The solution contains a mixture of maleic acid and the completely deprotonated m
ID: 933951 • Letter: T
Question
The solution contains a mixture of maleic acid and the completely deprotonated maleate ion (M^2-). The reaction between these two species results in the formation of the intermediate ion (HM^-). Pay attention to the stoichiometry of this reaction. Assume the volume of the solution is 1 L and determine which species and how much of each is present in the solution after the reaction between maleic acid and the maleate ion. The resulting solution contains a mixture of an acid and its conjugate base, meaning a buffer is present. A buffer prepared from a diprotic acid can be treated the same as a buffer prepared from a monoprotic acid. Based on the species present in the solution, use the Henderson-Hasselbalch equation that corresponds to the dissociation reaction for the species present in solution to solve for the pH. a) Maleic add (H2M) is a diprotic acid that dissociates when placed in water according to the following reactions. Calculate the pH of the following solutions. a) A solution containing 0.0170 M maleic acid and 0.0243 M disodium maleate. The K values for maleic acid are 1.20 x 10^-2 (ka1) and 5.37 x 10^-7 (Ka2).Explanation / Answer
in the problem two Ka values are there . Ka1>> Ka2 . this means maximum all H+ ions come in first reaction (ionisation) with base. so we can consider Ka1 .no need to take ka2
pKa1 = -log Ka1 = -log(1.2 x10^-2) = 1.92
pH = pKa + log[salt/acid]
moles of salt = 2 x 0.0243 (di sodium salt)
= 1.92 + log[2 x 0.0243/ 0.0170]
pH = 2.376