Problem 54 - Chemistry The Central Science In Si Units

Question

(a) Suppose that tests of a municipal water system reveal the presence of bromate ion, \(\mathrm{BrO}_{3}^{-}\). What are the likely origins of this ion? (b) Is bromate ion an oxidizing or reducing agent?

Step-by-Step Solution

Answer

Bromate is likely formed during water disinfection with ozone and acts as an oxidizing agent.

Step 1: Understand the Chemical Process of Bromate Formation

Bromate ion, \(\mathrm{BrO}_{3}^{-}\), is often formed as a by-product during the disinfection of drinking water. When water containing bromide ions is treated with ozone, a common water disinfectant, the bromide can be oxidized to create bromate ions. This process is more likely to occur during ozonation at high temperatures or under conditions where water has a neutral to alkaline pH.

Step 2: Determine if Bromate Ion is an Oxidizing or Reducing Agent

To determine if bromate is an oxidizing or reducing agent, we must consider its oxidation state and typical reactions. Bromate ion, \(\mathrm{BrO}_{3}^{-}\), has bromine in the +5 oxidation state. Substances in higher oxidation states tend to act as oxidizing agents because they can gain electrons (reduce) to lower oxidation states. Bromate ion can accept electrons, making it an oxidizing agent.

Key Concepts

Oxidizing Agent

An oxidizing agent is a substance that causes the oxidation of another substance by accepting electrons during a chemical reaction. The opposite happens for a reducing agent, which donates electrons. In simple terms, oxidizing agents gain electrons while reducing agents lose them. This concept is critical in understanding redox reactions, which are fundamental to many chemical processes.

Bromate ion, \[\mathrm{BrO}_3^-\], acts as an oxidizing agent. This is because the bromine within the bromate ion is in a high oxidation state. Specifically, bromine is in the +5 state, which sets the stage for it to accept electrons and be reduced. By doing so, bromate ion facilitates the oxidation of another species, playing a pivotal role in various reactions.

• Oxidizing agents are often involved in combustion reactions, bleaching, and disinfection.
• They are crucial in industries such as paper and textile manufacturing.

Once bromate accepts electrons, it undergoes reduction, often yielding bromite or bromide ions. This process is fundamental to understanding its behavior in natural and industrial settings.

Water disinfection

Water disinfection is the process of eliminating microorganisms and contaminants from water to ensure it is safe for consumption and use. This is particularly important in municipal water systems, where the goal is to protect public health.

There are several methods for disinfecting water:

• Chlorination: Adding chlorine to the water to kill bacteria and other pathogens.
• Ozonation: Using ozone gas to disinfect water. It is a powerful method because ozone is a strong oxidizing agent.
• Ultraviolet (UV) Treatment: Exposing water to UV light, which destroys microorganisms.

During ozonation, which involves reacting water with ozone, bromide ions (\[\mathrm{Br}^-\]) can be converted to bromate ions (\[\mathrm{BrO}_3^-\]). While effective in eliminating pathogens, this reaction is a concern because bromate is a potential health risk. Controlling the conditions, such as temperature and pH, is essential to minimize bromate formation.

Bromide ion oxidation

Bromide ions (\[\mathrm{Br}^-\]) are naturally present in some water sources, often resulting from the dissolution of salts. In water treatment processes, particularly during ozonation, these bromide ions can undergo oxidation to form bromate ions (\[\mathrm{BrO}_3^-\]).

The oxidation of bromide involves the loss of electrons, transforming the bromide into a higher oxidation state. The reaction can be described as follows:\[\mathrm{Br}^- \rightarrow \mathrm{BrO}_3^-\]To achieve this transformation, conditions often involve the presence of a strong oxidizing agent like ozone, especially at higher temperatures or alkaline pH levels. During this process:

• Each bromide ion loses a total of six electrons.
• It is converted through intermediate stages, potentially forming hypobromous acid before reaching the final bromate form.

Understanding bromide ion oxidation helps in controlling water treatment processes to ensure safe drinking water while minimizing the formation of undesirable by-products like bromate ions.