In each of the following cases, decide whether a precipitate will form when mixing the indicated reagents, and write a balanced equation for the reaction.

1. (a) Na₂SO₄(aq) + Mg(NO₃)₂(aq)
2. (b) K₃PO₄(aq) + FeCl₃(aq)

Interpretation: Write balanced chemical equation for the given reactions and also predict whether precipitate will form or not.

  Na2SO4(aq)+Mg(NO3)2(aq)

Concept introduction: Precipitation reaction takes place when anions and caations present in the solution combine to form insoluble salt. The salt will be soluble or insoluble depends upon the Ksp value of the salt. Higher the Ksp value soluble will be the salt. Salts having lower Ksp value are insoluble or dissolve very less in water.

Generally,

• Sulphates are soluble except formed by Ca2+, Sr2+ and Ba2+.
• Phosphates are insoluble.
• Chlorides, bromides, iodides are soluble except that of Ag+, Pb2+ and Hg22+.
• Nitrates are soluble.

Reaction of Na2SO4 with Mg(NO3)2 is an example of double displacement reaction. Each reactant dissociate to form corresponding ions in the solution and then exchange of ions between two reactant occurs on the basis of their charges either cation or anion to form product.  Therefore the chemical reaction is given as,

  Na2SO4(aq)+Mg(NO3)2(aq)→NaNO3(aq)+MgSO4(aq)

The reaction is balanced by multiplying NaNO3 by 2. The number of atoms of each element on both reactant side and product side should be equal for a reaction to be called as balanced chemical reaction.

  Na2SO4(aq)+Mg(NO3)2(aq)→2NaNO3(aq)+MgSO4(aq)

Sulphates and nitrates are soluble therefore no precipitate will form

Interpretation: Write balanced chemical equation for the given reactions and also predict whether precipitate will form or not.

  K3PO4(aq)+FeCl3(aq)

Concept introduction: Precipitation reaction takes place when anions and caations present in the solution combine to form insoluble salt. The salt will be soluble or insoluble depends upon the Ksp value of the salt. Higher the Ksp value soluble will be the salt. Salts having lower Ksp value are insoluble or dissolve very less in water.

Generally,

• Sulphates are soluble except formed by Ca2+, Sr2+ and Ba2+.
• Phosphates are insoluble.
• Chlorides, bromides, iodides are soluble except that of Ag+, Pb2+ and Hg22+.
• Nitrates are soluble.