Question

1. determine the substance being oxidized, the substance being reduced, the oxidizing agent, and the reducing agent in the following reactions.

a. 2k(s) + br₂(l) → 2kbr(s)
b. ca(s) + 2h⁺(aq) → ca²⁺(aq) + h₂(g)
c. fe₂o₃(s) + 3co(g) → 2fe(s) + 3co₂(g)

Explanation:

Step1: Recall oxidation - reduction definitions

Oxidation is the loss of electrons (increase in oxidation state), reduction is the gain of electrons (decrease in oxidation state). The oxidizing agent is the substance that causes oxidation (gets reduced), and the reducing agent is the substance that causes reduction (gets oxidized).

Step2: Analyze reaction a: $2K(s)+Br_2(l)

ightarrow2KBr(s)$

• Oxidation state of $K$ in $K(s)$ is $0$, in $KBr$ is $+ 1$. $K$ loses electrons, so $K$ is oxidized.
• Oxidation state of $Br$ in $Br_2$ is $0$, in $KBr$ is $-1$. $Br_2$ gains electrons, so $Br_2$ is reduced. $Br_2$ is the oxidizing agent and $K$ is the reducing agent.

Step3: Analyze reaction b: $Ca(s)+2H^+(aq)

ightarrow Ca^{2 +}(aq)+H_2(g)$

• Oxidation state of $Ca$ in $Ca(s)$ is $0$, in $Ca^{2+}$ is $+2$. $Ca$ loses electrons, so $Ca$ is oxidized.
• Oxidation state of $H$ in $H^+$ is $+1$, in $H_2$ is $0$. $H^+$ gains electrons, so $H^+$ is reduced. $H^+$ is the oxidizing agent and $Ca$ is the reducing agent.

Step4: Analyze reaction c: $Fe_2O_3(s)+3CO(g)

ightarrow2Fe(s)+3CO_2(g)$

• Oxidation state of $Fe$ in $Fe_2O_3$: Let the oxidation state of $Fe$ be $x$. In $Fe_2O_3$, $2x+3\times(-2)=0$, so $x = + 3$. In $Fe(s)$ it is $0$. $Fe_2O_3$ gains electrons, so $Fe_2O_3$ is reduced.
• Oxidation state of $C$ in $CO$: Let the oxidation state of $C$ be $y$. In $CO$, $y+( - 2)=0$, so $y = + 2$. In $CO_2$, the oxidation state of $C$ is $+4$. $CO$ loses electrons, so $CO$ is oxidized. $Fe_2O_3$ is the oxidizing agent and $CO$ is the reducing agent.

Answer:

a. Substance being oxidized: $K$, Substance being reduced: $Br_2$, Oxidizing agent: $Br_2$, Reducing agent: $K$
b. Substance being oxidized: $Ca$, Substance being reduced: $H^+$, Oxidizing agent: $H^+$, Reducing agent: $Ca$
c. Substance being oxidized: $CO$, Substance being reduced: $Fe_2O_3$, Oxidizing agent: $Fe_2O_3$, Reducing agent: $CO$