1. Based on your experimental data, compare the relative abilities of a buffer s
ID: 970211 • Letter: 1
Question
1. Based on your experimental data, compare the relative abilities of a buffer solution and distilled water to resist pH changes upon addition of either acidic or basic solutions. Briefly explain your reasoning.
2. Suppose you made a buffer solution that was 0.050M in both HC2H3O2 and NaC2H3O2. Would the pH changes resulting from the addition of 0.1M HCl solution to this buffer solution be the same as those you observed in the experiment? Briefly explain.
3. Calculate the pH of a buffer solution that is 0.40M in HC2H3O2 and 0.15M NaC2H3O2.
4. Assume you have a 1L of a buffer solution that is made from 0.4M of both HC2H3O2 and NaC2H3O2 and a 1 L of a second buffer solution that is made from 0.1M HC2H3O2 and 0.4M NaC2H3O2. To which buffer solution could you add 2L of 0.1M NaOH solution and cause the smaller pH change? Briefly explain.
5. Calculate Ka for the weak acid HA, given that a buffer solution that is (1.0x10^-1)M HA and (1.0x10^-1)M NaA and has a pH of (5.390x10^0).
Note: Your answer is assumed to be reduced to the highest power possible.
Explanation / Answer
1. Based on your experimental data, compare the relative abilities of a buffer solution and distilled water to resist pH changes upon addition of either acidic or basic solutions. Briefly explain your reasoning.
Water is not suitable for buffering, since a small amount of acid/base will change the pH drastically, so this is not a good buffer.
2. Suppose you made a buffer solution that was 0.050M in both HC2H3O2 and NaC2H3O2. Would the pH changes resulting from the addition of 0.1M HCl solution to this buffer solution be the same as those you observed in the experiment? Briefly explain.
No, we should expect a very small change in pH, due to the buffer formation of
HC2H3O2 and C2H3O2-
HC2H3O2 neutralizes the base (OH-)
C2H3O2- neutralizes the acid (H+)
3. Calculate the pH of a buffer solution that is 0.40M in HC2H3O2 and 0.15M NaC2H3O2.
for acetic acid, pKa = 4.75
the buffer equation
pH = pKa + log(C2H3O2- / HC2H3O2)
pH = 4.75 + log(A-/HA)
A- = 0.15, HA = 0.40
substitute
pH = 4.75 + log(0.15/0.40)
pH = 4.3240
4. Assume you have a 1L of a buffer solution that is made from 0.4M of both HC2H3O2 and NaC2H3O2 and a 1 L of a second buffer solution that is made from 0.1M HC2H3O2 and 0.4M NaC2H3O2. To which buffer solution could you add 2L of 0.1M NaOH solution and cause the smaller pH change? Briefly explain.
the first buffer has same amount of acid/base
the second buffer has much more base than acid
recall that NaOH is a base, so it will neutralize the acid
Then, the first solution will buffer it better, since there are 0.4 M of aci, whereas the second solution has only 0.1 M of acid.
5. Calculate Ka for the weak acid HA, given that a buffer solution that is (1.0x10^-1)M HA and (1.0x10^-1)M NaA and has a pH of (5.390x10^0).
apply buffer equation
pH = pKa + log(A-/HA)
5.39 = pKa + log(10^-1/10^-1)
5.39 = pKa
the Ka = 10^-5.39 = 4.0738*10^-6
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