaOH}_{(\mathrm{aq})} \rightarrow \mathrm{Na}_{(\mathrm{aq)}}+\mathrm{OH}_{(\mathrm{aq})}^{-}
$
One mole of $\mathrm{NaOH}$ would give one mole of $\mathrm{OH}^{-}$ions.
Therefore,
$
\begin{aligned}
{\left[\mathrm{OH}^{-}\right] } &=1 \times 10^{-4} \mathrm{~mol} \text { litre }^{-1} \\
\mathrm{pOH} &=-\log _{10}\left[\mathrm{OH}^{-}\right]=-\log _{10} \times\left[10^{-4}\right.\\
&=-\left(-4 \times \log _{10} 10\right)=-(-4)=4 \\
\mathrm{pH}+\mathrm{pOH} &=14 \\
\mathrm{pH} &=14-\mathrm{pOH}=14-4 \\
&=10
\end{aligned}
$
Question 7.
Calculate the $\mathrm{pH}$ of a solution in which the concentration of the hydrogen ions is $1.0 \times 10^{-8} \mathrm{~mol}$ litre $^{-1}$.
Solution:
Here, although the solution is extremely dilute, the concentration given is not of an acid or a base but that of $\mathrm{H}^{+}$ions. Hence, the $\mathrm{pH}$ can be calculated from the relation:
$
\begin{aligned}
\mathrm{pH} &=-\log _{10}\left[\mathrm{H}^{+}\right] \\
{\left[\mathrm{H}^{+}\right] } &=1.0 \times 10^{-8} \mathrm{~mol} \text { litre }^{-1} \\
\mathrm{pH} &=-\log _{10} 10^{-8}=-\left(-8 \times \log _{10} 10\right) \\
&=-(-8 \times 1)=8
\end{aligned}
$
Question $8 .$
If the $\mathrm{pH}$ of a solution is $4.5$, what is its $\mathrm{pOH}$ ?
Solution:
$
\begin{aligned}
&\mathrm{pH}+\mathrm{pOH}=14 \\
&\Rightarrow \mathrm{pOH}=14-4.5=9.5 \\
&\Rightarrow \mathrm{pOH}=9.5
\end{aligned}
$
I. Choose the correct answer.
Question 1.
$\mathrm{H}_{2(\mathrm{~g})}+\mathrm{Cl}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{HCl}_{(\mathrm{g})}$ is a
(a) Decomposition Reaction
(b) Combination Reaction
(c) Single Displacement Reaction
(d) Double Displacement Reaction.
Answer:
(b) Combination Reaction
Hint: It is a combination reaction between $\mathrm{H}_{2}$ and $\mathrm{Cl}_{2}$ to form $\mathrm{HCl}$ as product.
Question $2 .$
Photolysis is a decomposition reaction caused by:
(a) heat
(b) electricity
(c) light
(d) mechanical energy
Answer:
(c) light
Question 3 .
A reaction between carbon and oxygen is represented by $\mathrm{C}_{(\mathrm{s})}+\mathrm{O}_{2(\mathrm{~g})} \rightarrow \mathrm{CO}_{2(\mathrm{~g})}+$ Heat. In which of the type(s), the above reaction can be classified?
(i) Combination Reaction
(ii) Combustion Reaction
(iii) Decomposition Reaction
(iv) Irreversible Reaction
(a) $i$ and ii
(b) $i$ and iv
(c) $i$, ii and iii
(d) $i$, ii and iv.
Answer:
(d) $i$, ii and iv.
Hint:
- It is a combination reaction with one product.
- It involves the combustion of carbon to form $\mathrm{CO}_{2}$.
- The reaction is irreversible and we cannot reverse the reaction.
Question $4 .$
The chemical equation
$\mathrm{Na}_{2} \mathrm{SO}_{4(\mathrm{aq})}+\mathrm{BaCI}_{2(\mathrm{aq})} \rightarrow \mathrm{BaSO}_{4(\mathrm{~s})} \downarrow+2 \mathrm{NaCl}_{(\mathrm{aq})}$ represents which of the following types of reaction?
(a) Neutralisation
(b) Combustion
(c) Precipitation
(d) Single displacement
Answer:
(c) Precipitation
Question $5 .$
Which of the following statements are correct about a chemical equilibrium?
(i) It is dynamic in nature
(ii) The rate of the forward and backward reactions are equal at equilibrium
(iii) Irreversible reactions do not attain chemical equilibrium
(iv) The concentration of reactants and products may be different
(a) i, ii and iii
(b) $i$, ii and iv
(c) ii, iii and iv
(d) $i$, iii and iv.
Answer:
(a) i, ii and iii
Hint: Chemical equilibrium is dynamic in nature for a reversible reaction.
At equilibrium, Rate of forwarding reaction $=$ Rate of backward reaction.
Question $6 .$
A single displacement reaction is represented by
$\mathrm{X}_{(\mathrm{s})}+2 \mathrm{HCl}_{(\mathrm{aq})} \rightarrow \mathrm{XCl}_{2(\mathrm{aq})}+\mathrm{H}_{2}(\mathrm{~g})$. Which of the following(s) could be $\mathrm{X} ?$
(i) $\mathrm{Zn}$
(ii) $\mathrm{Ag}$
(iii) $\mathrm{Cu}$
(iv) Mg. Choose the best pair.
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (iii) and (iv)
(d) (i) and (iv)
Answer:
(d) (i) and (iv)
Question $7 .$
Which of the following is not an "element + element $\rightarrow$ compound" type reaction?
(a) $\mathrm{C}_{(\mathrm{s})}+\mathrm{O}_{2(\mathrm{~g})} \rightarrow \mathrm{CO}_{2(\mathrm{~g})}$
(b) $2 \mathrm{~K}_{(\mathrm{s})}+\mathrm{Br}_{2(l)} \rightarrow 2 \mathrm{KBr}_{(\mathrm{s})}$
(c) $2 \mathrm{CO}_{(\mathrm{g})}+\mathrm{O}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{CO}_{2(\mathrm{~g})}$
(d) $4 \mathrm{Fe}_{(\mathrm{s})}+3 \mathrm{O}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{Fe}_{2} \mathrm{O}_{3(\mathrm{~s})}$
Answer:
(c) $2 \mathrm{CO}_{(\mathrm{g})}+\mathrm{O}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{CO}_{2(\mathrm{~g})}$
Hint: It involves one reactant compound i.e., carbon monoxide (CO).
$$
2 \mathrm{CO}_{(\mathrm{g})}+\mathrm{O}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{CO}_{2}
$$
Question $8 .$
Which of the following represents a precipitation reaction?
(a) $A_{(s)}+B_{(s)} \rightarrow C_{(s)}+D_{(s)}$
(b) $\mathrm{A}_{(\mathrm{s})}+\mathrm{B}_{(\mathrm{aq})} \rightarrow \mathrm{C}_{(\mathrm{aq})}+\mathrm{D}_{(1)}$
(c) $\mathrm{A}_{(\mathrm{aq})}+\mathrm{B}_{(\mathrm{aq})} \rightarrow \mathrm{C}_{(\mathrm{s})}+\mathrm{D}_{(\mathrm{aq})}$
(d) $A_{(a q)}+B_{(s)} \rightarrow C_{(a q)}+D_{(1)}$
Answer:
(c) $\mathrm{A}_{(\mathrm{aq})}+\mathrm{B}_{(\mathrm{aq})} \rightarrow \mathrm{C}_{(\mathrm{s})}+\mathrm{D}_{(\mathrm{aq})}$
Hint: It involves the formation of solid precipitation by mixing of two aqueous solutions.
Question $9 .$
The $\mathrm{pH}$ of a solution is 3 . Its $\left[\mathrm{OH}^{-}\right]$concentration is:
(a) $1 \times 10^{-3} \mathrm{M}$
(b) $3 \mathrm{M}$
(c) $1 \times 10^{-11} \mathrm{M}$
(d) $11 \mathrm{M}$
Answer:
(c) $1 \times 10^{-11} \mathrm{M}$
Question $10 .$
Powdered $\mathrm{CaCO}_{3}$ reacts more rapidly than flaky $\mathrm{CaCO}_{3}$ because of
(a) large surface area
(b) high pressure
(c) high concentration
(d) high temperature.
Answer:
(a) large surface area
Hint: We know that greater the surface area, faster will be a chemical reaction. Hence powdered $\mathrm{CaCO}_{3}$
reacts more rapidly.
II. Fill in the blanks.
Question $1 .$
A reaction between an acid and a base is called________
Answer:
Neutralization.
Question $2 .$
When lithium metal is placed in hydrochloric acid, ________gas is evolved.
Answer:
Hydrogen.
Question 3 .
The equilibrium attained during the melting of ice is known as________
Answer:
Physical equilibrium.
Question 4.
The $\mathrm{pH}$ of a fruit juice is $5.6$. If you add slaked lime to this juice, its $\mathrm{pH}$________(increase/decrease)
Answer:
Increases.
Question $5 .$
The value of the ionic product of water at $25^{\circ} \mathrm{C}$ is________
Answer:
$1 \times 10^{-14}$
Question 6.
The normal $\mathrm{pH}$ of human blood is________
Answer:
7.4.
