The pH of weak monoacidic base is 11.2, its $OH^-$ ion concentration is: (a) $1.585 \times 10^{-3}\ mol\ dm^{-3}$ (b) $3.010 \times 10^{-11}\ mol\ dm^{-3}$ (c) $3.010 \times 10^{-3}\ mol\ dm^{-3}$ (d) $1.585 \times 10^{-11}\ mol\ dm^{-3}$

The pH of weak monoacidic base is 11.2, its OH^- ion concentration is: (a) 1.585 × 10⁻³moldm⁻³ (b) 3.010 × 10⁻

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Q. The pOH of 0.01 M HCl solution is _____.

(a) 1

(b) 2

(c) 11

(d) 12

›Reveal solution

For 0.01 M HCl, pH = 2, so pOH = 14 − 2 = 12.

HCl is a strong acid and ionizes completely: $HCl \rightarrow H^+ + Cl^-$ , so $[H^+] = 0.01\ M = 10^{-2}\ M$ .

$pH = -\log[H^+] = -\log(10^{-2}) = 2$

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Q. The pH of 0.001M HCl solution is _____.

(a) 10

(b) 3

(c) 2

(d) 11

›Reveal solution

$pH=-\log(10^{-3})=3$ for 0.001 M HCl.

HCl is a strong acid, fully ionised: $[H^+] = 0.001\ M = 10^{-3}\ M$ .

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OH^-

(a)

1.585 \times 10^{-3}\ mol\ dm^{-3}

(b)

3.010 \times 10^{-11}\ mol\ dm^{-3}

(c)

3.010 \times 10^{-3}\ mol\ dm^{-3}

(d)

1.585 \times 10^{-11}\ mol\ dm^{-3}

›Reveal solution

$pOH = 14 - pH$ , then $[OH^-]=10^{-pOH}$ .

$pH + pOH = 14 \Rightarrow pOH = 14 - 11.2 = 2.8$

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