To determine which of the given molecular equations represent the correct reaction of a metal with an acid that produces hydrogen gas, let's analyze each reaction carefully.
1. Reaction 1:
[tex]\[
Ni (s) + H_2SO_4(aq) \rightarrow NiSO_4(aq) + 2 H_2O(g) + SO_2(g)
\][/tex]
- This reaction does not produce hydrogen gas ([tex]\(H_2\)[/tex]). Instead, it produces [tex]\(H_2O\)[/tex] and [tex]\(SO_2\)[/tex].
2. Reaction 2:
[tex]\[
Zn (s) + 2 H^+(aq) \rightarrow Zn^{2+}(aq) + H_2(g)
\][/tex]
- Zinc reacts with hydrogen ions ([tex]\(H^+\)[/tex]) from the acid to produce zinc ions ([tex]\(Zn^{2+}\)[/tex]) and hydrogen gas ([tex]\(H_2\)[/tex]). This is a typical reaction of a metal with an acid producing hydrogen gas.
3. Reaction 3:
[tex]\[
Mg (s) + 2 HNO_3(aq) \rightarrow Mg(NO_3)_2(aq) + H_2(g)
\][/tex]
- Magnesium reacts with nitric acid ([tex]\(HNO_3\)[/tex]) to produce magnesium nitrate ([tex]\(Mg(NO_3)_2\)[/tex]) and hydrogen gas ([tex]\(H_2\)[/tex]). This is another example of a metal reacting with an acid to produce hydrogen gas.
4. Reaction 4:
[tex]\[
K (s) + 2 HNO_3(aq) \rightarrow KNO_3(aq) + NO_2(g) + H_2O(l)
\][/tex]
- Potassium reacts with nitric acid ([tex]\(HNO_3\)[/tex]) to produce potassium nitrate ([tex]\(KNO_3\)[/tex]), nitrogen dioxide ([tex]\(NO_2\)[/tex]), and water ([tex]\(H_2O\)[/tex]). This reaction does not produce hydrogen gas.
Based on the above analysis, the molecular equations that represent the reaction of a metal with an acid that produces hydrogen gas are:
[tex]\[
\text{(2) } Zn (s) + 2 H^+(aq) \rightarrow Zn^{2+}(aq) + H_2(g)
\][/tex]
[tex]\[
\text{(3) } Mg (s) + 2 HNO_3(aq) \rightarrow Mg(NO_3)_2(aq) + H_2(g)
\][/tex]
So, the correct molecular equations for the reaction of a metal and an acid that produce hydrogen gas are numbers 2 and 3.
