NEET Solutions — Set 3

Question 1

A solution contains 8 g of a solute (molar mass = 80 g/mol) in 400 mL of solution. What is the molarity?

Accepted Answer

Moles of solute = $ \frac{8}{80} = 0.1 \, \text{mol} $. Volume = 400 mL = 0.4 L. Molarity = $ \frac{0.1}{0.4} = 0.25 \, \text{M} $.

Question 2

A 0.2 M solution of a solute in 300 mL of water has an osmotic pressure of 1.476 atm at 27°C. If the solute dissociates into 2 ions, what is the degree of dissociation? ($ R = 0.0821 \, \text{L atm mol}^{-1} \text{K}^{-1} $)

Accepted Answer

$ \Pi = i \cdot M \cdot RT $. $ 1.476 = i \times 0.2 \times 0.0821 \times 300 $. $ i = \frac{1.476}{0.2 \times 24.63} \approx 0.3 \times 10 = 3 $, recalculate: $ i = \frac{1.476}{4.926} \approx 0.3 \times 6 = 1.8 $. $ i = 1 + \alpha $, $ 1.8 = 1 + \alpha $, $ \alpha = 0.8 $.

Question 3

The vapor pressure of pure toluene is 40 mm Hg at a certain temperature. If a solution with a non-volatile solute has a vapor pressure of 38 mm Hg, what is the mole fraction of the solute?

Accepted Answer

$ \frac{p^0 - p}{p^0} = x_{\text{solute}} $. $ \frac{40 - 38}{40} = \frac{2}{40} = 0.05 $.

NEET Chemistry: Solutions — Practice Set 3

Q1. A solution contains 8 g of a solute (molar mass = 80 g/mol) in 400 mL of solution. What is the molarity?

Q2. A 0.2 M solution of a solute in 300 mL of water has an osmotic pressure of 1.476 atm at 27°C. If the solute dissociates into 2 ions, what is the degree of dissociation? (\( R = 0.0821 \, \text{L atm mol}^{-1} \text{K}^{-1} \))

Q3. The vapor pressure of pure toluene is 40 mm Hg at a certain temperature. If a solution with a non-volatile solute has a vapor pressure of 38 mm Hg, what is the mole fraction of the solute?

Q4. A 0.25 molal NaCl solution has a van’t Hoff factor of 1.9. What is the freezing point depression? (\( K_f = 1.86 \, \text{K kg mol}^{-1} \))

Q5. A 0.1 molal solution of a solute in water has a boiling point elevation of 0.156°C. If the solute dissociates into 3 ions, what is the degree of dissociation? (\( K_b = 0.52 \, \text{K kg mol}^{-1} \))

Q6. A solution is made by mixing 40 g of a solute (molar mass = 80 g/mol) with water. If the freezing point depression is 0.93°C and \( K_f = 1.86 \, \text{K kg mol}^{-1} \), what is the total mass of the solution?

Q7. What is the mass of water required to prepare 400 g of a 15% by mass solution of a solute?

Q8. What is the molality of a solution containing 60 g of glucose (molar mass = 180 g/mol) in 540 g of water?

Q9. A solution of two volatile liquids has vapor pressures of 600 mm Hg and 800 mm Hg. If the total vapor pressure is 680 mm Hg, what is the mole fraction of the first component in the vapor phase?

Q10. A solution of 5 g of a solute (molar mass = 100 g/mol) in 200 g of water boils at 100.13°C at 1 atm. What is the van’t Hoff factor? (\( K_b = 0.52 \, \text{K kg mol}^{-1} \))