Question

In which of the following reactions, MgO is not formed :-
(1) Mg + CO2 →
(2) Mg + dil. HNO3 →
(3) Mg + NO→
(4) Mg + B2O3 →

Answer 1

Answer on Question #41368 – Chemistry – Inorganic Chemistry

Question:

In which of the following reactions, MgO is not formed:

(1) $\mathrm{Mg} + \mathrm{CO}_{2} \rightarrow$

(2) $\mathrm{Mg} + \mathrm{dil.}\ \mathrm{HNO}_{3} \rightarrow$

(3) $\mathrm{Mg} + \mathrm{NO} \rightarrow$

(4) $\mathrm{Mg} + \mathrm{B}_{2}\mathrm{O}_{3} \rightarrow$

Answer:

The following reactions occur in each case:

(1) $2\mathrm{Mg} + \mathrm{CO}_{2} \rightarrow 2\mathrm{MgO} + \mathrm{C}$;

(2) $4\mathrm{Mg} + 10\ \mathrm{dil.}\ \mathrm{HNO}_{3} \rightarrow 4\mathrm{Mg(NO}_{3})_{2} + \mathrm{N}_{2}\mathrm{O} + 5\mathrm{H}_{2}\mathrm{O}$;

(3) $\mathrm{Mg} + \mathrm{NO} \rightarrow \mathrm{MgO} + \mathrm{N}_{2}$

(4) $3\mathrm{Mg} + \mathrm{B}_{2}\mathrm{O}_{3} \rightarrow 3\mathrm{MgO} + 2\mathrm{B}$

In cases (1), (3) and (4) metallic Mg reacts with oxides which results in MgO and reduced compound. Only in case (2) Mg reacts with diluted $\mathrm{HNO}_{3}$, which oxidase $\mathrm{Mg}^{0}$ to $\mathrm{Mg}^{2+}$. (1), (3) are reactions of solid phase (Mg) with gases ($\mathrm{CO}_{2}$ and NO respectively) and (4) is a reaction of two solid phases (Mg and $\mathrm{B}_{2}\mathrm{O}_{3}$). On the contrary, in case (2) reaction undergoes in solution, so the formation of MgO does not take place.

In the reaction (2) MgO is not formed.

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