Question

Chlorine \(\left(\mathrm{Cl}_{2}\right)\) is a strong germicide used to disinfect drinking water and to kill microbes in swimming pools. If the product is \(\mathrm{Cl}^{-}\), was the elemental chlorine oxidized or reduced?

Short answer

The elemental chlorine was reduced.

Step-by-step solution

- Define Oxidation and Reduction

Oxidation is the loss of electrons, while reduction is the gain of electrons. To determine if chlorine was oxidized or reduced, we need to compare the oxidation states of chlorine in \(\text{Cl}_2\) and \(\text{Cl}^-\).

- Determine the Oxidation State of \(\text{Cl}_2\)

Elemental chlorine \(\text{Cl}_2\) is in its diatomic form, meaning each chlorine atom has an oxidation state of 0, as it is in its elemental form.

- Determine the Oxidation State of \(\text{Cl}^-\)

In the \(\text{Cl}^-\) ion, chlorine has an oxidation state of -1, since it has gained an electron to form the ion.

- Compare Oxidation States

Chlorine goes from an oxidation state of 0 in \(\text{Cl}_2\) to an oxidation state of -1 in \(\text{Cl}^-\). Since the oxidation state decreases, this indicates that chlorine has gained electrons.

- Identify the Process

Because chlorine \(\text{Cl}_2\) gains electrons to form \(\text{Cl}^-\), it has undergone reduction. Therefore, elemental chlorine was reduced in the process.

Key concepts

Oxidation States

Understanding oxidation states is essential in chemistry, as they help us track electron movement in reactions. An oxidation state is a number that represents the total number of electrons an atom gains, loses, or shares when forming chemical bonds.

For example, in elemental chlorine \( \text{Cl}_{2} \), each chlorine atom has an oxidation state of 0 because they share their electrons equally. However, in the chloride ion \( \text{Cl}^{-} \), chlorine has an oxidation state of -1 because it has gained an electron.

Electron Transfer

Electron transfer is a crucial concept in oxidation and reduction reactions (redox reactions). It refers to the movement of electrons from one atom or molecule to another.

In the context of chlorine disinfection, elemental chlorine (\( \text{Cl}_{2} \)) undergoes a redox reaction when it interacts with microbes. Each chlorine atom in \( \text{Cl}_{2} \) has an oxidation state of 0, but when it gains an electron to become \( \text{Cl}^{-} \), its oxidation state changes to -1. This gain of an electron is referred to as reduction.

Oxidation is the opposite process, where an atom loses electrons and increases its oxidation state.

Chlorine Disinfection

Chlorine disinfection is a widely used method for purifying water. When chlorine gas \( \text{Cl}_{2} \) is added to water, it reacts to form hypochlorous acid (\( \text{HOCl} \)) and hydrochloric acid (\( \text{HCl} \)). These substances are effective in killing bacteria, viruses, and other microbes.

The chemistry behind this disinfection process involves redox reactions. Elemental chlorine (\( \text{Cl}_{2} \)) undergoes reduction when it gains electrons to form chloride ions (\( \text{Cl}^{-} \)). This electron gain reduces the chlorine and helps in the disinfection process.

The effectiveness of chlorine as a disinfectant depends on various factors, including the concentration of chlorine, the presence of organic matter, and the pH of the water.