To find the molarity of pure water, we will follow these steps:
### Step 1: Understand the definition of molarity
Molarity (M) is defined as the number of moles of solute divided by the volume of solution in liters. In this case, we are considering pure water as the solvent, and we need to calculate the number of moles of water itself.
### Step 2: Calculate the number of moles of water
To calculate the number of moles (n) of water, we use the formula:
\[ n = \frac{\text{mass}}{\text{molar mass}} \]
### Step 3: Determine the mass of water
We can find the mass of water using its density. The density of water is approximately 1000 kg/m³. To convert this to grams for our calculations, we note that:
\[ 1000 \, \text{kg/m}^3 = 1000 \, \text{g/L} \]
For 1 liter of water, the mass is:
\[ \text{mass} = \text{density} \times \text{volume} = 1000 \, \text{g/L} \times 1 \, \text{L} = 1000 \, \text{g} \]
### Step 4: Calculate the molar mass of water
The molar mass of water (H₂O) is calculated as follows:
- Hydrogen (H) has a molar mass of approximately 1 g/mol, and there are 2 hydrogen atoms.
- Oxygen (O) has a molar mass of approximately 16 g/mol.
Thus, the molar mass of water is:
\[ \text{Molar mass of H₂O} = (2 \times 1) + 16 = 18 \, \text{g/mol} \]
### Step 5: Calculate the number of moles of water
Now we can calculate the number of moles of water:
\[ n = \frac{1000 \, \text{g}}{18 \, \text{g/mol}} \approx 55.56 \, \text{moles} \]
### Step 6: Calculate the molarity of pure water
Since we have 55.56 moles of water in 1 liter, the molarity (M) of pure water is:
\[ M = \frac{n}{\text{Volume in L}} = \frac{55.56 \, \text{moles}}{1 \, \text{L}} = 55.56 \, \text{mol/L} \]
### Final Answer
The molarity of pure water is approximately **55.56 mol/L**.
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