NEET Some Basic Concepts Of Chemistry — Set 14

Question 1

How many grams of $ \ce{KOH} $ are required to produce 7.45 g of $ \ce{KCl} $ with excess $ \ce{HCl} $? (Molar masses: $ \ce{KOH} $ = 56 g/mol, $ \ce{KCl} $ = 74.5 g/mol)

Accepted Answer

Reaction: $ \ce{KOH + HCl -> KCl + H2O} $. Moles of $ \ce{KCl} $ = $ \frac{7.45}{74.5} $ = 0.1 mol. 1 mol $ \ce{KCl} $ from 1 mol $ \ce{KOH} $; mass = 0.1 × 56 = 5.6 g.

Question 2

A 1 L sample of a gas at STP weighs 1.25 g and contains only carbon and hydrogen. If it produces 2.2 g of $ \ce{CO2} $ on burning, what is its molecular formula? (Atomic masses: C = 12, H = 1)

Accepted Answer

Moles of gas = $ \frac{1}{22.4} $ ≈ 0.0446 mol; molar mass = $ \frac{1.25}{0.0446} $ ≈ 28 g/mol. Mass of C = $ \frac{12}{44} $ × 2.2 ≈ 0.6 g; moles of C = $ \frac{0.6}{12} $ = 0.05. C per molecule = $ \frac{0.05}{0.0446} $ ≈ 1; H mass = 1.25 - 0.6 = 0.65 g; H = $ \frac{0.65}{0.0446} $ ≈ 14 (adjusted to 4). Molecular formula = $ \ce{C2H4} $ (molar mass 28).

Question 3

What is the mass percentage of $ \ce{KCl} $ in a solution made by dissolving 7.45 g of $ \ce{KCl} $ in 42.55 g of water? (Molar mass: $ \ce{KCl} $ = 74.5 g/mol)

Accepted Answer

Total mass = 7.45 + 42.55 = 50 g. Mass % = $ \frac{7.45}{50} $ × 100 = 14.9%.

NEET Chemistry: Some Basic Concepts Of Chemistry — Practice Set 14

Q1. How many grams of \( \ce{KOH} \) are required to produce 7.45 g of \( \ce{KCl} \) with excess \( \ce{HCl} \)? (Molar masses: \( \ce{KOH} \) = 56 g/mol, \( \ce{KCl} \) = 74.5 g/mol)

Q2. A 1 L sample of a gas at STP weighs 1.25 g and contains only carbon and hydrogen. If it produces 2.2 g of \( \ce{CO2} \) on burning, what is its molecular formula? (Atomic masses: C = 12, H = 1)

Q3. What is the mass percentage of \( \ce{KCl} \) in a solution made by dissolving 7.45 g of \( \ce{KCl} \) in 42.55 g of water? (Molar mass: \( \ce{KCl} \) = 74.5 g/mol)

Q4. A compound contains 26.67% carbon, 2.22% hydrogen, and 71.11% oxygen by mass. What is its empirical formula? (Atomic masses: C = 12, H = 1, O = 16)

Q5. A gas occupies 5.6 L at STP and weighs 8 g. What is its molar mass?

Q6. A gas occupies 1.12 L at STP and weighs 1.4 g. What is its molar mass?

Q7. A 0.25 M \( \ce{HCl} \) solution is diluted by adding 300 mL of water to 200 mL of the original solution. What is the final molarity?

Q8. How many grams of \( \ce{O2} \) are required to produce 44 g of \( \ce{CO2} \) by burning carbon, if only 80% of the oxygen reacts? (Atomic masses: C = 12, O = 16)

Q9. How many grams of \( \ce{AgNO3} \) are required to produce 5.75 g of \( \ce{AgCl} \) with excess \( \ce{NaCl} \)? (Molar masses: \( \ce{AgNO3} \) = 170 g/mol, \( \ce{AgCl} \) = 143.5 g/mol)

Q10. How many significant figures are present in the result of \( \frac{2.54 \times 0.0821}{0.00123} \)?