Question

A solution contains barium nitrate and lead (II) nitrate. What substance could be added to the solution to precipitate the lead (II) ions, but leave the barium ions in solution?

A) ammonium carbonate

B) no such substance exists

C) beryllium sulfate

D) silver nitrate

E) strontium bromide

Answer 1

To know this, let's refresh the solubility rules:

1. All compounds of Group 1 elements (the alkali metals) are soluble.

Rule 2. All ammonium salts (salts of NH₄⁺) are soluble.

Rule 3. All nitrate (NO₃^-), chlorate (ClO₃^-), perchlorate (ClO₄^-), and acetate (CH₃COO^- or C₂H₃O₂^-, sometimes abbreviated as Oac^-) salts are soluble.

Rule 4. All chloride (Cl^-), bromide (Br^-), and iodide (I^-) salts are soluble except for those of Ag⁺, Pb²⁺, and Hg₂²⁺.

Rule 5. All sulfate ( SO₄⁼) compounds are soluble except those of Ba²⁺, Sr²⁺, Ca²⁺, Pb²⁺, Hg₂²⁺, and Hg²⁺, Ca²⁺ and Ag⁺ sulfates are only moderately soluble.

Rule 6. All hydroxide (OH^-) compounds are insoluble except those of Group I-A (alkali metals) and Ba²⁺, Ca²⁺, and Sr²⁺.

Rule 7. All sulfide (S^2-) compounds are insoluble except those of Groups 1 and 2 (alkali metals and alkali earths).

Rule 8. All sulfites (SO₃⁼), carbonates (CO₃⁼), chromates (CrO₄⁼), and phosphates (PO₄^3-) are insoluble except for those of NH₄⁺ and Group 1 (alkali metals)(see rules 1 and 2).

So following these rules, let's analyze the solution and the posible options:

WE have Pb(NO₃)₂ and Ba(NO₃)₂ both of them in solution. If we add a solution with the properties we said before of the solubility rules, we can actually determine which compoud to add.

If you read carefully, Rule 4, it state that all chloride, bromide and halides in general are soluble, except compounds of Ag, Pb and Hg.

So the only compound that fix this rule is the last one, Option E, stromtium Bromide.