NEET Solutions — Set 8

Question 1

A solution of a non-volatile solute in water has a vapor pressure of 22.8 mm Hg at a temperature where pure water’s vapor pressure is 24 mm Hg. What is the relative lowering of vapor pressure?

Accepted Answer

Relative lowering = $ \frac{p^0 - p}{p^0} $. $ \frac{24 - 22.8}{24} = \frac{1.2}{24} = 0.05 $.

Question 2

What is the molality of a solution containing 16 g of sorbitol (molar mass = 182 g/mol) in 800 g of water?

Accepted Answer

Moles of sorbitol = $ \frac{16}{182} \approx 0.0879 \, \text{mol} $. Mass of solvent = 800 g = 0.8 kg. Molality = $ \frac{0.0879}{0.8} \approx 0.1099 \, \text{mol/kg} $.

Question 3

What is the boiling point elevation of a solution containing 6 g of urea (molar mass = 60 g/mol) in 500 g of water? ($ K_b = 0.52 \, \text{K kg mol}^{-1} $)

Accepted Answer

Moles of urea = $ \frac{6}{60} = 0.1 \, \text{mol} $. Molality = $ \frac{0.1}{0.5} = 0.2 \, \text{mol/kg} $. $ \Delta T_b = 0.52 \times 0.2 = 0.104 \, \text{K} $.

NEET Chemistry: Solutions — Practice Set 8

Q1. A solution of a non-volatile solute in water has a vapor pressure of 22.8 mm Hg at a temperature where pure water’s vapor pressure is 24 mm Hg. What is the relative lowering of vapor pressure?

Q2. What is the molality of a solution containing 16 g of sorbitol (molar mass = 182 g/mol) in 800 g of water?

Q3. What is the boiling point elevation of a solution containing 6 g of urea (molar mass = 60 g/mol) in 500 g of water? (\( K_b = 0.52 \, \text{K kg mol}^{-1} \))

Q4. What is the mole fraction of a solute if the vapor pressure of a solution is 23 mm Hg and that of pure solvent is 25 mm Hg?

Q5. A solution is prepared by dissolving 15 g of a non-volatile solute in 300 g of water. If the freezing point depression is 0.465°C and \( K_f = 1.86 \, \text{K kg mol}^{-1} \), what is the molar mass of the solute?

Q6. What is the molar mass of a solute if 4 g of it in 500 mL of solution produces an osmotic pressure of 0.492 atm at 27°C? (\( R = 0.0821 \, \text{L atm mol}^{-1} \text{K}^{-1} \))

Q7. What is the mass of water needed to prepare 150 g of a 20% by mass sugar solution?

Q8. A solution of two volatile liquids has vapor pressures of 400 mm Hg and 600 mm Hg. If the mole fraction of the first component in the liquid phase is 0.5 and the total vapor pressure is 480 mm Hg, what is the vapor pressure lowering of the first component?

Q9. A gas has a Henry’s law constant of 400 bar at 25°C. If the partial pressure is reduced from 8 bar to 4 bar, what is the percentage decrease in solubility?

Q10. A gas has a Henry’s law constant of 350 bar at 25°C. If 0.02 mole of the gas is dissolved in 800 g of water at 7 bar, what is the molality of the solution?