Question $7 .$
Electrolysis is type of________ reaction.
Answer:
Decomposition reaction.
Question 8.
The number of products formed in a synthesis reaction is________
Answer:
One.
Question $9 .$
Chemical volcano is an example for________ type of reaction.
Answer:
Decomposition reaction.
Question $10 .$
The ion formed by dissolution of $\mathrm{H}^{+}$in water is called________
Answer:
Hydronium ion.
III. Match the following
Question $1 .$
Identify the types of reaction.
.png)
Answer:
$$
\mathrm{i}-\mathrm{c}, \text { ii-a, iii }-\mathrm{d}, \mathrm{iv}-\mathrm{b} \text {. }
$$
IV. True or False: (If false give the correct statement)
Question $1 .$
Silver metal can displace hydrogen gas from nitric acid.
Answer:
False.
Correct statement: In the activity series, any metals that are below hydrogen will not react with $\mathrm{HNO}_{3}$.
Question 2.
The $\mathrm{pH}$ of rainwater containing dissolved gases like $\mathrm{SO}_{3}, \mathrm{CO}_{2}, \mathrm{NO}_{2}$ will be less than 7 .
Answer:
True.
Question $3 .$
At the equilibrium of a reversible reaction, the concentration of the reactants and the products will be equal.
Answer:
False.
Correct statement: At equilibrium rate of the forward reaction is equal to the rate of backward reaction.
Question $4 .$
Periodical removal of one of the products of a reversible reaction increases the yield.
Answer:
True.
Question $5 .$
On dipping a $\mathrm{pH}$ paper in a solution, it turns into yellow. Then the solution is basic.
Answer:
True.
V. Short Answer Questions
Question $1 .$
When an aqueous solution of potassium chloride is added to an aqueous solution of silver nitrate, a white precipitate is formed. Give the chemical equation of this reaction.
Answer:
$\mathrm{KCl}_{(\mathrm{aq})}+\mathrm{AgNO}_{3(\mathrm{aq})} \rightarrow \mathrm{AgCl}_{(\mathrm{s})}+\mathrm{KNO}_{3(\mathrm{aq})}$
Formation of white precipitate by the above reaction is due to formation of silver chloride (AgC1).
Question 2 .
Why does the reaction rate of a reaction increase on raising the temperature?
Answer:
The rate of a reaction increases at higher temperature, because the heat to the reactants provide energy to breakup more bonds and speeds up the reaction.
Question $3 .$
Define a combination reaction. Give one example of an exothermic combination reaction.
Answer:
A chemical reaction in which 2 or more reactants combine to form a single product, the reaction is known as combination reaction. Most of the combination reaction are exothermic because they involve formation of new bonds. For example,
$$
\begin{aligned}
&\mathrm{H}_{2(\mathrm{~g})}+\mathrm{Cl}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{HCl}_{(\mathrm{g})} \\
&\mathrm{SiO}_{2(\mathrm{~s})}+\mathrm{CaO}_{(\mathrm{s})} \rightarrow \mathrm{CaSiO}_{3(\mathrm{~s})}
\end{aligned}
$$
Question $4 .$
Differentiate reversible and irreversible reactions.
Answer:
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VI. Answer in detail.
Question 1.
What is called thermolysis reactions?
Answer:
A chemical reaction is a process in which old bond breaks up and new chemical bond get formed.
Thermolysis chemical reactions is a special type of chemical reaction in which the reactant get decomposed by heat. For example,
$$
\begin{aligned}
&\mathrm{CaCO}_{3(\mathrm{~s})}^{\stackrel{\mathrm{Heat}}{\rightleftharpoons}} \mathrm{CaO}_{(\mathrm{s})}+\mathrm{CO}_{2(\mathrm{~g})} \\
&2 \mathrm{HgO}_{(\mathrm{s})} \stackrel{\text { Heat }}{\longrightarrow} 2 \mathrm{Hg}_{(\mathrm{l})}+\mathrm{O}_{2(\mathrm{~g})}
\end{aligned}
$$
In these reactions heat is supplied to break the bonds, so generally they are endothermic in nature.
Question $2 .$
Explain the types of double displacement reactions with examples.
Answer:
When two compounds react, if their ions are interchanged, then the reaction is called double displacement reactions. There are two types of double displacement reactions. They are
(i) Precipitation reactions: When aqueous solutions of two compounds are mixed, if they react to form an insoluble compound and a soluble compound, then it is called precipitation reaction. Because the insoluble compound, formed as one of the products, is a precipitate and hence the reaction is so called.
(ii) When aqueous solutions of potassium iodide and lead (II) nitrate are mixed, a double displacement reaction takes place between them.
(iii) Potassium and lead displace or replace one other and form a yellow precipitate of lead (II) iodide.
(iv) Neutralization reactions: When an acid reacts with the base to form a salt and water. It is called 'neutralization reaction' as both acid and base neutralize each other.
(v) Reaction of sodium hydroxide with hydrochloric acid is a typical neutralization reaction. Here, sodium replaces hydrogen from hydrochloric acid forming sodium chloride, a neutral soluble salt.
$$
\mathrm{NaOH}_{(\mathrm{aq})}+\mathrm{HCl}_{(\mathrm{aq})} \rightarrow \mathrm{NaCl}_{(\mathrm{aq})}+\mathrm{H}_{2} \mathrm{O}_{(1)}
$$
Question $3 .$
Explain the factors influencing the rate of a reaction.
Answer:
The factors influencing the rate of a reaction are,
(i) Nature of the reactants: The reaction of sodium with hydrochloric acid is faster than that with acetic acid. Do you know why? Hydrochloric acid is a stronger acid than acetic acid and thus more reactive. So, the nature of the reactants influences the reaction rate.
$$
\begin{gathered}
2 \mathrm{Na}_{(\mathrm{s})}+2 \mathrm{HCl}_{(\mathrm{aq})} \rightarrow 2 \mathrm{NaCl}_{(\mathrm{aq})}+\mathrm{H}_{2(\mathrm{~g})}(\text { fast }) \\
2 \mathrm{Na}_{(\mathrm{s})}+2 \mathrm{CH}_{3} \mathrm{COOH}_{(a q)} \rightarrow 2 \mathrm{CH}_{3} \mathrm{COONa}_{(\mathrm{aq})}+\mathrm{H}_{2(\mathrm{~g})}(\text { slow })
\end{gathered}
$$
(ii) The concentration of the reactants: Changing the number of reactants also increases the reaction rate. The amount of the substance present in a certain volume of the solution is called 'concentration'. More the concentration, more particles per volume exist in it and hence faster the reaction. Granulated zinc reacts faster with $2 \mathrm{M}$ hydrochloric acid than $1 \mathrm{M}$ hydrochloric acid.
(iii) Temperature: Most of the reactions go faster at a higher temperature. Because adding heat to the reactants provides energy to break more bonds and thus speed up the reaction. Calcium carbonate reacts slowly with hydrochloric acid at room temperature. When the reaction mixture is heated the reaction rate increases.
(iv) Pressure: If the reactants are gases, increasing their pressure increases the reaction rate. This is because on increasing the pressure the reacting particles come closer and collide frequently.
(v) Catalyst: A catalyst is a substance which increases the reaction rate without being consumed in the reaction. In certain reactions, adding a substance as catalyst speeds up the reaction. For example, on heating potassium chlorate, it decomposes into potassium chloride and oxygen gas, but at a slower rate. If manganese dioxide is added, it increases the reaction rate.
(vi) The surface area of the reactants: When solid reactants are involved in a reaction, their powdered form reacts more readily. For example, powdered calcium carbonate reacts more readily with hydrochloric acid than marble chips. Because powdering of the reactants increases the surface area and more energy is available on the collision of the reactant particles. Thus, the reaction rate is increased. You will study more about reaction rate in your higher classes.
Question $4 .$
How does pH play an important role in everyday life?
Answer:
Our body works within the pH range of $7.0$ to $7.8$. Living organisms can survive only in a narrow range of $\mathrm{pH}$ change. Different body fluids have different $\mathrm{pH}$ values.
Eg: pH of blood is ranging from $7.35$ to $7.45$. Any increase or decrease in this value leads to diseases. The ideal $\mathrm{pH}$ for blood is $7.4$.
$\mathrm{pH}$ in our digestive system : It is very interesting to note that our stomach produces hydrochloric acid. It helps in the digestion of food without harming the stomach. During indigestion the stomach produces too much acid and this causes pain and irritation. pH of the stomach fluid is approximately $2.0$.
$\mathrm{pH}$ changes as the cause of tooth decay : $\mathrm{pH}$ of the saliva normally ranges between $6.5$ to $7.5$. White enamel coating of our teeth is calcium phosphate, the hardest substance in our body. When the pH of the mouth saliva falls below $5.5$, the enamel gets weathered. Toothpastes, which are generally basic ate used for cleaning the teeth that can neutralise the excess acid and prevent tooth decay.
$\mathrm{pH}$ of soil : In agriculture, the $\mathrm{pH}$ of the soil is very important. Citrus fruits require slightly alkaline soil, while rice requires acidic soil and sugarcane requires neutral soil.
