NEET Some Basic Concepts Of Chemistry — Set 11

Question 1

A solution contains 20 ppm of $ \ce{K2SO4} $ by mass in water. What is its molarity if the density is 1 g/mL? (Molar mass: $ \ce{K2SO4} $ = 174 g/mol)

Accepted Answer

20 ppm = 20 g $ \ce{K2SO4} $ in 10⁶ g solution. Volume = $ \frac{10⁶}{1} $ = 10⁶ mL = 1000 L. Moles = $ \frac{20}{174} $ ≈ 0.1149 mol; molarity = $ \frac{0.1149}{1000} $ ≈ 1.149 × 10⁻⁴ M.

Question 2

A hydrocarbon (C and H only) weighing 0.26 g produces 0.88 g of $ \ce{CO2} $ and 0.18 g of $ \ce{H2O} $ on complete combustion. What is its molecular formula if its molar mass is 26 g/mol? (Atomic masses: C = 12, H = 1, O = 16)

Accepted Answer

Mass of C = $ \frac{12}{44} $ × 0.88 ≈ 0.24 g; mass of H = $ \frac{2}{18} $ × 0.18 = 0.02 g. Total mass = 0.24 + 0.02 = 0.26 g (matches). Moles: C = $ \frac{0.24}{12} $ = 0.02, H = $ \frac{0.02}{1} $ = 0.02; ratio = 1 : 1; empirical formula = $ \ce{CH} $, mass = 13 g/mol. $ n = \frac{26}{13} = 2 $; molecular formula = $ \ce{C2H2} $.

Question 3

What volume of $ \ce{O2} $ at STP is required to burn 5 g of $ \ce{C2H5OH} $ completely to $ \ce{CO2} $ and $ \ce{H2O} $? (Molar mass: $ \ce{C2H5OH} $ = 46 g/mol)

Accepted Answer

Reaction: $ \ce{C2H5OH + 3O2 -> 2CO2 + 3H2O} $. Moles of $ \ce{C2H5OH} $ = $ \frac{5}{46} $ ≈ 0.1087 mol. 1 mol $ \ce{C2H5OH} $ needs 3 mol $ \ce{O2} $; 0.1087 mol needs 0.3261 mol. Volume = 0.3261 × 22.4 ≈ 7.3 L.

NEET Chemistry: Some Basic Concepts Of Chemistry — Practice Set 11

Q1. A solution contains 20 ppm of \( \ce{K2SO4} \) by mass in water. What is its molarity if the density is 1 g/mL? (Molar mass: \( \ce{K2SO4} \) = 174 g/mol)

Q2. A hydrocarbon (C and H only) weighing 0.26 g produces 0.88 g of \( \ce{CO2} \) and 0.18 g of \( \ce{H2O} \) on complete combustion. What is its molecular formula if its molar mass is 26 g/mol? (Atomic masses: C = 12, H = 1, O = 16)

Q3. What volume of \( \ce{O2} \) at STP is required to burn 5 g of \( \ce{C2H5OH} \) completely to \( \ce{CO2} \) and \( \ce{H2O} \)? (Molar mass: \( \ce{C2H5OH} \) = 46 g/mol)

Q4. How many grams of \( \ce{HCl} \) are needed to react with 10 g of \( \ce{CaCO3} \) to produce 4.4 g of \( \ce{CO2} \)? (Molar masses: \( \ce{CaCO3} \) = 100 g/mol, \( \ce{HCl} \) = 36.5 g/mol, \( \ce{CO2} \) = 44 g/mol)

Q5. A 500 mL solution of \( \ce{KNO3} \) has a molarity of 0.4 M and a density of 1.01 g/mL. What is the mass percentage of \( \ce{KNO3} \)? (Molar mass: \( \ce{KNO3} \) = 101 g/mol)

Q6. How many grams of \( \ce{Fe2O3} \) are required to produce 16.8 g of \( \ce{Fe} \) with excess \( \ce{CO} \)? (Molar masses: \( \ce{Fe2O3} \) = 160 g/mol, Fe = 56 g/mol)

Q7. A 1.5 L sample of a gas at STP contains 0.75 g of carbon and 0.25 g of hydrogen. What is its molecular formula? (Atomic masses: C = 12, H = 1)

Q8. A 0.42 g sample of a hydrocarbon produces 1.32 g of \( \ce{CO2} \) and 0.54 g of \( \ce{H2O} \) on complete combustion. What is its molecular formula if its molar mass is 42 g/mol? (Atomic masses: C = 12, H = 1, O = 16)

Q9. What is the mole fraction of \( \ce{CH3OH} \) in a solution containing 16 g of \( \ce{CH3OH} \) and 72 g of \( \ce{H2O} \)? (Molar masses: \( \ce{CH3OH} \) = 32 g/mol, \( \ce{H2O} \) = 18 g/mol)

Q10. A solution contains 10 ppm of \( \ce{K2SO4} \) by mass in water. What is its molality? (Molar mass: \( \ce{K2SO4} \) = 174 g/mol)