What will be the pH of a solution formed by mixing 10 mL 0.1 M NaH2PO4 and 15 mL 0.1 M Na2HPO4 ? [Given: for H3PO4 pKa1=2.12,pKa2=7.2 ]

Question

What will be the pH of a solution formed by mixing 10 mL 0.1 M NaH2PO4 and 15 mL 0.1 M Na2HPO4 ? [Given: for H3PO4 pKa1=2.12,pKa2=7.2 ] (A) 7.0 (B) 6.9 (C) 7.4 (D) 7.5

Tardigrade Admin · Accepted Answer

pH=pKa+log ([c o n j u g a t e text base]/[a c i d]) Number of moles of NaH2PO4=(10/1000)L× 0.1 mol textL- 1 =0.001 moles Number of moles of Na2HPO4=(15/1000)× L× 0.1 text mol textL- 1 =0.0015 moles pH=7.2+log ([0.0015]/[0.001]) =7.37≈ 7.4

Q. What will be the pH of a solution formed by mixing 10 mL 0.1 M NaH2​PO4​ and 15 mL 0.1 M Na2​HPO4​ ? [Given: for H3​PO4​ pKa1​​=2.12,pKa2​​=7.2 ]

7.0

6.9

7.4

7.5

pH=pKa​+log[acid][conjugate base]​ Number of moles of NaH2​PO4​=100010​L×0.1molL−1 =0.001 moles Number of moles of Na2​HPO4​=100015​×L×0.1 mol L−1 =0.0015 moles pH=7.2+log[0.001][0.0015]​ =7.37≈7.4

Q. What will be the pH of a solution formed by mixing 10 mL 0.1 M $N a H_{2} P O_{4}$ and 15 mL 0.1 M $N a_{2} H P O_{4}$ ?

[Given: for $H_{3} P O_{4}$ $p K_{a_{1}} = 2.12, p K_{a_{2}} = 7.2$ ]