Question

Write a balanced net ionic equation for the reaction of each of the following oxides with water: (a) \(\mathrm{Cl}_{2} \mathrm{O}_{7}\) (b) \(\mathrm{K}_{2} \mathrm{O}\) (c) \(\mathrm{SO}_{3}\)

Short answer

(a) \(\mathrm{Cl_{2}O_{7}} + \mathrm{H_2O} \rightarrow 2\mathrm{H^+} + 2\mathrm{ClO_4^-}\); (b) \(\mathrm{O^{2-} + H_2O \rightarrow 2\mathrm{OH^-}}\); (c) \(\mathrm{SO_3} + \mathrm{H_2O} \rightarrow 2\mathrm{H^+} + \mathrm{SO_4^{2-}}\).

Step-by-step solution

Identify the acid or base formed

When a non-metal oxide reacts with water, it forms an acid. For metal oxides, a base is formed. Identify the compound formed.(a) \(\mathrm{Cl_{2}O_{7}} + \mathrm{H_2O} \rightarrow 2\mathrm{HClO_4}\) (Perchloric acid).(b) \(\mathrm{K_2O} + \mathrm{H_2O} \rightarrow 2\mathrm{KOH}\) (Potassium hydroxide).(c) \(\mathrm{SO_3} + \mathrm{H_2O} \rightarrow \mathrm{H_2SO_4}\) (Sulfuric acid).

Dissociate the strong electrolytes into ions

Dissociate all strong electrolytes in solution into their respective ions.(a) \(2\mathrm{HClO_4} \rightarrow 2\mathrm{H^+} + 2\mathrm{ClO_4^-}\).(b) \(2\mathrm{KOH} \rightarrow 2\mathrm{K^+} + 2\mathrm{OH^-}\).(c) \(\mathrm{H_2SO_4} \rightarrow 2\mathrm{H^+} + \mathrm{SO_4^{2-}}\).

Write the net ionic equation

Eliminate the spectator ions to write the net ionic equations for each reaction.(a) \(\mathrm{Cl_{2}O_{7} + \mathrm{H_2O} \rightarrow 2\mathrm{H^+} + 2\mathrm{ClO_4^-}}\).(b) \(\mathrm{O^{2-} + \mathrm{H_2O} \rightarrow 2\mathrm{OH^-}}\).(c) \(\mathrm{SO_3} + \mathrm{H_2O} \rightarrow 2\mathrm{H^+} + \mathrm{SO_4^{2-}}\).

Key concepts

Reaction of Oxides with Water

Oxides react with water in fascinating and predictable ways, depending on whether they are metal or non-metal oxides. When a non-metal oxide is introduced to water, it typically forms an acid. This occurs because non-metal oxides are generally acidic in nature. For instance, when dichlorine heptoxide \((\text{Cl}_2 \text{O}_7)\) or sulfur trioxide \((\text{SO}_3)\) reacts with water, they form perchloric acid \((\text{HClO}_4)\) and sulfuric acid \((\text{H}_2\text{SO}_4)\) respectively.
In contrast, metal oxides react with water to form bases. This is because metal oxides are typically basic. For example, potassium oxide \((\text{K}_2\text{O})\) reacts with water to form potassium hydroxide \((\text{KOH})\), which is a strong base.
Understanding these reactions is crucial when predicting the products of oxide-water reactions. Recognizing whether an oxide will react to form an acid or a base is key to mastering these concepts.

Non-Metal Oxides

Non-metal oxides like \(\text{Cl}_2 \text{O}_7\) and \(\text{SO}_3\) behave differently than their metal oxide counterparts. When these non-metal oxides come into contact with water, they readily form acidic solutions. This is due to their inherent chemical properties that allow them to accept electrons and form acids.
For example, when \(\text{Cl}_2 \text{O}_7\) reacts with water, it forms perchloric acid, as shown in the equation: \[ \text{Cl}_2 \text{O}_7 + \text{H}_2\text{O} \rightarrow 2\text{HClO}_4 \]. Similarly, \(\text{SO}_3\) reacts to form sulfuric acid: \[ \text{SO}_3 + \text{H}_2\text{O} \rightarrow \text{H}_2\text{SO}_4 \].
In these reactions, the non-metal oxides are reduced, and their bonds are rearranged in water to create strong acids.

Metal Oxides

Metal oxides, such as \(\text{K}_2\text{O}\), are known for their basic nature. When these oxides react with water, they characteristically form bases. This occurs because metal oxides release oxide ions \((\text{O}^{2-})\), which then react with water molecules to form hydroxide ions \((\text{OH}^-)\):
The reaction is represented by \[ \text{O}^{2-} + \text{H}_2\text{O} \rightarrow 2\text{OH}^- \]. In the case of potassium oxide, the reaction creates potassium hydroxide, a strong base.
Recognizing the basic properties of metal oxides helps in predicting and understanding the types of reactions they will undergo when in contact with water.

Electrolytes Dissociation

When strong acids and bases dissolve in water, they dissociate into ions—this process is known as electrolytes dissociation. Strong acids, like perchloric acid \((\text{HClO}_4)\) and sulfuric acid \((\text{H}_2\text{SO}_4)\), and strong bases such as potassium hydroxide \((\text{KOH})\) fully dissociate into their respective ions.
For example:

• \(\text{HClO}_4\) dissociates into \(2\text{H}^+\) and \(2\text{ClO}_4^-\)
• \(\text{H}_2\text{SO}_4\) dissociates into \(2\text{H}^+\) and \(\text{SO}_4^{2-}\)
• \(\text{KOH}\) dissociates into \(2\text{K}^+\) and \(2\text{OH}^-\)

Understanding electrolytes dissociation is key to writing net ionic equations.
It involves eliminating spectator ions and focusing only on the species that are actively participating in a chemical reaction. This approach not only simplifies equations but also clarifies the core interactions taking place in solution.