Na₂S + FeBr₂ → 2NaBr + FeS(s)
MgSO₄ + CaCl₂ → MgCl₂ + CaSO₄(s)
AgNO₃ + NaCl → AgCl(s) + NaNO₃
Explanation:
You must recall the pertinent solubility rules:
Salts of Group 1 elements (Li⁺, Na⁺, K⁺) and of NH₄⁺ are soluble
Salts containing nitrate ion (NO₃⁻) are soluble.
Salts containing Cl⁻, Br⁻, and I⁻ are generally soluble. An important exception is Ag⁺. Thus, AgCl is insoluble.
Most sulfate (SO₄²⁻) salts are soluble. An important exception is CaSO₄, which is insoluble.
Most sulfide (S²⁻) salts of transition metals are insoluble.
Na₂S + FeBr₂ → 2NaBr + FeS(s)
NaBr is soluble (Rule 1). FeS is insoluble (Rule 5), so a precipitate forms.
MgSO₄ + CaCl₂ → MgCl₂ + CaSO₄(s)
MgSO₄ is soluble (Rule 3). CaSO₄ is insoluble (Rule 4), so a precipitate forms.
AgNO₃ + NaCl → AgCl(s) + NaNO₃
NaNO₃ is soluble (Rule 1). AgCl is insoluble (Rule 3) so a precipitate forms.
LiOH + NH₄I → LiI + NH₄OH and 2NaCl + K₂S → Na₂S + 2KCl
All products are soluble (Rule 1), so these are not precipitation reactions.
