a) How to do I calculate the pH of original buffer given mass ofNaC2H3O2*H2O (FW =136 g/mol) = 3.507 g
after measuring out 8.8 mL of 3.0 M acetic acid to add to thebeaker containing the sodium acetate. Then put in 55.6 mL ofdistilled water with the pH of original buffer solution =4.89

b) How then, how would I calculate the pH of a buffer + NCl aftertaking 32 mL of the solution noted above and pipet 1.0 mL of 6.0 MHCl with the pH of buffer + HCl = 4.41?

c) Finally, how to calculate the pH of buffer + NaOH with 32 mL ofthe first solution listed above and pipet 1.0 mL of 6.0 M NaOH withpH of buffer + NaOH = 5.28?

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Collen VonLv2

15 Jan 2019

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A) preparation of buffer solution:

6.606g of sodium acecate trihydrate was weighed out (MM=136 g/mole) in a small beaker. 25 ml of water was added to 100 ml volumetric flask. 8.00 ml of a 6 M acetic solution was added.

B) pH of water with added NaOH and HCl

Prepare two beakers (Beaker 1 and Beaker 2) and pipet 25 mL of deionized water into each beaker. Measure the pH of the water in the beaker. In Beaker 1, add 1 drop of 1 M NaOH into the beaker. Stir and read the pH of the resulting mixture. Add an additional drop of the 1 M NaOH solution to the beaker, stir and measure the pH. Add an addition 4 drops for a total of 6 mL and then 4 more drops for a total of 10 drops, add 10 more drops and finally using a volumetric or graduated pipet, add 1 mL of 1M NaOH and read the pH after each addition. To Beaker 2, add 1 drop of 1 M HCl into the beaker. Stir and read the pH of the resulting mixture. Add an addition 1 drop of the 1 M HCl solution to the beaker, stir and measure the pH. Add an addition 4 drops for a total of 6 drops and then an additional 4 drops for a total of 10 drops, add 10 more drops and finally add 1 mL of 1 M HCl, read the pH after each addition.

C) pH of buffer solution with added NaOH and HCl

Prepare two additional beakers (Beaker 3 and Beaker 4). Pipet 25 mL of the prepared buffer solution from part A into each beaker. Measure the pH of the buffer solution. To Beaker 3, using a graduated pipet, add 1 mL of 1 M NaOH. Stir and read the pH of the resulting mixture. Add an addition 1 mL of the 1 M NaOH solution to the beaker, stir and measure the pH. Add 4 mL more for a total of 6 mL and then an additional 4 mL for a total of 10 mL, finally add two 10 mL additions, read the pH after each addition. To Beaker 4 containing 25 mL of buffer, repeat the steps of beaker 3 with the addition of 1 M HCl into the beaker. Stir and read the pH after each addition.

Questions: only need 4-6

4)Calculate the pH of the buffer solution after 2 mL of NaOH was added to Beaker 3 and after 2 mL of HCl was added to Beaker 4. Compare this to your measured pH

5)Compare the measured pH for the addition of 1M NaOH and 1 M HCl to beaker 3 and 4 with the buffer solutions to the measured pH in Beaker 1 and 2 with the water.

6)From the measured pH of the acetic acid buffer solution above before the addition of any NaOH or HCl solution, calculate the K?a for acetic acid. Compare to CH3COOH Ka value which is 9.1x10^-6?

Water				Buffer solution
Beaker 1		Beaker 2		Beaker 3		Beaker 4
Total Volume of 1 M NaOH added	pH	Total Volume of 1 M HCl added	pH	Total Volume of 1 M NaOH added	pH	Total Volume of 1 M HCl added	pH
0 mL	7.08	0 mL	7.01	0 mL	6.02	0 mL	6.05
1 drop	9.86	1 drop	3.13	1 mL	11.87	1 mL	5.52
2 drops	10.38	2 drops	2.69	2 mL	12.38	2 mL	5.22
6 drops	10.86	6 drops	2.25	6 mL	12.74	6 mL	4.46
10 drops	11.08	10 drops	2.02	10 mL	12.87	10 mL	3.53
20 drops	11.35	20 drops	1.76	20 mL	12.99	20 mL	1.04
2 mL = (40 drops)	11.68	2 mL	1.47	30 mL	13.06	30 mL	0.89