Question

Which equations represent precipitation reactions?

A. Na2S + FeBr2 → 2NaBr + FeS
B. MgSO4 + CaCl2 → MgCl2 + CaSO4
C. LiOH + NH4I → LiI + NH4OH
D. 2NaCl + K2S → Na2S + 2KCl
E. AgNO3 + NaCl → AgCl + NaNO3

MAY CHOOSE MORE THAN ONE

Answer 1

In a precipitation reaction, one of the product formed is an insoluble precipitate.

The given reactions can be written with phases included as:

A.
`Na_(2)S(aq)+FeBr_(2)(aq)-->2NaBr(aq)+FeS(s)`: In this reaction one of the product, FeS is insoluble. Therefore, this is a precipitation reaction.

B.
`MgSO_(4)(aq)+CaCl_(2)(aq)-->MgCl_(2)(aq)+CaSO_(4)(s)`: In this reaction, the product
`CaSO_(4)`is a solid(insoluble). So, this is a precipitation reaction too.

C.
`LiOH(aq)+NH_(4)I(aq)-->LiI(aq)+NH_(4)OH(aq)`: In this reaction, both the products are soluble. So this is not a precipitation reaction.

D.
`2NaCl(aq)+K_(2)S(aq)-->Na_(2)S(aq)+2KCl(aq)`: In this reaction, both the products are soluble. So this is not a precipitation reaction.

E.
`AgNO_(3)(aq)+NaCl(aq)-->AgCl(s)+NaNO_(3)(aq)`: In this reaction, the product AgCl is a precipitate. So, it is a precipitation reaction.