$\mathrm{pH}$ of rain water : The $\mathrm{pH}$ of rain water is approximately 7, which means that it is neutral and also represents its high purity. If the atmospheric air is polluted with oxide gases of sulphur and nitrogen, they get dissolved in the rain water and make its pH less than 7 . Thus, if the $\mathrm{pH}$ of rain water is less than 7 , then it is called acid rain. When acid rain flows into the rivers it lowers the $\mathrm{pH}$ of the river water also. The survival of aquatic life in such rivers becomes difficult.
Question $5 .$
What is chemical equilibrium? What are its characteristics?
Answer:
Chemical equilibrium is the state for a reversible chemical reaction where the rate of forwarding direction is equally balanced by the rate of backward direction and the process seems like to be stopped.
Its characteristics are,
- The rate of the forward and backward reaction are equal in chemical equilibrium.
- The observable properties such as pressure, concentration, colour, density, viscosity, etc. of the system unchanged with time.
- In physical equilibrium, the volume of all phases remains constant.
VII. HOT Questions
Question $1 .$
A solid compound ' $A$ ' decomposes on heating into ' $B$ ' and a gas ' $C$ ' On passing the gas ' $C$ ' through water. It becomes acidic. Identify $\mathrm{A}, \mathrm{B}$ and $\mathrm{C}$.
$\mathrm{CaCO}_{3(\mathrm{~s})} \longrightarrow \mathrm{CaO}_{(\mathrm{s})}+\mathrm{CO}_{2(\mathrm{~g})}$
Calcium carbonate decomposes into solid Calcium oxide and a gas $\mathrm{CO}_{2}$. This $\mathrm{CO}_{2}$ dissolves in water and forms carbonic acid.
$\mathrm{H}_{2} \mathrm{O}+\mathrm{CO}_{2} \longrightarrow \mathrm{H}_{2} \mathrm{CO}_{3}$ (Carbonic acid).
Question $2 .$
Can a nickel spatula be used to stir copper sulphate solution? Justify your answer.
Answer:
No, a nickel spatula cannot be used to $\operatorname{stir} \mathrm{CuSO}_{4}$ solution, because Nickel will displace copper from $\mathrm{CuSO}_{3}$ solution and $\mathrm{Cu}$ gets deposited on the $\mathrm{Ni}$ spatula.
VIII. Solve the following problems.
Question $1 .$
Lemon juice has a $\mathrm{pH}=2$, what is the concentration of $\mathrm{H}^{+}$ions?
Solution:
$$
\begin{aligned}
&{\left[\mathrm{H}^{+}\right]=10^{-\mathrm{pH}}} \\
&{\left[\mathrm{H}^{+}\right]=10^{-2}} \\
&{\left[\mathrm{H}^{+}\right]=1 \times 10^{-2} \mathrm{M}}
\end{aligned}
$$
Question $2 .$
Calculate the $\mathrm{pH}$ of $1.0 \times 10^{-4}$ molar solution of $\mathrm{HNO}_{3}$ ?
Solution:
$$
\begin{aligned}
&\mathrm{HNO}_{3} \longrightarrow \mathrm{H}^{+}+\mathrm{NO}_{3}^{-} \\
&1 \times 10^{-4} \text { molar } 1 \times 10^{-4} \text { molar } \\
&\mathrm{pH}=-\log [\mathrm{H}+]=-\log \left[1 \times 10^{-4}\right] \\
&\mathrm{pH}=4
\end{aligned}
$$
Question 3.
What is the $\mathrm{pH}$ of $1.0 \times 10^{-5}$ molar solution of $\mathrm{KOH}$ ?
Solution:
$\mathrm{KOH} \longrightarrow \mathrm{K}^{+}+\mathrm{OH}^{-}$
$1 \times 10^{-5} \mathrm{molar} \quad 1 \times 10^{-5} \mathrm{~mol}$
$\left[\mathrm{OH}^{-}\right]=1 \times 10^{-5} \Rightarrow\left[\mathrm{H}^{+}\right]=10^{-9}$
$\mathrm{pH}=-\log \left[\mathrm{H}^{+}\right]=-\log \left[10^{-9}\right]=9$
Question $4 .$
The hydroxide ion concentration of a solution is $1 \times 10^{-11}$. What is the $\mathrm{pH}$ of the solution?
Solution:
$$
\begin{aligned}
{\left[\mathrm{H}^{+}\right]\left[\mathrm{OH}^{-}\right] } &=10^{-14} \\
{\left[\mathrm{H}^{+}\right] \times 1 \times 10^{-11} } &=10^{-14} \\
{\left[\mathrm{H}^{+}\right] } &=10^{-3} \\
\mathrm{pH} &=-\log \left[\mathrm{H}^{+}\right]=-\log \left[10^{-3}\right]=3
\end{aligned}
$$
I. Choose the best answer.
Question $1 .$
Methane + Oxygen $\rightarrow \mathrm{A}+$ Water. Identify $\mathrm{A}$
(a) Carbon monoxide
(b) Carbon dioxide
(c) ethane
(d) LPG.
Answer:
(i) Carbon dioxide
Question $2 .$
The chemical reaction in which electricity is used to bring about the change is:
(a) Thermal decomposition
(b) Photo decomposition
(c) Single displacement reaction
(d) Electrolytic decomposition
Answer:
(d) Electrolytic decomposition
Question $3 .$
Decomposition of the molecule occurs on passing an electric current through its aqueous solution. This process is termed as
(a) Thermolysis
(b) Photolysis
(c) Electrolysis
(d) None of these.
Answer:
(c) Electrolysis
Question $4 .$
The most reactive element in the activity series is:
(a) platinum
(b) potassium
(c) sodium
(d) gold
Answer:
(b) potassium
Question 5.
Which one of the following is a more reactive element?
(a) $\mathrm{Cu}$
(b) $\mathrm{Li}$
(c) $\mathrm{Zn}$
(d) $\mathrm{Pb}$.
Answer:
(b) $\mathrm{Li}$
Question 6.
Which one of the following is the least reactive element?
(a) $\mathrm{Au}$
(b) $\mathrm{Fe}$
(c) $\mathrm{Ca}$
(d) Na.
Answer:
(a) $\mathrm{Au}$
Question 7.
Double displacement reaction is also called as
(a) Metastasis
(b) Metathesis
(c) Methanolysis
(d) Metalysis.
Answer:
(b) Metathesis
Question $8 .$
The acidic solution among the following is:
(a) seawater
(b) coffee
(c) lime water
(d) antacid
Answer:
(b) coffee
Question 9.
The reaction of sodium hydroxide with hydrochloric acid is an example for
(a) Combination reaction
(b) Thermolysis reaction
(c) Neutralization reaction
(d) Precipitation reaction.
Answer:
(c) Neutralization reaction
Question 10 .
In agriculture, the nature of the soil for rice is:
(a) alkaline
(b) neutral
(c) acidic
(d) none of the above
Answer:
(c) acidic
Question 11 .
The role of manganese dioxide in the decomposition of potassium chlorate is
(a) act as a reactant
(b) act as a catalyst
(c) act as a reagent
(d) act as a reaction medium.
Answer:
(b) act as a catalyst
Question $12 .$
The ionic product of water $K_{W}$ is
(a) $\mathrm{K}_{\mathrm{W}}=\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]\left[\mathrm{OH}^{+}\right]$
(b) $\mathrm{K}_{\mathrm{W}}=\frac{\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]}{\left[\mathrm{OH}^{-}\right]}$
(c) $\mathrm{K}_{\mathrm{W}}=\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]\left[\mathrm{OH}^{-}\right]$
(d) $\mathrm{K}_{\mathrm{W}}=\left[\mathrm{H}_{3} \mathrm{O}^{-}\right]\left[\mathrm{OH}^{+}\right]$
Answer:
(c) $\mathrm{K}_{\mathrm{W}}=\left[\mathrm{H}_{3} \mathrm{O}^{+}\right]\left[\mathrm{OH}^{-}\right]$
Question $13 .$
Unit of ionic product of water is
(a) $\mathrm{mol}^{-2} \mathrm{dm}^{-6}$
(b) $\mathrm{mol}^{2} \mathrm{dm}^{-6}$
(c) $\mathrm{mol}^{2} \mathrm{dm}^{6}$
(d) mol $\mathrm{dm}^{-3}$.
Answer:
(b) $\mathrm{mol}^{2} \mathrm{dm}^{-6}$
Question $14 .$
What is the value of ionic product of water?
(a) $1 \times 10^{-4}$
(b) $1 \times 10^{-1}$
(c) $1 \times 10^{14}$
(d) $1 \times 10^{-14}$.
Answer:
(d) $1 \times 10^{-14}$,
Question $15 .$
$\mathrm{pH}$ of milk of magnesia is
(a) 10
(b) 15
(c) 14
(d) $10.5$.
Answer:
(a) 10
Question $16 .$
What is the relationship between $\mathrm{pH}$ and $\mathrm{pOH}$ ?
(a) $\mathrm{pH}-\mathrm{pOH}=14$
(b) $\mathrm{pH}+\mathrm{pOH}=14$
(c) $\mathrm{pH} / \mathrm{pOH}=14$
(d) $\mathrm{pH}+\mathrm{pOH}=1.4$.
