Question

Calculate the number of moles in 13.5 g of Mg(NO3)2.
Responses

0.0765 mol
0.0765 mol

1.5 mol
1.5 mol

148 mol
148 mol

0.0912 mol

Answer 1

To calculate the number of moles in 13.5 g of Mg(NO₃)₂, we first need to determine its molar mass.

1. Calculate the atomic masses of the elements in Mg(NO₃)₂:
- Magnesium (Mg): 24.31 g/mol
- Nitrogen (N): 14.01 g/mol
- Oxygen (O): 16.00 g/mol

2. Calculate the molar mass of Mg(NO₃)₂:
- There is 1 Mg, 2 N, and 6 O in Mg(NO₃)₂:
\[
\text{Molar mass of Mg(NO}_3\text{)}_2 = (1 \times 24.31 \text{ g/mol}) + (2 \times 14.01 \text{ g/mol}) + (6 \times 16.00 \text{ g/mol})
\]

\[
= 24.31 + 28.02 + 96.00 = 148.33 \text{ g/mol}
\]

3. Use the molar mass to find the number of moles in 13.5 g of Mg(NO₃)₂:
\[
\text{Number of moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} = \frac{13.5 \text{ g}}{148.33 \text{ g/mol}}
\]

\[
\approx 0.0911 \text{ mol}
\]

Therefore, rounding to three significant figures, the number of moles in 13.5 g of Mg(NO₃)₂ is approximately **0.0912 mol**.

So the correct answer is:
**0.0912 mol**.