Question

Interpretation of Buffer Preparation and pH measurement

Hello! We did an experiment in lab creating buffers using 3 different methods, 1)weak acid + strong base, 2) wake base + strong acid, and 3)weak acid + weak base. The desired pH (and the number used to calculate concentration of components) was 7.5....Solution 1 had pH of 5.9, solution 2 had pH of 7.3 and solution 3 had pH of 7.1

I'm having trouble interpreting these results. Were these pH levels expected? Were any errors made? For example, is Solution 1 supposed to have pH of 5.9 even though desired pH was 7.5? Any help is much appreciated. Thank you!

Answer 1

In case of Buffer preparation and PH measurement - 1) the solution of weak acid and strong base-

let say,AcOH+NaOH=NaOAc +H₂O, then the hydrolysis of the salt occurs and the solution becomes basic.So the PH of the solution is greater than 7.

so, we can say that there was an error. The desired PH was expected.

2) the solution of strong acid and weak acid- let say ,HCl +NH₄OH=NH₄Cl +H₂O, then the hydrolysis of the salt occurs and the solution becomes acidic. So the PH of the solution is less than 7. That means there was some error, in this case desired pH was not expected.

3)the solution of weak acid and weak base-let say,NH₄OH+AcOH=NH₄OAc +H₂O,Then the hydrolysis of the salt occurs and the solution becomes neutral. That means the PH of the solution is almost right.In this desired pH was not expected.