Text Book Back Questions and Answers - Chapter 9 Solutions 10th Science Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]

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Chapter 9 - Solutions - 10th Science Guide Samacheer Kalvi Solutions

I. Problems based on Solubility.
Question $1 .$
$1.5 \mathrm{~g}$ of solute is dissolved in $15 \mathrm{~g}$ of water to form a saturated solution at $298 \mathrm{~K}$. Find out the solubility of the solute at the temperature.
Solution:
Mass of the solute $=1.5 \mathrm{~g}$
Mass of the solvent $=15 \mathrm{~g}$
Solubility of the solute $=\frac{\text { Mass of the solute }}{\text { Mass of the solvent }} \times 100$ $=\frac{1.5}{15} \times 100=10 \mathrm{~g}$.
 

Question $2 .$
Find the mass of potassium chloride would be needed to form a saturated solution in $60 \mathrm{~g}$ of water
at $303 \mathrm{~K}$ ? Given that solubility of the $\mathrm{KCl}$ is $37 / 100 \mathrm{~g}$ at this temperature.
Solution:
Mass of potassium chloride in $100 \mathrm{~g}$ of water in saturated solution $=37 \mathrm{~g}$
Mass of potassium chloride in $60 \mathrm{~g}$ of water in saturated solution $=\frac{37}{100} \times 60=22.2 \mathrm{~g}$.

Question 3.
What is the mass of sodium chloride that would be needed to form a saturated solution in $50 \mathrm{~g}$ of water at $30^{\circ} \mathrm{C}$. Solubility of sodium chloride is $36 \mathrm{~g}$ at $30^{\circ} \mathrm{C}$ ?
Solution:
At $30^{\circ} \mathrm{C}, 36 \mathrm{~g}$ of sodium chloride is dissolved in $100 \mathrm{~g}$ of water.
Mass of sodium chloride that would be need for $100 \mathrm{~g}$ of water $=36 \mathrm{~g}$
Mass of sodium chloride dissolved in $50 \mathrm{~g}$ of water $=\frac{36 \times 50}{100}=18 \mathrm{~g}$.
 

Question $4 .$
The Solubility of sodium nitrate at $50^{\circ} \mathrm{C}$ and $30^{\circ} \mathrm{C}$ is $114 \mathrm{~g}$ and $96 \mathrm{~g}$ respectively. Find the amount of salt that will be thrown out when a saturated solution of sodium nitrate-containing $50 \mathrm{~g}$ of water is cooled from $50^{\circ} \mathrm{C}$ to $30^{\circ} \mathrm{C}$ ?
Answer:
Amount of sodium nitrate dissolved in $100 \mathrm{~g}$ of water at $50^{\circ} \mathrm{C}$ is $114 \mathrm{~g}$
Amount of sodium nitrate dissolving in $50 \mathrm{~g}$ of water at $50^{\circ} \mathrm{C}$ is $=\frac{114 \times 50}{100}=57 \mathrm{~g}$
Similarly amount of sodium nitrate dissolving in $50 \mathrm{~g}$ of water at $30^{\circ} \mathrm{C}$ is $=\frac{96 \times 50}{100}=48 \mathrm{~g}$
Amount of sodium nitrate thrown when $50 \mathrm{~g}$ of water is cooled from $50^{\circ} \mathrm{C}$ to $30^{\circ} \mathrm{C}$ is $57-48=9 \mathrm{~g}$.
 

II. Problems based on Mass percentage.
Question $1 .$
A solution was prepared by dissolving $25 \mathrm{~g}$ of sugar in $100 \mathrm{~g}$ of water. Calculate the mass
percentage of solute.
Solution:
Mass of the solute $=25 \mathrm{~g}$

Mass of the solvent $=100 \mathrm{~g}$
Mass percentage $=\frac{\text { Mass of the solute }}{\text { Mass of the solution }} \times 100$
Mass percentage $=\frac{\text { Mass of the solute }}{\text { Mass of the solute }+\text { Mass of the solvent }} \times 100$
$$
=\frac{25}{25+100} \times 100=\frac{25}{125} \times 100=20 \%
$$
 

Question 2.
16 grams of $\mathrm{NaOH}$ is dissolved in 100 grams of water at $25^{\circ} \mathrm{C}$ to form a saturated solution. Find the mass percentage of solute and solvent.
Solution:
Mass of the solute $(\mathrm{NaOH})=16 \mathrm{~g}$
Mass of the solvent $\mathrm{H}_{2} \mathrm{O}=100 \mathrm{~g}$
(i) Mass percentage of the solute
$=\frac{\text { Mass of the solute }}{\text { Mass of the solute }+\text { Mass of the solvent }} \times 100$
$=\frac{16 \times 100}{16+100}=\frac{1600}{116}$
Mass percentage of the solute $=13.79 \%$.
(ii) Mass percentage of solvent $=100-$ (Mass percentage of the solute) $=100-13.79=86.21 \%$.

Question $3 .$
Find the amount of urea which is to be dissolved in water to get $500 \mathrm{~g}$ of $10 \% \mathrm{w} / \mathrm{w}$ aqueous solution?
Solution:
Mass percentage $=\frac{\text { Mass of the solute }}{\text { Mass of the solution }} \times 100$
$$
\begin{aligned}
&10=\frac{\text { Mass of the urea }}{500} \times 100 \\
&\text { Mass of urea }=50 \mathrm{~g} \text {. }
\end{aligned}
$$

III. Problem based on Volume - Volume percentage.
Question $1 .$
The solution is made from $35 \mathrm{ml}$ of methanol and $65 \mathrm{ml}$ of water. Calculate the volume percentage.
Solution:
The volume of the ethanol $=35 \mathrm{ml}$
The volume of the water $=65 \mathrm{ml}$
Volume percentage $=\frac{\text { Volume of the solute }}{\text { Volume of the solution }} \times 100$
Volume percentage $=\frac{\text { Volume of the solute }}{\text { Volume of the solute }+\text { Volume of the solvent }} \times 100$
$$
=\frac{35}{35+65} \times 100=\frac{35}{100} \times 100=35 \%
$$

Question $2 .$
Calculate the volume of ethanol in $200 \mathrm{ml}$ solution of $20 \% \mathrm{v} / \mathrm{v}$ aqueous solution of ethanol.
Solution:
Volume of aqueous solution $=200 \mathrm{ml}$
Volume percentage $=20 \%$
Volume percentage $=\frac{\text { Volume of the solute }}{\text { Volume of the solution }} \times 100$
$$
20=\frac{\text { Volume of ethanol }}{200} \times 100
$$
Volume of ethanol $=\frac{20 \times 200}{100}=40 \mathrm{ml}$
 

Activity
Activity $1 .$
Look at the following pictures. Label them as a dilute and concentrated solution and justify your answer.

Solution:
In the above picture, the first teacup is more concentrated and the first beaker is more concentrated $\mathrm{CuSO}_{4}$ solution. The reason is the colour intensity is more in a concentrated solution.
 

