Question

What is the [H3O+] in a buffer that consists of 0.30 M HCOOH and 0.20 M HCOONa?
Ka = 1.7 × 10-4

I just need the steps to do it, not the answer

Answer 1

Are you reacting the acid into the base?

Answer 2

i believe so

Answer 3

In which case, this is a titration question?

Answer 4

these are the possible answers
A. 1.1 × 10-4 M
B. 2.6 × 10-4 M
C. 4.3 × 10-4 M
D. 6.7 × 10-5 M

but im looking more for the steps to getting the answer

Answer 5

and yea

Answer 6

oh OK. Titration is reaction then equilibrium, so first set up a mole chart.

Answer 7

so HCOOH to [H+] + [COOH]?

Answer 8

ohh an ice table

Answer 9

well, it's ICE but instead of concentration, it's moles

Answer 10

1.72*10^-4=(.2/.3)x
basically?

Answer 11

well you basically want to find how many moles react into H3O/H+, you'll get a response like the kind you would expect from ICE, which you can set equal to the Ka value.

Answer 12

so is it the equation i wrote?

Answer 13

well if that's the value you get, then it looks like what you are dealing with isn't necessarily a titration equation per se, the value looks like one of the answers.

Answer 14

i got 2.5*10^-4

Answer 15

I'm sorry if I've not been very helpful, but unfortunately I need to go. I hope you get someone who can definitely help you

Answer 16

its all good, thanks for your help

Answer 17

but since the question looks like it's asking for a post reaction concentration, 2.6x10^-4 might be the answer

Answer 18

I would probably try to be more sure though. Sorry :(

Answer 19

all good, il ask my professor tomorrow, thanks again

Answer 20

There is no reaction taking place here.

Simply use Henderson's equation:
http://en.wikipedia.org/wiki/Henderson-Hasselbalch_equation