Question

How many grams of solid sodium nitrite should be added to 2.00 L of 0.101 M nitrous acid solution to prepare a buffer with a pH of 2.460? (K, for nitrous acid = 4.50x104) g sodium nitrite

Answer 1

Answer :- 1.795 g of sodium nitrite should be added
ka= 4.5810-4 (for HNO2) so, pka = -log ka = -log(4.5x1004) = 3.35 from Henderson equation, pH for buffer is PHS pka + log CNANO] [HNO₂] 2.460 = 3.35 + log [Nano] 0.101 -0.89 = log CNaNO2] 0.101 - [Nano] = 10-0.89 = 0.1288 0.101 (NaNO₂] = 0.1288x0.10 = 0.01301 M

concentration = number of moles volume no. of moles = 0.01301x2 - 0.02601 no. of moles = mass (in grams) molar mass (glmoll mass = 0.02601 x 69 = 1.795 g So, 1.795 g of NaNo, should be added.