Question

pH of 0.1M Na2HPO4 and 0.2M NaH2PO4 are respectively : pKa for H3PO4 are 2.2, 7.2 and 12.0.

• A. 4.7, 9.6
• B. 9.6, 4.7
• C. 4.7, 5.6
• D. 5.6, 4.7

Answer 1

Answer: (B)

9.6, 4.7

Answer 2

For Na2HPO4, pH = $\frac { 7.28 + 12 } { 2 }$ = 9.6.

For Na2HPO4 , pH = $\frac { 2.2 + 7.2 } { 2 }$= 4.7.