What is the hypothetical van’t Hoff factor of magnesium nitrate, Mg(NO3)2?
The correct answer and explanation is:
The hypothetical van’t Hoff factor (i) for magnesium nitrate, Mg(NO₃)₂, is 3.
Explanation:
The van’t Hoff factor (i) is a measure of the number of particles a compound dissociates into when dissolved in a solution. It’s important for understanding colligative properties such as boiling point elevation, freezing point depression, vapor pressure lowering, and osmotic pressure.
Step 1: Understanding the formula of magnesium nitrate
- Magnesium nitrate has the chemical formula Mg(NO₃)₂.
- This indicates it contains:
- 1 magnesium ion: Mg²⁺
- 2 nitrate ions: NO₃⁻
Step 2: Dissociation in water
When magnesium nitrate dissolves in water, it dissociates into its ions: Mg(NO3)2→Mg2++2NO3−\text{Mg(NO}_3)_2 \rightarrow \text{Mg}^{2+} + 2 \text{NO}_3^-
So, from 1 formula unit of magnesium nitrate, 3 particles are produced:
1 Mg²⁺ ion + 2 NO₃⁻ ions = 3 ions.
Step 3: Hypothetical van’t Hoff factor
- The ideal van’t Hoff factor, assuming complete dissociation, is the total number of ions formed from one formula unit.
- For Mg(NO₃)₂, this is 3.
Real-world note:
- The actual van’t Hoff factor can be slightly less than 3 due to ion pairing or incomplete dissociation in solution, especially at higher concentrations.
- But for most calculations, especially in dilute solutions, we use the ideal value.
Summary:
- Mg(NO₃)₂ dissociates into 3 ions in solution.
- Hypothetical van’t Hoff factor (i) = 3.
This value is key in calculating colligative properties, because these properties depend on the number of particles in solution, not their identity. The more particles a compound dissociates into, the greater the effect on colligative properties.