6- The acid you used was vinegar, and the base you used was ammonia. Which subst

Question

6- The acid you used was vinegar, and the base you used was ammonia. Which substance caused a greater change in the pH of each system, and why do you think this is so? (Keep in mind that the pH of pure vinegar is about three and pure ammonia is about 12).

7-Write the total ionic equations for a) the addition of the acid to the buffer, and b) the addition of base to the buffer.

8-Write the net ionic equations for a) and b) from the previous questions?

9-Buffers are only useful over a certain pH range. For what pH is this buffer solution useful?

10- The buffer solution you made had nearly equal molar parts of weak acid and conjugate base. If you wanted to use this same buffer system (bicarbonate- carbonate) at a lower pH (more acidic), how would you need to change the proportions of weak acid and conjugate base to lower the pH of the buffer solution?

11- How would you change the proportions of the weak acid and conjugate base to make a buffer solution that is useful at a higher pH (more basic)?

12-What substance in this lab is amphoteric?

13- What empirical evidence do you have that this substance has amphoteric properties?

Buffering of a acid: (vinegar) Total number of Distilled Water drops of Vinegar NaHCO3 Na2003 Buffer (pH) 0 (start) Buffering of a base: (Ammonia) Total number of drops of Ammonia Distilled Water NaHCO3 Na2003 Buffer pH) 0 (Start)

Explanation / Answer

6) Vinegar caused a greater change in the pH. Vinegar which is essentially acetic acid, CH3COOH will react strongly with the conjugate base of the buffer system, Na2CO3 and this will change the pH.

7) Addition of acid to buffer: reaction with the conjugate base of the buffer

H^+ + NaCO3^- --------- NaHCO3

Addition of base to buffer: reaction with the acid of the buffer

OH^- + NaHCO3 ------ NaCO3^- + H2O

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