Updated By SaraNextGen

On March 11, 2024, 11:35 AM

Question 1.11:

What is the concentration of sugar (C₁₂H₂₂O₁₁) in mol L^–1 if its 20 g are dissolved in enough water to make a final volume up to 2 L?

Answer:

Molarity (M) of a solution is given by,

= 0.02925 mol L^–1

Molar concentration of sugar = 0.02925 mol L^–1

Question 1.12:

If the density of methanol is 0.793 kg L^–1, what is its volume needed for making 2.5 L of its 0.25 M solution?

Answer:

Molar mass of methanol (CH₃OH) = (1 × 12) + (4 × 1) + (1 × 16)

= 32 g mol^–1

= 0.032 kg mol^–1

Molarity of methanol solution 

= 24.78 mol L^–1

(Since density is mass per unit volume)

Applying,

M₁V₁ = M₂V₂

(Given solution) (Solution to be prepared)

(24.78 mol L^–1) V₁ = (2.5 L) (0.25 mol L^–1)

V₁ = 0.0252 L

V₁ = 25.22 mL

Question 1.13:

Pressure is determined as force per unit area of the surface. The SI unit of pressure, Pascal is as shown below:

1Pa = 1N m^–2

If mass of air at sea level is 1034 g cm^–2, calculate the pressure in Pascal.

Answer:

Pressure is defined as force acting per unit area of the surface.

= 1.01332 × 10⁵ kg m^–1s^–2

We know,

1 N = 1 kg ms^–2

Then,

1 Pa = 1 Nm^–2 = 1 kg m^–2s^–2

1 Pa = 1 kg m^–1s^–2

 Pressure = 1.01332 × 10⁵ Pa

Question 1.14:

What is the SI unit of mass? How is it defined?

Answer:

The SI unit of mass is kilogram (kg). 1 Kilogram is defined as the mass equal to the mass of the international prototype of kilogram.

Question 1.15:

Match the following prefixes with their multiples:

Answer:

Question 1.16:

What do you mean by significant figures?

Answer:

Significant figures are those meaningful digits that are known with certainty.

They indicate uncertainty in an experiment or calculated value. For example, if 15.6 mL is the result of an experiment, then 15 is certain while 6 is uncertain, and the total number of significant figures are 3.

Hence, significant figures are defined as the total number of digits in a number including the last digit that represents the uncertainty of the result.

Question 1.17:

A sample of drinking water was found to be severely contaminated with chloroform, CHCl₃, supposed to be carcinogenic in nature. The level of contamination was 15 ppm (by mass).

(i) Express this in percent by mass.

(ii) Determine the molality of chloroform in the water sample.

Answer:

(i) 1 ppm is equivalent to 1 part out of 1 million (10⁶) parts.

Mass percent of 15 ppm chloroform in water

(ii) 100 g of the sample contains 1.5 × 10^–3 g of CHCl_3.

⇒ 1000 g of the sample contains 1.5 × 10^–2 g of CHCl_3.

Molality of chloroform in water

Molar mass of CHCl₃ = 12.00 + 1.00 + 3(35.5)

= 119.5 g mol^–1

Molality of chloroform in water = 0.0125 × 10^–2 m

= 1.25 × 10^–4 m

Question 1.18:

Express the following in the scientific notation:

(i) 0.0048

(ii) 234,000

(iii) 8008

(iv) 500.0

(v) 6.0012

Answer:

(i) 0.0048 = 4.8× 10^–3

(ii) 234, 000 = 2.34 ×10⁵

(iii) 8008 = 8.008 ×10³

(iv) 500.0 = 5.000 × 10²

(v) 6.0012 = 6.0012

Question 1.19:

How many significant figures are present in the following?

(i) 0.0025

(ii) 208

(iii) 5005

(iv) 126,000

(v) 500.0

(vi) 2.0034

Answer:

(i) 0.0025

There are 2 significant figures.

(ii) 208

There are 3 significant figures.

(iii) 5005

There are 4 significant figures.

(iv) 126,000

There are 3 significant figures.

(v) 500.0

There are 4 significant figures.

(vi) 2.0034

There are 5 significant figures.

Question 1.20:

Round up the following upto three significant figures:

(i) 34.216

(ii) 10.4107

(iii) 0.04597

(iv) 2808

Answer:

(i) 34.2

(ii) 10.4

(iii) 0.0460

(iv) 2810

Question 1.21:

The following data are obtained when dinitrogen and dioxygen react together to form different compounds:

Mass of dinitrogen     Mass of dioxygen

(i)            14 g                            16 g

(ii)           14 g                            32 g

(iii)          28 g                            32 g

(iv)          28 g                            80 g

(a) Which law of chemical combination is obeyed by the above experimental data?Give its statement.

(b) Fill in the blanks in the following conversions:

(i) 1 km = …………………. mm = …………………. pm

(ii) 1 mg = …………………. kg = …………………. ng

(iii) 1 mL = …………………. L = …………………. dm³

Answer:

(a)

If we fix the mass of dinitrogen at 28 g, then the masses of dioxygen that will combine with the fixed mass of dinitrogen are 32 g, 64 g, 32 g, and 80 g.

The masses of dioxygen bear a whole number ratio of 1:2:2:5. Hence, the given experimental data obeys the law of multiple proportions. The law states that if two elements combine to form more than one compound, then the masses of one element that combines with the fixed mass of another element are in the ratio of small whole numbers.

(b)

(i) 1 km = 1 km ×

1 km = 10⁶ mm

1 km = 1 km ×

1 km = 10¹⁵ pm

Hence, 1 km = 10⁶ mm = 10¹⁵ pm

(ii) 1 mg = 1 mg ×

⇒ 1 mg = 10^–6 kg

1 mg = 1 mg × 

⇒ 1 mg = 10⁶ ng

1 mg = 10^–6 kg = 10⁶ ng

(iii) 1 mL = 1 mL × 

⇒ 1 mL = 10^–3 L

1 mL = 1 cm³ = 1 cm³

⇒ 1 mL = 10^–3 dm³

1 mL = 10^–3 L = 10^–3 dm³