# Homework Help: Henderson hasselback equation

1. Dec 6, 2012

### Hemolymph

1. The problem statement, all variables and given/known data

. You have solutions of 0.200 M HNO2 and 0.200 M KNO2 (Ka for HNO2 = 4.00 × 10–4). A buffer of pH 3.000 is needed. What volumes of HNO2 and KNO2 are required to make 1 liter of buffered solution?
A) 500 mL of each
B) 286 mL HNO2; 714 mL KNO2
C) 413 mL HNO2; 587 mL KNO2
D) 714 mL HNO2; 286 mL KNO2
E) 587 mL HNO2; 413 mL KNO2

2. Relevant equations

pH=pKa+log([A]-/[HA])

3. The attempt at a solution

3=3.4+log([A-]/[HA])
-.4=log([A-]/[HA])
10^-.4
.398=[A-]/[HA]
I get confused conceptually of what to do after this. I know I need .398M of conj base for every 1M of acid

2. Dec 7, 2012

### Staff: Mentor

This is one equation. The other is

$$V_{A^-} + V_{HA} = 1L$$

You need to combine volume with concentration - and you will have two equations in two unknowns. Just solve.