Question

Write a chemical equation showing how each of the following species can behave as an acid when dissolved in water. a. \(\mathrm{HBrO}_{3}\) b. \(HI\) c. \(\mathrm{O}^{2-}\) d. \(\mathrm{F}^{-}\)

Short answer

a. \[\mathrm{HBrO}_{3} \ + \ \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{H}_{3}\mathrm{O}^{+} \ + \ \mathrm{BrO}_{3}^{-}\] b. \[HI \ + \ \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{H}_{3}\mathrm{O}^{+} \ + \ I^{-}\] c. \[\mathrm{O}^{2-} \ + \ \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{OH}^{-} \ + \ \mathrm{OH}^{-}\] d. \[\mathrm{F}^{-} \ + \ \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{HF} \ + \ \mathrm{OH}^{-}\]

Step-by-step solution

1. Analyzing HBrO3

First, we have to analyze the chemical formula \(\mathrm{HBrO}_{3}\). The presence of a hydrogen atom in the formula suggests that it can behave as an acid. Let's write the chemical equation for its reaction with water.

2. Reaction of HBrO3 with water

When \(\mathrm{HBrO}_{3}\) dissolves in water, it can donate a proton (H+) to a water molecule, leaving behind \(\mathrm{BrO}_{3}^{-}\). So the chemical reaction will be: \[\mathrm{HBrO}_{3} \ + \ \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{H}_{3}\mathrm{O}^{+} \ + \ \mathrm{BrO}_{3}^{-}\]

3. Analyzing HI

Next, let's look at the species \(HI\). Since it is a hydrogen halide, it can also behave as an acid. Now, let's write the chemical equation for its reaction with water.

4. Reaction of HI with water

When \(HI\) dissolves in water, it can donate a proton (H+) to a water molecule, leaving behind \(I^{-}\). So the chemical reaction will be: \[HI \ + \ \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{H}_{3}\mathrm{O}^{+} \ + \ I^{-}\]

5. Analyzing O2-

Now, we will analyze the species \(\mathrm{O}^{2-}\). Although it is not common for a species without hydrogen to act as an acid, \(\mathrm{O}^{2-}\) can give up a proton in an acid-base reaction. Let's write the chemical equation for this reaction.

6. Reaction of O2- with Water

When \(\mathrm{O}^{2-}\) reacts with water, it can give up a proton (H+) to a water molecule, forming \(\mathrm{OH}^{-}\). So the chemical reaction will be: \[\mathrm{O}^{2-} \ + \ \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{OH}^{-} \ + \ \mathrm{OH}^{-}\]

7. Analyzing F-

Finally, let's analyze the species \(\mathrm{F}^{-}\). This is another case where a species without hydrogen can still act as an acid. We will now write the chemical equation for its reaction with water.

8. Reaction of F- with water

When \(\mathrm{F}^{-}\) reacts with water, it will accept a proton (H+) from a water molecule, forming \(\mathrm{HF}\) and releasing a hydroxide ion. So the chemical reaction will be: \[\mathrm{F}^{-} \ + \ \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{HF} \ + \ \mathrm{OH}^{-}\] Note: In the last step (step 8), even though F- does not donate a proton, it increases the concentration of H3O+ by accepting a proton from water causing it to be labeled as an acid according to Bronsted-Lowry acid definition.

Key concepts

Chemical Equations

Chemical equations are symbolic representations of chemical reactions where reactants transform into products. These equations articulate the substances involved, their physical states, and the number of moles that participate in the reaction.

For example, the equation
\[\mathrm{HBrO}_{3} + \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{H}_{3}\mathrm{O}^{+} + \mathrm{BrO}_{3}^{-}\]
showcases how bromic acid (\(\mathrm{HBrO}_{3}\)) behaves as an acid when dissolved in water. Each equation must be balanced, ensuring that the number of atoms for each element is the same on both sides to comply with the law of conservation of mass.

• Reactants are on the left-hand side.
• Products on the right-hand side.
• Physical states, when included, are denoted as (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solution.

Acid-Base Reactions

Acid-base reactions are processes in which an acid donates a proton (\(\mathrm{H}^+\)) to a base. In an aqueous solution, water often acts as the base that accepts the proton, forming hydronium ions (\(\mathrm{H}_3\mathrm{O}^+\)).

The acid-base reactions for the given species are as follows:
\[\mathrm{HBrO}_{3} + \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{H}_{3}\mathrm{O}^{+} + \mathrm{BrO}_{3}^{-}\]
\[\mathrm{HI} + \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{H}_{3}\mathrm{O}^{+} + \mathrm{I}^{-}\]

Notably, the oxygen anion (\(\mathrm{O}^{2-}\)) and the fluoride anion (\(\mathrm{F}^{-}\)) also participate in acid-base reactions by altering the concentration of \(\mathrm{H}_3\mathrm{O}^+\) in water through different mechanisms, as seen in their respective chemical equations.

• Acids donate protons.
• Bases accept protons.
• Water often acts as the proton acceptor in aqueous solutions.

In a broader sense, these reactions are essential for understanding acidity and basicity of different substances in various environments.

Bronsted-Lowry Acids

The Bronsted-Lowry theory extends the definition of acids and bases beyond the substances that contain hydrogen and hydroxide ions, respectively. In this theory, an acid is defined as a proton donor, and a base is a proton acceptor.

For instance, in the reaction:
\[\mathrm{F}^{-} + \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{HF} + \mathrm{OH}^{-}\]
the fluoride ion (\(\mathrm{F}^{-}\)) accepts a proton from water, thereby acting as a Bronsted-Lowry base, even though it increases the concentration of \(\mathrm{H_3O}^+\) in solution and displays acidic behavior. This duality showcases the versatility of the Bronsted-Lowry theory, as substances can act as either an acid or a base depending on the chemical context.

• Bronsted-Lowry acids donate protons.
• Bronsted-Lowry bases accept protons.
• Substances can be both acids or bases in different reactions.

Hydrogen Halides

Hydrogen halides are binary compounds composed of hydrogen and a halogen. In aqueous solutions, they are strong acids due to their high tendency to donate protons to water, forming hydronium ions and halide anions.

The chemical equation for hydrogen iodide (HI) in water is:
\[\mathrm{HI} + \mathrm{H}_{2}\mathrm{O} \longrightarrow \mathrm{H}_{3}\mathrm{O}^{+} + \mathrm{I}^{-}\]
This reaction is exemplary of hydrogen halides' acidic behavior. Each hydrogen halide has unique properties and strength as an acid, often influenced by the halogen's size and the bond strength to hydrogen.

• Hydrogen halides are composed of hydrogen and a halogen.
• They readily donate protons in water, acting as strong acids.
• Their acidic strength is influenced by the halogen's characteristics.