1. What would happen if acid was added to this buffering system?

HA<===>H+ + A-

The acid shift to the right, producing H+ so the pH is maintained.
Is my answer correct?

2. Hydrocarbonate exists in equilibrium with carbon dioxide and water inside of a soda can. What will happen to the equilibrium if you shake the soda can?

1 answer

If it shifts to right, pH goes up...Consider when adding the acid, it contains H+ ions,A-, and Ha
Adding more H+ will shift this to left. I assume your "if acid was added" is another acid, ie a strong acid.