Purpose: Self-check Kc, ICE tables, Le Chatelier, Ksp, pH/Ka/Kb, titration.
Q1
Write the Kc expression for: \( \text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g) \)
Show solution
$$K_c = \frac{[\text{NH}_3]^2}{[\text{N}_2][\text{H}_2]^3}$$
Q2
For H₂(g) + I₂(g) ⇌ 2HI(g), at equilibrium [H₂]=0.10, [I₂]=0.10, [HI]=0.74 M. Calculate Kc.
Show solution
Kc = (0.74)²/((0.10)(0.10)) = 0.548/0.010 = 54.8.
Q3
ICE: 0.500 mol N₂O₄ in 1.00 L flask; at eq 0.200 mol dissociates. N₂O₄ ⇌ 2NO₂. Find Kc.
Show solution
[N₂O₄]eq = 0.300; [NO₂]eq = 0.400. Kc = (0.400)²/0.300 = 0.533.
Q4
N₂(g) + 3H₂(g) ⇌ 2NH₃(g), ΔH = −92 kJ. Predict shift if T is increased.
Show solution
Exo forward; ↑T favours endo direction → shifts reverse (less NH₃).
Q5
Same reaction: predict effect of decreasing volume.
Show solution
↓V → ↑P → shifts toward fewer gas moles. Reactants 4 mol gas → products 2 mol → shifts forward.
Q6
Ksp of AgCl = 1.8×10⁻¹⁰. Find molar solubility in pure water.
Show solution
[Ag⁺][Cl⁻] = s² = 1.8×10⁻¹⁰ → s = 1.34×10⁻⁵ M.
Q7
For PbI₂(s) ⇌ Pb²⁺ + 2 I⁻, write Ksp.
Show solution
Ksp = [Pb²⁺][I⁻]². If solubility s, then Ksp = s·(2s)² = 4s³.
Q8
pH of 0.0010 M HCl?
Show solution
[H⁺] = 1.0×10⁻³ → pH = 3.00.
Q9
For 0.10 M acetic acid (Ka = 1.8×10⁻⁵), find pH.
Show solution
x² ≈ Ka·C = 1.8×10⁻⁶ → x = 1.34×10⁻³ M. pH = −log(1.34×10⁻³) = 2.87.
Q10
If Ka of HF = 6.6×10⁻⁴, find Kb of F⁻.
Show solution
Kb = Kw/Ka = 1.0×10⁻¹⁴/6.6×10⁻⁴ = 1.5×10⁻¹¹.
Q11
25.0 mL of 0.100 M HCl titrated with 0.100 M NaOH. Volume of NaOH at equivalence?
Show solution
Equal molarity → equal volume → 25.0 mL. pH at equivalence = 7 (strong–strong).
Q12
For weak acid + strong base titration, equivalence pH is:
Show solution
> 7 — conjugate base hydrolyzes, raising pH (e.g., titrating acetic acid with NaOH gives ~8.7 at equivalence).