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?

Short answer

The bromate ion (\(\mathrm{BrO}_{3}^-\)) in a municipal water system can originate from disinfection byproducts, contamination from industrial waste, or natural occurrence. Bromate ions mainly form when ozone is used to treat bromide-containing water or from bromine-containing industrial waste. In redox reactions, the bromate ion predominantly acts as an oxidizing agent, as indicated by its standard reduction potential of \(E^{\circ}_{\mathrm{BrO}_{3}^{-}/\mathrm{Br}^{-}} = 1.50\text{ V}\).

Step-by-step solution

(Part A: Origins of Bromate Ion)

The bromate ion (\(\mathrm{BrO}_{3}^-\)) can be formed in a municipal water system through various sources. Some of the possible origins include: 1. Disinfection byproducts: Bromate ions can be produced as a byproduct during the disinfection process when ozone is used to treat bromide-containing water. The reaction between ozone (\(\mathrm{O}_{3}\)) and bromide ions (\(\mathrm{Br}^-\)) can generate bromate ions as follows: \[2\mathrm{O}_{3} + \mathrm{Br}^- \rightarrow \mathrm{BrO}_{3}^- + 2\mathrm{O}_{2}\] 2. Contamination from industrial waste: Industries that use bromine or produce bromine-containing compounds can release wastewater containing bromate ions, which may enter the municipal water system. 3. Natural occurrence: Bromate ions can also form naturally in small amounts, when bromide minerals in the environment react with oxygen.

(Part B: Oxidizing or Reducing Agent)

To determine whether the bromate ion (\(\mathrm{BrO}_{3}^-\)) is an oxidizing or reducing agent, we need to look at its redox potential: - The half-reaction for the bromate ion acting as an oxidizing agent is: \[\mathrm{BrO}_{3}^{-} + 6\mathrm{H}^{+} + 6\mathrm{e}^{-} \rightarrow \mathrm{Br}^{-} + 3\mathrm{H}_{2}\mathrm{O}\] - The half-reaction for the bromate ion acting as a reducing agent is: \[\mathrm{BrO}_{3}^{-} \rightarrow \mathrm{Br}^{-} + 3\mathrm{O}_{2} + 6\mathrm{H}^{+} + 6\mathrm{e}^{-}\] Comparing their standard reduction potentials, we see that the reaction with the bromate ion acting as an oxidizing agent (first half-reaction) is more favorable: \[E^{\circ}_{\mathrm{BrO}_{3}^{-}/\mathrm{Br}^{-}} = 1.50\text{ V}\] Since the reaction with the bromate ion acting as an oxidizing agent has a higher standard reduction potential, we can conclude that the bromate ion (\(\mathrm{BrO}_{3}^-\)) predominantly acts as an oxidizing agent in redox reactions.

Key concepts

Oxidizing Agent

Bromate ion, \( \mathrm{BrO}_{3}^- \), plays a significant role in redox reactions where it primarily acts as an oxidizing agent. An oxidizing agent is a substance that gains electrons during a chemical reaction. It undergoes a reduction process while causing another substance to be oxidized.
Bromate ion, in particular, has the capability to accept electrons due to its reduced form bromide ion, \( \mathrm{Br}^- \). The reaction can be represented as: \[ \mathrm{BrO}_{3}^{-} + 6\mathrm{H}^{+} + 6\mathrm{e}^{-} \rightarrow \mathrm{Br}^{-} + 3\mathrm{H}_{2}\mathrm{O} \] This half-reaction shows bromate's electron-accepting nature.
With a high standard reduction potential \(E^{\circ} = 1.50 \text{ V}\), this ion strongly favors gaining electrons and acting as an oxidizing agent. Its capacity to facilitate oxidation makes it influential in many chemical processes, including water treatment and industrial applications.
Always remember, when a *substance oxidizes*, an atom or ion *loses electrons*. Contrary, when the very same agent *reduces* another, it *gains electrons*. In essence, bromate steps into the reaction ready to pounce on those free electrons.

Redox Reactions

Redox reactions are fascinating processes where reduction and oxidation occur simultaneously. This term stands for "reduction-oxidation" reactions. In these reactions, the transfer of electrons between substances happens.
Redox reactions are key to numerous biological, chemical, and environmental processes. Here is a brief explanation of how these processes work:

• **Oxidation** involves the loss of electrons from a substance. The substance that loses electrons is oxidized.
• **Reduction** involves the gain of electrons by a substance. The substance that gains electrons is reduced.

The bromate ion is a textbook example of an oxidizing agent in redox reactions.
Its presence indicates that it seeks to oxidize another component while itself becoming reduced. Thus, it's involved in driving significant chemical changes necessary for various processes.
In equations, these reactions are split into half-reactions to better understand electron flow and interaction. Not only do these reactions play a key role in industrial settings, like water purification, but they are also critical in biological systems and environmental contexts too.

Water Contamination

Water contamination is a pertinent issue, especially concerning essential natural resources. The bromate ion is an element of concern as a possible water contaminant. Its presence in water, particularly municipal water systems, can stem from several origins:

• **Disinfection byproducts**: Bromate can form when ozone is used for water purification, especially in the presence of bromide ions.
• **Industrial waste**: Industries involving bromine usage may inadvertently release bromate ions into water supplies.
• **Natural occurrences**: Sometimes, natural reactions in the environment can lead to bromate formation, though typically in minimal amounts.

Understanding these pathways is critical because bromate ion concerns relate to potential health impacts.
Water treatment processes need careful consideration to prevent excessive formation of undesirable byproducts like bromate.
Efficient monitoring and management ensure that water resources remain safe for human consumption and aligned with safety standards. As environmental awareness and advancement in treatment technologies continue, knowledge about contaminants like bromate ion becomes ever more crucial. Communities can thus aim to reduce contamination levels to protect public health.