Question

Although the \(\mathrm{ClO}_{4}^{-}\) and \(\mathrm{IO}_{4}^{-}\) ions have been known for a long time, \(\mathrm{BrO}_{4}^{-}\) was not synthesized until \(1965 .\) The ion was synthesized by oxidizing the bromate ion with xenon difluoride, producing xenon, hydrofluoric acid, and the perbromate ion. Write the balanced equation for this reaction.

Short answer

The balanced chemical equation for the reaction is \( \mathrm{BrO}_{3}^{-} + \mathrm{XeF}_{2} \rightarrow \mathrm{BrO}_{4}^{-} + \mathrm{Xe} + 2\,\mathrm{HF} \).

Step-by-step solution

1. Write down the unbalanced equation

First, we write down the unbalanced chemical equation using the formulae of the given compounds: \( \mathrm{BrO}_{3}^{-} + \mathrm{XeF}_{2} \rightarrow \mathrm{BrO}_{4}^{-} + \mathrm{Xe} + \mathrm{HF} \)

2. Balance the equation

To balance the equation, we need to count the number of each type of atom on both sides and make sure they are equal by adjusting the coefficients. Atoms on the left side: - Br: 1 - O: 3 - Xe: 1 - F: 2 Atoms on the right side: - Br: 1 - O: 4 - Xe: 1 - F: 1 We can see that we need one more oxygen and one more fluorine atom on the right side to balance the equation. To accomplish this, we can place a coefficient of 2 in front of hydrofluoric acid (HF): \( \mathrm{BrO}_{3}^{-} + \mathrm{XeF}_{2} \rightarrow \mathrm{BrO}_{4}^{-} + \mathrm{Xe} + 2\,\mathrm{HF} \) Now, the equation is balanced: - Br: 1 - O: 3 + 1 = 4 - Xe: 1 - F: 2 The balanced chemical equation is \( \mathrm{BrO}_{3}^{-} + \mathrm{XeF}_{2} \rightarrow \mathrm{BrO}_{4}^{-} + \mathrm{Xe} + 2\,\mathrm{HF} \)

Key concepts

Oxidation-Reduction Reactions

At the heart of many chemical processes is the concept of oxidation-reduction (redox) reactions. These include the transfer of electrons from one substance to another. The molecule that loses electrons gets oxidized, while the one that gains electrons becomes reduced. In the exercise, the bromate ion \( \mathrm{BrO_{3}^{-}} \) is being oxidized to form the perbromate ion \( \mathrm{BrO_{4}^{-}} \), as it gains an oxygen atom which is equivalent to losing electrons.

In the synthesis of \( \mathrm{BrO_{4}^{-}} \) ion, the redox reaction partners with the xenon difluoride \( \mathrm{XeF_{2}} \) which plays a role in this electron transfer process. Xenon difluoride itself gets reduced as it loses the oxygen that was originally bonded to bromine. This is evident as xenon is formed, and its oxidation state decreases from +2 in \( \mathrm{XeF_{2}} \) to 0 in \( \mathrm{Xe} \). By recognizing the changes in oxidation states of the reactants and products, the balancing of redox equations becomes more structured, which aids in understanding the underlying conversion process.

Chemical Stoichiometry

Chemical stoichiometry involves the quantitative relationship between reactants and products in a chemical reaction. It's fundamental in ensuring that atoms are conserved in a reaction, as per the law of conservation of mass. In the given exercise, the stoichiometry is illustrated through the process of balancing the chemical equation.

To achieve a balanced equation, it's essential to adjust the coefficients of the reactants and products. In this case, counting the number of each atom on both sides helps us determine that the coefficient of \( \mathrm{HF} \) must be 2 to ensure there are equal amounts of fluorine and oxygen atoms on both sides of the equation. This kind of stoichiometry is crucial for predicting how much of each substance is needed or produced in a chemical reaction. It is important, especially in the industry, to calculate the optimum amount of reactants to minimize waste and cost.

Perhalogenate Ions

Perhalogenate ions are a class of polyatomic ions where a halogen atom is bonded to oxygen atoms, typically in the highest oxidation state for that halogen. These ions are strong oxidizing agents. The \( \mathrm{ClO_{4}^{-}} \) and \( \mathrm{IO_{4}^{-}} \) ions are well-known members of this group. The exercise specifically deals with the perbromate ion, \( \mathrm{BrO_{4}^{-}} \) which is less commonly encountered and was only synthesized relatively recently.

The synthesis of \( \mathrm{BrO_{4}^{-}} \) is notable because it shows the trend of chemical reactivity in the halogens and their ability to form compounds in different oxidation states. Perhalogenates, like \( \mathrm{BrO_{4}^{-}} \), are important in understanding the reactivity and the synthesis of new compounds. Understanding these ions helps chemists to predict the behavior of halogens in various chemical contexts and their potential applications, which include uses in disinfection and as a component in rocket propellants due to their strong oxidizing properties.