Question

Question
Use the table of molar masses to answer the question.

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

2.049×1023
2 point 0 4 9 times 10 to the 23th power

1.251×1023
1 point 2 5 1 times 10 to the 23th power

6.022×1023
6 point 0 2 2 times 10 to the 23th power

1.503×1023
1 point 5 0 3 times 10 to the 23th power
Skip to navigation

Answer 1

To determine how many molecules of silicon dioxide (SiO₂) are in a 15-gram sample, we first need to calculate the molar mass of SiO₂.

1. **Calculate the molar mass of SiO₂:**
- Silicon (Si) has a molar mass of 28.09 g/mol.
- Oxygen (O) has a molar mass of 16.00 g/mol.
- Since there are two oxygen atoms in silicon dioxide, the molar mass of SiO₂ is:
\[
\text{Molar mass of SiO}_2 = (1 \times 28.09 \, \text{g/mol}) + (2 \times 16.00 \, \text{g/mol}) = 28.09 + 32.00 = 60.09 \, \text{g/mol}
\]

2. **Calculate the number of moles in a 15-gram sample:**
\[
\text{Number of moles of SiO}_2 = \frac{\text{mass}}{\text{molar mass}} = \frac{15 \, \text{g}}{60.09 \, \text{g/mol}} \approx 0.2497 \, \text{mol}
\]

3. **Calculate the number of molecules using Avogadro's number (\(6.022 \times 10^{23}\) molecules/mol):**
\[
\text{Number of molecules} = \text{Number of moles} \times \text{Avogadro's number} \approx 0.2497 \, \text{mol} \times 6.022 \times 10^{23} \, \text{molecules/mol}
\]

Performing the multiplication:
\[
\text{Number of molecules} \approx 0.2497 \times 6.022 \times 10^{23} \approx 1.503 \times 10^{23} \, \text{molecules}
\]

Thus, the number of molecules of silicon dioxide in a 15-gram sample is approximately:

**1.503 × 10²³ molecules** (This corresponds to the answer choice: **1.503×10²³**).