**2.1. Calculate the mass percentage of benzene (C _{6}H_{6}) and carbon tetrachloride (CCl_{4}) if 22 g of benzene is dissolved in 122 g of carbon tetrachloride.**

**Answer: **

Mass of solution = Mass of C_{6}H_{6} + Mass of CCl_{4}

= 22 g+122 g= 144 g

Mass % of benzene = 22/144 x 100 =15.28 %

Mass % of CCl_{4} = 122/144 x 100 = 84.72 %

**2.2. Calculate the mole fraction of benzene in solution containing 30% by mass in carbon tetrachloride.**

**Answer: **

30% by mass of C_{6}H_{6} in CCl_{4} => 30 g C_{6}H_{6} in 100 g solution

.’. no. of moles of C_{6}H_{6},(^{n}C_{6}h_{6}) = 30/78 = 0.385

**2.3. Calculate the molarity of each of the following solutions**

**(a) **30 g of Co(NO_{3})26H_{2}O in 4·3 L of solution**(b) **30 mL of 0-5 M H_{2}SO_{4} diluted to 500 mL.

**Answer: **

**2.4. Calculate the mass of urea (NH _{2}CONH_{2}) required in making 2.5 kg of 0.25 molal aqueous solution.**

**Answer: **

0.25 Molal aqueous solution to urea means that

moles of urea = 0.25 mole

mass of solvent (NH_{2}CONH_{2}) = 60 g mol^{-1}

.’. 0.25 mole of urea = 0.25 x 60=15g

Mass of solution = 1000+15 = 1015g = 1.015 kg

1.015 kg of urea solution contains 15g of urea

.’. 2.5 kg of solution contains urea =15/1.015 x 2.5 = 37 g

**2.5. Calculate**

**(a) molality****(b) molarity and****(c) mole fraction of KI if the density of 20% (mass/mass) aqueous KI solution is 1·202 g mL ^{-1}.**

**Answer: **

**Step I.** **Calculation of molality of solution**

Weight of KI in 100 g of the solution = 20 g

Weight of water in the solution = 100 – 20 = 80 g = 0-08 kg

Molar mass of KI = 39 + 127 = 166 g mol^{-1}.

**Step II.** **Calculation of molarity of solution**

**Step III. Calculation of mole fraction of Kl**

**2.6. H _{2 }S, a toxic gas with rotten egg like smell, is used for the qualitative analysis. If the solubility of H_{2}S in water at STP is 0.195 m, calculate Henry’s law constant.**

**Answer: **

Solubility of H_{2}S gas = 0.195 m

= 0.195 mole in 1 kg of solvent

1 kg of solvent = 1000g

**2.7. Henry’s law constant for CO _{2} in water is 1.67 x 10^{8 }Pa at 298 K. Calculate the quantity of CO_{2} in 500 mL of soda water when packed under 2.5 atm CO_{2} pressure at 298 K.**

**Answer: **

**2.8 The vapour pressures of pure liquids A and B are 450 mm and 700 mm of Hg respectively at 350 K. Calculate the composition of the liquid mixture if total vapour pressure is 600 mm of Hg. Also find the composition in the vapour phase.**

**Answer: **

Vapour pressure of pure liquid A (\({ P }_{ A }^{ \circ }\)) = 450 mm

Vapour pressure of pure liquid B (\({ P }_{ B }^{ \circ }\)) = 700 mm

Total vapour pressure of the solution (P) = 600 mm

**2.9. Vapour pressure of pure water at 298 K is 23.8 m m Hg. 50 g of urea (NH _{2}CONH_{2}) is dissolved in 850 g of water. Calculate the vapour pressure of water for this solution and its relative lowering.**

**Answer: **

**2.10. Boiling point of water at 750 mm Hg is 99.63°C. How much sucrose is to be added to 500 g of water such that it boils at 100°C.**

**Answer: **

**2.11 Calculate the mass of ascorbic acid (vitamin C, C _{6}H_{8}O_{6}) to be dissolved in 75 g of acetic acid to lower its melting point by 1·5°C. (K_{f} for CH_{3}COOH) = 3·9 K kg mol^{-1})**

**Answer: **

**2.12. Calculate the osmotic pressure in pascals exerted by a solution prepared by dissolving 1.0 g of polymer of molar mass 185,000 in 450 mL of water at 37°C.**

**Answer: **