How many atoms are in 19.1 g of potassium oxide (K2O)?

Answer 1

Each molecule (formula unit) of K2O contains 3 atoms (2 K atoms and 1 O atom). So, if we can find the number of molecules we have, we can then find number of atoms (3 x as many).

To find the number of molecules, we first find number of moles using molar mass of K2O of 94.20 g/mol; and then use Avogadro's number to convert to molecules (formula units):

19.1 g K2O x 1 mol K2O / 94.20 g = 0.2028 moles K2O

0.2028 moles K2O x 6.022x10²³ molecules / mol = 3.37x10²¹ molecules/formula units

Recalling that each molecule (formula unit) contains 3 atoms, we can now find the number of atom...

3.37x10²¹ molecules x 3 atoms/molecule = 1.01x10²² atoms