Question

Which one of the following reactions is not possible?

• A. $Ca+H_2{SO}_4\to {CaSO}_4+H_2$
• B. $Cu+H_2{SO}_4\to {CuSO}_4+H_2$
• C. $Zn+H_2{SO}_4\to {ZnSO}_4+H_2$
• D. $Mg+H_2{SO}_4\to {MgSO}_4+H_2$

Answer 1

The correct option is B

$\mathrm{Cu}+{\mathrm{H}}_2{\mathrm{SO}}_4\to {\mathrm{CuSO}}_4+{\mathrm{H}}_2$

An explanation for the correct option:

The correct option is B:

• Electrochemical series is a series of elements, in which the elements are arranged according to their reactivity.
• According to the Electrochemical series, a metal that has a higher position in the electrochemical series will relace that element that has a lower position in the electrochemical series.
• In the electrochemical series the position of $\mathrm{Ca},\mathrm{Cu},\mathrm{Mg},H\mathrm{and}\mathrm{Zn}$ are as follows: $\mathrm{Ca}>\mathrm{Mg}>\mathrm{Zn}>\mathrm{H}>\mathrm{Cu}$
• Clearly, Copper $\left(\mathrm{Cu}\right)$ has a lower position in the electrochemical series than hydrogen, that's why it cannot replace hydrogen from sulphuric acid. Thus, the equation given below is not possible: $\underset{\left(\mathrm{Copper}\right)}{\mathrm{Cu}\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Hydrogen}\mathrm{sulphate}\right)}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}\to \underset{\left(\mathrm{Copper}\mathrm{sulphate}\right)}{{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)}+\underset{\left(\mathrm{Hydrogen}\mathrm{gas}\right)}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$.

An explanation for the incorrect options:

Option A:

• $\underset{\mathrm{Calcium}}{\mathrm{Ca}\left(\mathrm{s}\right)}+\underset{\mathrm{Sulphuric}\mathrm{acid}}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}\to \underset{\mathrm{Calcium}\mathrm{Sulphate}}{{\mathrm{CaSO}}_4\left(\mathrm{aq}\right)}+\underset{\mathrm{Hydrogen}\mathrm{gas}}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$ , this reaction is possible because in the reactivity series the place of Calcium is above Hydrogen so it can displace Hydrogen from the Calcium sulphate.

Option C:

• According to the electrochemical series $\underset{\left(\mathrm{Zinc}\right)}{\mathrm{Zn}\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Sulphuric}\mathrm{acid}\right)}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}\to \underset{\left(\mathrm{Zinc}\mathrm{Sulphate}\right)}{{\mathrm{ZnSO}}_4\left(\mathrm{aq}\right)}+\underset{\left(\mathrm{Hydrogen}\right)}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$, Zinc is more reactive to Hydrogen so it has the capability to displace Hydrogen from the solution, therefore, this reaction is possible.

Option D:

• $\underset{\left(\mathrm{Magnesium}\right)}{\mathrm{Mg}\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Sulphuric}\mathrm{acid}\right)}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}\to \underset{\left(\mathrm{Magnesium}\mathrm{sulphate}\right)}{{\mathrm{MgSO}}_4\left(\mathrm{aq}\right)}+\underset{\left(\mathrm{Hydrogen}\mathrm{gas}\right)}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$, this reaction can take place because the reactivity of Magnesium is more than the Hydrogen. And we know that the more reactive element can displace the lower reactive element from the solution.

Final Answer: Hence, option B is correct.$\underset{\left(\mathrm{Copper}\right)}{\mathrm{Cu}\left(\mathrm{s}\right)}+\underset{\left(\mathrm{Hydrogen}\mathrm{sulphate}\right)}{{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)}\to \underset{\left(\mathrm{Copper}\mathrm{sulphate}\right)}{{\mathrm{CuSO}}_4\left(\mathrm{aq}\right)}+\underset{\left(\mathrm{Hydrogen}\mathrm{gas}\right)}{{\mathrm{H}}_2\left(\mathrm{g}\right)}$ is not possible.