Question

Calculate the number of moles in each of the following cases:
a) 3.2g of oxygen
b) 3.011x23 molecules of CO2
c) 11.2ltr of N2 at STP

Answer 1

a) if oxygen gas, then moles =3.2/32 =0.1
b) 6.022 x 10^23 =1 mole
so 3.011 x 10^23 = 1/2 =0.5 mole
c) 22.4 ltr =1 mole
so 11.2 ltr has 11.2/22.4 =1/2 = 0.5 mole

Answer 2

1)Number of moles=mass/mol. Mass
=3.2/16
=1/5
=0.2 moles

2)Number of moles=number of atoms or molecules/Avagadro's number
Avagadro's number=6.022*10^23
=3.011*10^23/6/022*10^23
=1/2
=0.5 moles

3)Number of moles=volume(litres) /22.4
=11.2/22.4
=1/2
=0.5 moles