Question

Calculate the number of O atoms in 0.0672 g of CaSO₄ · 2H₂O.

Answer 1

To find the number of oxygen atoms in 0.0672 g of CaSO₄ · 2H₂O, determine the moles of compound, calculate the moles of oxygen based on the formula, and multiply by Avogadro's number. This results in approximately 9.38 × 10²19 oxygen atoms in the sample.

Step-by-step explanation:

To calculate the number of oxygen atoms in a sample of CaSO₄ · 2H₂O, follow these steps:

1. Determine the molar mass of CaSO₄ · 2H₂O by adding together the atomic masses of each atom in the formula.
2. Convert the mass of the sample to moles using the formula: moles = mass (g) / molar mass (g/mol).
3. Use the fact that one mole of CaSO₄ · 2H₂O contains 4 moles of oxygen (1 from sulfate and 3 from the two water molecules) to find the total moles of oxygen.
4. Multiply the moles of oxygen by Avogadro's number (6.022 × 10²23) to find the number of oxygen atoms.

The molar mass of CaSO₄ · 2H₂O is (1×40.08) + (1×32.07) + (4×16.00) + (2×1.01) + (2×18.02) = 172.17 g/mol. Using the provided sample mass:

• 0.0672 g × (1 mol/172.17 g) = 0.000390 moles of CaSO₄ · 2H₂O.
• 0.000390 moles × 4 moles O = 0.00156 moles of O.
• Number of O atoms = 0.00156 moles × (6.022 × 10²23 atoms/mol) = 9.38 × 10²19 atoms of O.