Question

How many representative particles are in a 53.79 gram sample of SrCO3?

Answer 1

Remember representative particles/ molecules/ atoms are all the same 

convert from grams -> moles 

hope this clears thing

Answer 2

To find the number of particles, you need to use Avogadro's number

6.02 x 10^23= 1 mol

As you can see, before we can convert to particles, we need moles. So let's first convert grams to moles using the molar mass (molecular weight) of the compound

molar mass of SrCO₃= 87.6 + 12.0 + (3 x 16.0)= 147.6 g/mol

53.79 g (1 mol/ 147.6 g)= 0.364 mol

now let's convert moles to particles using Avogadro's number

0.364 mol SrCO₃ (6.02x10^23/ 1 mol)= 2.19 x 10^23