Why does H2PO4 donate a proton to HS if both are amphoteric?

[Seinfeld4]

Homework Statement

The Ka of H2PO4 is 6.3 * 10^-8. The Ka of HS is 1.3 * 10^-13. Write a formula for the reaction of these substances and explain your results. Both are amphoteric.

The Attempt at a Solution

The formula is:

H2PO4 + HS <--> HPO4 + H2S

I figured that the H2PO4 will act more like the acid in this particular situation because it has a higher value of Ka. So, H2PO4 will donate a proton while HS will receive a proton.

Is this the correct train of thought?

Thanks.

 

[Borek]

Is this the correct train of thought?

Yes. Just don't ignore charges - use [noparse]^-[/noparse] to get ^-.