I. Choose the best answer.
Question $1 .$
A solution is a mixture.
(a) homogeneous
(b) heterogeneous
(c) homogeneous and heterogeneous
(d) non-homogeneous.
Answer:
(a) homogeneous

Question $2 .$
The number of components in a binary solution is:
(a) 2
(b) 3
(c) 4
(d) 5
Answer:
(a) 2
 

Question $3 .$
Which of the following is the universal solvent?
(a) Acetone
(b) Benzene
(c) Water
(d) Alcohol.
Answer:
(c) Water
 

Question $4 .$
A solution in which no more solute can be dissolved in a definite amount of solvent at a given temperature is called:
(a) Saturated solution
(b) Unsaturated solution
(c) Supersaturated solution
(d) Dilute solution
Answer:
(a) Saturated solution
 

Question $5 .$
Identify the non - aqueous solution

(a) sodium chloride in water
(b) glucose in water
(c) copper sulphate in water
(d) sulphur in carbon-di-sulphide.
Answer:
(d) sulphur in carbon-di-sulphide.
 

Question 6.
When pressure is increased at a constant temperature the solubility of gases in liquid:
(a) No change
(b) increases
(c) decreases
(d) no reaction
Answer:
(b) increases
 

Question 7.
The solubility of $\mathrm{NaCl}$ in $100 \mathrm{ml}$ water is $36 \mathrm{~g}$. If $25 \mathrm{~g}$ of salt is dissolved in $100 \mathrm{ml}$ of water how much more salt is required for saturation
(a) $12 \mathrm{~g}$
(b) $11 \mathrm{~g}$
(c) $16 \mathrm{~g}$
(d) $20 \mathrm{~g}$.
Answer:
(b) $11 \mathrm{~g}$
 

Question 8 .
A $25 \%$ alcohol solution means:
(a) $25 \mathrm{ml}$ alcohol in $100 \mathrm{ml}$ of water
(b) $25 \mathrm{ml}$ alcohol in $25 \mathrm{ml}$ of water
(c) $25 \mathrm{ml}$ alcohol in $75 \mathrm{ml}$ of water
(d) $75 \mathrm{ml}$ alcohol in $25 \mathrm{ml}$ of water
Answer:
(c) $25 \mathrm{ml}$ alcohol in $75 \mathrm{ml}$ of water

Question $9 .$
Deliquescence is due to
(a) Strong affinity to water
(b) Less affinity to water
(c) Strong hatred of water
(d) Inertness to water.
Answer:
(a) Strong affinity to water
 

Question $10 .$
Which of the following is hygroscopic in nature?
(a) ferric chloride
(b) copper sulphate penta hydrate
(c) silica gel
(d) none of the above
Answer:
(c) silica gel
 

II. Fill in the blanks.
Question $1 .$
The component present in a lesser amount, in a solution, is called_______
Answer:
Solute.
 

Question 2.
Example for liquid in solid type solution is_______
Answer:
Sodium chloride dissolved in water.

Question $3 .$
Solubility is the amount of solute dissolved in g of solvent.
Answer:
$100 .$
 

Question $4 .$
Polar compounds are soluble in solvents.
Answer:
Polar.
 

Question $5 .$
Volume percentage decreases with increases in temperature because of
Answer:
Expansion of liquid.
 

III. Match the following.
Question $1 .$

Answer:
$$
1-(c), 2-(a), 3-(d), 4-(b)
$$
 

IV. True or False: (If false give the correct statement)
Question $1 .$
Solutions which contain three components are called binary solution.
Answer:
False.
Correct Statement: Solutions which contain two components are called binary solution.
 

Question $2 .$
In a solution, the component which is present in a lesser amount is called solvent.
Answer:
False.
Correct Statement:
- In a solution, the component which is present in a larger amount is called a solvent.
- In a solution, the component which is present in a lesser amount is called solute.
 

Question 3 .
Sodium chloride dissolved in water forms a non-aqueous solution.
Answer:
False.
Correct Statement: Sodium chloride dissolved in water forms an aqueous solution.
 

Question $4 .$
The molecular formula of green vitriol is $\mathrm{MgSO}_{4}, 7 \mathrm{H}_{2} \mathrm{O}$
Answer:
False.
Correct Statement: The molecular formula of green vitriol is $\mathrm{FeSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}$
 

Question 5 .
When Silica gel is kept open, it absorbs moisture from the air, because it is hygroscopic in nature.
Answer:
True.
 

V. Short Answer Questions.
Question $1 .$
Define the term Solution.

Answer:
A solution is a homogeneous mixture of two or more substances.
 

Question $2 .$
What is mean by binary solution?
Answer:

Solutions which are made of one solute and one solvent, then it is called binary solution.
 

Question $3 .$
Give an example each
1. gas in liquid
2. solid in liquid
3. solid in solid
4. gas in gas.
Answer:
1. Carbon - di - oxide dissolved in water (Soda water).
2. Sodium chloride dissolved in water.
3. Copper dissolved in gold (Alloy).
4. A mixture of Helium - Oxygen gases.
 

Question $4 .$
What is aqueous and non-aqueous solution? Give an example.
Answer:
(i) Aqueous solution : The solution in which water acts as a solvent.
(ii) Non-aqueous solution : The solution in which any liquid other than water acts as a solvent.
Eg: Alcohol, benzene, $\mathrm{CS}_{2}$ acetone.

Question $5 .$
Define Volume percentage.
Answer:
Volume percentage is defined as the percentage by volume of solute (in $\mathrm{ml}$ ) present in the given volume of the solution.
Volume percentage $=\frac{\text { Volume of the solute }}{\text { Volume of the solution }} \times 100$.
 

Question $6 .$
The aquatic animals live more in cold region Why?
Answer:
Aquatic animals live more in cold regions because the solubility of $\mathrm{O}_{2}$ in water is more at low temperature and therefore the amount of dissolved $\mathrm{O}_{2}$ is more in the water of cold regions.
 

Question $7 .$
Define Hydrated salt.
Answer:
The number of water molecules found in the crystalline substance or salts is called water of crystallization. Such salts are called hydrated salts.

Question 8.
A hot saturated solution of copper sulphate forms crystals as it cools. Why?
Answer:
A hot saturated solution of $\mathrm{CuSO}_{4}$ forms crystal as it cools. Because on cooling the water molecules move closer together and there is less space for the solution to hold on to as much of the dissolved solid and so it forms crystals.
 

Question $9 .$
Classify the following substances into deliquescent, hygroscopic. Conc. Sulphuric acid, Copper sulphate penta hydrate, Silica gel, Calcium chloride, and Gypsum salt.
Answer:
1. Deliquescent substances: Calcium chloride
2. Hygroscopic substances: Conc Sulphuric acid, Copper sulphate penta hydrate, Silica gel and Gypsum salt.
 

