Question

Label three test tubes as either "Carbonate Ion Test", "Sulfate Ion Test", or "Phosphate Ion Test".
Add two mL of the unknown solution into each test tube.
Using the unknown solution, follow the procedures for the Test for Carbonate Ion, Test for Sulfate Ion, and the Test for Phosphate determination in the corresponding test tubes. The unknown solution is used as a substitute for the known samples which were used in Experiment 1.
Record your results of each test in Table 7. Record a positive result if a reaction took place and a negative result if there was no reaction.

Answer 1

Addition of HCl to all the three samples under go reaction with Nitric acid to give soluble precipitates

This confimrs that the three test tubes contain carbonate ion, sulfate and phosphates.

Carbonates upon heating under goes decomposition to give rise to CO2. The CO2 is buubled through lime water and it gives to insoluble Calcium Carbonate

XCO3(s) ------> XO(s) + CO2(g) or
X2CO3(s) ------> X2O(s) + CO2(g) or
X2(CO3)3(s) --------> X2O3(s) + CO2(g)

CO2+ Ca(OH)2 --> CaCO3+H2O ( reactino of CO2 with lime)

Barium chloride is used for testing Sulfates.If Barium chloride is added to a solution expected to contains sulfate ions, Barium sulfate is formed which is insoluble in water and precripiares out

Ba²⁺_(aq) + SO₄^2-_(aq) BaSO_4(s)

When a solution containing phosphate ions is heated with a solution of ammonium molybdate [(NH4)2MoO4] and dilute nitric acid a bright yellow precipitate of ammonium phosphomolybdate [(NH4)3PO4 • 12MoO4] is formed. The yellow precipitate is extremely insoluble in nitric acid.

7PO3- + 12(NH4)6Mo7O24 + 36H2O → 7(NH4)3PO4 .12Mo + 51NH4+ + 72 OH-