Question

Tell how you could distinguish chemically between the following pairs of substances (in separate test tubes) in one or two steps. In each case, tell what you would observe. Include equations for reactions occurring. NaCl and NaNO3 solutions. KI and Na2SO4 solutions. KNO3 and K3PO4 solutions. BaCO3 and Ba(PO4)2 solids.

Answer 1

1)NaCl and NaNO3

Explaination: Add silver nitrate solution. The NaCl will produce a white precipitate of AgCl, and the NaNO3 will give no visible change.

AgNO3 --------> AgCl(ppt) + KNO3

2)KI and Na2SO4

Explaination: When Pb(NO3)2 and KI are mixed together the form a bright yellow precipitate.

Pb(NO₃)₂ + 2 KI -----> 2 KNO₃ + PBI_2(ppt)

Sodium sulfate is a typical ionic sulfate, containing Na⁺ ions and SO₄²⁻ ions. Aqueous solutions can produce precipitates when combined with salts of Ba²⁺ , which form insoluble sulfates.

Na₂SO₄(aq) + BaCl₂₍aq) → 2 NaCl(aq) + BaSO₄(ppt)

3)KNO₃ and K₃PO₄

Explaination: K₃PO₄ reacts with calcium nitrate to form calcium phosphate precipitate. KNO3 will give no visible change.

2 K₃PO₄(s) + 3 Ca(NO₃)₂(aq) = 6 KNO₃(aq) + Ca₃(PO₄)₂(ppt)

4)BaCO3 and Ba3(PO4)2

Add HCl, when HCl reacts with BaCO3 evolution of CO2 gas takes place which is visible. Ba3(PO4)2  will give no visible change.

2HCl(aq)+BaCO3(s)=BaCl2(aq)+H2O(l)+CO2(g)

6HCl(aq)+Ba3(PO4)2(s)=3BaCl2(aq)+3H3PO4(aq)

Also check by analysis of H2CO3, H3PO4 by titration

H2CO3 - pKa1, pKa2

H3PO4 - pKa1, pKa2, pKa3