Question

What is the predominant form of citric acid (H3C6H5O7) at pH 4.37 and pH 6.12? Citric acid has pKa values of 3.128 (pKa1), 4.761(pKa2), and 6.396 (pKa3). (These are all multiple choice) Please help!

PH 4.37 a) H2C6H5O7– b) H3C6H5O7 c)HC6H5O72– d) C6H5O73–

PH 6.12 a)C6H5O73– b)H2C6H5O7– c)H3C6H5O7 d) HC6H5O72–

What is the second most abundant species of citric acid at each pH? PH 4.37 a)H3C6H5O7 b)H2C6H5O7– c)HC6H5O72– d)C6H5O73–

PH 6.12 a)HC6H5O72– b)H2C6H5O7– c)H3C6H5O7 d)C6H5O73–

Answer 1

at pH 4.37 it will loose only one proton and form the single anion other two acidic protons pKa is higher than 4.97

so 4.37 pH a) H2C6H5O7–

similarly at pH 6.12 it will exist as a dianion

so answer is d) HC6H5O72–

second most abundant species of citric acid at each pH? PH 4.37 is c)HC6H5O72–

at pH 6.12 d)C6H5O73–