How many formula units of Na_2SO_4 are present in a 450 g sample?

• A. 3.84 × 10^{23} formula units
• B. 2.50 × 10^{22} formula units
• C. 1.91 × 10^{24} formula units
• D. 7.89 × 10^{25} formula units

Answer: (C)

Verified step by step guidance

1. Determine the molar mass of sodium sulfate (Na_2SO_4) by summing the atomic masses of its constituent atoms: sodium (Na), sulfur (S), and oxygen (O). Use the atomic masses: Na = 22.99 g/mol, S = 32.07 g/mol, and O = 16.00 g/mol. The molar mass is calculated as \$2 \times 22.99 + 32.07 + 4 \times 16.00$ g/mol.
2. Calculate the number of moles of Na_2SO_4 in the 450 g sample using the formula: \(\text{moles} = \frac{\text{mass}}{\text{molar mass}} = \frac{450}{\text{molar mass}}\).
3. Recall that one mole of any substance contains Avogadro's number of formula units, which is \$6.022 \times 10^{23}$ formula units/mol.
4. Multiply the number of moles calculated in step 2 by Avogadro's number to find the total number of formula units: \(\text{formula units} = \text{moles} \times 6.022 \times 10^{23}\).
5. Express the final answer in scientific notation to match the format of the given options.