Phosphate buffer questions Phosphate is a special buffer tha

Phosphate buffer questions. Phosphate is a special buffer that can be protonated 3 times. The pKa\'s are for phosphate are 2.12, 7.21, and 12.67, respectively. Which of the following is not a possible form of phosphate? PO_4^3 HPO_4^2 H_3PO_4 H_4PO_4^1+ At which of the following values of pH would phosphate make a good buffer. pH 4 pH 5 pH 8 pH 9 What ionic form would phosphate most commonly be in at pH = l? PO_4^3 HPO_4^2- H_3PO_4 H_4PO_4^1+

Solution

13. Phosphate buffer exists either in monobasic hydrogen phosphate or dibasic phosphate. The dissociation of phosphoric acid (H₃PO₄) may yield H⁺ ion and mono or dihydrogen phosphate respectively. Dissociation of dibasic hydrogen phosphate may yield PO₄^3- and Hydrogen phosphate (HPO₄^2-). Generally PO₄^3- form is not possible form of phosphate. Option A is correct.

14. The buffer having pKa value between 6 to 8 makes a good buffer. Option C is correct.

15. At pH = 1, phosphate >90% exist in phosphoric acid (H₃PO₄ ). This is because pH 1 is not suitable for dissociation of phosphoric acid. Phosphoric acid is protonated at pH 2.12. Option C is correct.