amount of substance: content

Question 1

equation linking
number of particles
number of moles (AoS)
avogadro constant

Answer 1

number of particles = moles x avogadro constant
N = n * 6.02x10²³

Question 2

equation linking
mass
relative mass
moles

Answer 2

mass = moles * relative mass
m = n * Mᵣ

mass in grams

Question 3

equation linking
mass
volume
density

Answer 3

mass = density * volume
m = ρ V

density in grams per [unit volume]
can use for all states (solid liquid gas)

Question 4

equation linking
moles
volume

Answer 4

volume = moles * 24
V = 24 n

volume in dm³
GAS ONLY

Question 5

ideal gas equation

Answer 5

pressure * volume = moles * gas constant * temperature
PV=nRT

pressure in Pa
volume in m³
temperature in K
R= 8.31K⁻¹mol⁻¹

Question 6

equation linking
concentration
[moles/mass]
volume

Answer 6

[moles/mass] = conc * vol

concentration in [mol/g]dm⁻³
volume in dm³
mass in g

Question 7

equation linking
concentration in moles
concentration in mass

Answer 7

conc in gdm⁻³ = conc in moldm⁻³ * Mᵣ

Question 8

limiting reagent calculations

Answer 8

use empirical formula ratio to find which reactant is limiting and which is in excess
use the amount of the limiting reagent as the base for calculations

[don’t forget the reagent in excess as a product]

Question 9

reacting gas volumes under the same condition

Answer 9

at a fixed temperature and pressure, 1mol of all gases will occupy the same volume
changes in volume are only affected by changes in the number of moles

don’t always need to convert: work with ratios

PV = nRT P,R,T constant
V ∝ n
V₁ : n₁ = V₂ : n₂

Question 10

atom economy equation

Answer 10

% atom economy = (Mᵣ of useful product) ÷ (Mᵣ of all products)

Question 11

how to improve atom economy of a reaction

Answer 11

• find uses for by-products
• use different reactants (with lower Mᵣs)

benefits: costs less and is more environmentally sustainable

Question 12

reasons why percentage yield is often less than 100%

Answer 12

• reaction incomplete
• side reactions occurred
• impure reactants
• loss of product
  
  • washing
  • recrystallisation
  • during transfer between equipment

Question 13

percentage yield equation

Answer 13

% yield = (experimental mass of product) ÷ (theoretical maximum mass of product)

Question 14

percentage purity equation

Answer 14

% purity = (mass of pure substance) ÷ (mass of impure substance)

use stoichiometry/molar equations if needed