VI. Long Answer Questions.
Question $1 .$
Write notes on
(i) saturated solution
(ii) unsaturated solution
Answer:
(i) Saturated solution : A solution in which no more solute can be dissolved in a definite amount of the solvent at a given temperature is called saturated solution.
Eg: $36 \mathrm{~g}$ of sodium chloride in $100 \mathrm{~g}$ of water at $25^{\circ} \mathrm{C}$ forms saturated solution.
(ii) Unsaturated solution : Unsaturated solution is one that contains less solute than that of the saturated solution at a given temperature.

Eg: $10 \mathrm{~g}$ or $20 \mathrm{~g}$ or $30 \mathrm{~g}$ of Sodium chloride in $100 \mathrm{~g}$ of water at $25^{\circ} \mathrm{C}$ forms an unsaturated solution.
 

Question $2 .$
Write notes on various factors affecting solubility.
Answer:
Factors affecting solubility: There are three main factors which govern the solubility of the solute. They are
(i) Nature of the solute and solvent

(ii) Temperature
(iii) Pressure
(i) Nature of the solute and solvent: The nature of the solute and solvent plays an important role insolubility. Although water dissolves an enormous variety of substances, both ionic and covalent, it does not dissolve everything. The phrase that scientists often use when predicting solubility is "like dissolves like." This expression means that dissolving occurs when similarities exist between the solvent and the solute. For example, Common salt is a polar compound and dissolves readily in polar solvent like water.

Non - polar compounds are soluble in non-polar solvents. For example, Fat dissolved in ether. But non-polar compounds, do not dissolve in polar solvents; polar compounds do not dissolve in nonpolar solvents.
(ii) Effect of Temperature
The solubility of Solids in Liquid: Generally, the solubility of a solid solute in a liquid solvent increases with increase in temperature. For example, a greater amount of sugar will dissolve in warm water than in cold water.

In the endothermic process, solubility increases with increase in temperature. In the exothermic process, solubility decreases with increase in temperature.
The solubility of Gases in liquid: Solubility of gases in liquids decreases with increase in temperature. Generally, water contains dissolved oxygen. When water is boiled, the solubility of oxygen in water decreases, so oxygen escapes in the form of bubbles. Aquatic animals live more in cold regions because more amount of dissolved oxygen is present in the water of cold regions. This shows that the solubility of oxygen in water is more at low temperatures.
(iii) Effect of Pressure: Effect of pressure is observed only in the case of solubility of a gas in a liquid. When the pressure is increased, the solubility of a gas in liquid increases.

The common examples for solubility of gases in liquids are carbonated beverages, i.e. soft drinks, household cleaners containing an aqueous solution of ammonia, formalin aqueous solution of formaldehyde, etc.

Question 3 .
(a) What happens when $\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}$ is heated? Write the appropriate equation.
(b) Define solubility.
Answer:
(a) $\mathrm{MgSO}_{4}, 7 \mathrm{H}_{2} \mathrm{O}$ has a water of crystallization is 7 . When magnesium sulphate heptahydrate crystals are gently heated, it loses seven water molecules and becomes anhydrous magnesium sulphate.

(b) Solubility: It is defined as the number of grams of a solute that can be dissolved in $100 \mathrm{~g}$ of a solvent to form its saturated solution at a given temperature and pressure.

Question $4 .$
In what way, hygroscopic substances differ from deliquescent substances.
Answer:
Difference between hygroscopic and deliquescent substances is in the extent to which each material can absorb moisture. This is because both of these terms are very much related to each other and they refer to the property of observing and the retention of moisture from the air.

However, they differ in the extent of absorption of moisture where hygroscopic materials absorb moisture but not to the extent the original substance dissolves in it, which is the case with deliquescence. Therefore deliquescence can be regarded as an extreme condition of hygroscopic activity.
Difference between hygroscopic substances and deliquescence

Question $5 .$
A solution is prepared by dissolving $45 \mathrm{~g}$ of sugar in $180 \mathrm{~g}$ of water. Calculate the mass percentage of solute.
Answer:
Mass of sugar (solute) $=45 \mathrm{~g}$
Mass of water (solvent) $=180 \mathrm{~g}$.
$$
\begin{aligned}
\text { Mass percentage } &=\frac{\text { Mass of the solute }}{\text { Mass of the solute }+\text { Mass of the solvent }} \times 100 \\
&=\frac{45}{45+180} \times 100=\frac{45}{225} \times 100 \\
&=20 \%
\end{aligned}
$$

Question $6 .$
$3.5$ litres of ethanol is present in 15 litres of an aqueous solution of ethanol. Calculate volume per cent of the ethanol solution.
Answer:
Volume of ethanol (solute) $=3.5$ litre
Volume of aqueous solution $=15$ litre
Volume of the solution $=\frac{\text { Volume of the solute }}{\text { Volume of the solution }} \times 100$
$=\frac{3.5}{15} \times 100$
Volume percentage $=23.33 \%$.

VII. HOT Questions.
Question $1 .$
Vinu dissolves $50 \mathrm{~g}$ of sugar in $250 \mathrm{ml}$ of hot water, Sarath dissolves $50 \mathrm{~g}$ of same sugar in $250 \mathrm{ml}$ of cold water. Who will get faster dissolution of sugar? and Why?
Answer:
Vinu will get faster dissolution of sugar. Because Vinu dissolves $50 \mathrm{~g}$ of sugar in $250 \mathrm{ml}$ of hot
water, whereas Sarath dissolves $50 \mathrm{~g}$ of sugar in $250 \mathrm{ml}$ of cold water. Solubility of a solid in liquid increases with increase in temperature.
 

Question $2 .$
' $A$ ' is a blue coloured crystalline salt. On heating, it loses a blue colour and to give ' $B$ '. When water is added, ' $B$ ' gives back to ' $A$ '. Identify $A$ and $B$, write the equation.
Answer:
- Blue coloured crystalline salt is copper sulphate pentahydrate (A)
- On heating Copper sulphate pentahydrate it loses blue colour and to give anhydrous copper sulphate (B).
- When water is added to the anhydrous copper sulphate (B) gives back to copper sulphate pentahydrate (A).

Question 3 .
Will the cool drinks give more fizz at top of the hills or at the foot? Explain.
Answer:
Carbonated cool drinks give more fizz at the foot hill because solubility of gases in liquid decrease with increase in temperature. At higher altitudes, the temperature is low and the dissolved $\mathrm{CO}_{2} \mathrm{} \mathrm{will}^{2}$ not escape as fizz, whereas at the foot hill it does.
 

