NEET Solutions — Set 6

Question 1

A mixture of ethanol (molar mass = 46 g/mol) and water has a total mass of 138 g. If the mole fraction of ethanol is 0.25, what is the mass of ethanol in the mixture?

Accepted Answer

Moles of ethanol = $ n_e $, moles of water = $ n_w $, total moles = $ n_e + n_w $. $ \frac{n_e}{n_e + n_w} = 0.25 $. Mass: $ 46 n_e + 18 n_w = 138 $. From mole fraction: $ n_w = 3 n_e $. $ 46 n_e + 18 (3 n_e) = 138 $, $ 46 n_e + 54 n_e = 138 $, $ 100 n_e = 138 $, $ n_e = 1.38 $. Mass of ethanol = $ 1.38 \times 46 = 63.48 \, \text{g} $.

Question 2

What is the mole fraction of benzene (molar mass = 78 g/mol) in a solution containing 39 g of benzene and 92 g of toluene (molar mass = 92 g/mol)?

Accepted Answer

Moles of benzene = $ \frac{39}{78} = 0.5 \, \text{mol} $. Moles of toluene = $ \frac{92}{92} = 1 \, \text{mol} $. Total moles = $ 0.5 + 1 = 1.5 $. Mole fraction = $ \frac{0.5}{1.5} \approx 0.333 $.

Question 3

A gas has a Henry’s law constant of 500 bar at 25°C. If the partial pressure increases from 5 bar to 10 bar, what is the percentage increase in solubility?

Accepted Answer

Initial $ x = \frac{5}{500} = 0.01 $. New $ x = \frac{10}{500} = 0.02 $. Percentage increase = $ \frac{0.02 - 0.01}{0.01} \times 100 = 100\% $.

NEET Chemistry: Solutions — Practice Set 6

Q1. A mixture of ethanol (molar mass = 46 g/mol) and water has a total mass of 138 g. If the mole fraction of ethanol is 0.25, what is the mass of ethanol in the mixture?

Q2. What is the mole fraction of benzene (molar mass = 78 g/mol) in a solution containing 39 g of benzene and 92 g of toluene (molar mass = 92 g/mol)?

Q3. A gas has a Henry’s law constant of 500 bar at 25°C. If the partial pressure increases from 5 bar to 10 bar, what is the percentage increase in solubility?

Q4. A 0.5 M solution of Na₂SO₄ (molar mass = 142 g/mol) has a density of 1.2 g/mL. What is the mass of the solute in 200 mL of this solution?

Q5. A solution of NaCl (molar mass = 58.5 g/mol) in 500 g of water freezes at -1.116°C. If \( K_f = 1.86 \, \text{K kg mol}^{-1} \), what is the mass of NaCl? (Assume complete dissociation, i = 2)

Q6. A solution of two volatile liquids with vapor pressures 300 mm Hg and 500 mm Hg has a total vapor pressure of 380 mm Hg. What is the mole fraction of the second component in the vapor phase?

Q7. A solution contains 10 g of a solute in 90 g of water. What is the mass percentage of the solute?

Q8. The vapor pressure of pure water is 28 mm Hg at a certain temperature. A solution with a non-volatile solute has a vapor pressure of 26.6 mm Hg. If the solute’s molar mass is 50 g/mol, what is the mass of solute in 360 g of water?

Q9. What is the molar mass of a solute if 6 g of it in 300 mL of solution produces an osmotic pressure of 0.821 atm at 27°C? (\( R = 0.0821 \, \text{L atm mol}^{-1} \text{K}^{-1} \))

Q10. A solution is made by dissolving 12 g of a solute in water to make 300 mL of solution. If the osmotic pressure is 0.984 atm at 27°C, what is the molar mass of the solute? (\( R = 0.0821 \, \text{L atm mol}^{-1} \text{K}^{-1} \))