We have 100 mL of 0.1 MKCI solution . To make it 0.2 M

Options

A. evaporate 50 mL water
B. evaporate 50 mL solution
C. add 0.1 mol KCI
D. add 0.01 mol KCI

Answer

To solve the problem of how to change the concentration of a KCl solution from 0.1 M to 0.2 M, we can follow these steps:

### Step 1: Understand the relationship between molarity, volume, and moles.
Molarity (M) is defined as the number of moles of solute per liter of solution. The relationship can be expressed as:
\[ \text{Molarity (M)} = \frac{\text{Number of moles (n)}}{\text{Volume (L)}} \]

### Step 2: Calculate the number of moles in the initial solution.
Given:
- Initial molarity (M1) = 0.1 M
- Initial volume (V1) = 100 mL = 0.1 L (since 1000 mL = 1 L)

Using the formula for moles:
\[ n_1 = M_1 \times V_1 \]
\[ n_1 = 0.1 \, \text{mol/L} \times 0.1 \, \text{L} = 0.01 \, \text{moles} \]

### Step 3: Determine the desired molarity and calculate the required volume.
We want to achieve a final molarity (M2) of 0.2 M. We can use the same formula for moles:
\[ n_2 = M_2 \times V_2 \]
Since the number of moles remains constant during dilution or concentration:
\[ n_1 = n_2 \]
Thus:
\[ 0.01 \, \text{moles} = 0.2 \, \text{mol/L} \times V_2 \]

### Step 4: Solve for the final volume (V2).
Rearranging the equation gives:
\[ V_2 = \frac{n_2}{M_2} = \frac{0.01 \, \text{moles}}{0.2 \, \text{mol/L}} = 0.05 \, \text{L} = 50 \, \text{mL} \]

### Step 5: Determine the change in volume.
Since the initial volume was 100 mL and the final volume needs to be 50 mL, we need to reduce the volume by:
\[ \text{Volume to reduce} = 100 \, \text{mL} - 50 \, \text{mL} = 50 \, \text{mL} \]

### Step 6: Conclusion.
To achieve a 0.2 M KCl solution from a 0.1 M KCl solution, we need to reduce the volume of the solution by 50 mL. This can be done by evaporating 50 mL of water or the solution.

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