Chapter 21, Problem 21.74QP

The following are two reaction schemes involving magnesium. Scheme I: When magnesium burns in oxygen, a white solid (A) is formed. A dissolves in 1 M HCl to give a colorless solution (B). Upon addition of Na₂CO₃ to B, a white precipitate is formed (C). On heating, C decomposes to D and a colorless gas is generated (E). When E is passed through limewater [an aqueous suspension of Ca(OH)₂], a white precipitate appears (F). Scheme II: Magnesium reacts with 1 M H₂SO₄ to produce a colorless solution (G). Treating G with an excess of NaOH produces a white precipitate (H). H dissolves m 1 M HNO₃ to form a colorless solution. When the solution is slowly evaporated, a white solid (I) appears. On heating I, a brown gas is given off. Identify A–I, and write equations representing the reactions involved.

Interpretation Introduction

Interpretation:

The equations representing A-I involved reactions has to be written.

Concept introduction:

• To write a chemical reaction from the given information we must understand which is going to react and which is going to form as product in a particular chemical reaction.
• First write down the reactants in left side and analyze carefully the possibility of product obtained and this has to be placed in right side of a reaction.
• We can represent a reaction by writing reactants in left side and products in the right side.

Explanation of Solution

To identify A in the reaction of ${\text{2Mg}}_{\text{(s) }}{\text{+ O}}_{\text{2(g)}}\to \text{A}$

2 moles of magnesium reacts with 1 mole of oxygen to produce 2 moles of magnesium oxide in solid form and the reaction scheme has to be represented as follows

${\text{2Mg}}_{\text{(s) }}{\text{+ O}}_{\text{2(g)}}\to {\text{2MgO}}_{\text{(s)}}$

A= ${\text{MgO}}_{\text{(s)}}$

To identify B in the reaction of ${\text{MgO}}_{\text{(s)}}{\text{ + 2HCl}}_{\text{(aq)}}\to \text{ B}$

1 mole of magnesium oxide reacts with 2 moles of hydrogen chloride to produce 1 mole of magnesium chloride in aqueous form and the reaction scheme has to be represented as follows

${\text{MgO}}_{\text{(s)}}{\text{ + 2HCl}}_{\text{(aq)}}\to {\text{ MgCl}}_{\text{2(aq)}}{\text{ + H}}_{\text{2}}{\text{O}}_{\text{(l)}}$

B= ${\text{MgCl}}_{\text{2(aq)}}$

To identify C in the reaction of ${\text{MgCl}}_{\text{2(aq)}}{\text{ + Na}}_{\text{2}}{\text{CO}}_{\text{3(aq)}}\to \text{C}$

1 mole of magnesium chloride reacts with 1 mole of sodium carbonate to produce 1 mole of magnesium carbonate in solid form and 2 moles of sodium chloride and the reaction scheme has to be represented as follows

${\text{MgCl}}_{\text{2(aq)}}{\text{ + Na}}_{\text{2}}{\text{CO}}_{\text{3(aq)}}\to {\text{MgCO}}_{\text{3(s)}}{\text{ + 2NaCl}}_{\text{(aq)}}$

C= ${\text{MgCO}}_{\text{3(s)}}$

To identify D in the reaction of ${\text{MgCO}}_{\text{3(s) }}\to \text{D}\text{+}\text{E}$

On heating, magnesium carbonate decomposed into magnesium oxide and carbon dioxide and the reaction has to be represented as follows

${\text{MgCO}}_{\text{3(s) }}\to {\text{MgO}}_{\text{(s) }}{\text{+ CO}}_{\text{2(g)}}$

D = ${\text{MgO}}_{\text{(s)}}$ E = ${\text{ CO}}_{\text{2(g)}}$

To identify F in the reaction of ${\text{CO}}_{\text{2(g) }}{\text{+ Ca(OH)}}_{\text{2(aq)}}\to \text{F}$

Carbon dioxide reacts with calcium hydroxide to produce calcium carbonate and water and the reaction has to be represented as follows

${\text{CO}}_{\text{2(g) }}{\text{+ Ca(OH)}}_{\text{2(aq)}}\to {\text{CaCO}}_{\text{3(s)}}{\text{ + H}}_{\text{2}}{\text{O}}_{\text{(l)}}$

F = ${\text{CaCO}}_{\text{3(s)}}$

To identify G in the reaction of ${\text{Mg}}_{\text{(s) }}{\text{+ H}}_{\text{2}}{\text{SO}}_{\text{4(aq)}}\to \text{G}$

Magnesium reacts with sulfuric acid to produce magnesium sulfate and hydrogen gas and the reaction is represented as follows

${\text{Mg}}_{\text{(s) }}{\text{+ H}}_{\text{2}}{\text{SO}}_{\text{4(aq)}}\to {\text{MgSO}}_{\text{4(aq) }}{\text{+ H}}_{\text{2(g)}}$

G = ${\text{MgSO}}_{\text{4(aq) }}$

To identify H in the reaction of ${\text{MgSO}}_{\text{4(aq) }}{\text{+ 2NaOH}}_{\text{(aq)}}\to \text{H}$

Magnesium sulfate reacts with sodium hydroxide to produce magnesium hydroxide and sodium sulfate and the reaction has to be represented as follows

${\text{MgSO}}_{\text{4(aq) }}{\text{+ 2NaOH}}_{\text{(aq)}}\to {\text{Mg(OH)}}_{\text{2(s) }}{\text{+ Na}}_{\text{2}}{\text{SO}}_{\text{4(aq)}}$

H= ${\text{Mg(OH)}}_{\text{2(s) }}$

To identify I in the reaction of ${\text{Mg(OH)}}_{\text{2(aq)}}{\text{ + 2HNO}}_{\text{3(aq)}}\to \text{I}$

Magnesium hydroxide reacts with nitric acid to produce magnesium nitrate and water after evaporation and the reaction is represented as follows

${\text{Mg(OH)}}_{\text{2(aq)}}{\text{ + 2HNO}}_{\text{3(aq)}}\to {\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2(aq)}}{\text{ + 2H}}_{\text{2}}{\text{O}}_{\text{(l)}}$

I = ${\text{Mg(NO}}_{\text{3}}{\text{)}}_{\text{2(aq)}}$

${\text{2Mg(NO}}_{\text{3}}{\text{)}}_{\text{2(s)}}\to {\text{2MgO}}_{\text{(s) }}{\text{+ 4NO}}_{\text{2(g)}}{\text{ + O}}_{\text{2(g)}}$

And ${\text{NO}}_{\text{2}}$ is the brown gas.

Conclusion

The equations representing A-I involved reactions was identified.