Molarity of pure water is

Options

A. 1
B. 55.55
C. 0.1
D. 5.55

Answer

To find the molarity of pure water, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Definition of Molarity**:
Molarity (M) is defined as the number of moles of solute (n) divided by the volume of the solution in liters (V).
\[ M = \frac{n}{V} \]

2. **Relate Density and Molarity**:
We know that density (d) is defined as mass (m) divided by volume (V).
\[ d = \frac{m}{V} \]
Rearranging this gives us:
\[ m = d \times V \]

3. **Convert Density to Molarity**:
If we divide both sides of the density equation by the molar mass (M_m), we can express the number of moles (n) in terms of density and molar mass:
\[ \frac{d}{M_m} = \frac{n}{V} \]
Therefore, we can express molarity as:
\[ M = \frac{d}{M_m} \]

4. **Substitute Values for Water**:
For pure water:
- The density (d) is approximately \(1 \, \text{g/mL}\) or \(1000 \, \text{g/L}\).
- The molar mass (M_m) of water (H₂O) is \(18 \, \text{g/mol}\).

5. **Calculate Molarity**:
Plugging in the values:
\[ M = \frac{1000 \, \text{g/L}}{18 \, \text{g/mol}} = \frac{1000}{18} \, \text{mol/L} \]
Simplifying this gives:
\[ M \approx 55.55 \, \text{mol/L} \]

### Final Answer:
The molarity of pure water is approximately \(55.55 \, \text{mol/L}\).

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