Question

In: Chemistry

Determine the pH of a solution created by mixing 240mL of 0.172M HCHO2 with 275.2mL of...

Determine the pH of a solution created by mixing 240mL of 0.172M HCHO2 with 275.2mL of 0.150M NaOH.

The answer key says the answer is 8.32, but I keep getting 8.18

Solutions

Expert Solution

the Pka is missing for formic acid 3.75

       HCHO2                    +    NaOH ------------->         HCO2Na +   H2O

240mL of 0.172M            275.2mL of 0.150M

41.28                                           41.28                                 complete neutralisation takes place so its a salt hydrolysis question

[salt ] =c = 41.28/515.2 = 0.080 M

pH   = 7 + 1/2 Pka + 1/2logC = 7 + 1/2(3.75) + 1/2log(0.08) = 7 + 1.875 -0.548 = 8.327


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