How many atoms are in 127 g of calcium?

Question

How many atoms are in 127 g of calcium?

Answer 1

Hi Nicole,

For a question like this, moles and Avogadro's number are very important.

First, convert the mass of Ca to moles, by using the molar mass of Ca on the periodic table.

The periodic table shows that 1 mole of Ca = 40.078 g of Ca

We have 127 g of Ca and we need to find out how many moles that is based on the relationship in bold above.

127 g x 1 mol/40.078 g = 3.17 mols of Ca

After we have found the moles of Ca, we can use the relationship between moles and Avogadro's number:

1 mole of atoms = 6.022 × 10²³ atoms

From our previous answer, we have 3.17 mols of Ca and we're trying to find out how many atoms there in that.

So, 3.17 mols × 6.022 × 10²³ atoms/1 mol = 1.91 × 10²⁴ atoms