Write a balanced equation for the reaction between aqueous magnesium nitrate and aqueous potassium hydroxide to form solid magnesium hydroxide and aqueous potassium nitrate.
The correct answer and explanation is:
The reaction between aqueous magnesium nitrate (Mg(NO₃)₂) and aqueous potassium hydroxide (KOH) can be represented by the following balanced chemical equation:
Mg(NO₃)₂ (aq)+2KOH (aq)→Mg(OH)₂ (s)+2KNO₃ (aq)\text{Mg(NO₃)₂ (aq)} + 2\text{KOH (aq)} \rightarrow \text{Mg(OH)₂ (s)} + 2\text{KNO₃ (aq)}
Explanation:
- Write the molecular equation: The first step is to identify the compounds involved in the reaction. Magnesium nitrate is a soluble ionic compound, so it dissociates in water into magnesium ions (Mg²⁺) and nitrate ions (NO₃⁻). Potassium hydroxide also dissociates into potassium ions (K⁺) and hydroxide ions (OH⁻). Magnesium hydroxide, however, is only slightly soluble in water and precipitates out of the solution as a solid (Mg(OH)₂). Potassium nitrate (KNO₃) remains soluble and dissociates into potassium ions (K⁺) and nitrate ions (NO₃⁻).
- Balance the equation: The next step is to ensure that the number of atoms of each element is the same on both sides of the equation. Initially, we have one magnesium atom on the left and one on the right, so magnesium is balanced. For nitrate ions (NO₃⁻), there are two on the left (from Mg(NO₃)₂), so two potassium nitrate molecules (KNO₃) are required on the right to balance the nitrates. For hydroxide ions (OH⁻), we have two on the left (from 2 KOH), so we need two hydroxide ions on the right to balance the equation.
- Confirm the charge balance: Both sides of the equation must have the same total charge. On the left, we have the charges from Mg²⁺, NO₃⁻, and KOH, and on the right, we have the charges from Mg(OH)₂ and KNO₃. The charges balance, confirming that the equation is correct.
- State symbols: Finally, it is important to include the state symbols. Magnesium nitrate and potassium hydroxide are aqueous (aq), magnesium hydroxide is a solid (s), and potassium nitrate is aqueous (aq).
This equation shows a double displacement reaction where magnesium hydroxide precipitates from the solution.