NEET Solutions — Set 7

Question 1

A solution is prepared by dissolving 18 g of a solute in water to make 500 mL of solution with a density of 1.2 g/mL. If the molality is 0.2 mol/kg, what is the molar mass of the solute?

Accepted Answer

Total mass = $ 500 \times 1.2 = 600 \, \text{g} $. Mass of water = $ 600 - 18 = 582 \, \text{g} = 0.582 \, \text{kg} $. Molality = $ \frac{\text{moles}}{0.582} = 0.2 $. Moles = $ 0.2 \times 0.582 = 0.1164 $. Molar mass = $ \frac{18}{0.1164} \approx 154.64 \, \text{g/mol} $.

Question 2

What is the mole fraction of a solute if the vapor pressure of a solution is 28 mm Hg and that of pure solvent is 30 mm Hg?

Accepted Answer

$ \frac{p^0 - p}{p^0} = x_{\text{solute}} $. $ \frac{30 - 28}{30} = \frac{2}{30} \approx 0.0667 $.

Question 3

A solution is made by dissolving 15 g of a solute (molar mass = 30 g/mol) in water. If the boiling point elevation is 0.26°C and $ K_b = 0.52 \, \text{K kg mol}^{-1} $, what is the mass of water?

Accepted Answer

Moles = $ \frac{15}{30} = 0.5 $. $ \Delta T_b = K_b \cdot m $. $ 0.26 = 0.52 \times \frac{0.5}{w} $, $ w = \frac{0.5 \times 0.52}{0.26} = 1 \, \text{kg} = 1000 \, \text{g} $.

NEET Chemistry: Solutions — Practice Set 7

Q1. A solution is prepared by dissolving 18 g of a solute in water to make 500 mL of solution with a density of 1.2 g/mL. If the molality is 0.2 mol/kg, what is the molar mass of the solute?

Q2. What is the mole fraction of a solute if the vapor pressure of a solution is 28 mm Hg and that of pure solvent is 30 mm Hg?

Q3. A solution is made by dissolving 15 g of a solute (molar mass = 30 g/mol) in water. If the boiling point elevation is 0.26°C and \( K_b = 0.52 \, \text{K kg mol}^{-1} \), what is the mass of water?

Q4. What is the mass percentage of a solution if 20 g of a solute is dissolved in 180 g of water?

Q5. A solute dissociates into 2 ions with a van’t Hoff factor of 1.4. What is the degree of dissociation?

Q6. What is the boiling point elevation of a solution containing 5 g of glucose (molar mass = 180 g/mol) in 250 g of water? (\( K_b = 0.52 \, \text{K kg mol}^{-1} \))

Q7. A solution is prepared by mixing 50 g of a solute with 150 g of water. If the solute’s mass percentage in a second solution (made with the same solute and water) is 40%, what mass of water is required for the second solution?

Q8. What is the molar mass of a solute if 5 g of it in 250 mL of solution produces an osmotic pressure of 0.984 atm at 27°C? (\( R = 0.0821 \, \text{L atm mol}^{-1} \text{K}^{-1} \))

Q9. The van’t Hoff factor of a 0.05 m NaCl solution is 1.9. What is the osmotic pressure at 27°C? (\( R = 0.0821 \, \text{L atm mol}^{-1} \text{K}^{-1} \), assume 1 L solution)

Q10. A solution of two volatile liquids has vapor pressures of 250 mm Hg and 350 mm Hg for pure components. If the total vapor pressure is 310 mm Hg, what is the mole fraction of the first component in the vapor phase?