I. Choose the best answer.
Question $1 .$
Find out the homogeneous mixture.
(a) Salt + Water
(b) Sand + Water
(c) Clay + Water
(d) Gold + Water.
Answer:
(a) Salt + Water

Question $2 .$
The aqueous solution is:
(a) $\mathrm{S}$ in $\mathrm{CS}_{2}$
(b) $\mathrm{I}_{2}$ in $\mathrm{CCl}_{4}$
(c) Salt in $\mathrm{H}_{2} \mathrm{O}$
(d) None of the above
Answer:
(c) Salt in $\mathrm{H}_{2} \mathrm{O}$
 

Question 3 .
In a solution, the component which is present in a larger amount is called

(a) solvent
(b) dissolution
(c) solute
(d) mole.
Answer:
(a) solvent
 

Question $4 .$
The solubility of ammonia gas at $25^{\circ} \mathrm{C}$ is:
(a) $36 \mathrm{~g}$
(b) $48 \mathrm{~g}$
(c) $80 \mathrm{~g}$
(d) $184 \mathrm{~g}$
Answer:
(b) $48 \mathrm{~g}$
 

Question $5 .$
Example for liquid in liquid binary solution is
(a) Copper dissolved in gold
(b) Water vapour in the air
(c) Ethyl alcohol dissolved in water
(d) $\mathrm{NaCl}$ dissolved in water.
Answer:
(c) Ethyl alcohol dissolved in water
 

Question $6 .$
Which one of the following is an aqueous solvent?
(a) Benzene
(b) Acetone
(c) Alcohol
(d) Water.
Answer:
(d) Water.
 

Question 7.
Mass percentage of a solution is independent of:
(a) temperature
(b) amount of solute
(c) amount of solvent
(d) chemical nature of the solute
Answer:
(a) temperature

Question 8 .
Solubility is equal to
(a) $\frac{\text { Mass of the solute }}{\text { Mass of the solution }} \times 100$
(b) $\frac{\text { Mass of the solution }}{\text { Mass of the solute }} \times 100$
(c) $\frac{\text { Mass of the solute }}{\text { Mass of the solvent }} \times 100$
(d) $\frac{\text { Mass of the solvent }}{\text { Mass of the solute }} \times 100$
Answer:
(c) $\frac{\text { Mass of the solute }}{\text { Mass of the solvent }} \times 100$
 

Question $9 .$
In which case solubility increases with increase in temperature?
(a) Endothermic process
(b) Exothermic process
(c) Both (a) and (b)
(b) None of these.
Answer:
(a) Endothermic process
 

Question $10 .$
The factor/factors which affect the solubility of a solute:
(a) Nature of the solute and solvent
(b) Temperature
(c) Pressure
(d) All of these
Answer:
(d) All of these

Question $11 .$
The effect of pressure on the solubility of a gas in a liquid is given by
(a) Hess's law
(b) Ohm's law
(c) Henry's law
(d) Gases law.
Answer:
(c) Henry's law
 

Question $12 .$
$5 \%$ sugar solution means
(a) $5 \mathrm{~g}$ of sugar in $95 \mathrm{~g}$ of water
(b) $50 \mathrm{~g}$ of sugar in $50 \mathrm{~g}$ of water
(c) $20 \mathrm{~g}$ of sugar in $80 \mathrm{~g}$ of water
(d) $95 \mathrm{~g}$ of sugar in $5 \mathrm{~g}$ of water.
Answer:
(a) $5 \mathrm{~g}$ of sugar in $95 \mathrm{~g}$ of water
 

Question $13 .$
The water of crystallisation present in white vitriol is:
(a) 2
(b) 7
(c) 5
(d) 24
Answer:
(b) 7

Question $14 .$
Mass percentage is independent of
(a) density
(b) volume
(c) pressure
(d) temperature.
Answer:
(d) temperature.
 

Question $15 .$
Volume percentage is expressed as
(a) $v / v$
(b) $w / w$
(c) $v / w$
(d) $w / v$.
Answer:
(a) $\mathrm{v} / \mathrm{v}$
 

Question $16 .$
When the temperature increases, volume percentage
(a) Increases
(b) Decreases
(c) no change
(d) increases then decrease.
Answer:
(b) Decreases

Question 17 .
The mass of $\mathrm{NaCl}$ needed to form saturated solution in $50 \mathrm{~g}$ of water at $30^{\circ} \mathrm{C}$. When the solubility of $\mathrm{NaCl}$ is $36 \mathrm{~g}$ at $30^{\circ} \mathrm{C}$ is:
(a) $9 \mathrm{~g}$
(b) $18 \mathrm{~g}$
(c) $57 \mathrm{~g}$
(d) $19 \mathrm{~g}$
Answer:
(b) $18 \mathrm{~g}$
 

Question $18 .$
Zinc sulphate heptahydrate is also called as
(a) Blue Vitriol
(b) Epsom salt
(c) Green Vitriol
(d) White Vitriol.
Answer:
(d) white Vitriol.
 

Question $19 .$
Water of crystallization of blue vitriol is
(a) 1
(b) 5
(c) 4
(d) 2 .
Answer:
(b) 5
 

Question $20 .$
On heating copper sulphate pentahydrate crystals
(a) blue colour changes into green
(b) green colour changes into blue
(c) blue colour changes into colourless
(d) no colour changes.
Answer:
(c) blue colour changes into colourless

Question 21 .
Water of crystallization of Epsom salt is
(a) 1
(b) 5
(c) 4
(d) 1 .
Answer:
(d) $7 .$
 

Question 22.
Hygroscopic substances are used as
(a) drying agents
(b) hydrating agents
(c) freezing agents
(d) reducing agents.
Answer:
(a) drying agents
 

Question $23 .$
If two liquids are mutually soluble, they are called _______ liquids.
(a) miscible
(b) immiscible
(c) insoluble
(d) viscous.
Answer:
(a) miscible

Question $24 .$
Aquatic species are more comfortable in cold water because of
(a) as the temperature decreases, the solubility of dissolved oxygen increases
(b) as the temperature increases, the solubility of dissolved oxygen increases
(c) as the temperature increases, the solubility of dissolved oxygen decreases
(d) None of these.
Answer:
(a) as the temperature decreases, the solubility of dissolved oxygen increases
 

Question $25 .$
The process of food assimilation by man is in the form of
(a) solution
(b) solid
(c) solute
(d) solvent.
Answer:
(a) solution
 

Question $26 .$
Common salt in water is an example of
(a) Colloidal solution
(b) Binary solution
(c) Suspension
(d) all the above.
Answer:
(b) Binary solution

Question $27 .$
$36 \mathrm{~g}$ of $\mathrm{NaCl}$ in $100 \mathrm{~g}$ of water is a_______ solution.
(a) Non-aqueous
(b) Unsaturated
(c) Supersaturated
(d) Saturated.
Answer:
(d) Saturated.
 

