Question 1

Which of the following salts will hydrolyze in water to produce an acidic solution?

Accepted Answer

NH₄Cl is the salt of a weak base (NH₃) and strong acid (HCl); the NH₄⁺ ion hydrolyzes to release H⁺ ions, making the solution acidic.

Question 2

What is the oxidation state of sulfur in H₂S₂O₃?

Accepted Answer

In H₂S₂O₃, using 2(+1) + 2(x) + 3(−2) = 0, we get 2x = 4, so average oxidation state is +2, but sulfur exists in mixed oxidation states with one at +4 and one at +2, averaging +3.

Question 3

The ionic product of water (Kw) at 25°C is 1.0 × 10⁻¹⁴. What is the pH of a neutral solution at this temperature?

Accepted Answer

At neutrality, [H⁺] = [OH⁻], and since [H⁺] × [OH⁻] = Kw = 10⁻¹⁴, we get [H⁺] = 10⁻⁷ M, giving pH = 7.

Question 4

The solubility product (Ksp) of AgCl at 25°C is 1.8 × 10⁻¹⁰. If the concentration of Cl⁻ ions in a saturated solution is 1.34 × 10⁻⁵ M, what is the concentration of Ag⁺ ions?

Accepted Answer

Using Ksp = [Ag⁺][Cl⁻], we have 1.8 × 10⁻¹⁰ = [Ag⁺] × 1.34 × 10⁻⁵, giving [Ag⁺] ≈ 1.5 × 10⁻⁴ M.

Question 5

In the reaction 2KMnO₄ + 3H₂O₂ + 3H₂SO₄ → K₂SO₄ + 2MnSO₄ + 5O₂ + 8H₂O, what is the oxidation state change of manganese?

Accepted Answer

Mn in KMnO₄ has oxidation state +7, and in MnSO₄ it has +2, a reduction of 5 electrons per Mn atom.

Question 6

In the redox reaction 3Cu + 8HNO₃(dilute) → 3Cu(NO₃)₂ + 2NO + 4H₂O, how many electrons are transferred per mole of Cu oxidized?

Accepted Answer

Cu is oxidized from 0 to +2, losing 2 electrons per Cu atom; total 6 electrons transferred among 3 Cu atoms means 2 electrons per Cu.

Question 7

In the equilibrium: PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), if temperature is increased, the equilibrium shifts to the right. This indicates that the forward reaction is:

Accepted Answer

According to Le Chatelier's principle, if increasing temperature shifts equilibrium to the right, the forward reaction must be endothermic (absorbs heat).

Question 8

Which of the following is an extensive property in thermodynamics?

Accepted Answer

Enthalpy depends on the amount of substance (extensive), while density, temperature, and specific heat capacity are intensive properties independent of quantity.

Question 9

If the enthalpy change (ΔH) for a reaction is negative, the reaction is classified as:

Accepted Answer

Negative ΔH indicates heat is released to surroundings, defining an exothermic reaction.

Question 10

A weak acid HA has a Ka value of 1.8 × 10⁻⁵. Which of the following correctly describes the strength of this acid relative to strong acids?

Accepted Answer

Weak acids have Ka < 1 and ionize only partially; the small Ka value (10⁻⁵) confirms incomplete ionization compared to strong acids which fully ionize.

Question 11

The first law of thermodynamics states that ΔU = q + w. What does 'w' represent?

Accepted Answer

In the equation ΔU = q + w, 'w' represents work done ON the system (positive when work is done on it).

Question 12

The Ka of acetic acid is 1.8 × 10⁻⁵ and its Kb is 5.6 × 10⁻¹⁰. What is the relationship between Ka, Kb, and Kw for the acetate ion (CH₃COO⁻)?

Accepted Answer

For a conjugate acid-base pair, Kb of the conjugate base = Kw / Ka of the conjugate acid; thus Kb(acetate) = 10⁻¹⁴ / 1.8 × 10⁻⁵.

Question 13

At constant pressure and temperature, a spontaneous process must have:

Accepted Answer

The Gibbs free energy equation ΔG = ΔH - TΔS shows that spontaneity requires ΔG < 0 at constant P and T.

Question 14

Which species acts as the reducing agent in the reaction: Cl₂ + 2KBr → 2KCl + Br₂?

Accepted Answer

The reducing agent is oxidized; Br⁻ in KBr is oxidized from −1 to 0 in Br₂, so KBr is the reducing agent.

Question 15

The standard enthalpy of formation (ΔH°f) of an element in its standard state is:

Accepted Answer

By definition, the standard enthalpy of formation of an element in its standard state is zero.

Question 16

For the reaction: N₂(g) + 3H₂(g) ⇌ 2NH₃(g), if the equilibrium constant is Kc = 0.5 at 400°C, what is the relationship between forward and reverse reaction rates at equilibrium?

Accepted Answer

At chemical equilibrium, the forward and reverse reaction rates are equal regardless of the Kc value; Kc only indicates the position of equilibrium, not the rates.

Question 17

For the equilibrium: 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), the equilibrium constant expression Kc is:

Accepted Answer

Kc is the ratio of products raised to their stoichiometric coefficients divided by reactants raised to their stoichiometric coefficients.

Question 18

When the pressure on the equilibrium system: N₂(g) + O₂(g) ⇌ 2NO(g) is increased, how does the equilibrium shift?

Accepted Answer

Since there are 2 moles of gas on both sides of the equation, the equilibrium position is unaffected by pressure changes according to Le Chatelier's principle.

Question 19

For the reaction: H₂(g) + I₂(g) ⇌ 2HI(g), Kc = 50 at 440°C. What is the value of Kc for the reverse reaction: 2HI(g) ⇌ H₂(g) + I₂(g)?

Accepted Answer

The equilibrium constant for the reverse reaction is the reciprocal of the forward reaction: Kc(reverse) = 1/50 = 0.02.

Question 20

In the reaction Fe²⁺ + MnO₄⁻ + H⁺ → Fe³⁺ + Mn²⁺ + H₂O, what is the ratio of Fe²⁺ to MnO₄⁻ that must be used for complete redox balance?

Accepted Answer

Mn in MnO₄⁻ gains 5 electrons (+7 to +2), and each Fe²⁺ loses 1 electron; therefore 5 Fe²⁺ are needed per MnO₄⁻.

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