Q19E - Chemistry (OpenStax)

Question

Classify the following as acid-base reaction or oxidation-reduction reactions.

(a)\(N{a_2}S\left( {aq} \right) + 2HCl\left( {aq} \right) \to 2NaCl\left( {aq} \right) + {H_2}S\left( g \right)\)

(b)\(2Na\left( s \right) + 2HCl\left( {aq} \right) \to 2NaCl\left( {aq} \right) + {H_2}\left( g \right)\)

(c)\(Mg\left( s \right) + C{l_2}\left( g \right) \to MgC{l_2}\left( s \right)\)

(d)\(MgO\left( s \right) + 2HCl\left( {aq} \right) \to MgC{l_2}\left( {aq} \right) + {H_2}O\left( l \right)\)

(e)\({K_3}P\left( s \right) + 2{O_2}\left( g \right) \to {K_3}P{O_4}\left( s \right)\)

(f)\(3KOH\left( {aq} \right) + {H_3}P{O_4}\left( {aq} \right) \to {K_3}P{O_4}\left( {aq} \right) + 3{H_2}O\left( l \right)\)

Step-by-Step Solution

Answer

The classification of reactions isas follows:

(a) Acid-base reaction

(b) Oxidation-reduction reaction

(c) Oxidation-reduction reaction

(d) Acid-base reaction

(e) Oxidation-reduction reaction

(f) Acid-base reaction.

Step 1: Classification of the reaction in part (a)

\(N{a_2}S\left( {aq} \right) + 2HCl\left( {aq} \right) \to 2NaCl\left( {aq} \right) + {H_2}S\left( g \right)\)

In this reaction there is no change in the oxidation state of the ions involved. Further, there is transfer of protons leading to formation of the sodium chloridesalt.Therefore, it is an acid-base reaction.

Step 2: Classification of the reaction in part (b)

\(2Na\left( s \right) + 2HCl\left( {aq} \right) \to 2NaCl\left( {aq} \right) + {H_2}\left( g \right)\)

Here elemental sodium is oxidised from 0 to +1 state and hydrogen is reduced from +1 to 0 state.Therefore, it is an oxidation-reduction reaction.

Step 3: Classification of the reaction in part(c)

\(Mg\left( s \right) + C{l_2}\left( g \right) \to MgC{l_2}\left( s \right)\)

Here magnesium is oxidised from 0 to +2 state and chlorine is reduced from 0 to -1 state.Therefore, it is an oxidation-reduction reaction.

Step 4: Classification of the reaction in part(d)

\(MgO\left( s \right) + 2HCl\left( {aq} \right) \to MgC{l_2}\left( {aq} \right) + {H_2}O\left( l \right)\)

Here the transfer of proton leadsto the formation of the magnesium chloride salt.No oxidation state change of the ions involved is observed.Therefore, it is an acid-base reaction.

Step 5: Classification of the reaction in part(e)

\({K_3}P\left( s \right) + 2{O_2}\left( g \right) \to {K_3}P{O_4}\left( s \right)\)

Here phosphorus is oxidised from -3 to +5 state and oxygen is reduced from 0 to -2 state.Therefore, it is an oxidation-reduction reaction.

Step 6: Classification of the reaction in part (f)

\(3KOH\left( {aq} \right) + {H_3}P{O_4}\left( {aq} \right) \to {K_3}P{O_4}\left( {aq} \right) + 3{H_2}O\left( l \right)\)

In this reaction the transfer of the protons and the hydroxyl ion leadsto the formation of the potassium phosphate salt.Therefore, it is an acid-base reaction.