Answer:
(b) $\mathrm{pH}+\mathrm{pOH}=14$
Question $17 .$
$\mathrm{Zn}+2 \mathrm{HCl} \rightarrow \mathrm{ZnCl}_{2}+\mathrm{H}_{2} \uparrow$
The above reaction is an example of
(a) Combination reaction
(b) Double displacement reaction
(c) Displacement reaction
(d) Decomposition reaction.
Answer:
(c) Displacement reaction
Question $18 .$
A student tests the $\mathrm{pH}$ of pure water using a $\mathrm{pH}$ paper. It shows a green colour. If a pH paper is after adding lemon juice to water, what colour will he observe?
(a) Green
(b) Red
(c) Yellow
(d) Pink.
Answer:
(b) Red
Question $19 .$
When aqueous solution of silver nitrate and sodium chloride are mixed,________ precipitate is immediately formed.
(a) white
(b) yellow
(c) red
(d) black.
Answer:
(a) white
Question $20 .$
$\mathrm{pH}=-\log _{10}\left[\mathrm{H}^{+}\right]$. The $\mathrm{pH}$ of a solution containing hydrogen ion concentration of $0.001 \mathrm{M}$ solution is
(a) 3
(b) 11
(c) 14
(d) 15 .
Answer:
(a) 3
Question 21.
Silver anklet has got tarnished due to the formation of
(a) $\mathrm{Ag}_{2} \mathrm{O}$
(b) $\mathrm{AgNO}_{3}$
(c) $\mathrm{Ag}_{2} \mathrm{~S}$
(d) $\mathrm{AgBr}$.
Answer:
(c) $\mathrm{Ag}_{2} \mathrm{~S}$
Question $22 .$
The colour of the precipitate formed by the reaction of lead nitrate with potassium iodide is
(a) white
(b) yellow
(c) black
(d) red.
Answer:
(b) yellow
Question 23 .
The reaction of calcium oxide with water is a ________reaction.
(a) exothermic
(b) endothermic
(c) isothermic
(d) adiabatic.
Answer:
(a) exothermic
Question 24 .
The gas released when calcium carbonate reacts with dilute hydrochloric acid is
(a) $\mathrm{NO}_{2}$
(b) $\mathrm{CO}$
(c) $\mathrm{CO}_{2}$
(d) $\mathrm{H}_{2}$.
Answer:
(c) $\mathrm{CO}_{2}$
Question $25 .$
The chemical used in whitewashing on the walls is
(a) $\mathrm{CaO}$
(b) $\mathrm{CaCl}_{2}$
(c) $\mathrm{CaOCl}_{2}$
(d) $\mathrm{Ca}(\mathrm{OH})_{2}$
Answer:
(d) $\mathrm{Ca}(\mathrm{OH})_{2}$.
Question $26 .$
The chemical formula of marble is
(a) $\mathrm{CaCO}_{3}$
(b) $\mathrm{CaOCl}_{2}$
(c) $\mathrm{CaSO}_{4} \cdot \frac{1}{2} \mathrm{H}_{2} \mathrm{O}$
(d) $\mathrm{Ca}(\mathrm{OH})_{2}$.
Answer:
(a) $\mathrm{CaCO}_{3}$
Question $27 .$
Combustion of coal is an example of _______reaction.
(a) displacement
(b) reduction
(c) decomposition
(d) combination.
Answer:
(d) combination.
Question $28 .$
The colour change takes place when copper carbonate is strongly heated is_______
(a) green to black
(b) green to blue
(c) blue to green
(d) blue to black.
Answer:
(a) green to black
Question $29 .$
The reaction of heat on copper carbonate into copper (II) oxide is_______ reaction.
(a) combination
(b) decomposition
(c) displacement
(d) redox.
Answer:
(b) decomposition
Question $30 .$
The dissolution of glucose in water is a _______reaction.
(a) exothermic
(b) endothermic
(c) neutralisation
(d) combination.
Answer:
(b) endothermic
Question 31.
All combustion reactions are _______reactions.
(a) combination
(b) exothermic
(c) endothermic
(d) neutralisation.
Answer:
(b) exothermic
Question 32 .
The factor that affects the rate of the chemical reaction is_______
(a) temperature
(b) concentration
(c) catalyst
(d) all the above.
Answer:
(d) all the above.
Question 33 .
Magnesium ribbon reacts at a very faster rate with_______ acid.
(a) hydrochloric
(b) acetic
(c) formic
(d) oxalic.
Answer:
(a) hydrochloric
Question 34 .
Our body metabolism is carried out by means of _______secreted in our stomach.
(a) sulphuric acid
(b) hydrochloric acid
(c) nitric acid
(d) acetic acid.
Answer:
(b) hydrochloric acid
Question 35 .
Which metals do not liberate gas on reaction with acids?
(a) $\mathrm{Zn}, \mathrm{Mg}$
(b) $\mathrm{Ag}, \mathrm{Cu}$
(c) $\mathrm{Na}, \mathrm{K}$
(d) $\mathrm{Cr}, \mathrm{Al}$.
Answer:
(b) $\mathrm{Ag}, \mathrm{Cu}$
Question $36 .$
When $\mathrm{CO}_{2}$ is passed through lime water, it turns
(a) millcy
(b) black
(c) red
(d) blue.
Answer:
(a) milky
Question 37 .
The physical form of calcium carbonate is_______
(a) limestone
(b) chalk
(c) marble
(d) all the above.
Answer:
(d) all the above.
Question 38 .
The colour change takes place when copper (II) oxide reacts with dilute hydrochloric acid is_______
(a) blue to green
(b) black to green
(c) green to black
(d) green to blue.
Answer:
(b) black to green
Question $39 .$
Which of the following is a strong base?
(a) $\mathrm{NH}_{4} \mathrm{OH}$
(b) $\mathrm{Ca}(\mathrm{OH})_{2}$
(c) $\mathrm{Al}(\mathrm{OH})_{3}$
(d) $\mathrm{NaOH}$.
Answer:
(d) $\mathrm{NaOH}$.
Question $40 .$
Zinc reacts with sodium hydroxide to form_______
(a) Zinc hydroxide $+\mathrm{H}_{2} \mathrm{O}$
(b) Sodium zincate $+\mathrm{H}_{2}$
(c) Zinc oxide $+\mathrm{H}_{2}$
(d) Zinc oxide $+\mathrm{H}_{2} \mathrm{O}$.
Answer:
(b) Sodium zincate $+\mathrm{H}_{2}$
Question $41 .$
_______reacts with sodium hydroxide.
(a) $\mathrm{Cu}$
(b) Ag
(c) $\mathrm{Cr}$
(d) $Z n$.
Answer:
(d) $\mathrm{Zn}$.
Question $42 .$
_______is used as a medicine for stomach disorder.
(a) Sodium hydroxide
(b) Ammonium hydroxide
(c) Magnesium hydroxide
(d) Calcium hydroxide.
Answer:
(c) Magnesium hydroxide
Question 43 .
The $\mathrm{pH}$ of stomach fluid is_______
(a) 12
(b) 14
(c) 2
(d) 1 .
Answer:
(c) 2
Question $42 .$
The hardest substance in the human body is_______
(a) bone
(b) the enamel coating of teeth
(c) brain
(d) liver.
Answer:
(b) the enamel coating of teeth
Question $43 .$
Sugarcane requires _______soil.
(a) acidic
(b) alkaline
(c) neutral
(d) amphoteric.
Answer:
(c) neutral
Question $44 .$
Rice requires _______soil.
(a) acidic
(b) basic
(c) alkaline
(d) neutral.
Answer:
(a) acidic
Question $45 .$
_______is a double salt.
(a) Sodium chloride
(b) Washing soda
(c) Potash alum
(d) Bleaching powder.
Answer:
(c) Potash alum
II. Fill in the blanks.
Question $1 .$
During chemical changes_______ are formed and these changes are more_______ than physical changes.
Answer:
New products, permanent.
Question $2 .$
Calcium oxide reacts with water to produce_______ and the reaction is_______
Answer:
Slaked lime, exothermic.
Question $3 .$
During whitewashing,_______ reacts slowly with carbon dioxide in the air to form a thin layer of_______ on the walls.
Answer:
Calcium hydroxide, calcium carbonate.
Question $4 .$
When copper carbonate is heated, the products formed are_______,_______ and change of colour from _______to_______ is observed.
Answer:
$\mathrm{CuO}, \mathrm{CO}_{2}$, green, black
Question $5 .$
When lead nitrate is heated, the gas liberated is_______ and its colour is_______
Answer:
$\mathrm{NO}_{2}$, Reddish - brown
Question $6 .$
Copper sulphate solution changes its blue colour into_______ colour when an iron nail is added to it and it acquires _______colour.
Answer:
Green, brownish.
Question $7 .$
When Barium chloride reacts with sodium sulphate, the product formed is_______ and it is a_______ precipitate.
Answer:
Barium sulphate, white.
Question $8 .$
Powdered _______ reacts more quickly with hydrochloric acid than marble chips.
Answer:
$\mathrm{CaCO}_{3}$
Question $9 .$
Calcium carbonate present in the marble reacts with hydrochloric acid at a faster rate at _______ temperature.
