Question

Mass of one atom of an element is 6.645×10-²³g.How many moles of element are there in 0.320 kg?

Answer 1

total mass of the element = 0.320kg = 0.320×10³g = 320g
mass of the one element = 6.645×10^-23 g
then number of atoms = x = ?

1 atom : x atoms :: 6.645×10^-23g : 320g

x = mass of element/mass of one element
x = 320×1/6.645×10^-23
x = 48.165× 10^23

1 mole = 6.022×10^23
x mole = 48.165 × 10^23 atoms

x = 48.165 × 10^23/6.022×10^23
x = 7.998 × 10^0
x = 7.998 × 1
x = 7.998 mol

so there are 7.998 mol of atoms