Question

question 1
which of the following reactions is a double - replacement reaction?
mg(oh)₂(s) + h₂so₄(aq) → 2 h₂o(l) + mgso₄(aq)
mg(s) + cu(no₃)₂(aq) → mg(no₃)₂(aq) + cu(s)
2 mgo(s) → 2 mg(s) + o₂(g)
3 mg(s) + n₂(g) → mg₃n₂(g)

Explanation:

• A double - replacement reaction has the general form \(AB + CD

ightarrow AD+CB\).

• For \(Mg(OH)_2(s)+H_2SO_4(aq)

ightarrow 2H_2O(l)+MgSO_4(aq)\), \(Mg(OH)_2\) can be thought of as \(Mg(OH)_2 = Mg^{2 + }+2OH^-\) and \(H_2SO_4=2H^++SO_4^{2 - }\). The \(H^+\) and \(OH^-\) combine to form \(H_2O\) (\(H^++OH^-
ightarrow H_2O\)) and \(Mg^{2+}\) combines with \(SO_4^{2 - }\) to form \(MgSO_4\).

• For \(Mg(s)+Cu(NO_3)_2(aq)

ightarrow Mg(NO_3)_2(aq)+Cu(s)\), it is a single - replacement reaction (\(A + BC
ightarrow AC + B\), where \(A = Mg\), \(B = Cu\), \(C=NO_3^-\)).

• For \(2MgO(s)

ightarrow 2Mg(s)+O_2(g)\), it is a decomposition reaction (\(AB
ightarrow A + B\)).

• For \(3Mg(s)+N_2(g)

ightarrow Mg_3N_2(g)\), it is a combination reaction (\(A + B
ightarrow AB\)).

Answer:

\(\text{Mg(OH)}_2(s)+\text{H}_2\text{SO}_4(aq)
ightarrow 2\text{H}_2\text{O}(l)+\text{MgSO}_4(aq)\)