\( K_a \) for \( \text{CH}_3 \text{COOH} \) is \( 1.8 \times 10^{-5} \) and \( K_b \) for \( \text{NH}_4 \text{OH} \) is \( 1.8 \times 10^{-5} \). The pH of ammonium acetate solution will be:
Correct Answer: 7
Solution and Explanation
The pH is given by:
\(\text{pH} = \frac{pK_a + pK_b}{2}\)
Since \(pK_a = pK_b\),
\(\text{pH} = \frac{7 + 7}{2} = 7\)
Top Questions on Acid-base equilibria
Your teacher uses a weighing balance to take equal amounts of two substances, tartaric acid and washing soda, say 1g. Each is dissolved separately into 100 cc of water.
(A) In 1 drop of the acid solution and 1 drop of the basic solution, we have:
1. equal amount of acid and base respectively
2. equally acidic and basic substance respectively
3. acidity in one and basicity in the other are not equal
4. equal magnitude of the quantity —pH-7—
(B) Take a few cc of the acidic solution in a test-tube and mix a few drops of coloured
phenolphthaline solution (prepared in basic medium) into it. Which of the following may be 4
happening:
1. The colour of the solution instantly changes pink
2. remains colourless as the colour of the added drops disappears
3. the colour diffuses through the solution and finally disappears
4. the colour diffuses through the solution and finally the entire solution acquires a faint pink
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