Question $28 .$
Nitrogen in soil is an example of_______ solution in nature.
(a) saturated
(b) unsaturated
(c) supersaturated
(d) aqueous.
Answer:
(a) saturated
 

Question $29 .$
The solubility of $\mathrm{CuSO}_{4}$ in $\mathrm{H}_{2} \mathrm{O}$ is_______ at $20^{\circ} \mathrm{C}$.
(a) $36 \mathrm{~g}$
(b) $20.7 \mathrm{~g}$
(c) $10 \mathrm{~g}$
(d) $95 \mathrm{~g}$.
Answer:
(b) $20.7 \mathrm{~g}$
 

Question $30 .$
The solubility of $\mathrm{NaNO}_{3}$ in $100 \mathrm{~g}$ water at $25^{\circ} \mathrm{C}$ is_______
(a) $36 \mathrm{~g}$
(b) $95 \mathrm{~g}$
(c) $184 \mathrm{~g}$
(d) $92 \mathrm{~g}$.
Answer:
(d) $92 \mathrm{~g}$.
 

Question $31 .$
Which of the following affect solubility?

(a) Temperature
(b) Nature of solute and solvent
(c) Pressure
(d) all the above.
Answer:
(d) all the above.
 

Question $32 .$
In_______process, solubility increases with increase in temperature.
(a) exothermic
(b) endothermic
(c) isothermic
(d) adiabatic.
Answer:
(b) endothermic
 

Question $33 .$
In_______process, solubility decreases with increase in temperature.
(a) exothermic
(b) adiabatic
(c) endothermic
(d) isothermic.
Answer:
(a) exothermic
 

Question $34 .$
Increase in_______ increases the solubility of gases.
(a) temperature
(b) pressure
(c) no. of moles
(d) concentration.
Answer:
(b) pressure

Question $35 .$
The solubility of $\mathrm{NaBr}$ in $\mathrm{H}_{2} \mathrm{O}$ is_______
(a) $36 \mathrm{~g}$
(b) $95 \mathrm{~g}$
(c) $184 \mathrm{~g}$
(d) $92 \mathrm{~g}$.
Answer:
(b) $95 \mathrm{~g}$
 

Question $36 .$
The gas - filled in soft drinks in_______
(a) $\mathrm{O}_{2}$
(b) $\mathrm{N}_{2}$
(c) $\mathrm{CO}_{2}$
(d) $\mathrm{H}_{2}$
Answer:
(c) $\mathrm{CO}_{2}$
 

Question $37 .$
The solubility of $\mathrm{KNO}_{3}$ in water is_______ process.
(a) Exothermic
(b) endothermic
(c) Isothermic
(d) Adiabatic.
Answer:
(b) endothermic

Question $38 .$
The solubility of $\mathrm{CaO}$ in water is_______ process.
(a) Exothermic
(b) endothermic
(c) Adiabatic
(d) Isothermic.
Answer:
(a) Exothermic
 

Question 39.
The solubility of NaI in water is_______
(a) $184 \mathrm{~g}$
(b) $92 \mathrm{~g}$
(c) $95 \mathrm{~g}$
(d) $36 \mathrm{~g}$.
Answer:
(a) $184 \mathrm{~g}$
 

II. Fill in the blanks.
Question $1 .$
A solution is a_______ mixture of two or more substances.
Answer:
Homogeneous.
 

Question $2 .$
Common salt dissolved in water is an example for_______ solution.
Answer:
Binary.

Question $3 .$
In a solution, the component present in a lesser amount by weight is called_______ and in a large amount by weight is called_______
Answer:
Solute, solvent.
 

Question $4 .$
The solution in which water acts as a solvent is called_______ and the solution in which Benzene acts as a solvent is called_______
Answer:
1. The aqueous solution,
2. Non - aqueous solution.
 

Question $5 .$
$20 \mathrm{~g}$ of $\mathrm{NaCl}$ in $100 \mathrm{~g}$ of water is_______ solution.
Answer:
Unsaturated.
 

Question $6 .$
$36 \mathrm{~g}$ of $\mathrm{NaCl}$ in $100 \mathrm{~g}$ of water at room temperature forms a _______solution.
Answer:
Saturated.
 

Question $7 .$
Nitrogen in soil is an example for_______ in nature.
Answer:
Saturated solution.
 

Question 8.
A solution which has more of solute than the saturated solution at a given temperature is called_______ solution.
Answer:
Supersaturated.
 

Question $9 .$
In_______ process, solubility increases with in_______ temperature.
Answer:
Endothermic, increase.

Question $10 .$
In an _______process, solubility decreases with in_______ temperature.
Answer:
Exothermic, increase.
 

Question $11 .$
The solubility of $\mathrm{KNO}_{3}$ increases with the_______ in temperature.
Answer:
Increase.
 

Question $12 .$
The solubility of $\mathrm{CaO}$ decreases with the_______ in temperature.
Answer:
Increase.
 

Question $13 .$
The solubility of oxygen is_______ in cold water.
Answer:
More.
 

Question $14 .$
A polar compound is insoluble in_______ solvent.
Answer:
Non - polar.
 

Question $15 .$
An increase in_______ increases the solubility of a gas in a liquid.
Answer:
Pressure.
 

Question $16 .$
_______gas is filled in soft drinks using the effect of pressure.
Answer:
$\mathrm{CO}_{2}$
 

Question $17 .$
Hygroscopic substances are used as_______
Answer:
Drying agents.

Question $18 .$
Anhydrous calcium chloride is an example of_______
Answer:
hygroscopic substance.
 

Question 19.
Hygroscopic substances absorb moisture without changing their_______
Answer:
Physical state.
 

Question $20 .$
Deliquescent substances lose their_______
Answer:
Crystalline shape.
 

Question $21 .$
Ferric chloride is an example of_______
Answer:
Deliquescent substances.
 

Question $22 .$
On heating, hydrated crystalline salts lose their_______
Answer:
Water of crystallization.
 

Question $23 .$
The number of water molecules in blue vitriol is_______
Answer:
Five.

Question $24 .$
The number of water molecules in magnesium sulphate heptahydrate is_______
Answer:
Seven.
 

Question $25 .$
Mass percentage is_______to temperature.
Answer:
Independent.
 

Question $26 .$
To qualify the solute in a solution, we can use the term_______
Answer:
Concentration.
 

Question $27 .$
Based on the amount of solute, the solution is classified into _______types.
Answer:
Three.
 

Question $28 .$
Zinc dissolved in copper is an example of_______ solution.
Answer:
Solid in solid.
 

Question $29 .$
_______is an example of gas in the liquid.
Answer:
Carbon dioxide dissolved in water.

Question 30 .
_______and _______are in the form of solution to decide the physiological activity of human beings.
Answer:
Blood, Lymph.
 

III. Match the following.
Question $1 .$

Answer:
$$
i-b, i i-d, i i i-a, i v-c \text {. }
$$
 

Question $2 .$

Answer:
$$
i-d, i i-c, i i i-b, i v-a \text {. }
$$
 

Question 3 .

Answer:
$i-c, i i-a, 1 i i-d, i v-b$.

