Chemical Analysis Flashcards
(29 cards)
What is a pure substance in chemistry?
A single element or compound that has not been mixed with any other substance
How can we distinguish pure substances from mixtures?
Pure elements and compounds melt and boil at specific temperatures. The melting and boiling point data can be used to distinguish
What is a pure substance in everyday language?
A substance that has had nothing added to it, so it is unadulterated and in its natural state e.g. pure milk
What is a formulation?
A mixture that has been designed as a useful product, They are often complex mixtures where each chemical has a particular purpose
How are formulations made?
By mixing the components in carefully measured quantities to ensure that the product has the required properties.
Give examples of formulations
Fuels, cleaning agents, paints, medicines, alloys, fertilisers and foods
What is chromatography used for?
To separate mixtures and to give info to help identify substances
What are the two phases involved in chromatography?
The mobile phase and the stationary phase
What does the separation of substances in chromatography depend on?
The distribution between the stationary and mobile phases
What is expressed as an Rf value?
The ratio of the distance moved by a compound (centre of the spot to origin) to the distance moved by the solvent
Give the formula for the Rf value
What from chromatography can be used to identify the compounds in a mixture?
Different compounds have different Rf values in different solvents.
How can chromatographic methods can be used to distinguish pure substances from impure substances?
Compounds in mixture may separate into different spots depending on the solvent, but pure compounds will produce a single spot in all solvents.
What is the test for hydrogen?
Use a burning splint held at the open end of a test tube of the gas. Hydrogen will burn rapidly with a pop sound
What is the test for oxygen?
Use a glowing splint inserted into a test tube of the gas. The splint will relight if oxygen is present
What is the test for carbon dioxide?
Use an aqueous solution of calcium hydroxide (lime water). When it is shaken with or bubbled through limewater, it will turn milky (cloudy)
What is the test for chlorine?
Damp litmus paper is bleached and turns white when inserted into chlorine gas
What are flame tests used for?
Used to identify some metal ions. Lithium, sodium, potassium, calcium, and copper compounds all produce distinctive colours in flame tests
What are the colours from flame tests for each cation?
lithium compounds result in a crimson flame
sodium compounds result in a yellow flame
potassium compounds result in a lilac flame
calcium compounds result in an orange-red flame
copper compounds result in a green flame.
What happens if a flame test is used on a mixture of ions?
Some flame colours can be masked
What is sodium hydroxide used for?
Can be used to identify some metal ions
What do solutions of aluminium, calcium and magnesium ions form in NaOH?
They form white precipitates with NaOH solution. Only aluminium hydroxide precipitate dissolves in excess NaOH
What do solutions of copper II, iron II and iron III ions form in NaOH?
They form coloured precipitates
Copper II forms a blue precipitate
Iron II forms a green precipitate
Iron III forms a brown precipitate
What do carbonates react with dilute acids to form?
A salt, water and carbon dioxide gas. The carbon dioxide can be identified with limewater
