Question

How many grams of solid potassium nitrite should be added to 0.500 L of a 0.174 M nitrous acid solution to prepare a buffer with a pH of 4.2527 grams potassium nitrite = Submit Answer Try Another Version 10 tem attempts remaining

Answer 1

pKa of nitrous acid (HNO₂) = 3.15

pH = 4.282

Molarity of HNO₂ = 0.174 M

Molarity of KNO₂ = X M

Volume = 0.5 l

According to Henderson - Hasselbalch equation

pH = pKa + log [KNO₂]/[HNO₂]

4.282 = 3.15 + log (X/0.174)

4.282-3.15 = log (X/0.174)

1.132 = log (X/0.174)

(X/0.174) = 10^1.132 = 13.552

X = 13.552 x 0.174 = 2.36 M

[KNO₂] = 2.36 M

No. of moles of KNO₂ = Molarity x vol in lts = 2.36 M x 0.5 l = 1.18 moles

Molar mass of KNO₂ = 85.1 g/mol

Mass of KNO₂ = moles x molar mass = 1.18 mol x 85.1 g/mol = 100.42 gms