Grade 12 Chemistry practice questions – Lebanese curriculum

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They are a sample from EduRise's Grade 12 Chemistry question bank (1,664 questions across 16 chapters), written to follow the Lebanese curriculum. Each chapter on EduRise has its own practice set and a timed exam.

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Question 1

A gas thermometer reads T = 294 K. What is the Celsius temperature?

Accepted Answer

21 °C. θ = T − 273 = 294 − 273 = 21 °C.

Question 2

A gas thermometer reads T = 412 K. What is the Celsius temperature?

Accepted Answer

139 °C. θ = T − 273 = 412 − 273 = 139 °C.

Question 3

The unit mol·L⁻¹·min⁻¹ is the unit of:

Accepted Answer

a volumetric rate. Volumetric rate = change of concentration per unit time.

Question 4

For 2 MnO₄⁻ + 5 H₂C₂O₄ + 6 H₃O⁺ → 2 Mn²⁺ + 10 CO₂ + 14 H₂O, n₀(MnO₄⁻) = 3.0 mmol. At time t, n(MnO₄⁻) = 1.0 mmol. What amount of Mn²⁺ has been formed (none initially)?

Accepted Answer

2.00 mmol. n(MnO₄⁻) = n₀ − 2x → x = (3.0 − 1.0)/2 = 1.00 mmol; n(Mn²⁺) = 2x = 2.00 mmol.

Question 5

Why does zinc powder react faster with acid than a zinc piece of the same mass?

Accepted Answer

the powder has a larger contact surface. A solid reacts at its surface; dividing it increases the surface in contact with the acid.

Question 6

What type of catalysis is it: a slice of raw potato (containing catalase) dropped into hydrogen peroxide?

Accepted Answer

enzymatic catalysis. Catalase is an enzyme (a protein): enzymatic catalysis.

Question 7

The equilibrium constant Kc depends only on:

Accepted Answer

the temperature. Kc is fixed at a given temperature.

Question 8

What is the expression of the equilibrium constant of Fe³⁺ + SCN⁻ ⇌ FeSCN²⁺?

Accepted Answer

Kc = [FeSCN²⁺]/([Fe³⁺][SCN⁻]). Kc = products/reactants at equilibrium, each to the power of its coefficient (here 1).

Question 9

The pH meter reads pH = 6.49 at 25 °C. What is [H₃O⁺] in the solution?

Accepted Answer

3.2 × 10⁻⁷ mol/L. [H₃O⁺] = 10⁻ᵖᴴ = 10^(−6.49) = 3.2 × 10⁻⁷ mol/L.

Question 10

At 25 °C, a solution has [H₃O⁺] = 6.0 × 10⁻⁵ mol/L. What is its pH?

Accepted Answer

4.22. pH = −log[H₃O⁺] = −log(6.0 × 10⁻⁵) = 4.22: the solution is acidic.

Question 11

The acid constant of a pair is Ka = 2.5 × 10⁻¹⁰ at 25 °C. What is its pKa?

Accepted Answer

9.60. pKa = −log Ka = −log(2.5 × 10⁻¹⁰) = 9.60.

Question 12

What is the conjugate base of NH₄⁺?

Accepted Answer

NH₃. The conjugate base is obtained by removing one H⁺: NH₄⁺ ⇌ NH₃ + H⁺; the pair is NH₄⁺/NH₃.

Question 13

Which equation describes the titration of ammonia by hydrochloric acid?

Accepted Answer

NH₃ + H₃O⁺ → NH₄⁺ + H₂O. The base NH₃ reacts with the strongest acid present, H₃O⁺; the reaction is complete (K = 10⁹·²).

Question 14

During the titration of a weak acid by sodium hydroxide, V_bE = 10.0 mL. At what volume of base is pH = pKa?

Accepted Answer

5.0 mL. pH = pKa at half-equivalence, V_bE/2 = 10.0/2 = 5.0 mL, where n(HA) = n(A⁻).

Question 15

Which functional group characterises the carboxylic acids?

Accepted Answer

carboxyl group –COOH. Carboxylic acid: carboxyl group –COOH; name ending -oic acid.

Grade 12 Chemistry Questions and Answers

15 Grade 12 Chemistry practice questions

1. A gas thermometer reads T = 294 K. What is the Celsius temperature?

2. A gas thermometer reads T = 412 K. What is the Celsius temperature?

3. The unit mol·L⁻¹·min⁻¹ is the unit of:

4. For 2 MnO₄⁻ + 5 H₂C₂O₄ + 6 H₃O⁺ → 2 Mn²⁺ + 10 CO₂ + 14 H₂O, n₀(MnO₄⁻) = 3.0 mmol. At time t, n(MnO₄⁻) = 1.0 mmol. What amount of Mn²⁺ has been formed (none initially)?

5. Why does zinc powder react faster with acid than a zinc piece of the same mass?

6. What type of catalysis is it: a slice of raw potato (containing catalase) dropped into hydrogen peroxide?

7. The equilibrium constant Kc depends only on:

8. What is the expression of the equilibrium constant of Fe³⁺ + SCN⁻ ⇌ FeSCN²⁺?

9. The pH meter reads pH = 6.49 at 25 °C. What is [H₃O⁺] in the solution?

10. At 25 °C, a solution has [H₃O⁺] = 6.0 × 10⁻⁵ mol/L. What is its pH?

11. The acid constant of a pair is Ka = 2.5 × 10⁻¹⁰ at 25 °C. What is its pKa?

12. What is the conjugate base of NH₄⁺?

13. Which equation describes the titration of ammonia by hydrochloric acid?

14. During the titration of a weak acid by sodium hydroxide, V_bE = 10.0 mL. At what volume of base is pH = pKa?

15. Which functional group characterises the carboxylic acids?

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