Question

2.0 mL of 0.5M HCl was added to 50 mL of 0.5M Formate-formic acid buffer at pH 3.6. (pKa= 3.75) What is the resulting pH after the addition of HCl?

2.0 mL of 0.5M HCl was added to 50 mL of 0.0625M Formate-formic acid buffer at pH 3.6. (pKa= 3.75) What is the resulting pH after the addition of HCl?

1.0 mL of 0.6M NaOH was added to 10 mL of 0.5M Acetate-acetic acid buffer at pH 4.2. What is the resulting pH after the addition of NaOH?

0.5 mL of 0.3M NaOH was added to 10 mL of 0.5M Acetate-acetic acid buffer at pH 4.2. What is the resulting pH after the addition of NaOH?

Answer 1

First of all, we need to calculate the ratio of moles of formiate and formic acid in the given buffer, using the Henderson-Hasselbach equation:

The total number of moles in the buffer is:

So we have:

And:

When we add HCl, it reacts to form HA, consuming A^-. The number of moles of HCl added is:

So we have a new buffer:

For the second case, we have the same ration of acid and base, but a different total concentration:

The total number of moles in the buffer is:

So we have:

And:

When we add HCl, it reacts to form HA, consuming A^-. The number of moles of HCl added is:

So we have a new buffer:

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For the acetic buffer:

First of all, we need to calculate the ratio of moles of formiate and formic acid in the given buffer, using the Henderson-Hasselbach equation:

The total number of moles in the buffer is:

So we have:

And:

When we add NaOH, it reacts to form A^-, consuming HA. The number of moles of NaOH added is:

So we have a new buffer:

For the second case, we we have the same buffer, but ad a different amount of base:

So we have a new buffer: