NEET Solutions — Set 11

Question 1

What is the mole fraction of acetone (molar mass = 58 g/mol) in a solution containing 29 g of acetone and 54 g of water?

Accepted Answer

Moles of acetone = $ \frac{29}{58} = 0.5 \, \text{mol} $. Moles of water = $ \frac{54}{18} = 3 \, \text{mol} $. Total moles = $ 0.5 + 3 = 3.5 $. Mole fraction = $ \frac{0.5}{3.5} \approx 0.143 $.

Question 2

A 0.25 M solution of MgCl₂ (assuming complete dissociation) has an osmotic pressure of 1.845 atm at a certain temperature. What is the temperature? ($ R = 0.0821 \, \text{L atm mol}^{-1} \text{K}^{-1} $)

Accepted Answer

For MgCl₂, $ i = 3 $ (Mg²⁺ + 2Cl⁻). $ \Pi = i \cdot M \cdot RT $. $ 1.845 = 3 \times 0.25 \times 0.0821 \times T $. $ T = \frac{1.845}{0.75 \times 0.0821} \approx 30 \, \text{K} $.

Question 3

A solution of a non-volatile solute in water boils at 100.39°C at 1 atm. If the solute’s molality is 0.75 mol/kg, what is the value of $ K_b $ for water?

Accepted Answer

$ \Delta T_b = K_b \cdot m $. $ 100.39 - 100 = 0.39 $. $ 0.39 = K_b \times 0.75 $. $ K_b = \frac{0.39}{0.75} = 0.52 \, \text{K kg mol}^{-1} $.

NEET Chemistry: Solutions — Practice Set 11

Q1. What is the mole fraction of acetone (molar mass = 58 g/mol) in a solution containing 29 g of acetone and 54 g of water?

Q2. A 0.25 M solution of MgCl₂ (assuming complete dissociation) has an osmotic pressure of 1.845 atm at a certain temperature. What is the temperature? (\( R = 0.0821 \, \text{L atm mol}^{-1} \text{K}^{-1} \))

Q3. A solution of a non-volatile solute in water boils at 100.39°C at 1 atm. If the solute’s molality is 0.75 mol/kg, what is the value of \( K_b \) for water?

Q4. A solution of two volatile liquids has vapor pressures of 200 mm Hg and 300 mm Hg for pure components. If the mole fraction of the first is 0.7, what is the total vapor pressure?

Q5. A solution contains 7 g of a solute (molar mass = 140 g/mol) in 350 mL of solution. What is the molarity?

Q6. A solute dissociates into 2 ions with a van’t Hoff factor of 1.6. What is the degree of dissociation?

Q7. A solution is made by mixing 30 g of a solute (molar mass = 60 g/mol) with water. If the molality is 0.5 mol/kg, what is the total mass of the solution?

Q8. A solution contains 25 g of a solute in 75 g of water. If the mass percentage of the solute is reduced to 20% by adding water, what is the total mass of the new solution?

Q9. The vapor pressure of pure ethanol is 60 mm Hg. What is the vapor pressure of a solution with a solute mole fraction of 0.2?

Q10. A solution contains 20 g of a solute in 80 g of solvent. If the mass percentage is 20%, what is the mass of the solution?