The labels of bottles that contain barium hydroxide, hydrochloric acid and sodium carbonate had fallen off. When the contents of the bottle A were mixed with B's Contents, a white precipitate formed, A with C yielded a gas and B with C gave heat. Identify A, B,C and write molecular and net ionic equations for the chemical changes observed.

A is SODIUM BICARBONATE,

                  B is BARIUM HYDROXIDE and

                    C= HYDROCHLORIC ACID

Explanation:

Given Hydrochloric acid, Sodium Carbonate and Barium Chloride.

When A reacts C, a gas is formed. and we know that hydrochloric acid reacts with a carbonate to give a  gas.

also Given that A reacts with B to give a white precipitate gives a conclusion that A and B  must be a barium hydroxide or Sodium Carbonate therefore means that  C  must contains HCL

So we are left with Barium hydroxide and Sodium Carbonate which when they react together gives  a white precipitate is formed

Reacting Sodium carbonate witrh Hydrochloric acid gives

A + C--- GAS

Molecular equation

Na2co3 (aq) +2HCl(aq)---2NaCl(aq)+ CO(g)+H20  (l)

Net Ionic equation  

3(aq) +2H+(aq) -- C02(g) +H2O(l)

When Barium hydroxide reacts with Hydrochloric acis, neutralization occurs and heat is released

B+C---------.> Heat

Molecular Equation

Ba(OH)2 + 2HCl(aq)--- BaCl2 +2H2(l)

Ionic Equation

OH- (aq) +H+(aq)----H20(l)

Therefore A is SODIUM BICARBONATE,

                  B is BARIUM HYDROXIDE and

                    C= HYDROCHLORIC ACID

the ratio of the conjugate base to the acid required to attain the desired ph.