Answer:
Higher.
Question $10 .$
_______is a substance which furnishes $\mathrm{H}^{+}$ions when dissolved in water and a_______ is a substance which furnishes $\mathrm{OH}^{-}$ions in water.
Answer:
Acid, Base.
Question $11 .$
Acids present in plants and animals are_______ and the acids in rocks and minerals are_______
Answer:
Organic acid, inorganic acid.
Question $12 .$
Metal displaces_______ gas from dilute acid and the flame goes off with a _______sound.
Answer:
Hydrogen, popping.
Question $13 .$
_______is used in the manufacturing of soap and_______ is used in whitewashing buildings.
Answer:
Sodium hydroxide, calcium hydroxide.
Question 14.
pH scale was introduced by _______and the $\mathrm{pH}$ of the solution is 7 , it is a _______solution.
Answer:
S.P.L. Sorenson, neutral.
Question $15 .$
The $\mathrm{pH}$ of a normal healthy human skin is_______and the $\mathrm{pH}$ of the stomach fluid is_______
Answer:
$7.4,5.5$.
Question $16 .$
The ideal $\mathrm{pH}$ for blood is_______ and $\mathrm{pH}$ of the mouth falls below_______.
Answer:
$7.35-7.45$, Sulphuric acid.
Question 17.
All photo decomposition reaction are _______reactions.
Answer:
Endothermic.
Question $18 .$
Precipitation reactions give a_______ as the product.
Answer:
Insoluble salt.
Question $19 .$
Plants cannot grow in a_______ soil.
Answer:
Acidic.
Question 20 .
Equilibrium is possible in a_______system.
Answer:
Closed.
Question $21 .$
Pure water is a_______electrolyte.
Answer:
Weak.
Question $22 .$
Most of the combination reactions are_______ in nature.
Answer:
Exothermic.
Question $23 .$
Silicon dioxide reacts with calcium oxide to form_______
Answer:
Calcium silicate.
Question $24 .$
Our mobile phones get energy from its _______battery by chemical reaction.
Answer:
Lithium.
Question $25 .$
A _______ is a substance which increases the reaction rate.
Answer:
Catalyst.
Question $26 .$
$\mathrm{pH}$ range of human saliva is_______
Answer:
$6-8 .$
Question $27 .$
pH range of fresh milk is_______
Answer:
$5 .$
Question $28 .$
The $\mathrm{pH}$ of a solution can be determined by using a_______ indicator.
Answer:
Universal.
Question $29 .$
$\mathrm{pH}$ is_______
Answer:
$-\log _{10}\left[\mathrm{H}^{+}\right]$
Question 30 .
The white enamel coating of our teeth is_______
Answer:
Calcium phosphate.
III. Match the following.
Question $1 .$
.png)
Answer:
$i-b$, ii $-a$, iii $-d, i v-c$.
Question $2 .$
.png)
Answer:
$$
i-c, \text { ii }-d, \text { iii }-b, i v-a \text {. }
$$
Question $3 .$
.png)
.png)
Answer:
$$
i-b, i i-a, i i i-d, i v-c \text {. }
$$
Question $4 .$
.png)
Answer:
$$
i-c, \text { ii }-d, \text { iii }-a, i v-b .
$$
Question $5 .$
.png)
Answer:
$$
i-c, i i-d, \text { iii }-b, i v-a \text {. }
$$
Question $6 .$
.png)
Answer:
$i-d$, ii-a, iii $-b$, iv $-e .$
IV. State true or false. If false, give the correct statement.
Question $1 .$
Chemical changes are reversible changes.
Answer:
False.
Correct statement: Chemical changes are irreversible changes.
Question $2 .$
The silver anklet has got tarnished when exposed to air due to the formation of silver oxide. ( $\operatorname{Ag}_{2} \mathrm{O}$ ).
Answer:
False.
Correct statement: The silver anklet has got tarnished when exposed to air due to the formation of silver sulphide $\left(\mathrm{Ag}_{2} \mathrm{~S}\right)$
Question $3 .$
Brisk effervescence takes place with the evolution of $\mathrm{CO}_{2}$ when calcium carbonate reacts with dilute hydrochloric acid.
Answer:
True.
Question $4 .$
The chemical formula for marble is $\mathrm{CaCl}_{2}$.
Answer:
False.
Correct statement: The chemical formula for marble is $\mathrm{CaCO}_{3}$
Question $5 .$
A reaction in which a single product is formed from two or more reactants is known as displacement reaction.
Answer:
False.
Correct statement: A reaction in which a single product is formed from two or more reactants is known as a combination reaction.
Question $6 .$
Lead Nitrate on heating decomposes to give lead oxide with the evolution of reddish-brown gas $\mathrm{NO}_{2}$ and $\mathrm{O}_{2}$ gas.
Answer:
True.
Question $7 .$
Any reaction that produces a precipitate is called a redox reaction.
Answer:
False.
Correct statement: Any reaction that produces a precipitate is called a precipitation reaction.
Question $8 .$
The reaction in which a more reactive element displaces a less reactive element from its compound is called displacement reaction.
Answer:
True.
Question $9 .$
The chemical reactions which take place with the evolution of heat energy are called endothermic reaction.
Answer:
False.
Correct statement: The chemical reactions which take place with the evolution of heat energy are called exothermic reaction.
Question $10 .$
All combustion reactions are endothermic reactions.
Answer:
False.
Correct statement: All combustion reactions are exothermic reactions.
Question $11 .$
Our body metabolism is carried out by means of sulphuric acid secreted in our stomach.
Answer:
False.
Correct statement: Our body metabolism is carried out by means of hydrochloric acid secreted in our stomach.
Question $12 .$
Limestone, chalk and marble are different physical forms of calcium oxide.
Answer:
False.
Correct statement: Limestone, chalk and marble are different physical forms of calcium carbonate.
Question $13 .$
The atmosphere of earth is made up of thick white and yellowish clouds of sulphuric acid.
Answer:
False.
Correct statement: The atmosphere of Venus is made up of thick white and yellowish clouds of sulphuric acid.
Question $14 .$
Bond breaking releaser energy whereas bond formation absorbs energy.
Answer:
False.
Correct statement: Bond breaking absorbs energy whereas bond formation releases energy.
Question $15 .$
More active elements readily displace less active elements from their aqueous solution.
Answer:
True.
Question $16 .$
The irreversible reaction is relatively slow.
Answer:
False.
Correct statement: Irreversible reaction is fast.
V. Assertion and Reason
Question 1.
Assertion (A): The lustrous white colour of the silver anklet slowly changes into slightly back colour. Reason (R): silver anklet reacts with $\mathrm{H}_{2} \mathrm{~S}$ in the air to form $\mathrm{Ag}_{2} \mathrm{~S}$ (Silver Sulphide) which is black in colour.
(a) Both (A) and (R) are correct
(b) $(A)$ is correct but (R) is wrong
(c) Both (A) and (R) are wrong
(d) (A) is wrong but (R) is correct.
Answer:
(a) Both (A) and (R) are correct
Question 2.
Assertion (A): The reaction of calcium oxide with water is an exothermic reaction.
Reason (R): The reaction is accompanied by a hissing sound and formation of bubbles leading to the absorption of a considerable amount of heat.
(a) Both $(A)$ and $(R)$ are wrong
(b) Both $(A)$ and (R) are correct
(c) $(A)$ is correct but (R) is wrong
(d) $(A)$ is wrong but (R) is correct.
Answer:
(c) (A) is correct but (R) is wrong
Question 3.
Assertion (A): During the reaction of calcium carbonate with dilute hydrochloric acid, brisk effervescence takes place.
Reason (R): Brisk effervescence is due to the evolution of carbon dioxide gas.
(a) $B$ oth $(A)$ and $(R)$ are wrong
(b) Both (A) and (R) are correct
(c) (A) is correct but (R) is wrong
(d) $(A)$ is wrong but (R) is correct.
Answer:
(b) Both (A) and (R) are correct
Question $4 .$
Assertion: When copper carbonate is heated strongly, the green colour is changed into a black colour.
Reason $(R)$ : The colour change is due to the decomposition of copper carbonate into copper oxide.
(a) Both (A) and (R) are correct
(b) Both (A) and (R) are wrong
(c) $(A)$ is correct but $(R)$ is wrong
(d) $(A)$ is wrong but (R) is correct.
Answer:
(a) Both (A) and (R) are correct
Question 5 .
Assertion (A): when lead nitrate is heated, the gas released has red - orange colour and it is lead oxide. Reason (R): Lead nitrate on heating undergoes combination reaction.
(a) Both (A) and (R) are correct
(b) Both $(A)$ and (R) are wrong
(c) (A) is correct but (R) is wrong
(d) $(A)$ is wrong but (R) is correct.
Answer:
(b) Both (A) and (R) are wrong
Question 6.
Assertion (A): iron js more reactive than copper.
Reason (R): iron js displaced from iron sulphate by copper.
(a) Both (A) and (R) are correct
(b) (A) is correct but (R) is wrong
(c) (A) is wrong but (R) is correct
(d) Both $(A)$ and (R) are wrong.
Answer:
(b) (A) is correct but (R) is wrong
Question 7.
