Purity and Formulations

Question 1

what is chemical analysis (analytical chemistry)?

Answer 1

the science of separating, identifying and quantifying different substances and then instruments and methods we use to do this

Question 2

what is a ‘chemically pure’ substance?

Answer 2

a single element or compound that hasn’t been mixed with any other substance e.g. pure water only contains water molecules

Question 3

how can impurities affect the melting and boiling points of the sample?

Answer 3

• lower the melting point.
• increase the boiling point
• increase the range over which a substance melts or boils

Question 4

what physical test can you do to check that a substance is pure?

Answer 4

heat it until it melts or boils. If it melts or boils at a specific temperature (rather than over a range of temperatures) then it is pure

Question 5

what is a formulation?

Answer 5

formulations are mixtures that have been prepared using a specific formula

Question 6

what are formulations made from?

Answer 6

formulations are made from precise amounts of different components, and each component has a particular function. Different components are always present in the same proportion and each of the different components might contribute to a different property

Question 7

examples of substances that might contain a formulation

Answer 7

• medicines
• cleaning agents
• fuels
• paints
• alloys
• fertilisers
• food and drink
• cosmetics

Question 8

what is a mixture?

Answer 8

contains 2 or more elements or compounds that are not chemically combined together. The chemical properties of each substance in the mixture are unchanged

Question 9

how can you use melting point to distinguish between pure substances and mixtures?

Answer 9

pure substances have a sharp exact melting point whereas mixtures melt over a range of temperatures since they consist of several elements/compounds

Question 10

what do impure substances not have?

Answer 10

specific melting and boiling points