1) The number of moles present in a given mass of a substance can be found by dividing the mass in grams by the Ar or Mr. Calculate the number of moles in:

a 6 g of C

b 48 g of Mg

c 8 g of O2

d 170 g of NH3

e 45 g of H2O

f 176 g CO2.

2 Calculate the mass of:

a 20 moles of Fe

b 2 moles of H2SO4

c 0.5 moles of CO2

d 5 moles of H2O

e. 0.1 mole of Na2CO3.

3 How many atoms are there in:

a 23 g of Na?

b 12 g of Mg?

Extension

1 One mole of a substance contains the same number of atoms or molecules as one mole of any other substance.

a Which contains more atoms: 56 g of Fe or 16 g of S? Show your working.

b Which contains more molecules: 340 g of NH3 or 90 g of H2O? Show your working.

c How many more atoms are there in 48 g of C compared to 48 g of Mg? Explain your answer.

d Explain why 2 g of H2 contains more molecules than 2 g of O2.

2 Calculate which substance in the following pairs is heavier:

a 1 mole of NaCl or 1 mole of Na2CO3

b 0.5 moles of Mg or 5 moles of H2

c 10 moles of He or 1.5 moles of O2.