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

Options

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

Explanation

To solve the problem of how to make a 100 mL solution of 0.1 M KCl into a 0.2 M KCl solution, 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 (n) divided by the volume of solution in liters (V):
\[ M = \frac{n}{V} \]

### Step 2: Calculate the initial number of moles of KCl.
Given:
- Molarity (M1) = 0.1 M
- Volume (V1) = 100 mL = 0.1 L

Using the formula:
\[ n = M \times V \]
\[ n_1 = 0.1 \, \text{M} \times 0.1 \, \text{L} = 0.01 \, \text{moles} \]

### Step 3: Set up the equation for the final concentration.
We want to find the new volume (V2) that will give us a concentration of 0.2 M (M2):
- Molarity (M2) = 0.2 M

Using the same formula for the final state:
\[ n_2 = M_2 \times V_2 \]

### Step 4: Since the number of moles remains constant, set n1 equal to n2.
\[ n_1 = n_2 \]
\[ 0.01 \, \text{moles} = 0.2 \, \text{M} \times V_2 \]

### Step 5: Solve for V2.
Rearranging the equation gives:
\[ V_2 = \frac{0.01 \, \text{moles}}{0.2 \, \text{M}} = 0.05 \, \text{L} = 50 \, \text{mL} \]

### Step 6: Determine how to achieve the desired concentration.
Since we started with 100 mL and need to reduce it to 50 mL to achieve 0.2 M, we can either:
1. Evaporate 50 mL of the solution.
2. Add more KCl to increase the concentration.

### Conclusion:
To make the 0.1 M KCl solution into a 0.2 M solution, we need to reduce the volume to 50 mL by either evaporating 50 mL of the solution or adding 0.01 moles of KCl.

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