NEET Solutions — Set 17

Question 1

A gas has a Henry’s law constant of 250 bar. If its mole fraction in a solution is 0.008, what is its partial pressure?

Accepted Answer

Henry’s law: $ p = K_H \cdot x $. $ p = 250 \times 0.008 = 2 \, \text{bar} $.

Question 2

The vapor pressure of pure benzene is 100 mm Hg at a certain temperature. If a solution with a non-volatile solute has a vapor pressure of 95 mm Hg, what is the mole fraction of benzene in the solution?

Accepted Answer

Raoult’s law: $ p = p^0 \cdot x_{\text{benzene}} $. $ 95 = 100 \cdot x_{\text{benzene}} $. $ x_{\text{benzene}} = \frac{95}{100} = 0.95 $.

Question 3

A solution of 8 g of a solute (molar mass = 80 g/mol) in 500 g of water freezes at -0.372°C. What is the van’t Hoff factor? ($ K_f = 1.86 \, \text{K kg mol}^{-1} $)

Accepted Answer

Moles = $ \frac{8}{80} = 0.1 $. Molality = $ \frac{0.1}{0.5} = 0.2 \, \text{mol/kg} $. $ \Delta T_f = i \cdot K_f \cdot m $. $ 0.372 = i \times 1.86 \times 0.2 $, $ i = \frac{0.372}{1.86 \times 0.2} = 1 $.

NEET Chemistry: Solutions — Practice Set 17

Q1. A gas has a Henry’s law constant of 250 bar. If its mole fraction in a solution is 0.008, what is its partial pressure?

Q2. The vapor pressure of pure benzene is 100 mm Hg at a certain temperature. If a solution with a non-volatile solute has a vapor pressure of 95 mm Hg, what is the mole fraction of benzene in the solution?

Q3. A solution of 8 g of a solute (molar mass = 80 g/mol) in 500 g of water freezes at -0.372°C. What is the van’t Hoff factor? (\( K_f = 1.86 \, \text{K kg mol}^{-1} \))

Q4. A solution is prepared by dissolving 15 g of a solute in water to make 250 mL of solution. If the osmotic pressure is 1.476 atm at 27°C, what is the molar mass of the solute? (\( R = 0.0821 \, \text{L atm mol}^{-1} \text{K}^{-1} \))

Q5. What is the freezing point depression of a solution containing 12 g of a non-electrolyte solute (molar mass = 60 g/mol) in 200 g of water? (\( K_f = 1.86 \, \text{K kg mol}^{-1} \))

Q6. What is the vapor pressure of a solution made by mixing two volatile liquids with vapor pressures 300 mm Hg and 400 mm Hg, if their mole fractions in the solution are 0.4 and 0.6, respectively?

Q7. The vapor pressure of a pure solvent is 40 mm Hg. What is the vapor pressure of a solution with a mole fraction of solute 0.25?

Q8. A solution is made by dissolving 20 g of a solute (molar mass = 40 g/mol) in water. If the freezing point depression is 0.465°C and \( K_f = 1.86 \, \text{K kg mol}^{-1} \), what is the total mass of the solution?

Q9. What is the mole fraction of methanol (molar mass = 32 g/mol) in a solution containing 16 g of methanol and 72 g of water?

Q10. A 0.2 molal solution of NaBr in water has a freezing point depression of 0.744°C. What is the van’t Hoff factor? (\( K_f = 1.86 \, \text{K kg mol}^{-1} \))