Define mass number
The total number of protons and neutrons in an atom
Atoms of the same element that have different numbers of neutrons but the same number of protons
How is the relative atomic mass calculated?
An atom’s mass is compared with an atom of carbon-12’s. An average value for the isotopes of the element
Define a mole
The relative formula mass of a substance, in grams
Formula for working out the percentage of an element in a compound
mass of element ÷ total mass of compound x 100
Define empirical formula
The simplest whole number ratio of a compound
Working out empirical formulae
Percentage to mass (skip if mass given): imagine 100g
Moles: ÷ each mass by its Ar
Simplify ratio: ÷ by smallest number
What might cause the yield of a reaction not to be 100%?
Reactants may be reversible
Products may be unexpected
Product lost in handling or left in apparatus
Impurity of reactants
More than one product produced so difficult to separate
Formula for percentage yield
Percentage yield = amount of product produced ÷ maximum amount of product possible x 100%
How to work out percentage yield
Symbol equation and balance
Mr of reactant(s) and useful product(s)
Relate to reactant(s) mass and find max product
Substitute in formula
Why maximise yield and minimise energy waste?
Wastes less material and energy
Conserves limited resources and reduces pollution from fossil fuels as energy sources
Why might be additives be present in food?
To improve taste, appearance or shelf life
How do food scientists analyse foods to identify additives?
How might compounds in a mixture be separated and then how can they be identified?
Gas chromatography and then mass spectrometry
Why is argon often used as a carrier gas in mass spectrometry?
It is inert and cheaper than other inert gases
Define retention time
Time taken for compounds to pass through the mass spectrometry column
What makes instrumental analysis useful?
It is accurate, sensitive and rapid and is particularly useful when the amount of a sample is very small
What does a molecular ion peak show in a mass spectrum?
The Mr of the substance