Moles and Molar Mass

Question 1

What is molar mass?

Answer 1

The relative formula mass in grams, eg. CaCO3 is 100g/mol.

Question 2

What is the calculation for number of moles?

Answer 2

Moles = mass/Mr

Question 3

How can we predict the mass of PbO formed when PbCO3 thermally decomposes if we have 267g of PbCO3?

Answer 3

• Mr of PbCO3 = 267
• This gives a 1:1 ratio
• Therefore the Mr of PbO = mass of PbO
• PbO = 223g

Question 4

What would the mass of PbO be if we had 534g of PbCO3?

Answer 4

• Mr of PbCO3 = 267
• 534 / 267 = 2
• Therefore the mass would be the Mr of PbO X2
• Mass of PbO = 223 X 2 = 446g