The molarity of 720 g of pure water is

Options

A. 40 M
B. 4 M
C. 55.5 M
D. unpredictable

Explanation

To find the molarity of 720 g of pure water, we can follow these steps:

### Step 1: Understand the formula for molarity
Molarity (M) is defined as the number of moles of solute divided by the volume of solution in liters. The formula is:
\[ M = \frac{\text{Number of moles of solute}}{\text{Volume of solution in liters}} \]

### Step 2: Calculate the number of moles of water
To find the number of moles, we use the formula:
\[ \text{Number of moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} \]

The molar mass of water (H₂O) can be calculated as follows:
- Hydrogen (H) has a molar mass of approximately 1 g/mol, and there are 2 hydrogen atoms in water.
- Oxygen (O) has a molar mass of approximately 16 g/mol.

Thus, the molar mass of water is:
\[ \text{Molar mass of H₂O} = (2 \times 1) + 16 = 18 \text{ g/mol} \]

Now, substituting the values into the moles formula:
\[ \text{Number of moles of water} = \frac{720 \text{ g}}{18 \text{ g/mol}} = 40 \text{ moles} \]

### Step 3: Convert the mass of water to volume
Since the density of water is approximately 1 g/mL, the volume of 720 g of water can be calculated as:
\[ \text{Volume (mL)} = \text{mass (g)} \]
\[ \text{Volume (L)} = \frac{720 \text{ g}}{1000} = 0.720 \text{ L} \]

### Step 4: Calculate the molarity
Now we can substitute the number of moles and the volume into the molarity formula:
\[ M = \frac{40 \text{ moles}}{0.720 \text{ L}} \]

Calculating this gives:
\[ M = 55.56 \text{ M} \]

### Conclusion
The molarity of 720 g of pure water is approximately 55.56 M.

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