Question

Ferrous sulfate \(\left(\mathrm{FeSO}_{4}\right)\) is often used as a coagulant in water purification. The iron(II) salt is dissolved in the water to be purified, then oxidized to the iron(III) state by dissolved oxygen, at which time gelatinous \(\mathrm{Fe}(\mathrm{OH})_{3}\) forms, assuming the \(\mathrm{pH}\) is above approximately \(6 .\) Write balanced chemical equations for the oxidation of \(\mathrm{Fe}^{2+}\) to \(\mathrm{Fe}^{3+}\) by dissolved oxygen and for the formation of \(\mathrm{Fe}(\mathrm{OH})_{3}(s)\) by reaction of \(\mathrm{Fe}^{3+}(a q)\) with \(\mathrm{HCO}_{3}^{-}(a q)\).

Short answer

The balanced chemical equations for the water purification process using ferrous sulfate are: 1. The oxidation of iron(II) ions to iron(III) ions by dissolved oxygen: \(4 \ Fe^{2+} (aq) + O_{2} (aq) + 4 \ H^{+} (aq) \rightarrow 4 \ Fe^{3+} (aq) + 2 \ H_{2}O (l)\) 2. The formation of gelatinous iron(III) hydroxide precipitate by the reaction of iron(III) ions with bicarbonate ions: \(Fe^{3+} (aq) + 3 \ HCO_{3}^{-} (aq) \rightarrow Fe(OH)_{3} (s) + 3 \ CO_{2} \ (g) + 3 \ H^{+} (aq)\)

Step-by-step solution

Oxidation of Fe²⁺ to Fe³⁺ by Dissolved Oxygen

First, we have to write a balanced equation for the oxidation of iron(II), which is represented as Fe²⁺, to iron(III), represented as Fe³⁺, by dissolved oxygen (O₂). In this process, the iron ions will lose one electron (e⁻) due to oxidation. To balance the equation, we must ensure that there are the same number of atoms of each element on both sides of the equation. Here is the balanced equation for the oxidation of Fe²⁺ to Fe³⁺ by dissolved oxygen: \(4 \ Fe^{2+} (aq) + O_{2} (aq) + 4 \ H^{+} (aq) \rightarrow 4 \ Fe^{3+} (aq) + 2 \ H_{2}O (l)\)

Formation of Fe(OH)₃ by the Reaction of Fe³⁺ with HCO₃⁻

Now we need to write a balanced chemical equation for the formation of gelatinous Fe(OH)₃(s) from the reaction of Fe³⁺ with bicarbonate ions (HCO₃⁻). This dissolved iron(III) will react with the bicarbonate ions to form the precipitate Fe(OH)₃(s) and the gaseous carbon dioxide (CO₂). Here is the balanced equation for the formation of Fe(OH)₃(s) by the reaction of Fe³⁺ with HCO₃⁻: \(Fe^{3+} (aq) + 3 \ HCO_{3}^{-} (aq) \rightarrow Fe(OH)_{3} (s) + 3 \ CO_{2} \ (g) + 3 \ H^{+} (aq)\) In summary, the balanced equations for the water purification process using ferrous sulfate are: 1. The oxidation of iron(II) ions to iron(III) ions by dissolved oxygen: \(4 \ Fe^{2+} (aq) + O_{2} (aq) + 4 \ H^{+} (aq) \rightarrow 4 \ Fe^{3+} (aq) + 2 \ H_{2}O (l)\) 2. The formation of gelatinous iron(III) hydroxide precipitate by the reaction of iron(III) ions with bicarbonate ions: \(Fe^{3+} (aq) + 3 \ HCO_{3}^{-} (aq) \rightarrow Fe(OH)_{3} (s) + 3 \ CO_{2} \ (g) + 3 \ H^{+} (aq)\)

Key concepts

Oxidation-Reduction Reactions

In the world of chemistry, oxidation-reduction reactions, often simply called redox reactions, are vital processes. These reactions involve the transfer of electrons between substances.

Oxidation occurs when a substance loses electrons, while reduction happens when a substance gains electrons.

• In our specific exercise, iron(II) ions, represented as \( Fe^{2+} \), lose an electron to become iron(III) ions, \( Fe^{3+} \). This is the oxidation part of the reaction.
• Meanwhile, the oxygen molecule, \( O_2 \), is reduced, as it gains electrons from the iron ions.

This balanced exchange ensures that the number of electrons lost and gained is equal.

Understanding these reactions is key in many fields such as energy storage, metallurgy, and indeed water purification, where controlling electron transfers can help modify the chemical state of pollutants for easier removal.

Iron Hydroxide Formation

Iron hydroxide formation is an important process in the water treatment industry. This is because the creation of iron hydroxide solids can help get rid of contaminants.

For this to happen, iron(III) ions \( Fe^{3+} \) from a previous oxidation step react with bicarbonate ions \( HCO_3^- \) in water.

• The chemical reaction results in the formation of gelatinous iron(III) hydroxide, represented as \( Fe(OH)_3 \), which is seen as a solid precipitate.
• At the same time, carbon dioxide gas \( CO_2 \) is released and hydrogen ions \( H^+ \) are produced.

This complex reaction is helpful in water purification as the formed gelatinous iron hydroxide clusters together impurities, making them easier to remove.

Thus, understanding this reaction is essential to leveraging its benefits in the purification process.

Water Purification Chemistry

Water purification chemistry often relies on a series of chemical reactions to remove impurities and make water safe for consumption. Coagulation is a critical process in this field, which involves clumping together of particles so that they can be easily separated from the water.

In the context of ferrous sulfate, \( FeSO_4 \), being used as a coagulant:

• First, the chemical reactions convert dissolved iron(II) ions, \( Fe^{2+} \), to iron(III) ions, \( Fe^{3+} \).
• The iron(III) ion subsequently reacts to form iron(III) hydroxide, \( Fe(OH)_3 \), which is a substantive agent of purification.

This system of reactions ensures efficient coagulation and is crucial for removing contaminants from water, including suspended solids and some heavy metals.

Mastering water purification chemistry can significantly improve water quality and protect public health.