Assertion (A): Copper displaces zinc (or) lead from the salt solution.
Reason (R): Copper is more reactive than zinc and lead.
(a) Both $(A)$ and (R) are correct
(b) (A) is correct but (R) is wrong
(c) (A) is wrong but (R) is correct
(d) Both (A) and (R) are wrong.
Answer:
(d) Both (A) and (R) are wrong.
Question 8.
Assertion (A): All combustion reactions are exothermic reactions.
Reason (R): During combustion reaction, heat energy is liberated.
(a) Both $(A)$ and (R) are correct
(b) (A) is correct but (R) is wrong
(c) $(A)$ is wrong but $(R)$ is correct
(d) Both (A) and (R) are wrong.
Answer:
(a) Both (A) and (R) are correct
Question $9 .$
Assertion (A): when glucose is kept on our tongue, a cooling effect is felt.
Reason (R): It is an endothermic reaction in which heat is absorbed.
(a) $B$ oth $(A)$ and $(R)$ are correct
(b) Both $(A)$ and (R) are wrong
(c) (A) is correct but (R) is wrong
(d) $(A)$ is wrong but (R) is correct.
Answer:
(a) $\operatorname{Both}(A)$ and $(R)$ are correct
Question $10 .$
Assertion (A): Powdered calcium carbonate reacts more quickly with hydrochloric acid than marble chips. Reason (R): Powdered calcium carbonate offers a large surface area than marble chips. Because the greater the surface area, the greater is the rate of the reaction.
(a) $B$ oth $(A)$ and $(R)$ are wrong
(b) Both (A) and (R) are correct
(c) (A) is correct but (R) is wrong
(d) $(A)$ is wrong but (R) is correct.
Answer:
(b) Both $(A)$ and (R) are correct
Question $11 .$
Assertion (A): Combination reaction is exothermic in nature.
Reason (R): During the formation of new bonds, releases a huge amount of energy in the form of heat.
(a) $(A)$ is correct and (R) explains (A)
(b) $(A)$ is correct but $(R)$ does not explain $(A)$
(c) (A) is correct but (R) is wrong
(d) $(A)$ is wrong but (R) is correct.
Answer:
(a) (A) is correct and (R) explains (A)
Question $12 .$
Assertion (A): When glucose is kept on our tongue, a cooling effect is felt.
Reason (R): It is an endothermic reaction in which heat is absorbed.
(a) (A) is correct and (R) explains (A)
(b) $(A)$ is correct but $(R)$ does not explain $(A)$
(c) (A) is correct but (R) is wrong
(d) $(A)$ is wrong but (R) is correct.
Answer:
(a) (A) is correct and (R) explains (A)
VI. Short Answer Questions.
Question 1.
What type of chemical reaction takes place when
(i) limestone is heated
(ii) a magnesium ribbon is burnt in air?
Answer:
(i) When limestone is heated, the reaction takes place is a decomposition reaction.
.png)
(ii) When a magnesium ribbon is burnt in air, it is an oxidation reaction.
.png)
Question 2 .
What is a combustion reaction?
Answer:
A combustion reaction is one in which the reactant rapidly combines with oxygen to form one or more oxides and energy (heat). So in combustion reactions, one of the reactants must be oxygen.
Question $3 .$
Which of the following is a combustion?
1. Digestion of food
2. Rusting of iron.
Answer:
1. Digestion of food : Not a combustion reaction, because it is a endothermic process and where energy is utilized.
2. Rusting of iron: Combustion reaction.
Question $4 .$
When the lead powder is added to copper chloride solution, a displacement reaction occurs and solid copper is formed.
(i) Write the equation for the reaction.
(ii) Why does the displacement reaction occur?
Answer:
.png)
(ii) Copper is less reactive than lead. So lead has displaced copper from copper chloride. It is a displacement reaction.
Question $5 .$
What happens when lead nitrate reacts with potassium iodide solution?
Answer:
Lead nitrate solution when reacts with a potassium iodide solution, a deep yellow precipitate of $\mathrm{Pbl}_{2}$ is formed.
.png)
Question $6 .$
Differentiate Exothermic reaction and Endothermic reaction.
Answer:
.png)
Question $7 .$
Why the study of reaction rate is important?
Answer:
Faster the reaction, more will be the amount of the product in a specified time. So, the rate of a reaction is important for a chemist for designing a process to get a good yield of a product. Rate of reaction is also important for a food processor who hopes to slow down the reactions that cause food to spoil.
Question $8 .$
What is meant by decomposition reaction? Give an example.
Answer:
A single compound breaks down to produce two or more substances. Such type of reaction is called decomposition reaction.
.png)
Question $9 .$
Give reason.
(a) Granulated Zinc reacts faster with $2 \mathrm{M} \mathrm{HCl}$ than $1 \mathrm{M} \mathrm{HCl}$.
Answer:
Reason: As the concentration of the reactant increases the rate of the reaction increases.
(b) Food kept at room temperature spoils faster than that kept in the refrigerator.
Answer:
Reason: In the refrigerator the temperature is lower than room temperature, so the reaction rate is less.
Question $10 .$
What is meant by double displacement reaction? Give an example.
Answer:
A double decomposition reaction is a reaction in which the exchange of ions between two reactants occur leading to the formation of two different products.
.png)
Question $11 .$
Why the toothpastes are generally basic in nature?
Answer:
The $\mathrm{pH}$ of the saliva is usually between $6.5$ to $7.5$, when the $\mathrm{pH}$ of the mouth saliva falls below $5.5$ the enamel coating of our teeth calcium phosphate gets weathered. That is why the tooth pastes are generally basic in nature.
Question 12 .
What happens to food containing fat and oil kept open for a long time?
Answer:
When food containing fat and oil is left as such for a long time, it becomes stale. The stale food develops bad taste and foul smell. This is very common in curd and cheese, particularly in summer. Oils and fats are slowly oxidised to certain foul - smelling compounds.
Question $13 .$
Define the rate of a chemical reaction.
Answer:
The rate of a chemical reaction is defined as the change in concentration of any one of the reactants or product per unit time.
Rate $=-\frac{d[A]}{d t} .$
Question $14 .$
Define catalyst.
Answer:
A substance which alters the rate of a reaction without undergoing any change in mass and composition is known as a catalyst.
Question 15 .
What happens during a chemical reaction?
Answer:
- In a chemical reaction, the atoms of the reacting molecules or elements are rearranged to form new molecules.
- Old chemical bonds between atoms are broken and new chemical bonds are formed.
- Bond breaking absorbs energy whereas bond formation releases energy.
Question $16 .$
What; is a balanced chemical equation?
Answer:
A balanced chemical equation is the simplified representation of a chemical reaction which describes the chemical composition, the physical state of the reactants and the products, and the reaction conditions.
Question $17 .$
What are the main classes of decomposition reactions?
Answer:
There are three main classes of decomposition reactions. They are,
- Thermal decomposition reactions
- Electrolytic decomposition reactions
- Photo decomposition reactions
Question $18 .$
What are thermal decomposition reactions?
Answer:
In a thermal decomposition reaction, the reactant is decomposed by applying heat.
For example, on heating mercury (II) oxide is decomposed into mercury metal and oxygen gas.
$$
2 \mathrm{HgO}_{(v)} \stackrel{\Delta}{\longrightarrow} 2 \mathrm{Hg}_{(*)}+\mathrm{O}_{2(\mathrm{~g})} \text {. }
$$
Question $19 .$
What are Electrolytic decomposition reactions?
Answer:
In this type of reaction, the reactant is decomposed by applying electricity.
For example, decomposition of sodium chloride occurs on passing electric current through its aqueous solution.
$2 \mathrm{NaCl}_{(\mathrm{aq})} \stackrel{\text { Electricity }}{\longrightarrow} 2 \mathrm{Na}(\mathrm{s})+\mathrm{Cl}_{2(\mathrm{~g})}$
Question $20 .$
What is the photodecomposition reaction?
Answer:
In this type of reaction, the reactant is decomposed by applying light.
For example, when silver bromide is exposed to light, it breaks down into silver metal and bromine gas.
$2 \mathrm{AgBr}_{(s)} \stackrel{\text { Light }}{\longrightarrow} 2 \mathrm{Ag}_{(*)}+\mathrm{Br}_{2(\mathrm{~g})}$.
Question $21 .$
What is Metathesis reaction?
Answer:
The ion of one compound is replaced by the ion of another compound. Ions of identical charges are only interchanged, i.e. a cation can be replaced by another cation. This reaction is called metathesis reaction.
Question $22 .$
What is a precipitation reaction?
Answer:
When aqueous solution of two compounds are mixed, if they react to form an insoluble compound and a soluble compound, then it is called precipitation reaction.
$$
\text { e.g., } \mathrm{Pb}\left(\mathrm{NO}_{3}\right)_{2(\mathrm{aq})}+2 \mathrm{KI}_{(\mathrm{aq})} \longrightarrow \mathrm{PbI}_{2(\mathrm{~s})} \downarrow+2 \mathrm{KNO}_{3(\mathrm{aq})} \text {. }
$$
Question $23 .$
How will you distinguish between combination and decomposition reactions?
