What is the minimum pH required to prevent the precipitation of ZnS in a solution containing 0.01 M ZnCl₂ and saturated with 0.10 M H₂S?

(Given: Ksp of ZnS = 10⁻²¹, and Ka₁ × Ka₂ of H₂S = 10⁻²⁰)

1. Four (4)

2. Three (3)

3. Two (2)

4. One (1)

Which of the following is an amphiprotic (can accept and give protons) ion?

1. ${\mathrm{HPO}}_3^{-}$

2. ${\mathrm{H}}_2{\mathrm{PO}}_2^{-}$

3. ${\mathrm{H}}_3{\mathrm{PO}}_4$

4. ${\mathrm{H}}_2{\mathrm{PO}}_4^{-}$

The ratio of F^- and HCOO^- in a mixture of 0.1 M HF $({\mathrm{K}}_{\mathrm{a}}=6.6\times {10}^{-4})$ and 0.2 M HCOOH $({\mathrm{K}}_{\mathrm{a}}=2\times {10}^{-4})is:$

A buffer solution is prepared by mixing 10 mL of 1.0 M acetic acid with 20 mL of 0.5 M sodium acetate which is then diluted
to 100 mL with distilled water. If the pK_a of ${\mathrm{CH}}_3\mathrm{COOH}$ is 4.76, the pH of the buffer solution prepared is -
1. 5.21

2. 4.76

3. 4.34

4. 5.35

What is the pH of a solution obtained by mixing equal volumes of two solutions, one with a pH of 3 and the other with a pH of 4?
[log 5.5=0.7404]

1. 3.26

2. 3.5

3. 4.0

4. 3.42

What is the concentration of Ag⁺ ions in a buffer solution of pH = 10 when solid AgNO₃ is added slowly and AgOH is precipitated? 
\([K_{sp}(AgOH) = 10^{-10}]\)

If pK_b for ${\mathrm{CN}}^{-}$ at $25°\mathrm{C}$ is 4.7, the pH of 0.5 M aqueous NaCN solution is:

1. 10

2. 11.5

3. 11

4. 12

A buffer solution is prepared by mixing 20 ml of 0.1 M CH₃COOH and 40 ml of 0.5 M CH₃COONa and then diluted by adding 100 ml of distilled water. The pH of the resulting buffer solution is : (Given pKa of CH₃COOH=4.76)

An acid-base indicator has ${\mathrm{K}}_{\mathrm{a}}=3.0\times {10}^{-5}$. The acidic form of the indicator is red and the basic form is blue. The [H⁺] required to change the indicator from 75% red to 75% blue is:

1. \(8 \times 10^{- 5} M \)

2. \(9 \times 10^{- 5}~ \text M\)

3. \(1 \times 10^{- 5}~ \text M\)

4. \(3 \times 10 ^{- 4}~ \text M\)

The self-ionization constant for pure formic acid, K = [\(H C O O H_{2}^{+} \left]\right. \left[\right. H C O O^{-} \left]\right.\) ] has been estimated as \(\left(10\right)^{- 4}\) at room temperature. The percentage of formic acid molecules in pure formic acid that are converted to formate ions is

\(\left(\right. Given : d_{HCOOH} = 1 . 22\ g / cc \left.\right)\)

1. 0.0185%

2. 0.0073%

3. 0.074%

4. 0.037%