A 0.244 g sample of calcium carbonate, CaCO3 was recovered from a sample of hard water. How many formula units of CaCO3 were in the sample?

Here's how to calculate it:

1. Calculate the molar mass of CaCO3:

• Ca: 40.08 g/mol
• C: 12.01 g/mol
• O: 3 * 16.00 g/mol = 48.00 g/mol
• Molar mass of CaCO3 = 40.08 + 12.01 + 48.00 = 100.09 g/mol

2. Convert the mass of CaCO3 to moles:

• Moles = Mass / Molar mass
• Moles = 0.244 g / 100.09 g/mol = 0.0024378 mol

3. Convert moles to formula units using Avogadro's number (6.022 x 10^23 formula units/mol):

• Formula units = Moles * Avogadro's number
• Formula units = 0.0024378 mol * 6.022 x 10^23 formula units/mol
• Formula units = 1.46746 x 10^21 formula units

4. Round to the appropriate number of significant figures (3, based on 0.244 g):

• Formula units = 1.47 x 10^21 formula units