What volume of a `0.8M` solution contains 100 millimoles of the solute .

Options

A. `100 mL`
B. `125mL`
C. `500 mL`
D. `62.5mL`

Explanation

To solve the problem of finding the volume of a 0.8 M solution that contains 100 millimoles of solute, we can follow these steps:

### Step 1: Convert millimoles to moles
We know that:
1 millimole = \(10^{-3}\) moles.

So, to convert 100 millimoles to moles:
\[ \text{Number of moles} = 100 \text{ millimoles} \times 10^{-3} \text{ moles/millimole} = 0.1 \text{ moles} \]

### Step 2: Use the molarity formula
The formula for molarity (M) is given by:
\[ \text{Molarity (M)} = \frac{\text{Number of moles of solute}}{\text{Volume of solution in liters}} \]

We can rearrange this formula to find the volume of the solution:
\[ \text{Volume of solution (L)} = \frac{\text{Number of moles of solute}}{\text{Molarity (M)}} \]

### Step 3: Substitute the values into the formula
We have:
- Number of moles of solute = 0.1 moles
- Molarity = 0.8 M

Substituting these values into the formula gives:
\[ \text{Volume of solution (L)} = \frac{0.1 \text{ moles}}{0.8 \text{ M}} = 0.125 \text{ L} \]

### Step 4: Convert volume from liters to milliliters
Since the question asks for the volume in milliliters, we convert liters to milliliters:
\[ \text{Volume (mL)} = 0.125 \text{ L} \times 1000 \text{ mL/L} = 125 \text{ mL} \]

### Final Answer
The volume of the 0.8 M solution that contains 100 millimoles of solute is **125 mL**.

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