Question

How many grams to prepare a buffer?

How many grams of solid potassium cyanide should be added to 2.00 L of a 0.178 M hydrocyanic acid solution to prepare a buffer with a pH of 10.205 ?

Answer 1

I'll use `pK_A = 9.21`. The addition of the solid may change the volume, but that shouldn't matter since See below `log((base)/(acid))` has L/L. See below

Explanation:

The pH of the buffer follows the Hendeson-Hasselbalch equation
`pH = pK_A + log((base)/(acid))`
`10.205 = 9.21 + log((base)/(0.356 mol HCN))`
do the subtraction, then raise both sides to power of 10.
`10^0.995 = ((base)/(0.356 mol HCN))`
`9.885 = ((mol base)/(0.356 mol HCN))`

3.52 moles KCN
`3.52 mol KCN((65.12 g)/(1 mol))`

229.22 grams KCN