4.3.2 Use of amount of substance in relation to masses of pure substances

Question 1

What is avogadros constant?

Answer 1

The number of atoms, ions, or molecules in a mole of a given substance. The value of the constant is 6.02 x 10^23.

Question 2

What is the formula that links mass, molecular mass and moles togethe.

Answer 2

Mass = Mr x Moles

Question 3

What is the mass of 20 moles of calcium carbonate, CaCO3

Answer 3

Mass = Mr x Moles
Mr = 100
1000 x 20 = 2000g

Question 4

State what we mean by a limiting reactant in a chemical reaction.

Answer 4

In a chemical reaction involving two reactants, it is common to use an excess of one of the reactants to ensure that all of the other reactant is used. The reactant that is completely used up is called the limiting reactant because it limits the amount of product.

Question 5

Write down the two formulae linking, concentration, mass and volume together.

Answer 5

• Concentration (g per dm^3) = Mass (g)/Volume (dm^3)
• concentration (mol per dm^3) = nr of moles/Volume (dm^3)