Question

Which equation above represents a precipitate in a double replacement reaction?

A. H_2CO_3(aq) + CO_2(g) + H_2O(l)
B. 2HCl(aq) + Na_2S(aq) → 2NaCl(aq) + H_2S(g)
C. 2NaOH(aq) + MgCl2(aq) → 2NaCl(aq) + Mg(OH)2(s)
D. H_2SO_4(aq) + 2NaOH(aq) → Na_2SO_4(aq) + 2H_2O(l)

Answer 1

Option C, 2NaOH(aq) + MgCl2(aq) → 2NaCl(aq) + Mg(OH)2(s), represents a double replacement reaction where Mg(OH)2 is the precipitate formed.

Step-by-step explanation:

The question asks which equation represents a precipitate in a double replacement reaction. A precipitate is an insoluble solid that emerges from the solution during a chemical reaction. Among the provided choices, option C shows the formation of a precipitate:

2NaOH(aq) + MgCl2(aq) → 2NaCl(aq) + Mg(OH)2(s)

In this double replacement reaction, the positive ions Na+ and Mg2+ swap partners with the negative ions OH- and Cl-, leading to the formation of soluble salt NaCl and an insoluble solid Mg(OH)2, indicating it is a precipitate as denoted by the (s) following its formula.