NEET Some Basic Concepts Of Chemistry — Set 20

Question 1

A 0.98 g sample of a hydrocarbon produces 3.08 g of $ \ce{CO2} $ and 1.26 g of $ \ce{H2O} $ on complete combustion. What is its molecular formula if its molar mass is 98 g/mol? (Atomic masses: C = 12, H = 1, O = 16)

Accepted Answer

Mass of C = $ \frac{12}{44} $ × 3.08 ≈ 0.84 g; mass of H = $ \frac{2}{18} $ × 1.26 = 0.14 g. Total = 0.84 + 0.14 = 0.98 g (matches). Moles: C = $ \frac{0.84}{12} $ = 0.07, H = $ \frac{0.14}{1} $ = 0.14; ratio = 1 : 2; empirical formula = $ \ce{CH2} $, mass = 14 g/mol. $ n = \frac{98}{14} = 7 $; molecular formula = $ \ce{C7H14} $.

Question 2

What is the molality of a solution prepared by dissolving 12 g of glucose ($ \ce{C6H12O6} $) in 48 g of water, if the density of water is 1 g/mL? (Molar mass: $ \ce{C6H12O6} $ = 180 g/mol)

Accepted Answer

Moles of glucose = $ \frac{12}{180} $ ≈ 0.0667 mol. Mass of water = 48 g = 0.048 kg. Molality = $ \frac{0.0667}{0.048} $ ≈ 1.39 m.

Question 3

A gas occupies 2.24 L at STP and weighs 3.2 g. What is its molar mass?

Accepted Answer

Moles = $ \frac{2.24}{22.4} $ = 0.1 mol. Molar mass = $ \frac{3.2}{0.1} $ = 32 g/mol.

NEET Chemistry: Some Basic Concepts Of Chemistry — Practice Set 20

Q1. A 0.98 g sample of a hydrocarbon produces 3.08 g of \( \ce{CO2} \) and 1.26 g of \( \ce{H2O} \) on complete combustion. What is its molecular formula if its molar mass is 98 g/mol? (Atomic masses: C = 12, H = 1, O = 16)

Q2. What is the molality of a solution prepared by dissolving 12 g of glucose (\( \ce{C6H12O6} \)) in 48 g of water, if the density of water is 1 g/mL? (Molar mass: \( \ce{C6H12O6} \) = 180 g/mol)

Q3. A gas occupies 2.24 L at STP and weighs 3.2 g. What is its molar mass?

Q4. What is the mass percentage of \( \ce{NaCl} \) in a solution made by dissolving 5.85 g of \( \ce{NaCl} \) in 44.15 g of water? (Molar mass: \( \ce{NaCl} \) = 58.5 g/mol)

Q5. A compound contains 36.36% carbon, 6.06% hydrogen, and 57.58% oxygen by mass. What is its empirical formula? (Atomic masses: C = 12, H = 1, O = 16)

Q6. What is the mole fraction of \( \ce{C6H12O6} \) in a solution containing 18 g of \( \ce{C6H12O6} \) and 72 g of \( \ce{H2O} \)? (Molar masses: \( \ce{C6H12O6} \) = 180 g/mol, \( \ce{H2O} \) = 18 g/mol)

Q7. How many grams of \( \ce{O2} \) are required to react with 12 g of \( \ce{Mg} \) to form \( \ce{MgO} \) if the reaction proceeds with 75% efficiency? (Atomic masses: Mg = 24, O = 16)

Q8. What volume of \( \ce{O2} \) at STP is required to burn 9 g of \( \ce{C3H8} \) completely to \( \ce{CO2} \) and \( \ce{H2O} \)? (Molar mass: \( \ce{C3H8} \) = 44 g/mol)

Q9. A 300 mL solution contains 6 g of urea (\( \ce{NH2CONH2} \)) and has a density of 1.02 g/mL. What is its molarity? (Molar mass: urea = 60 g/mol)

Q10. A gas occupies 5.6 L at STP and weighs 2 g. What is its molar mass?