1. The problem statement, all variables and given/known data 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. 3. 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 recieve a proton. Is this the correct train of thought? Thanks.