High School

A scientist has a 98.3 g sample of silicon. How many silicon atoms are in the sample?

A. \(1.72 \times 10^{23}\) atoms
B. \(2.11 \times 10^{24}\) atoms
C. \(1.69 \times 10^{25}\) atoms
D. \(6.92 \times 10^{25}\) atoms

Answer :

The number of silicon atoms that are in this sample is: B. [tex]2.11 \times 10^{23} \;atoms[/tex]

Given the following data:

  • Mass of silicon = 98.3 grams

Scientific data:

  • Avogadro's number = [tex]6.02 \times 10^{23}[/tex]
  • Molar mass of silicon = 28.09 g/mol.

To determine the number of silicon atoms that are in this sample:

First of all, we would determine the number of moles contained in 98.3 grams of silicon.

[tex]Number\;of\;moles = \frac{mass}{molar\;mass}\\\\Number\;of\;moles = \frac{98.3}{28.09}[/tex]

Number of moles = 3.4995 moles

By stoichiometry:

1 mole of silicon = [tex]6.02 \times 10^{23}[/tex] atoms

3.4995 moles of silicon = X atoms

Cross-multiplying, we have:

[tex]X = 6.02 \times 10^{23} \times 3.4995\\\\X= 2.11 \times 10^{23} \;atoms[/tex]

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Final answer:

The 98.3 g sample of silicon contains approximately 2.11 × 10²´ atoms, which is option B.

Explanation:

To calculate the number of silicon atoms in a 98.3 g sample, we need to first determine the molar mass of silicon and how many moles are in the sample. From the periodic table, the molar mass of silicon (Si) is approximately 28.1 g/mol. This means each mole of silicon comprises 6.022 × 10²³ atoms (Avogadro's number). The calculation to convert grams to moles is as follows:

  • Number of moles = mass of sample (g) / molar mass (g/mol)
  • Number of moles of silicon = 98.3 g / 28.1 g/mol ≈ 3.498 moles of Si

With the number of moles of silicon established, we can now find the number of atoms:

  • Number of atoms = number of moles × Avogadro's number
  • Number of Si atoms = 3.498 moles × 6.022 × 10²³ atoms/mol ≈ 2.11 × 10²´ atoms

Therefore, the correct answer is (B) 2.11 × 10²´ atoms of silicon in the 98.3 g sample.

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