Calculations

Question 1

Relative isotopic mass

Answer 1

The mass of an atom of a particular isotope on the scale where one atom of C-12 has a mass of exactly 12
AKA mass number

Question 2

Relative atomic mass (Ar)

Answer 2

The weighted average mass of all the atoms in a normal isotopic sample of the element on the scale where 1 atom of C-12 has a mass of exactly 12
AKA mass number

(% isotope 1 x mass isotope 1) + (% isotope 2 x mass isotope 2) / 100

Question 3

Relative molecular mass (Mr)

Answer 3

Mr of a covalent substance. It is the mass of 1 molecule relative to 1/12 the mass of one atom of C-12

E.g. Cl2 = 71

Question 4

Relative formula mass (Mr)

Answer 4

Mass of an ionic substance formula unit relative to 1/12 the mass of one atom of C-12

E.g. Na2CO3=106

Question 5

Mole

Answer 5

The amount of a substance that contains the same number of particles as there are atoms of carbon in 12g of C-12
Represents 6.022x10^23 (Avogardro’s constant); the number of atoms per mole

Question 6

Molar mass = Mr

Answer 6

Molar mass of a compound is the mass of 1 mole of that compound
One mole of a substance (g/mol) has a mass = to the Mr of the substance
E.g. molar mass MgCl2 = 95.3 g/mol

Question 7

Empirical formula

Answer 7

Simplest formula of a substance which shows the ratio of the numbers of atoms or ions in each element present

(1) Molecular –> empirical formula
(2) n = (molecular mass/empirical formula mass) x empirical formula

Question 8

Percentage yield

Answer 8

Theoretical yield = mass of product/reactant
Theoretical yield = (Mr product / Mr reactant) x amount of yield
% yield = (mass of product/max theoretical yield) x 100

Question 9

Atom economy

Answer 9

Determines efficiency of a reaction in terms of how many atoms of starting material are converted into useful product

Atom economy = mass of required product / total mass of reactants
Atom economy = molar mass of required products / total molar mass of reactants

Question 10

Stoichiometry

Answer 10

The study and calculation of quantitative relationships between reactants and products in chemical reactions

Question 11

Molarity

Answer 11

The concentration of a substance in solution, expressed as the number moles of solute per L of solution

Question 12

Molality

Answer 12

The concentration of a substance in solution, expressed as the number of moles of solute per kg of solvent