Answer:
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Question $24 .$
What is a neutralization reaction?
Answer:
It is another type of displacement reaction in which the acid reacts with the base to form a salt and water. It is called neutralization reaction as both acid and base neutralizes each other.
.png)
Question $25 .$
What is Combustion reaction?
Answer:
A combustion reaction is one in which the reactant rapidly combines with oxygen to form one or more oxides and energy (heat).
.png)
Question $26 .$
What are reversible and irreversible reactions?
Answer:
Reversible reaction : A reversible reaction is a reaction that can be reversed, i.e., the products can be converted back to the reactants.
e.g., $\mathrm{PCl}_{5(\mathrm{~g})} \rightleftharpoons \mathrm{PCl}_{3(\mathrm{~g})}+\mathrm{Cl}_{2(\mathrm{~g})}$
Irreversible reaction: The reaction that cannot be reversed is called irreversible reaction. The irreversible reactions are unidirectional.
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Question $27 .$
Why is the reaction rate important?
Answer:
Faster the reaction, more will be the amount of the product in a specified time. So, the rate of a reaction is important for a chemist for designing a process to get a good yield of a product. Rate of reaction is also important for a food processor who hopes to slow down the reactions that cause food to spoil.
VII. Long Answer Questions.
Question $1 .$
Suggest a reason for each observation given below.
Answer:
(i) In fireworks, powdered $\mathrm{Mg}$ is used rather than $\mathrm{Mg}$ ribbon.
Powdered Mg will have larger surface area than $\mathrm{Mg}$ ribbon and the rate of the reaction increases.
(ii) $\mathrm{Zn}$ and dil. $\mathrm{H}_{2} \mathrm{SO}_{4}$ react much more quickly when a few drops of $\mathrm{CuSO}_{4}$ solution are added.
When few drops of $\mathrm{CuSO}_{4}$ are added to the solution containing $\mathrm{Zn}$ and dil. $\mathrm{H}_{2} \mathrm{SO}_{4}$, the rate of the reaction increases, because $\mathrm{CuSO}_{4}$ acts as catalyst.
(iii) The reaction between $\mathrm{MgCO}_{3}$ and dil. $\mathrm{HCl}$ speeds up when some con. $\mathrm{HCl}$ is added. As the concentration of the reactant increases, the rate of the reaction increases.
Question $2 .$
Observe the given chemical change and answer the following:
.png)
1. Identify ' $A$ ' and ' $B$ '.
2. Write the commercial name of calcium hydroxide.
3. Identify products ' $\mathrm{C}^{\text {' }}$ and ' $\mathrm{D}$ ' when $\mathrm{HCl}$ is allowed to oxide react with calcium oxide.
4. Say whether calcium oxide is acidic or basic.
Answer:
.png)
1. A is calcium carbonate. B is carbon-di-oxide.
2. Slaked lime is the commercial name of calcium hydroxide.
3. The products $\mathrm{C}$ and $\mathrm{D}$ are calcium chloride $\left(\mathrm{CaCl}_{2}\right)$ and water $\left(\mathrm{H}_{2} \mathrm{O}\right)$.
4. Calcium oxide is basic in nature.
Question 3 .
Take copper nitrate in a test tube and heat it over the flame.
1. What is the colour of cupric nitrate?
2. What do you observe?
3. Name the type of reaction that takes place.
4. Write the balanced equation.
Answer:
1. The colour of cupric nitrate is Blue.
2. When cupric nitrate is heated in a test tube, we can observe the evolution of reddish-brown gas $\left(\mathrm{NO}_{2}\right)$ Nitrogen dioxide.
3. The reaction takes place is a decomposition reaction.
.png)
Question $4 .$
Redox reactions are reactions during which electron transfer takes place. Here magnesium atom transfers two electrons one each to the two chlorine atoms.
(i) What are the products of this reaction?
(ii) Write the balanced equation for the complete reaction.
(iii) Which element is being oxidized?
(iv) Which element is being reduced?
(v) Write the reduction part of the reaction.
Answer:
(i) Magnesium atom is converted to $\mathrm{Mg}^{2+}$ ion. Two chlorine atoms are converted to $2 \mathrm{Cl}^{-}$ions. So the products are $\mathrm{Mg}^{2+}$ ion and $2 \mathrm{Cl}^{-}$ions.
(ii) .png)
(iii) $\mathrm{Mg}$ atom is being oxidised by donating 2 electrons.
(iv) $\mathrm{Cl}_{2}$ molecule is being reduced by accepting 2 electrons.
(v) $\mathrm{Cl}_{2}+2 \mathrm{e}^{-} \rightarrow 2 \mathrm{Cl}^{-}$. It is a reduction reaction in which gain of $\mathrm{e}^{-}$take place.
Question $5 .$
Take $\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}$ in a test tube and heat it over the flame.
(i) What is the colour of $\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2}$ ?
Answer:
Blue
(ii) What do you observe?
Answer:
Evolution of reddish-brown gas.
(iii) Name the type of reaction that takes place.
Answer:
Decomposition.
(iv) Write the balanced equation.
Answer:
$$
\mathrm{Cu}\left(\mathrm{NO}_{3}\right)_{2} \rightarrow 2 \mathrm{CuO}+4 \mathrm{NO}_{2}+\mathrm{O}_{2} \uparrow
$$
Question 6 .
Sodium hydroxide and hydrochloric acid react as shown in this equation.
$\mathrm{NaOH}_{(\text {aq })}+\mathrm{HCl}_{\text {aq) }} \longrightarrow \mathrm{NaCl}_{(a q)}+\mathbf{H}_{2} \mathrm{O}_{(7)}$
(i) Which type of chemical reaction is this?
(ii) The reaction is exothermic. Explain what that means.
(iii) Differentiate exothermic reaction and endothermic reaction.
(iv) What happens to the temperature of the solution as the chemicals react?
Answer:
(i) It is a neutralisation reaction.
(ii) An exothermic reaction is a chemical reaction in which the evolution of heat energy takes place.
(iii).png)
(iv) When $\mathrm{NaOH}$ reacts with $\mathrm{HCl}$ to give $\mathrm{NaCl}$ and water, heat is evolved. So the solution's temperature increases.
VIII. HOT Questions.
Question $1 .$
Equal lengths of magnesium ribbons are taken in test tubes $\mathrm{A}$ and $\mathrm{B}$. Hydrochloric acid is added to test tube A, while acetic acid is added to test tube B. The amount and concentration taken for both the acids are same. In which test tube does the reaction occur more vigorously and why?
Answer:
In the test tube, the reaction occurs more vigorously.
Comparing hydrochloric acid and acetic acid, $\mathrm{HCl}$ (hydrochloric acid) is a strong acid and more reactive whereas acetic acid is a weak organic acid and less reactive.
$\mathrm{Mg}+2 \mathrm{HCl} \stackrel{\text { Fast reactiou }}{\longrightarrow} \mathrm{MgCl}_{2}+\mathrm{H}_{2} \uparrow$.
Question $2 .$
Classify the following reactions based on the rate of the reactions as very fast or instantaneous slow and moderate reactions.
(a) $\mathrm{AgNO}_{3 \text { (aq) }}+\mathrm{NaCl}_{\text {(aq) }} \rightarrow \mathrm{AgCl} \downarrow+\mathrm{NaNO}_{3 \text { (aq) }}$
Answer:
Very fast reaction (or) Instantaneous reaction.
(b) $2 \mathrm{Na}_{(\mathrm{s})}+2 \mathrm{H}_{2} \mathrm{O}_{(\mathrm{l})} \rightarrow 2 \mathrm{NaOH}_{(\mathrm{aq})}+\mathrm{H}_{2(\mathrm{~g})}$
Answer:
Very fast reaction.
(c) Rusting of iron.
Answer:
Very slow reaction.
(d) Inversion of cane sugar into Glucose and fructose.
Answer:
Moderately slow reaction.
(e) Fermentation of sugar into alcohol.
Answer:
Very slow reaction.
Question $3 .$
What is the chemical reaction taken place in the tarnishing of silver anklet?
Answer:
The lustrous white colour of the silver anklet slowly changes into a slightly black colour. It is due to the formation of silver sulphide $\left(\mathrm{Ag}_{2} \mathrm{~S}\right)$ as a result of the reaction between silver and hydrogen sulphide in the air.
Question $4 .$
Why toothpaste are basic in nature?
Answer:
The white enamel coating of our teeth is calcium phosphate, the hardest substance in our body. It does not dissolve in water. If the pH of mouth falls below $5.5$, the enamel gets corroded. Toothpaste is generally basic and used for cleaning the teeth can neutralize the excess acid and prevent tooth decay.
Question $5 .$
Why the solution of slaked lime is used for whitewashing?
Answer:
A solution of slaked lime is used for whitewashing walls. Calcium hydroxide reacts slowly with the carbon dioxide in the air to form a thin layer of calcium carbonate on the walls. Calcium carbonate is formed after two to three days of whitewashing and gives a shiny finish to the walls. It is interesting to note that the chemical formula for marble is also $\mathrm{CaCO}_{3}$.
.png)
Question 6 .
Complete the following reactions.
