Question

How many molecules of silicon triiodide (SiI₃) are in 450 grams?

Answer 1

To find the number of molecules of silicon triiodide (SiI₃) in 450 grams, we first need to determine the molar mass of SiI₃.

1. **Calculate the Molar Mass of SiI₃:**
- Silicon (Si) has an atomic mass of about 28.09 g/mol.
- Iodine (I) has an atomic mass of about 126.90 g/mol.
- Since SiI₃ contains one silicon atom and three iodine atoms, the total molar mass can be calculated as follows:

\[
\text{Molar mass of SiI₃} = (1 \times 28.09 \, \text{g/mol}) + (3 \times 126.90 \, \text{g/mol})
\]

\[
= 28.09 \, \text{g/mol} + 380.70 \, \text{g/mol}
\]

\[
= 408.79 \, \text{g/mol}
\]

2. **Calculate the Number of Moles in 450 grams:**
To find the number of moles, we use the formula:

\[
\text{Number of moles} = \frac{\text{mass (grams)}}{\text{molar mass (g/mol)}}
\]

\[
\text{Number of moles} = \frac{450 \, \text{g}}{408.79 \, \text{g/mol}} \approx 1.1 \, \text{moles}
\]

3. **Calculate the Number of Molecules:**
To find the total number of molecules, we multiply the number of moles by Avogadro's number (\( N_A \approx 6.022 \times 10^{23} \, \text{molecules/mol} \)):

\[
\text{Number of molecules} = \text{Number of moles} \times N_A
\]

\[
\text{Number of molecules} \approx 1.1 \, \text{moles} \times 6.022 \times 10^{23} \, \text{molecules/mol}
\]

\[
\approx 6.63 \times 10^{23} \, \text{molecules}
\]

Therefore, there are approximately \( 6.63 \times 10^{23} \) molecules of silicon triiodide (SiI₃) in 450 grams.