Question

How you calculate the mass of a substance when you only know the number of moles.

Then explain how you calculate the number of moles in a substance when you only know the mass.

Answer 1

Formulae: mass = number of moles × Mr or Ar

The substance may be a compound or an element

so if it is a compound, find its Mr

it is an element find its Ar in the periodic table

the original formula is that:

number of moles = mass ÷ Mr or Ar

so if they ask for mass, make make mass the subject of formula

if they ask for number of moles, make number of moles the subject of formula

then replace the value......