Answer to Question #208353 in General Chemistry for Special torque

Question

A student plotted a titration curve after titrating nitrous acid (HNO2) with potassium hydroxide

(KOH). The student started by placing 45.0 ml of 0.150 M HNO2 in a beaker and titrated to the endpoint and beyond with 0.120 M KOH.

Ka for HNO2 = 4.5 x 10-4

a) Draw a sketch of the titration curve with labels on the following: 1) endpoint volume (show the value)

2) approximate endpoint pH (relative to 7)

3) half-equivalence point (show the value)

 b) Write the chemical equation for the dissociation of nitrous acid and then the equilibrium constant expression (Ka).

c) Determine the pH of the solution at the half equivalence point.

d) Determine the pH of the solution at the endpoint of the titration.

Answer 1

3)

3b) HNO₂(aq) + H₂O(l) ⇌ H₃O⁺(aq) + NO₂^–(aq)

For nitrous acid, HNO2, Ka = 4.0 × 10^-4

3c) pH = 2

3d) pH = 12