Question $4 .$

Answer:
$$
i-b, i i-c, i i i-d, i v-a \text {. }
$$
 

Question $5 .$

Answer:
$$
i-c, i i-d, i i i-a, i v-b \text {. }
$$
 

Question $6 .$

Answer:
$i-b$, ii $-d$, iii $-a, i v-c$
 

IV. State whether true or false. If false, give the correct statement.
Question 1 .
A solution is a heterogeneous mixture of two or more substances.
Answer:
False.
Correct statement: A solution is a homogeneous mixture of two or more substances.
 

Question $2 .$
A solution contains four components, it is called as a binary solution.
Answer:
False.
Correct statement: A solution contains two components, it is called as a binary solution.
 

Question $3 .$
The solution in which water acts as a solvent, it is called a non-aqueous solution.
Answer:
False.
Correct statement: The solution in which water acts as a solvent, it is called an aqueous solution.
 

Question $4 .$
The solution of sulphur in $\mathrm{CS}_{2}$ is a suitable example of a non-aqueous solution.
Answer:
True.
 

Question $5 .$
Nitrogen in soil is an example of a supersaturated solution.
Answer:
False.
Correct statement: Nitrogen in the soil is an example of a saturated solution.
 

Question $6 .$
The solubility of $\mathrm{CuSO}_{4}$ in $\mathrm{H}_{2} \mathrm{O}$ is $36 \mathrm{~g}$ at $25^{\circ} \mathrm{C}$.
Answer:
False.
Correct statement: Solubility of $\mathrm{CuSO}_{4}$ in $\mathrm{H}_{2} \mathrm{O}$ is $20.7 \mathrm{~g}$ at $20^{\circ} \mathrm{C}$.

Question $7 .$
$100 \mathrm{ml}$ of water can dissolve $36 \mathrm{~g}$ of $\mathrm{NaCl}$ at $25^{\circ} \mathrm{C}$ to attain saturation.
Answer:
True.
 

Question 8.
In an endothermic process, solubility decreases with increase in temperature.
Answer:
False.
Correct statement: In an endothermic process, solubility increases with increase in temperature.
 

Question 9 .
In an exothermic process, solubility decreases with increase in temperature.
Answer:
True.
 

Question $10 .$
The solubility of $\mathrm{CaO}$ increases with the increase in temperature.
Answer:
False.
Correct statement: The solubility of $\mathrm{CaO}$ decreases with the increase in temperature.
 

Question 11 .
The solubility of oxygen is more in cold water.
Answer:
True.
 

Question $12 .$
$\mathrm{SO}_{2}$ gas is filled in soft drinks using the effect of pressure.
Answer:
False.
Correct statement: $\mathrm{CO}_{2}$ gas is filled in soft drinks using the effect of pressure.
 

Question $13 .$
Ether act as a universal solvent.

Answer:
False.
Correct statement: Water acts universal solvent.

Question $14 .$
Covalent compounds are soluble in water.
Answer:
False.
Correct statement: Covalent compounds are insoluble in water.
 

Question $15 .$
$36 \mathrm{~g}$ of sodium chloride in $100 \mathrm{~g}$ of water at $25^{\circ} \mathrm{C}$ forms a saturated solution.
Answer:
True.
 

Question $16 .$
$40 \mathrm{~g}$ of sodium chloride in $100 \mathrm{~g}$ of water at $25^{\circ} \mathrm{C}$ forms an unsaturated solution.
Answer:
False.
Correct statement: $40 \mathrm{~g}$ of sodium chloride in $100 \mathrm{~g}$ of water at $25^{\circ} \mathrm{C}$ forms a supersaturated solution.
 

Question $17 .$
Aquatic animals live more in hot regions.
Answer:
False.
Correct statement: Aquatic animals live more in cold regions.
 

Question $18 .$
Mass percentage is dependent of temperature.
Answer:
False.
Correct statement: Mass percentage is independent of temperature.

Question $19 .$
Hygroscopic substances do not change their physical state on exposure to air.
Answer:
True.
 

Question $20 .$
Deliquescent substances do not change their physical state on exposure to air.
Answer:
False.
Correct statement: Deliquescent substances change its physical state on exposure to air.
 

V. Assertion and Reason
Question $1 .$
Assertion (A): Salt solution-common salt dissolved in water is an example of a binary solution.
Reason (R): A solution with two components is called a binary solution.
(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 $2 .$
Assertion (A): Sugar in water is a true solution.
Reason (R): True solution is a homogeneous mixture that contains small solute particles that are dissolved throughout the solvent.
(a) Both (A) and (R) are wrong
(b) Both $(A)$ and $(R)$ are correct
(c) $(A)$ is wrong but (R) is correct
(d) $(A)$ is correct but (R) is wrong.
Answer:
(b) Both $(A)$ and $(R)$ are correct
 

Question $3 .$
Assertion (A): Solution of sulphur in $\mathrm{CS}_{2}$ is an example of a non-aqueous solution.
Reason (R): The solution in which any liquid other than water acts as a solvent is called the non aqueous solution.
(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 $4 .$
Assertion (A): Solubility of $\mathrm{KNO}_{3}$ increases with increase in temperature.
Reason (R): Solubility of $\mathrm{KNO}_{3}$ is an endothermic process.
(a) Both $(A)$ and (R) are wrong
(b) $B$ oth $(A)$ 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 $5 .$
Assertion (A): Aquatic species are more comfortable in cold water.
Reason (R): Solubility of oxygen is more in cold water.
(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) Both (A) and (R) are correct
 

Question $6 .$
Assertion (A): $\mathrm{CO}_{2}$ gas is filled in soft drinks using the effect of pressure.
Reason (R): A decrease in pressure increases the solubility of a gas in a liquid.
(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:
(c) (A) is correct but (R) is wrong
 

Question $7 .$
Assertion (A): Aqueous copper sulphate is a binary solution.
Reason (R): Copper sulphate solution contains two components i.e., one solute-copper sulphate and one solvent-water.
(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 8.
Assertion (A): Water act as a universal solvent.
Reason (R): Most of the substances are soluble in water.
(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 $9 .$
Assertion (A): When Blue vitriols are gently heated it turns colourless.
Reason (R): It loses five water molecules and becomes anhydrous compounds.
(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 $10 .$
Assertion (A): Anhydrous calcium chloride is an example of a hygroscopic substance.
Reason $(R)$ : Anhydrous calcium chloride changes its physical state on exposure to air.
(a) Both (A) and (R) are correct
(b) Both (A) and (R) are wrong
(c) (A) is wrong but (R) is correct
(d) $(A)$ is correct but (R) is wrong
Answer:
(d) (A) is correct but (R) is wrong.
 

VI. Short Answer Questions.
Question $1 .$
State Henry's Law.
Answer:
The solubility of a gas in liquid is directly proportional to the pressure of the gas over the solution at a definite temperature.

Question $2 .$
Define solute and solvent.
Answer:
In a solution, the component present in a lesser amount by weight is called solute and the component present in a large amount by weight is called solvent.
 

