Test Session Chapter 9 Acid Base Chemistry (1st Year Chemistry)

Q1. Choose the correct option. (10×1=10)

If the pH of a solution is 11, what is the [OH⁻] concentration in the solution?

(A) 1 × 10⁻³ M

(B) 1 × 10⁻¹ M

(D) 1 × 10⁻⁴ M

Water ionizes to give:

(A) OH⁻ only

(B) H₂O⁻ and OH⁻

(D) H⁺ only

Kw increases with:

(A) Increases in temperature

(B) Decrease in pressure

(D) Adding base

The sum of pH and pOH is always:

(A) 7

(B) 1

(D) 14

If a solution has pH 2 and another has pH 5, how many times more acidic is the first?

(A) 1000 times

(B) 10 times

(D) 5 times

Which of the following correctly relates pH and pOH at 25°C?

(A) pH + pOH = 14

(B) pH – pOH = 7

(D) pH + pOH = 7

Ka is the ionization constant of:

(A) Acids

(B) Bases

(D) Water

A strong acid has a:

(A) Low Ka

(B) High Ka

(D) Donates an electron pair

For weak acids, the value of Ka is:

(A) Zero

(B) Large

(D) Small

Which of the following is used to compare acid strengths?

(A) Ka values

(B) pOH values

(D) Molecular weight

Q2. Write down short answers of following questions. (15×2=30)

[1] Define the following with an example for each:

(i) Ionization constant

(ii) Solubility product

(iii) Common ion effect

(iv) Acid-base Indicator

[ii] Why does common ion effect decrease solubility of a less soluble salt?

[iii] A solution is prepared by mixing equal volumes of two solutions: one with a pH of 4.0 and another with a pH of 10.0. Calculate the Kw for this mixture at 25 °C. (Quick Check 9.2)

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[iv] At a specific temperature, the ionic product of water Kw is 1.0 × 10⁻⁴. If the concentration of OH⁻ ions in a solution is 2.5×10⁻³ M. Calculate the concentration of H⁺ ions and the pH of the solution. (Quick Check 9.2)

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[v] How does a buffer maintain pH stability? (Quick Check 9.4)

[vi] What is water called a weak electrolyte?

[vii] Why does [OH⁻] decrease when acid is added to water?

[viii] Define pOH.

[ix] What is the formula to calculate pOH?

[x] Explain why lower pH means higher acidity.

[xi] What happens to pH when a strong base is added to water?

[xii] What does a high Ka value indicate?

[xiii] Define common ion effect.

[xiv] Write any one function of a buffer.

[xv] Why are buffers important in chemical and biological systems?

Q3. Write detailed answers of the following questions. (Answer any 2) (2×5=10)

1. Define ionization constant (Ka) of acids. Derive the expression for Ka of a weak acid and explain its significance.

2. What is the common ion effect? Explain with examples how the addition of a common ion affects the ionization of weak acids and weak bases using Le Chatelier’s Principle.

3. Describe the composition, working, and significance of the CH₃COOH/CH₃COONa and NH₄OH/NH₄Cl buffer systems.

CH₃COOH ⇌ CH₃COO⁻ + H⁺

NH₄OH ⇌ NH₄⁺ + OH⁻

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