(a) $\mathrm{PCl}_{3}+\mathrm{Cl}_{2} \rightarrow$ ?
(b) $\mathrm{SiO}_{2}+? \rightarrow \mathrm{CaSiO}_{3}$
(c) $2 \mathrm{HgO} \stackrel{\Delta}{\longrightarrow} ?+\mathrm{O}_{2}$
(d) $\mathrm{CaCO}_{3} \stackrel{\Delta}{\longrightarrow} ?+\mathrm{CO}_{2}$
(e) $\mathrm{Ca}(\mathrm{OH})_{2} \stackrel{\mathrm{CO}_{2}}{\longrightarrow} ?+\mathrm{H}_{2} \mathrm{O}$
Answer:
(a) $\mathrm{PCl}_{3}+\mathrm{Cl}_{2} \rightarrow \mathrm{PCl}_{5}$
(b) $\mathrm{SiO}_{2}+\mathrm{CaO} \rightarrow \mathrm{CaSiO}_{3}$
(c) $2 \mathrm{HgO} \stackrel{\Delta}{\longrightarrow} 2 \mathrm{Hg}+\mathrm{O}_{2}$
(d) $\mathrm{CaCO}_{3} \stackrel{\Delta}{\longrightarrow} \mathrm{CaO}+\mathrm{CO}_{2}$
(e) $\mathrm{Ca}(\mathrm{OH})_{2} \stackrel{\mathrm{CO}_{2}}{\longrightarrow} \rightarrow \mathrm{CaCO}_{3}+\mathrm{H}_{2} \mathrm{O}$
Question $7 .$
Let us consider the following two reactions.
$$
\begin{array}{ll}
2 \mathrm{NaCl}_{(\mathrm{aq})}+\mathrm{F}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{NaF}_{\text {(aq) }}+\mathrm{Cl}_{2(\mathrm{~g})} & -1^{\text {st }} \text { reaction } \\
2 \mathrm{NaF}_{(\mathrm{aq})}+\mathrm{Cl}_{2}(\mathrm{~g}) \rightarrow 2 \mathrm{NaCl}_{(\mathrm{aq})}+\mathrm{F}_{2(\mathrm{~g})} & -2^{\text {nd }} \text { reaction }
\end{array}
$$
Which reaction will not occur. Why?
Answer:
The first reaction involves the displacement of chlorine from $\mathrm{NaCl}$, by fluorine. In the second reaction, chlorine displaces fluorine from $\mathrm{NaF}$. Out of these two, the second reaction will not occur. Because fluorine is more active than chlorine and occupies the upper position in the periodic table. So, in displacement reactions, the activity of the elements and their relative position in the periodic table are the key factors to determine the feasibility of the reactions. More active elements readily displace less active elements from their aqueous solutions.
Question $8 .$
Which of the metals displaces hydrogen gas from hydrochloric acid? Silver or zinc. Give the chemical equation of the reaction and justify your answer.
Answer:
Zinc displaces hydrogen gas from hydrochloric, acid.
Zinc is more reactive than silver.
$$
\mathrm{Zn}+2 \mathrm{HCl} \rightarrow \mathrm{ZnCl}_{2}+\mathrm{H}_{2} \uparrow \text {. }
$$
Question $9 .$
Foods kept at room temperature spoils faster than that kept in the refrigerator. Why?
Answer:
Food kept at room temperature spoils faster than that kept in the refrigerator. In the refrigerator, the temperature is lower than the room temperature and hence the reaction rate is less.
Question $10 .$
How will you enhance the rate of decomposition of potassium chlorate?
Answer:
On heating potassium chlorate, it decomposes into potassium chloride and oxygen gas, but at a slower rate. If manganese dioxide is added, it increases the reaction rate.
$$
2 \mathrm{KClO}_{3} \stackrel{\mathrm{MnO}_{2}}{\Delta} 2 \mathrm{KCl}+3 \mathrm{O}_{2} \uparrow
$$
Here $\mathrm{MnO}_{2}$ is the catalyst. Therefore the addition of $\mathrm{MnO}_{2}$ enhances the rate of decomposition of potassium chlorate.
Question $11 .$
Powdered calcium carbonate reacts more readily with hydrochloric acid than marble chips. Why?
Answer:
Powdering of the reactants increases the surface area and more energy is available on the collision of the reactant particles. Thus, the reaction rate is increased. Hence powdered calcium carbonate reacts more readily with hydrochloric acid than marble chips.
Question $1 .$
The $\left[\mathrm{OH}^{-}\right]$ion concentration of a solution is $1.0 \times 10^{-8} \mathrm{M}$. What is the $\mathrm{pH}$ of the solution?
Solution:
The concentration of hydroxide ion $=\left[\mathrm{OH}^{-}\right]=1.0 \times 10^{-8} \mathrm{M}$.
$$
\begin{aligned}
\mathrm{pOH} &=-\log _{10}\left[\mathrm{OH}^{-}\right] \\
\mathrm{pOH} &=-\log _{10}\left(1.0 \times 10^{-8}\right) \\
&=\log 1-\log 1 \times 10^{-8} \\
&=0.0000-8.0000 \\
\mathrm{pOH} &=8 \\
\mathrm{pH}+\mathrm{pOH} &=14 \\
\therefore \mathrm{pH} &=14-8 \Rightarrow \mathrm{pH}=6
\end{aligned}
$$
Question $2 .$
The hydrogen ion concentration of a solution is $1.0 \times 10^{-9} \mathrm{~m}$. What is the $\mathrm{pH}$ of the solution? Find out whether the given solution is acidic, basic or neutral.
Solution:
$$
\begin{aligned}
\mathrm{pH} &=-\log _{10}\left[\mathrm{H}^{+}\right] \\
\mathrm{pH} &=-\log _{10}\left(1.0 \times 10^{-9}\right) \\
\mathrm{pH} &=\log 1-\log 1 \times 10^{-9} \\
&=0.0000-9.0000 \\
\mathrm{pH} &=9
\end{aligned}
$$
$\mathrm{pH}>7$, so the solution is basic.
Question $3 .$
The hydroxide ion concentration of a solution is $0.001 \mathrm{~m}$. What is the $\mathrm{pH}$ of the solution?
Solution:
$$
\begin{aligned}
\mathrm{pOH} &=-\log _{10}\left[\mathrm{OH}^{-}\right] \\
\mathrm{pOH} &=-\log _{10}\left(1 \times 10^{-3}\right) \\
&=\log 1-\log 10^{-3} \\
&=0.0000-3.0000 \\
\mathrm{pH}+\mathrm{pOH} &=14 \\
\mathrm{pH} &=14-\mathrm{pOH} \\
\mathrm{pH} &=14-3=11 \\
\mathrm{pH} &=11 .
\end{aligned}
$$
Question $4 .$
The hydroxide ion concentration of a solution is $1.0 \times 10^{-9} \mathrm{~m}$. What is the $\mathrm{pH}$ of the solution?
Solution:
$$
\begin{aligned}
\mathrm{pOH} &=-\log _{10}\left[\mathrm{OH}^{-}\right] \\
\mathrm{pOH} &=-\log _{10}\left(1 \times 10^{-9}\right) \\
\mathrm{pOH} &=9 \\
\mathrm{pH}+\mathrm{pOH} &=14 \\
\mathrm{pH} &=14-\mathrm{pOH} \\
\mathrm{pH} &=14-9 \\
\mathrm{pH} &=5
\end{aligned}
$$
Question $5 .$
The hydrogen ion concentration of a solution is $1 \times 10^{-4} \mathrm{~m}$. Calculate the $\mathrm{pH}$ and $\mathrm{pOH}$ of that solution.
Solution:
$$
\begin{aligned}
{\left[\mathrm{H}^{+}\right] } &=1 \times 10^{-4} \mathrm{M} \\
\mathrm{pH} &=-\log _{10}\left[\mathrm{H}^{+}\right] \\
\mathrm{pH} &=-\log _{10}\left[1 \times 10^{-4}\right] \\
&=\log 1-\log 1 \times 10^{-4} \\
&=0.0000-4.0000 \\
\mathrm{pH} &=4 \\
\mathrm{pH}+\mathrm{pOH} &=14 \\
\therefore \mathrm{pOH} &=14-\mathrm{pH} \\
&=14-4=10 \\
\mathrm{pH} &=4 ; \mathrm{pOH}=10
\end{aligned}
$$
Question $6 .$
Calculate the $\mathrm{pH}$ of sodium hydroxide solution having the concentration of $\mathrm{OH} 0.01 \mathrm{~mL}^{-1}$.
Solution:
$$
\begin{aligned}
\mathrm{pOH} &=-\log _{10}\left[\mathrm{OH}^{-}\right] \\
\mathrm{pOH} &=-\log _{10}\left[1 \times 10^{-2}\right] \\
\mathrm{pOH} &=2 \\
\mathrm{pH}+\mathrm{pOH} &=14 \\
\therefore \mathrm{pH} &=14-\mathrm{pH}=14-2 \\
\mathrm{pH} &=12
\end{aligned}
$$
Also Read : Text-Book-Back-Questions-and-Answers-Chapter-11-Carbon-and-its-Compounds-10th-Science-Guide-Samacheer-Kalvi-Solutions
