I did forget about the concentration of F
- in the solution, so I tried the problem again, and this time I got one of the answers, but not the right answer (which is C), so I think I'm still doing something wrong.
I got that the first reaction between HF and NaOH is a neutralization reaction, which would be HF + NaOH
H
2O + NaF. And then I had that 0.010 L*0.10 M HF - 0.010 L * 0.040 M NaOH = 0.0006 mol HF leftover again, but that this produced 0.010 L * 0.040 M = 0.0004 mol NaF. I divided both 0.0006 mol HF and 0.004 mol F
- by 0.020 L to get 0.03 M HF and 0.02 M F
-.
And then I set up the other equation for HF + H
2O
H
3O
+ + F
-. It's given that K
a= 6.7*10
-4. And after the ICE chart, K
a= (0.02-x)(x)/(0.03+x). I assumed that x was small enough to let 0.02-x=0.02 and 0.03+x=0.03. Using a calculator, I then got that the pH = 3.0, which is D, but the right answer is C?