Question

I need to prepare 100.0mL of a 0.200M acetate buffer of pH 5.00. All I am given is solid sodium acetate and 1.00M of acetic acid. What is the volume of acetic acid used and the mass of sodium acetate used?

Answer 1

Recall,

`"pH" = "pK"_"a" + log(([A^-])/([HA]))`

If your only source of water is the one molar solution of acetic acid, the calculation will be less challenging. Moreover, if you're actually doing this I will assume you know how to look up a `"pK"_"a"` value in a table. So with this assumption,

`[CH_3COO^-] = [HC_3COO] * 10^("pH" - "pK"_"a") approx 0.174"M"`

And by extension,

`0.174"M" * 0.1"L" (82"g")/"mol" approx 1.42"g"` of `NaCH_3COO`

Hence, to prepare this solution, go into the lab, and combine,

`100"mL"` of `1.0"M"` acetic acid, and

`1.42"g"` of sodium acetate salt.

The `"pH"` per the meter should be pretty close to 5! Good luck.