8th Chapter Solved Exercise MCQs of FSC First Year Chemistry
written by Almas AnwarThe 8th chapter Solved Exercise MCQs of FSC 1st-year Chemistry offers a comprehensive collection of multiple-choice questions with answers. Each question is accompanied by a short explanation to clarify the correct choice. These solutions aim to assist students in exam preparation by simplifying complex concepts and building a strong foundation for success.
8th chapter solved MCQs with explanation
1. For which system does the equilibrium constant, K, have units of (concentration)?
(a) N₂ + 3H₂ ⇌ 2NH₃
(b) H₂ + I₂ ⇌ 2HI
(c) 2NO₂ ⇌ N₂O
(d) 2HF ⇌ H₂ + F₂
Explanation: The correct answer is (c). Because the units of the equilibrium constant depend on the number of moles of reactants and products. When the number of moles of reactants equals the total number of moles of products, the equilibrium constant has no units.
2. Which statement about the following equilibrium is correct?
2SO₂ (g) + O₂ (g) ⇌ 2SO₃ (g) ΔH = -188.3 kJ mol⁻¹
(a) The value of K falls with a rise in temperature
(b) The value of K falls with increasing pressure
(c) Adding V₂O₅ catalyst increases the equilibrium yield of sulphur trioxide
(d) The value of K is equal to K
Explanation: The correct answer is (a). Because
Kp = Kc(RT)^n
^n = 2 – (2+1) = -1
So,
Kp = Kc R-1 T-1 = Kp x 1 / T
3. The pH of 10 mol dm⁻³ of an aqueous solution of H₂SO₄ is:
(a) 3.0
(b) 2.7
(c) 2.0
(d) 1.5
Explanation: The correct answer is (d). Because:
- H₂SO₄ is a strong acid and gives 2 H⁺ ions for each molecule.
- For a 10 mol/dm³ solution, the H⁺ concentration is 20 mol/dm³.
- pH = −log [H⁺].
- Since –log (20) ≈ −1.3 , the pH is close to 1.5.
4. The solubility product of AgCl is 2.0 × 10⁻¹⁰ mol² dm⁻⁶. The maximum concentration of Ag⁺ ions in the solution is:
(a) 2.0 × 10⁻¹⁰ mol dm⁻³
(b) 1.41 × 10⁻⁵ mol dm⁻³
(c) 1.0 × 10⁻¹ mol dm⁻³
(d) 4.0 × 10² mol dm⁻³
Explanation: The correct answer is (b).
- What is Ksp? The solubility product (Ksp) tells us how much a substance can dissolve in water. For silver chloride (AgCl) Ksp = 2.0×10−10 mol² dm⁻⁶.
- Dissolving AgCl in Water: When AgCl dissolves in water, it breaks into silver ions (Ag+) and chloride ions (Cl−): AgCl → Ag+ + Cl−
- Setting Up the Equation: Let x be the concentration of Ag+ ions in the solution. Since each AgCl gives one Ag+ and one Cl−, the concentration of Cl− is also x.
The solubility product (Ksp) formula is:
Ksp= [Ag+] [Cl−]
So, Ksp= x × x = x2
- Finding the Concentration of Ag+ :
We know Ksp=2.0×10−10.- – Plugging this into the equation: x2= 2.0 × 10−10
To find x, took the square root of both sides and here’s the answer:
x = 1.41 × 10−5 mol dm−3
5. An excess of aqueous silver nitrate is added to aqueous barium chloride and the precipitate is removed by filtration. What are the main ions in the filtrate?
(a) Ag⁺ and NO₃⁻ only
(b) Ag⁺, Ba²⁺, and NO₃⁻
(c) Ba²⁺ and NO₃⁻ only
(d) Ba²⁺, NO₃⁻, and Cl⁻
Explanation: The correct answer is (c). Because:
- When silver nitrate (AgNO₃) is added to barium chloride (BaCl₂), silver chloride (AgCl) forms as a solid precipitate.
- This precipitate is removed by filtration.
- The filtrate contains barium ions (Ba²⁺) and nitrate ions (NO₃⁻), because they are left in the solution after the reaction.
Thus, the main ions in the filtrate are Ba²⁺ and NO₃⁻.
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