NEET Solutions — Set 2

Question 1

What is the mole fraction of chloroform (molar mass = 119.5 g/mol) in a solution containing 59.75 g of chloroform and 36 g of water?

Accepted Answer

Moles of chloroform = $ \frac{59.75}{119.5} = 0.5 \, \text{mol} $. Moles of water = $ \frac{36}{18} = 2 \, \text{mol} $. Total moles = $ 0.5 + 2 = 2.5 $. Mole fraction = $ \frac{0.5}{2.5} = 0.2 $.

Question 2

The vapor pressure of a solvent decreases from 50 mm Hg to 47 mm Hg when a non-volatile solute is added. If an additional amount of the same solute is added to double the molality, what will be the new vapor pressure?

Accepted Answer

$ \frac{p^0 - p}{p^0} = x_{\text{solute}} $. Initial: $ \frac{50 - 47}{50} = 0.06 $. Doubling molality doubles $ x_{\text{solute}} $ (approximately for dilute solutions), so new $ x_{\text{solute}} = 0.12 $. New $ p = p^0 (1 - x_{\text{solute}}) = 50 (1 - 0.12) = 44 \, \text{mm Hg} $.

Question 3

A gas has a partial pressure of 3 bar above a solution, and its Henry’s law constant is 150 bar. What is the mole fraction of the gas in the solution?

Accepted Answer

Henry’s law: $ p = K_H \cdot x $. $ x = \frac{3}{150} = 0.02 $.

NEET Chemistry: Solutions — Practice Set 2

Q1. What is the mole fraction of chloroform (molar mass = 119.5 g/mol) in a solution containing 59.75 g of chloroform and 36 g of water?

Q2. The vapor pressure of a solvent decreases from 50 mm Hg to 47 mm Hg when a non-volatile solute is added. If an additional amount of the same solute is added to double the molality, what will be the new vapor pressure?

Q3. A gas has a partial pressure of 3 bar above a solution, and its Henry’s law constant is 150 bar. What is the mole fraction of the gas in the solution?

Q4. How many grams of NaCl (molar mass = 58.5 g/mol) are required to prepare 400 mL of a 0.25 M solution?

Q5. What is the mass percentage of a solution prepared by dissolving 25 g of sugar in 75 g of water?

Q6. A solution boils at 100.208°C at 1 atm. What is the molality if \( K_b = 0.52 \, \text{K kg mol}^{-1} \)?

Q7. A solution of two volatile liquids has vapor pressures of 500 mm Hg and 700 mm Hg. If the total vapor pressure is 580 mm Hg, what is the mole fraction of the first component in the vapor phase?

Q8. A solution boils at 100.13°C at 1 atm. What is the molality if \( K_b = 0.52 \, \text{K kg mol}^{-1} \)?

Q9. How many grams of MgCl₂ (molar mass = 95 g/mol) are needed to prepare 500 mL of a 0.3 M solution?

Q10. A gas has a Henry’s law constant of 200 bar. If its partial pressure is 4 bar, what is the mole fraction in the solution?