3.1.2 - AMOUNT OF SUBSTANCE

Mole definition

Unit of measurement of amount of substance

Avogadro’s constant

Number of particles in a mole

Formula for number of particles

Num of particles = Moles * Avogadro’s constant

Formula for moles

Moles = mass (g) / Mᵣ

Formula for concentration of solution

Moles = conc. (mol dm⁻³) * volume (dm³)

Ideal gas equation

pV = nRT

What does each symbol in ideal gas equation stand for?

p = pressure (Pa)

V = volume (m³)

n = num of moles

R = gas constant

T = temp. (K)

Empirical formula definition

Smallest whole number ratio of atoms of each element in a compound

Example empirical formula calculation

Molecular formula

Gives the actual numbers of atoms of each element in a compound

Relationship between molecular and empirical formula

Molecular formula is made up of a whole number of empirical units

Ionic equations

• Can be written for any reaction involving ions that happens in solution

• Only includes reacting particles (and the products they form)

• Charges must be balanced on either side

What is a spectator ion?

Ion that’s present in reaction mixture, but not involved in reaction

What is theoretical yield?

Mass of product that should be formed in reaction - assuming no chemicals are lost in process

Calculated using masses of reactants and balanced equation

Actual yield is always ____ than theoretical yield

less

Reasons why actual yield may be less than theoretical

• Not all reactants react fully

• Some reactants lost, e.g. lost during transfer between containers

Formula for percentage yield

Percentage yield = Actual yield / Theoretical yield * 100

Atom economy definition

A measure of the proportion of reactant atoms that become part of desired product (rather than by-products)

Formula for atom economy

% atom economy = Mᵣ of desired product / sum of Mᵣ of all reactants * 100

Example atom economy calculation

Advantages of processes with high atom economies

• Better for environment - less waste

• More sustainable - make more efficient use of raw materials

• Less expensive - less money spent on separating waste from desired product