Question $3 .$
What is a
(i) saturated and
(ii) supersaturated solution?
Answer:
(i) Saturated : A solution in which no more solute can be dissolved in a definite amount of the solvent at a given temperature.
(ii) Super saturated solution : A solution which contains more solute than the saturated solution at a given temperature.
 

Question $4 .$
Why water is known as a universal solvent?
Answer:
Most of the solutes (substances) are soluble in water and so it is called universal solvent.
 

Question $5 .$
Common salt dissolves in water easily. Give reason.
Answer:
Common salt is an electrolyte. It is easily dissociated into its ions like $\mathrm{Na}^{+}$and $\mathrm{Cl}^{-}$in polar solvent water. So $\mathrm{NaCl}$ (common salt) an inorganic compound readily dissolves in water.

Question 6 .
What is meant by the ternary solution?
Answer:
Solutions which contain three components are called ternary solutions.
E.g. If salt and sugar are added to water, both dissolves in water forming a solution. Here two solutes are dissolved in one solvent. Therefore it is a ternary solution.
 

Question 7.
Name the type of solution formed in the following cases;
1. $20 \mathrm{~g}$ of $\mathrm{NaCl}$ in $100 \mathrm{~g}$ of water at $25^{\circ} \mathrm{C}$
2. $36 \mathrm{~g}$ of $\mathrm{NaCl}$ in $100 \mathrm{~g}$ of water at $25^{\circ} \mathrm{C}$
3. Nitrogen in soil
4. Sulphur in $\mathrm{CS}_{2}$.
Answer:
1. Unsaturated
2. Saturated
3. Saturated
4. Non-aqueous solution
 

Question 8.
What are concentrated and dilute solutions?
Answer:
Two solutions having the same solute and solvent, the one which contains a higher amount of solute per the given amount of solvent is said to be concentrated solution and the other is said to be dilute solution.
 

Question $9 .$
Define Henry's law.
Answer:
To quantify the solute in a solution, we can use the term concentration. The concentration of a
solution may be defined as the amount of solute present in a given amount of solution or solvent.
(or)
The solubility of a gas in a liquid is directly proportional to the pressure of the gas over the solution at a definite temperature.

Question 10 .
Define Mass percentage.
Answer:
Mass percentage of a solution is defined as the percentage by mass of the solute present in the solution.
Mass percentage,
$$
=\frac{\text { Mass of the solute }}{\text { Mass of the solution }} \times 100 \text {. }
$$
 

Question $11 .$
What is water crystallization?
Answer:
The number of water molecules found in the crystalline substance is called water of crystallization.
 

Question $12 .$
What are hygroscopic substances?
Answer:
Certain substances, when exposed to the atmospheric air at ordinary temperature, absorb moisture without changing their physical state. Such substances are called hygroscopic substances and this property is called hygroscopy.
 

Question $13 .$
List out the examples for hygroscopic substances.
Answer:
- Conc.Sulphuric acid $\left(\mathrm{H}_{2} \mathrm{SO}_{4}\right)$.
- Phosphorus Pentoxide $\left(\mathrm{P}_{2} \mathrm{O}_{5}\right)$.
- Quick lime (CaO).
- Silica gel $\left(\mathrm{SiO}_{2}\right)$.
- Anhydrous calcium chloride $\left(\mathrm{CaCl}_{2}\right)$.

Question $14 .$
What are the Deliquescent substances?
Answer:
Certain substances which are so hygroscopic, when exposed to the atmospheric air at ordinary temperatures, absorb enough water and get completely dissolved. Such substances are called deliquescent substances and this property is called deliquescence.
 

Question $15 .$
When is deliquescence is maximum?
Answer:
- The temperature is low
- The atmosphere is humid.
 

Question $16 .$
Give examples for deliquescent substances.
Answer:
- Calcium chloride $\left(\mathrm{CaCl}_{2}\right)$
- Caustic soda $(\mathrm{NaOH})$
- Caustic potash $(\mathrm{KOH})$
- Ferric chloride $\left(\mathrm{FeCl}_{3}\right)$.
 

VII. Long Answer Questions.
Question $1 .$
From the table given below, furnish your points of inference.

Answer:
Inferences:
- At $25^{\circ} \mathrm{C}, 36 \mathrm{~g} \mathrm{NaCl}$ is dissolved in $100 \mathrm{~g}$ water to give a saturated solution.
- At $25^{\circ} \mathrm{C}, 95 \mathrm{~g} \mathrm{NaBr}$ is dissolved in $100 \mathrm{~g}$ water to get a saturated solution.
- At $25^{\circ} \mathrm{C}, 184 \mathrm{~g} \mathrm{Nal}$ is dissolved in $100 \mathrm{~g}$ water to get a saturated solution.
- The solubility of a solute at a given solvent at a particular temperature is defined as the number of grams of solute necessary to saturate $100 \mathrm{~g}$ of the solvent at that temperature.
- In the above tabular column, we infer that the solubility of NaI is the highest and the solubility of $\mathrm{NaCl}$ is the lowest.
- All the $\mathrm{NaCl}, \mathrm{NaBr}, \mathrm{Nal}$ solution in water are called aqueous solutions.
- Depending upon the amount of the solute, the solutions are classified as a saturated and unsaturated solution.
- The above solutions are saturated solutions.
 

Question $2 .$
Distinguish between the saturated and unsaturated solution at a temperature of $25^{\circ} \mathrm{C}$ using the data given below (Note: Solubility of $\mathrm{NaCl}$ is $36 \mathrm{~g}$ ).
1. $16 \mathrm{~g} \mathrm{NaCl}$ in $100 \mathrm{~g}$ water
2. $36 \mathrm{~g} \mathrm{NaCl}$ in $100 \mathrm{~g}$ water.
Answer:
The solubility of $\mathrm{NaCl}$ is $36 \mathrm{~g}$.
1. $16 \mathrm{~g} \mathrm{NaCl}$ in $100 \mathrm{~g}$ water is an unsaturated solution.
2. $36 \mathrm{~g} \mathrm{NaCl}$ in $100 \mathrm{~g}$ water is a saturated solution.

Question $3 .$
Write a note on the type of solution based on the amount of solute present in a solution.
Answer:
Based on the amount of solute, in the given amount of solvent, solutions are classified into the following types.
(i) Saturated solution: A solution in which no more solute can be dissolved in a definite amount of the solvent at a given temperature is called saturated solution. Eg: $36 \mathrm{~g}$ of sodium chloride in $100 \mathrm{~g}$ of water at $25^{\circ} \mathrm{C}$ forms saturated solution. Further addition of sodium chloride, leave it undissolved.
(ii) Unsaturated solution : Unsaturated solution is one that contains less solute than that of the saturated solution at a given temperature. Eg: $10 \mathrm{~g}$ or $20 \mathrm{~g}$ or $30 \mathrm{~g}$ of Sodium chloride in $100 \mathrm{~g}$ of water at $25^{\circ} \mathrm{C}$ forms an unsaturated solution.
(iii) Super saturated solution: Supersaturated solution is one that contains more solute than the saturated solution at a given temperature. Eg: $40 \mathrm{~g}$ of sodium chloride in $100 \mathrm{~g}$ of water at $25^{\circ} \mathrm{C}$ forms super saturated solution. This state can be achieved by altering any other conditions liken temperature, pressure. Super saturated solutions are unstable, and the solute is reappearing as crystals when the solution is disturbed.
 

