Topic 8 - Chemical Analysis Flashcards
What is a pure substance?
A single element or compound, not mixed with any other substance
What is significant about the melting and boiling point of pure elements?
They melt and boil at specific temperatures so can be distinguished by this data
What is a formulation?
A mixture that has been designed as a useful product
How are formulations made?
By mixing the components in carefully measured quantities to insure that the product has its required properties
Give examples of formulations
Fuel, cleaning agents, paint, medicines, alloys, fertilisers, foods
What are complex mixtures?
Many products are complex mixtures in which each chemical has a particular purpose
What is chromatography used for?
To separate mixtures and give information to help identify substances
What are the phases involved in chromatography?
The stationary phase and a mobile phase
What does separation by chromatography depend on?
The distribution of substances between the phases
What is a compounds Rf value?
The ratio of the distance moved by a compound to the distance moved by the solvent
Why can you identify a compound from its RF value?
Different compounds have different Rf values in different solvents
What happens to the compounds in a mixture during chromatography?
They may separate into different spots depending on the solvent
What happens to a pure compound during chromatography?
It will produce a single spot in all solvents
What is the test for hydrogen?
Hold a burning splint at the end of an open test tube - hydrogen burns rapidly with a pop sound
What is the test for oxygen?
Insert a glowing splint into a test tube – the splint relights in oxygen
What is the test for carbon dioxide?
Use an aqueous solution of calcium hydroxide (lime water) – when carbon dioxide is shaken with or bubbled through limewater it turns cloudy
What is the test for chlorine?
When damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white
What can flame tests be used for?
To identify some metal ions (Cations)
What colour does lithium compounds go during a flame test?
Crimson
What colour does sodium compounds go in a flame test?
Yellow flame
What colour do potassium compounds go in flame tests?
Lilac
What colour do calcium compounds go in flame tests?
Orange – red flame
What colour do copper compounds go in a flame test?
Green
What happens if a sample containing a mixture of ions is used for a flame test?
Some flame colours can be masked
