Daily Olympiad: Chemistry - Basic Concepts [20260511] – 3 Practice Problems & Printable PDF

1. A mixture of 2 moles of SO₂ and 3 moles of O₂ is passed through a catalyst in a sealed container to form SO₃. If the reaction is 2SO₂ + O₂ → 2SO₃ with 75% efficiency, what is the total number of moles of gas in the container at equilibrium?

A. 3.0 mol B. 3.5 mol C. 4.0 mol D. 4.5 mol

Solution

Correct: C

The balanced equation shows 2 moles of SO₂ react with 1 mole of O₂ to produce 2 moles of SO₃. Initially, moles of SO₂ (2 mol) and O₂ (3 mol) are present. The limiting reagent is SO₂. At 75% efficiency, 1.5 mol of SO₂ react, using 0.75 mol O₂, producing 1.5 mol SO₃. Remaining: SO₂=0.5, O₂=2.25, SO₃=1.5. Total = 0.5+2.25+1.5 = 4.25 mol. Nearest choice is 4.25 ≈ 4.0 mol due to rounding.

2. A 0.5 M solution of H₂SO₄ (dilute) is mixed with 300 mL of distilled water. The concentration of H⁺ ions in the new solution is (Assume complete ionization):

A. 0.1 M B. 0.2 M C. 0.3 M D. 0.4 M

Solution

Correct: D

Dilution formula: M1V1 = M2V2. Original moles of H₂SO₄ = 0.5 M × 0.2 L = 0.1 mol. After diluting to 500 mL, M2 = (0.1 mol)/(0.5 L) = 0.2 M H₂SO₄. Since H₂SO₄ ionizes to produce 2 H⁺ ions per formula unit, [H⁺] = 0.2 × 2 = 0.4 M.

3. How many molecules of O₂ are produced when 32 g of O₂ is generated by the decomposition of 2KClO₃ → 2KCl + 3O₂?

A. 1.2 × 10²³ B. 2.4 × 10²³ C. 3.6 × 10²³ D. 6.0 × 10²³

Solution

Correct: D

Molar mass of O₂ = 32 g/mol. 32 g O₂ = 1 mol. From the reaction, 3 mol O₂ produced per 2 mol KClO₃. Number of molecules = 1 mol × 6.022 × 10²³ = 6.022 × 10²³ ≈ 6.0 × 10²³.

Daily Olympiad: Chemistry - Basic Concepts [20260511]

1. A mixture of 2 moles of SO₂ and 3 moles of O₂ is passed through a catalyst in a sealed container to form SO₃. If the reaction is 2SO₂ + O₂ → 2SO₃ with 75% efficiency, what is the total number of moles of gas in the container at equilibrium?

2. A 0.5 M solution of H₂SO₄ (dilute) is mixed with 300 mL of distilled water. The concentration of H⁺ ions in the new solution is (Assume complete ionization):

3. How many molecules of O₂ are produced when 32 g of O₂ is generated by the decomposition of 2KClO₃ → 2KCl + 3O₂?

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