1. ⇒ (MHT CET 2023 12th May Evening Shift )

A buffer solution is prepared by mixing $0.01 M$ weak acid and $0.05 M$ solution of a salt of weak acid and strong base. What is the $pH$ of buffer solution? $(pKa = 4.74)$

A.

3.34

B.

4.80

C.

5.44

D.

6.93

Correct Option is (C)

$\begin{aligned} pH & = {pK}_{a} + \log_{10} \frac{[salt]}{[acid]} \\ = 4.74 + \log_{10} \frac{0.05}{0.01} \\ = 4.74 + 0.7 = 5.44 \end{aligned}$

2. ⇒ (MHT CET 2023 12th May Morning Shift )

What is $pH$ of solution containing $50 mL$ each of $0.1 M$ sodium acetate and $0.01 M$ acetic acid? $({pK}_{a} {CH}_{3} COOH = 4.50)$

A. 2.5

B. 3.5

C. 4.5

D. 5.5

Correct Option is (D)

For acidic buffer solution,

$\begin{aligned} pH = {pK}_{a} + \log_{10} \frac{[Salt]}{[Acid]}; \\ pH = 4.50 + \log_{10} \frac{0.1}{0.01}; \\ pH = 4.50 + \log 10; pH = 5.50 \end{aligned}$

For acidic buffer, if [Salt] $>$ [Acid], then $pH > {pK}_{a}$ of acid. Hence, only option (D) is valid.

3. ⇒ (MHT CET 2023 9th May Evening Shift )

What is the concentration of $[H_{3} O^{+}]$ ion in $mol L^{- 1}$ of $0.001 M$ acetic acid $(α = 0.134)$ ?

A.

1.34 \times 10^{- 4}

B.

1.54 \times 10^{- 4}

C.

1.80 \times 10^{- 4}

D.

1.70 \times 10^{- 4}

Correct Option is (A)

$\begin{aligned} [H_{3} O^{+}] = α \times c & = 0.134 \times 0.001 \\ = 1.34 \times 10^{- 4} mol {dm}^{- 3} \end{aligned}$

⇒Ionic Equilibrium