Question

Write a net ionic equations to show how each of hte buffer mixtures below would neutralize added H+ and OH-

a. C6H5COOH and NaC6H5COO H+ + _______ ---> _____________

OH- + _______----> _____________

H+ + ________-----> _____________

b. NH4Cl and NH3 H+ + ________ ------> _____________

OH- + ________-------> ______________

Answer 1

Part a:
First write the molecular equation:
C6H5COOH(s) + NaOH(aq) ==> H2O(l) + NaC6H5COO(aq)
Convert it into ionic equation:
C6H5COOH(s) + Na+(aq) + OH-(aq) ==> H2O(l) + Na+(aq) + C6H5COO-(aq)
which becomes
C6H5COOH(s) + OH-(aq) <---> H2O(l) + C6H5COO-(aq)
When H+ is added, some of OH- will react with H+ ans this will shift the equilibrium reaction to left. Hence OH- will regenerate and pH will be constant.
When OH- is added, equilibrium will shift to right to use up the OH- and hence pH will not change.

Part b:
Molecular equation:
NH3+HCl -->NH4Cl
Ionic equation will be:
NH3 + H+ + Cl- --->NH4+ + Cl- which turns out to be
Net ionic equation will be:
NH3(g) + H+(aq) = NH4+ (aq)
When H+ is added --> reaction shifts to right and H+ is consumed -->hence pH will not change
When OH- is added --> H+ will react with OH- --->reaction shifts to left and H+ is produced back -->hence pH will not change