Which solution has the highest vapour presssure ?

Options

A. `0.02 M` `NaCl` at `50^(@)C`
B. `0.03 M` sucrose at `15^(@)`C
C. `0.005M` `CaCl_(2)` at `500 ^(@)C`
D. `0.005 M` `CaCl_(2)` at `25^(@)C`

Answer

To determine which solution has the highest vapor pressure, we need to analyze the vapor pressures of the given solutions based on their concentrations and the degree of dissociation of the solutes. Here’s a step-by-step solution:

### Step 1: Understand Vapor Pressure
Vapor pressure is the pressure exerted by a vapor in equilibrium with its liquid at a given temperature. For a pure solvent, the vapor pressure is higher, while for a solution, the vapor pressure decreases due to solute-solvent interactions.

**Hint:** Remember that the presence of solute lowers the vapor pressure of the solvent.

### Step 2: Identify the Solutions
We have the following solutions to consider:
1. 0.02 M NaCl
2. 0.03 M sucrose
3. 0.05 M CaCl₂ at 50°C
4. Another solution (not specified in the transcript)

**Hint:** Make sure to note the concentration and the nature of the solute (whether it dissociates or not).

### Step 3: Calculate the Effective Concentration for Each Solution
- **For NaCl:**
- NaCl dissociates into Na⁺ and Cl⁻, giving an i value of 2.
- Effective concentration = 0.02 M × 2 = 0.04.

- **For Sucrose:**
- Sucrose does not dissociate, so the i value is 1.
- Effective concentration = 0.03 M × 1 = 0.03.

- **For CaCl₂:**
- CaCl₂ dissociates into Ca²⁺ and 2 Cl⁻, giving an i value of 3.
- Effective concentration = 0.05 M × 3 = 0.15.

### Step 4: Consider the Temperature Effect
The vapor pressure also depends on temperature. Higher temperatures generally lead to higher vapor pressures. In this case, the CaCl₂ solution is at a higher temperature (50°C), which can influence its vapor pressure.

**Hint:** Remember that temperature can significantly affect vapor pressure, especially for solutions with lower concentrations.

### Step 5: Compare the Effective Concentrations
Now we compare the effective concentrations:
- NaCl: 0.04
- Sucrose: 0.03
- CaCl₂: 0.15 (at 50°C)

### Step 6: Determine the Highest Vapor Pressure
Despite the effective concentration of CaCl₂ being the highest, we must also consider the temperature. The higher temperature at which the CaCl₂ solution is measured (50°C) means that its vapor pressure will be higher than that of the other solutions, which are at lower temperatures.

### Conclusion
The solution with the highest vapor pressure is the **CaCl₂ solution at 50°C** due to its higher temperature and effective concentration.

**Final Answer:** The solution with the highest vapor pressure is the **0.05 M CaCl₂ at 50°C**.