The Mole Concept and Stoichiometry

Question 1

what is relative atomic mass (Aᵣ)?

Answer 1

average mass of one atom of that element compared to 1/12 of the mass of one carbon-12 atom

*average mass of one atom of an element / 1/12 mass of an atom of carbon-12

Question 2

what is relative molecular mass (Mᵣ)?

Answer 2

average mass of one molecule of the substance compared to 1/12 of the mass of one carbon-12 atom

*average mass of one molecule of a substance / 1/12 mass of an atom of carbon-12

Question 3

what is relative formula mass (Mᵣ)?

Answer 3

average mass of one formula unit of the substance compared to 1/12 of the mass of one carbon-12 atom

*average mass of one formula unit of a substance / 1/12 mass of an atom of carbon-12

Question 4

how do you find percentage mass of an element in a compound?

Answer 4

(Aᵣ x no. of atoms of the element in the formula / Mᵣ of compound) x 100%

Question 5

what is a mole?

Answer 5

amount of substance that contains the same number of particles as the number of atoms in 12g of carbon-12

*one mole of any substance will always contain 6.02 × 10²³ particles of that substance (Avogadro’s constant/number)

Question 6

what are the 4 formulae to find the number of moles?

Answer 6

1) n = N / L
- N = no. of particles
- L = Avogadro’s constant (6.02 × 10²³)

2) n = m / Aᵣ or Mᵣ
- m = mass of substance (g)

3) n = v / Vₘ
- v = volume of gas/liquid
- Vₘ = molar volume (24dm³)

4) n = cv

Question 7

what is the unit for molar mass?

Answer 7

g/mol

*literally the same as Aᵣ/Mᵣ

Question 8

how do you find the concentration of a solution (g/dm³)?

Answer 8

concentration (mol/dm³) x molar mass (g/mol)

Question 9

what is stoichiometry?

Answer 9

ratio between the number of moles of reactants and the number of moles of products of the reaction

Question 10

how do you find percentage yield?

Answer 10

actual yield / theoretical yield x 100%

Question 11

how do you find percentage purity?

Answer 11

mass of pure element in sample / mass of impure sample x 100%