Question

Use the table of molar masses to answer the question.

Molar Mass (g/mol) of Silicon and Oxygen
Element Molar Mass (g/mol)
silicon 28.09
oxygen 16.00
How many molecules of silicon dioxide (SiO2) are there in a 15-gram sample?

(1 point)
Responses

1.251×10231 point 2 5 1 times 10 to the 23th power

2.049×10232 point 0 4 9 times 10 to the 23th power

6.022×10236 point 0 2 2 times 10 to the 23th power

1.503×1023

Answer 1

To find how many molecules of silicon dioxide (SiO₂) are present in a 15-gram sample, follow these steps:

1. Calculate the molar mass of SiO₂:
- Molar mass of Si = 28.09 g/mol
- Molar mass of O = 16.00 g/mol
- For 2 oxygen atoms: 2 × 16.00 g/mol = 32.00 g/mol
- Total molar mass of SiO₂ = 28.09 g/mol + 32.00 g/mol = 60.09 g/mol

2. Determine the number of moles in the 15-gram sample:
\[
\text{Number of moles} = \frac{\text{mass (g)}}{\text{molar mass (g/mol)}} = \frac{15 \, \text{g}}{60.09 \, \text{g/mol}} \approx 0.2496 \, \text{moles}
\]

3. Use Avogadro's number (approximately \(6.022 \times 10^{23}\) molecules/mol) to find the number of molecules:
\[
\text{Number of molecules} = \text{Number of moles} \times \text{Avogadro's number}
\]
\[
\text{Number of molecules} \approx 0.2496 \, \text{moles} \times 6.022 \times 10^{23} \, \text{molecules/mol} \approx 1.503 \times 10^{23} \, \text{molecules}
\]

Thus, the answer is:
1.503×10²³ (1.503 times 10 to the 23rd power).