Question $4 .$
Find the concentration of a solution in terms of weight per cent if $20 \mathrm{~g}$ of common salt is dissolved in $50 \mathrm{~g}$ of water.
Answer:

Weight percent $=\frac{\text { Weight of the solute }}{\text { Weight of the solute }+\text { Weight of the solvent }} \times 100$
Weight of the common salt (solute) $=20 \mathrm{~g}$
Weight of water (solvent)
$=50 \mathrm{~g}$
$$
\begin{aligned}
\therefore \text { Weight percent } &=\frac{20}{20+50} \times 100 \\
&=\frac{20}{70} \times 100=28.57 \% \\
\therefore \text { Weight percent } &=28.57 \%
\end{aligned}
$$

VIII. HOT Questions.
Question $1 .$
Observe the diagram.
1. Which is a concentrated solution and why?
2. Which is dilute solution and why?

Answer:
1. Flask (b) is a concentrated solution. Because (b) flask contains a large number of solute particles than (a) flask.
2. Flask (a) is a dilute solution. Because (a) flask contains a lesser number of solute particles than (b) flask.
 

Question $2 .$
Where we use the phrase - "Like dissolves Like" and explain the meaning of the phrase?
Answer:
The phrase "like dissolves like" is often used for predicting solubility. This expression means that dissolving occurs when similarities exist between the solvent and the solute. For example, Common salt is a polar compound and dissolves readily in polar solvent like water.
 

Question $3 .$
Why bubbling occurs when water is boiled?
Answer:
The solubility of a gas in liquid decrease with increase in temperature. Generally, water contains dissolved oxygen. When water is boiled, the solubility of oxygen in water decreases, so oxygen escapes in the form of bubbles.
 

Question $4 .$
What happens when blue vitriol is heated? Explain.
Answer:
When blue vitriol (Copper sulphate pentahydrate) crystals are gently heated, it loses it five water molecules and becomes colourless anhydrous copper sulphate.

Question $1 .$
Take $10 \mathrm{~g}$ of common salt and dissolve it in $40 \mathrm{~g}$ of water. Find the concentration of a solution in terms of weight per cent.
Solution:
Weight percent $=\frac{\text { Weight of the solute }}{\text { Weight of solute }+\text { Weight of solvent }} \times 100$
$$
=\frac{10}{10+40} \times 100=20 \% \text {. }
$$
 

Question $2 .$
$2 \mathrm{~g}$ of potassium sulphate was dissolved in $12.5 \mathrm{ml}$ of water. On cooling, the first crystals appeared at $60^{\circ} \mathrm{C}$. What is the solubility of potassium sulphate in water at $60^{\circ} \mathrm{C}$ ? Solution. $12.5 \mathrm{ml}$ of water weighs $12.5 \mathrm{~g}$.
Solution:
In $12.5 \mathrm{~g}$ of water, the amount of potassium sulphate dissolved is $2 \mathrm{~g}$.
In $1 \mathrm{~g}$ of water, the amount of potassium sulphate dissolved is $2 / 12.5 \mathrm{~g}$.
Hence in $100 \mathrm{~g}$ of water, the amount of potassium sulphate dissolved is $(2 \times 100) / 12.5=16 \mathrm{~g}$.
The solubility of potassium sulphate in the water at $60^{\circ} \mathrm{C}$ is $16 \mathrm{~g}$.

Question $3 .$
$50 \mathrm{~g}$ of a saturated solution of $\mathrm{NaCl}$ at $30^{\circ} \mathrm{C}$ is evaporated to dryness and $13.2 \mathrm{~g}$ of dry NaCl was obtained. Find the solubility of $\mathrm{NaCl}$ at $30^{\circ} \mathrm{C}$ in water.
Solution:
Mass of water in solution $=50-13.2=36.8 \mathrm{~g}$
Solubility of $\mathrm{NaCl}$
$$
\begin{aligned}
=& \frac{\text { Mass of } \mathrm{NaCl}}{\text { Mass of water }} \\
=& \frac{13.2}{36.8} \times 100=36 \mathrm{~g}
\end{aligned}
$$
Solubility of $\mathrm{NaCl}=36 \mathrm{~g}$ (approx).
 

Question $4 .$
An empty evaporating dish weighs $20.0 \mathrm{~g}$. After adding a saturated solution of $\mathrm{NaNO}_{3}$, the dish weighs $66.0 \mathrm{~g}$. When evaporated to dryness, the dish with crystals weighs $42.5 \mathrm{~g}$. Find the solubility of $\mathrm{NaNO}_{3}$ at $20^{\circ} \mathrm{C}$.
Solution:
Weight of saturated solution of $\mathrm{NaNO}_{3}=(66.0-20.0) \mathrm{g}=46.0 \mathrm{~g}$
Weight of crystals of $\mathrm{NaNO}_{3}=(41.5-20.0) \mathrm{g}=21.5 \mathrm{~g}$
Weight of water in saturated solution $=(46.0-21.5) \mathrm{g}=24.5 \mathrm{~g}$
Solubility of $\mathrm{NaNO} 3=\frac{\text { Weight of } \mathrm{NaNO}_{3} \text { crystals }}{\text { Weight of water }} \times 100$
$=\frac{21.5}{24.5} \times 100=87.7 \mathrm{~g}$
Solubility of $\mathrm{NaNO}_{3}$ at $20^{\circ} \mathrm{C}$ is $=87.7 \mathrm{~g}$ in $100 \mathrm{~g} \mathrm{H}_{2} \mathrm{O}$.
 

Question $5 .$
$30 \mathrm{~g}$ sugar is dissolved in $170 \mathrm{~g}$ of water. Calculate the concentration of solution in terms of weight percent.
Solution:
Weight percent $=\frac{\text { Weight of the solute }}{\text { Weight of solute }+\text { Weight of solvent }} \times 100$
$=\frac{30}{30+170} \times 10=15 \%$.

Question 6 .
$50 \mathrm{~g}$ common salt is dissolved in $150 \mathrm{~g}$ of water; Find oat the concentration of solution in terms of weight percent.
Solution:
Weight percent $=\frac{\text { Weight of the solute }}{\text { Weight of solute }+\text { Weight of solvcnt }} \times 100$
$$
\begin{aligned}
&=\frac{50}{50+150} \times 100 \\
&=25 \% .
\end{aligned}
$$