Ammonium formate is the salt of HCOOH (pK_a = 3.75) and NH3 (pK_b = 4.75). Use pH = 7 + tfrac12(pK_a - pK_b). The pH of its aqueous solution is

JEE Main levelSingle correct optionDifficulty 2 of 3ia008

Ammonium formate is the salt of $HCOOH$ ( $p K_{a} = 3.75$ ) and $NH X_{3}$ ( $p K_{b} = 4.75$ ). Use $pH = 7 + \frac{1}{2} (p K_{a} - p K_{b})$ . The pH of its aqueous solution is

For the salt of a weak acid and a weak base,

pH = 7 + \frac{1}{2} (p K_{a} - p K_{b}) = 7 + \frac{1}{2} (3.75 - 4.75) = 6.50

. The acid is the stronger of the two, so the solution is slightly acidic.