Question

How many moles are there in 10.8 g of water? (Hint: You need the Mr of water)

Answer 1

To calculate the number of moles in a given mass of water, you need to know the molar mass (Mr) of water (H₂O).

1. **Calculate the Molar Mass of Water (H₂O)**:
- Hydrogen (H): approximately 1.01 g/mol
- Oxygen (O): approximately 16.00 g/mol

Molar mass of water:
\[
\text{Mr of H₂O} = (2 \times 1.01 \, \text{g/mol}) + (1 \times 16.00 \, \text{g/mol}) = 2.02 \, \text{g/mol} + 16.00 \, \text{g/mol} = 18.02 \, \text{g/mol}
\]

2. **Calculate the number of moles**:
Use the formula:
\[
\text{Number of moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}}
\]

For 10.8 g of water:
\[
\text{Number of moles} = \frac{10.8 \, \text{g}}{18.02 \, \text{g/mol}} \approx 0.599 \, \text{moles}
\]

So, there are approximately **0.599 moles** of water in 10.8 g.