An aqueous solution is 1.00 molalin KI. Which change will cause the vapour pressure of the solution to increase ?

Options

A. addition of water
B. addtion of NaCl
C. addtion of `Na_(2)So_(4)`
D. Addition of 1.0 molal KI

Answer

To solve the question regarding the increase in vapor pressure of a 1.00 molal KI aqueous solution, we can follow these steps:

### Step 1: Understand Vapor Pressure in Solutions
In a pure solvent, the vapor pressure is determined by the number of solvent molecules present at the surface. When a non-volatile solute (like KI) is added to the solvent, it occupies some of the surface area, which decreases the number of solvent molecules that can evaporate. Therefore, the vapor pressure of the solution is lower than that of the pure solvent.

**Hint:** Remember that the presence of a non-volatile solute lowers the vapor pressure of a solution compared to that of the pure solvent.

### Step 2: Identify the Effect of Adding More Solvent
When we consider the options provided, one of the changes that can be made is the addition of more solvent (water in this case). Adding more water increases the number of solvent molecules in the solution. This means that there will be more molecules available at the surface to evaporate, which will increase the vapor pressure.

**Hint:** Adding more solvent increases the number of volatile molecules at the surface, which can lead to an increase in vapor pressure.

### Step 3: Analyze Other Options
The other options involve adding more non-volatile solutes (like NaCl or Na2SO4). Since these solutes do not evaporate, their addition would further decrease the vapor pressure of the solution. Therefore, these changes would not lead to an increase in vapor pressure.

**Hint:** Non-volatile solutes do not contribute to vapor pressure and will lower it instead.

### Step 4: Conclusion
The only change that will cause the vapor pressure of the 1.00 molal KI solution to increase is the addition of more water. This is because it increases the number of solvent molecules, which can evaporate and contribute to the vapor pressure.

**Final Answer:** The correct change that will cause the vapor pressure of the solution to increase is the addition of water.