Problem 68 - Chemistry: The Central Science

Question

Write balanced equations for the following reactions: (a) potassium oxide with water, (b) diphosphorus trioxide with water, (c) chromium(III) oxide with dilute hydrochloric acid, (d) selenium dioxide with aqueous potassium hydroxide.

Step-by-Step Solution

Answer

(a) K₂O + H₂O → 2KOH (b) P₂O₃ + 3H₂O → 2H₃PO₃ (c) Cr₂O₃ + 6HCl → 2CrCl₃ + 3H₂O (d) SeO₂ + 2KOH → K₂SeO₃ + H₂O

Step 1: (a) Potassium oxide with water

Reactants: Potassium oxide (K₂O) and water (H₂O) Products: Potassium hydroxide (KOH) Unbalanced equation: K₂O + H₂O → KOH Balanced equation: K₂O + H₂O → 2KOH

Step 2: (b) Diphosphorus trioxide with water

Reactants: Diphosphorus trioxide (P₂O₃) and water (H₂O) Products: Phosphorous acid (H₃PO₃) Unbalanced equation: P₂O₃ + H₂O → H₃PO₃ Balanced equation: P₂O₃ + 3H₂O → 2H₃PO₃

Step 3: (c) Chromium(III) oxide with dilute hydrochloric acid

Reactants: Chromium(III) oxide (Cr₂O₃) and hydrochloric acid (HCl) Products: Chromium(III) chloride (CrCl₃) and water (H₂O) Unbalanced equation: Cr₂O₃ + HCl → CrCl₃ + H₂O Balanced equation: Cr₂O₃ + 6HCl → 2CrCl₃ + 3H₂O

Step 4: (d) Selenium dioxide with aqueous potassium hydroxide

Reactants: Selenium dioxide (SeO₂) and potassium hydroxide (KOH) Products: Potassium selenite (K₂SeO₃) and water (H₂O) Unbalanced equation: SeO₂ + KOH → K₂SeO₃ + H₂O Balanced equation: SeO₂ + 2KOH → K₂SeO₃ + H₂O

Key Concepts

Potassium Oxide Reaction with Water

When potassium oxide (\( \text{K}_2\text{O} \) reacts with water (\( \text{H}_2\text{O} \)), the result is a base called potassium hydroxide (\( \text{KOH} \)). This reaction is a type of synthesis reaction where two reactants combine to form a more complex product.

The balanced equation for this reaction is:
\( \text{K}_2\text{O} + \text{H}_2\text{O} \rightarrow 2\text{KOH} \)
This indicates that one molecule of potassium oxide reacts with one molecule of water to produce two molecules of potassium hydroxide. Understanding the stoichiometry of the reaction helps ensure that the chemical equation is balanced, meaning the number of atoms for each element is the same on both sides of the equation.

Diphosphorus Trioxide Chemical Equation

Diphosphorus trioxide (\( \text{P}_2\text{O}_3 \) reacts with water to form phosphorous acid (\( \text{H}_3\text{PO}_3 \)). In this acid-base reaction, the diphosphorus trioxide serves as an acidic oxide, reacting with the water, a polar molecule, to yield an oxyacid.

The balanced chemical equation is:
\( \text{P}_2\text{O}_3 + 3\text{H}_2\text{O} \rightarrow 2\text{H}_3\text{PO}_3 \)
This tells us that one molecule of diphosphorus trioxide reacts with three molecules of water to produce two molecules of phosphorous acid. Balancing the equation is crucial to accurately reflect the conservation of mass and the equivalence of atoms on both sides of the reaction.

Chromium(III) Oxide Reaction with Hydrochloric Acid

Chromium(III) oxide (\( \text{Cr}_2\text{O}_3 \) is an amphoteric oxide, meaning it can react with both acids and bases. When it reacts with hydrochloric acid (\( \text{HCl} \) here, the products are chromium(III) chloride (\( \text{CrCl}_3 \) and water.

The balanced equation for this acid-base reaction is:
\( \text{Cr}_2\text{O}_3 + 6\text{HCl} \rightarrow 2\text{CrCl}_3 + 3\text{H}_2\text{O} \)
The equation shows that one molecule of chromium(III) oxide requires six molecules of hydrochloric acid to yield two molecules of chromium(III) chloride and three molecules of water. The balance of the equation reflects the stoichiometry needed for the atoms of each element to be conserved during the reaction.

Selenium Dioxide Reaction with Aqueous Potassium Hydroxide

Selenium dioxide (\( \text{SeO}_2 \) is a solid that reacts with aqueous potassium hydroxide (\( \text{KOH} \)) to form potassium selenite (\( \text{K}_2\text{SeO}_3 \) and water as products. This type of reaction is a neutralization reaction, common when an oxide reacts with a hydroxide.

The balanced equation for the reaction is:
\( \text{SeO}_2 + 2\text{KOH} \rightarrow \text{K}_2\text{SeO}_3 + \text{H}_2\text{O} \)
This balanced equation demonstrates that it takes one molecule of selenium dioxide and two molecules of potassium hydroxide to produce one molecule of potassium selenite and one molecule of water. As with all reactions, the act of balancing ensures that there is strict adherence to the law of conservation of mass.