Question

Draw the sequential donation of the protons from carbonic acid (H2CO3) to water (lose one H⁺ in each step to water) and label each step as Ka 1 or 2. Label which species are amphiprotic and/or polyprotic.

Answer 1

Solution:

The sequential donation of H+ ions from carbonic acid to water are given below

Step 1)

H2CO3(aq) + H2O(aq) --> HCO3-(aq)+ H3O+(aq)

Ka1 = [HCO3-] [H3O+] / [H2CO3]

Step 2)

HCO3-(aq) + H2O(aq) --> CO3^2-(aq) + H3O+(aq)

Ka2 = [CO3^2-] [H3O+] / [HCO3-]

The amphiprotic species are those species which posses the ability to both donate and accept protons (H+), whereas polyprotic species posses the ability to donate or accept more than one protons.

Hence,

HCO3- is the amphiprotic species, while H2CO3 and CO3^2- are polyprotic species.