Question

Succinic acid (H2C4H6O4), which we will denote H2Suc, is a biologically relevant diprotic acid with the structure shown below он он о нн Q Tap image to zoom . It is closely related to tartaric acid and malic acid. At 25°C the acid-dissociation constants for succinic acid are Kai-6.9 10-5 and Ka2-2.5 x 10-6 Part A Determine the pH of a 0.37 M solution of H2Suc at 25 C, assuming that only the first dissociation is relevant. Express your answer numerically as a pH pH -

Answer 1

We know that organic acids like tartaric acid, succinic acids are weak acids It is also evident from their acid dissociation constant which are very less (k_a lessthanorequalto 10^-5) Now before solving the problem: Lets derive some relations about weak acid Let HA be a weak acid having concentration = C MOIL^-1 degree of Ionization (or dissociation) = alpha therefore Amount of acid ionized = C alpha MOIL^-1 HA (aq) rightharpoonoverleftharpoon H^+ (aq) + A^-(aq) k_a = [H^+] [A^-]/[HA] = C alpha times C alpha/C - C alpha = C^2 alpha^2/C(1 - alpha) = C alpha^2/1 - alpha Now for weak acid: degree of Ionization 'alpha ' is negligible in compare to 1 ie alpha < < < 1 therefore 1 - alpha almostequalto 1 therefore alpha = squareroot k_a/C [as k_a = C alpha^2] so, [H^+] = [A^-] = C alpha = C alpha times squareroot k_a/C