Question

how many water molecules are present in a 10.0g sample of H20 is it mass to mole?

Answer 1

To find the number of water molecules in a 10.0 g sample of H₂O, you can use the following steps:

1. **Calculate the molar mass of water (H₂O):**
- Hydrogen (H) has a molar mass of approximately 1.01 g/mol.
- Oxygen (O) has a molar mass of approximately 16.00 g/mol.
- Therefore, the molar mass of H₂O is:
\[
2 \times 1.01 \, \text{g/mol} + 16.00 \, \text{g/mol} = 2.02 \, \text{g/mol} + 16.00 \, \text{g/mol} = 18.02 \, \text{g/mol}
\]

2. **Convert grams to moles:**
- Use the formula:
\[
\text{moles of H₂O} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}
\]
- For a 10.0 g sample:
\[
\text{moles of H₂O} = \frac{10.0 \, \text{g}}{18.02 \, \text{g/mol}} \approx 0.555 \, \text{moles}
\]

3. **Convert moles to molecules:**
- Use Avogadro's number, which is approximately \(6.022 \times 10^{23}\) molecules/mole:
\[
\text{number of molecules} = \text{moles} \times 6.022 \times 10^{23} \, \text{molecules/mole}
\]
- Therefore:
\[
\text{number of molecules} \approx 0.555 \, \text{moles} \times 6.022 \times 10^{23} \, \text{molecules/mole} \approx 3.34 \times 10^{23} \, \text{molecules}
\]

Thus, there are approximately \(3.34 \times 10^{23}\) water molecules in a 10.0 g sample of H₂O.