Question

choose which of the following are oxidation - reduction reactions(select all that apply.)
ohcl(g) + nh₃(g) → nh₄cl(s)
2 cucl(aq) → cucl₂(aq) + cu(s)
osicl₄(l) + 2 h₂o(l) → 4 hcl(aq) + sio₂(s)
zn(s) + 2 hcl(aq) → zncl₂(aq) + h₂(g)
och₄(g) + 2 o₂(g) → co₂(g) + 2 h₂o(g)

Explanation:

Step1: Analyze the first reaction \( \text{HCl}(g)+\text{NH}_3(g)\to\text{NH}_4\text{Cl}(s) \)

In this reaction, there is no change in the oxidation states of the elements. For example, in \( \text{HCl} \), \( H = + 1 \), \( Cl=-1 \); in \( \text{NH}_3 \), \( N=-3 \), \( H = + 1 \); and in \( \text{NH}_4\text{Cl} \), \( N=-3 \), \( H = + 1 \), \( Cl=-1 \). So, it is not an oxidation - reduction reaction.

Step2: Analyze the second reaction \( 2\text{CuCl}(aq)\to\text{CuCl}_2(aq)+\text{Cu}(s) \)

The oxidation state of \( Cu \) in \( \text{CuCl} \) is \( + 1 \). In \( \text{CuCl}_2 \), \( Cu = + 2 \) (oxidation), and in \( \text{Cu}(s) \), \( Cu = 0 \) (reduction). Since there is a change in oxidation states, this is an oxidation - reduction reaction.

Step3: Analyze the third reaction \( \text{SiCl}_4(l)+2\text{H}_2\text{O}(l)\to4\text{HCl}(aq)+\text{SiO}_2(s) \)

In \( \text{SiCl}_4 \), \( Si = + 4 \), \( Cl=-1 \); in \( \text{H}_2\text{O} \), \( H = + 1 \), \( O=-2 \); in \( \text{HCl} \), \( H = + 1 \), \( Cl=-1 \); and in \( \text{SiO}_2 \), \( Si = + 4 \), \( O=-2 \). There is no change in oxidation states, so it is not an oxidation - reduction reaction.

Step4: Analyze the fourth reaction \( \text{Zn}(s)+2\text{HCl}(aq)\to\text{ZnCl}_2(aq)+\text{H}_2(g) \)

The oxidation state of \( Zn \) changes from \( 0 \) (in \( Zn(s) \)) to \( + 2 \) (in \( \text{ZnCl}_2 \)) (oxidation), and the oxidation state of \( H \) changes from \( + 1 \) (in \( \text{HCl} \)) to \( 0 \) (in \( \text{H}_2 \)) (reduction). So, it is an oxidation - reduction reaction.

Step5: Analyze the fifth reaction \( \text{OCH}_4(g)+2\text{O}_2(g)\to\text{CO}_2(g)+2\text{H}_2\text{O}(g) \)

In \( \text{CH}_4 \), \( C=-4 \), \( H = + 1 \); in \( \text{O}_2 \), \( O = 0 \); in \( \text{CO}_2 \), \( C = + 4 \), \( O=-2 \); and in \( \text{H}_2\text{O} \), \( H = + 1 \), \( O=-2 \). The oxidation state of \( C \) increases (oxidation) and the oxidation state of \( O \) decreases (reduction). So, it is an oxidation - reduction reaction.

Answer:

\( \text{Zn}(s)+2\text{HCl}(aq)\to\text{ZnCl}_2(aq)+\text{H}_2(g) \), \( 2\text{CuCl}(aq)\to\text{CuCl}_2(aq)+\text{Cu}(s) \), \( \text{OCH}_4(g)+2\text{O}_2(g)\to\text{CO}_2(g)+2\text{H}_2\text{O}(g) \)