NEET Some Basic Concepts Of Chemistry — Set 18

Question 1

What is the mole fraction of $ \ce{C2H5OH} $ in a solution containing 23 g of $ \ce{C2H5OH} $ and 18 g of $ \ce{H2O} $? (Molar masses: $ \ce{C2H5OH} $ = 46 g/mol, $ \ce{H2O} $ = 18 g/mol)

Accepted Answer

Moles of $ \ce{C2H5OH} $ = $ \frac{23}{46} $ = 0.5 mol; moles of $ \ce{H2O} $ = $ \frac{18}{18} $ = 1 mol. Total moles = 0.5 + 1 = 1.5. Mole fraction = $ \frac{0.5}{1.5} $ ≈ 0.333.

Question 2

A 0.54 g sample of a hydrocarbon produces 1.76 g of $ \ce{CO2} $ and 0.36 g of $ \ce{H2O} $ on complete combustion. If its molar mass is 54 g/mol, what is its molecular formula? (Atomic masses: C = 12, H = 1, O = 16)

Accepted Answer

Mass of C = $ \frac{12}{44} $ × 1.76 ≈ 0.48 g; mass of H = $ \frac{2}{18} $ × 0.36 = 0.04 g. Total = 0.48 + 0.04 = 0.52 g (≈0.54 g, combustion assumption). Moles: C = $ \frac{0.48}{12} $ = 0.04, H = $ \frac{0.04}{1} $ = 0.04; ratio = 1 : 1; empirical formula = $ \ce{CH} $, mass = 13 g/mol. $ n = \frac{54}{13} $ ≈ 4; molecular formula = $ \ce{C4H4} $.

Question 3

What is the mole fraction of $ \ce{H2O} $ in a solution containing 9 g of $ \ce{H2O} $ and 23 g of $ \ce{C2H5OH} $? (Molar masses: $ \ce{H2O} $ = 18 g/mol, $ \ce{C2H5OH} $ = 46 g/mol)

Accepted Answer

Moles of $ \ce{H2O} $ = $ \frac{9}{18} $ = 0.5 mol; moles of $ \ce{C2H5OH} $ = $ \frac{23}{46} $ = 0.5 mol. Total moles = 0.5 + 0.5 = 1. Mole fraction = $ \frac{0.5}{1} $ = 0.5.

NEET Chemistry: Some Basic Concepts Of Chemistry — Practice Set 18

Q1. What is the mole fraction of \( \ce{C2H5OH} \) in a solution containing 23 g of \( \ce{C2H5OH} \) and 18 g of \( \ce{H2O} \)? (Molar masses: \( \ce{C2H5OH} \) = 46 g/mol, \( \ce{H2O} \) = 18 g/mol)

Q2. A 0.54 g sample of a hydrocarbon produces 1.76 g of \( \ce{CO2} \) and 0.36 g of \( \ce{H2O} \) on complete combustion. If its molar mass is 54 g/mol, what is its molecular formula? (Atomic masses: C = 12, H = 1, O = 16)

Q3. What is the mole fraction of \( \ce{H2O} \) in a solution containing 9 g of \( \ce{H2O} \) and 23 g of \( \ce{C2H5OH} \)? (Molar masses: \( \ce{H2O} \) = 18 g/mol, \( \ce{C2H5OH} \) = 46 g/mol)

Q4. What is the mole fraction of \( \ce{CH3OH} \) in a solution containing 16 g of \( \ce{CH3OH} \) and 36 g of \( \ce{H2O} \)? (Molar masses: \( \ce{CH3OH} \) = 32 g/mol, \( \ce{H2O} \) = 18 g/mol)

Q5. A 1.5 L sample of a gas at STP weighs 2.1 g and contains only carbon and hydrogen. If it produces 2.64 g of \( \ce{CO2} \) on burning, what is its molecular formula? (Atomic masses: C = 12, H = 1)

Q6. How many significant figures are present in the result of \( \frac{0.0456 \times 273.15}{0.0821} \)?

Q7. A 0.5 M solution of \( \ce{NaOH} \) is diluted from 200 mL to 1 L. What is the new molarity?

Q8. What is the mass of \( \ce{CaSO4} \) produced when 13.6 g of \( \ce{Ca(OH)2} \) reacts with excess \( \ce{H2SO4} \)? (Molar masses: \( \ce{Ca(OH)2} \) = 74 g/mol, \( \ce{CaSO4} \) = 136 g/mol)

Q9. How many grams of \( \ce{CuO} \) are required to produce 6.4 g of \( \ce{Cu} \) with excess \( \ce{CO} \)? (Molar masses: \( \ce{CuO} \) = 79.5 g/mol, Cu = 64 g/mol)

Q10. How many grams of \( \ce{K2CO3} \) are required to produce 13.8 g of \( \ce{KCl} \) with excess \( \ce{HCl} \)? (Molar masses: \( \ce{K2CO3} \) = 138 g/mol, \( \ce{KCl} \) = 74.5 g/mol)