C12: Chemical Analysis Flashcards
What is a pure substance in chemistry?
A single element or compound, not mixed with any other substance
What can be used to distinguish pure substances from mixtures?
Melting and boiling points
What is a pure substance in everyday language?
A substance that has had nothing added to it
What is a formulation?
A mixture that has been designed as a useful product
How are formulations made?
By mixing the components in carefully measure quantities to ensure that the product has the required properties
What 7 things to formulations include?
Fuels, cleaning agents, paints, medicine, alloys, fertilisers and food
Give 2 reasons why chromatography is useful
It can separate mixtures and can give information to help identify substances
What does the separation of mixtures depend on?
The distribution of substances between the phases
What is the Rf value in words?
The ratio of the distance moved by a compound to the distance moved by a solvent
What is the formula for the Rf value?
Distance by substance/distance by solvent
How can you identify a pure substance using paper chromatography?
If it produces a single spot in all solvents
What is the test for hydrogen?
The use of a burning splint held at the open end of the test tube of the gas. Hydrogen burns rapidly with a squeaky pop sound
What is the test for oxygen?
The use of a glowing splint is inserted into a test tube of gas. The splint relights in oxygen
What is the test for carbon dioxide?
The use of an aqueous solution of calcium hydroxide (limewater). When carbon dioxide is shaken with or bubbled through limewater, the limewater turns milky
What is the test for chlorine?
The use of damp litmus paper being put into chlorine gas. It is bleached and turns white
What are flame tests used for?
To identify some metal ions (cations)
What colour is the flame when lithium compound is used?
Crimson red
What compound produces a yellow flame?
Sodium
What colour is the flame when calcium compound is used?
Orange-red
What compound produces a lilac flame?
Potassium
What colour is the flame when copper compound is used?
Green
What elements in sodium hydroxide form a white precipitate?
Aluminium, calcium and magnesium
What happens to aluminium hydroxide in excess sodium hydroxide?
The precipitate dissolves
What colour is the copper(II) precipitate when sodium hydroxide is added in excess?
Blue
What element forms a green precipitate when sodium hydroxide is added in excess?
Iron (II)
What colour is the iron (III) precipitate when sodium hydroxide is added in excess?
Brown
What 2 things react to form a salt, carbon dioxide gas and water?
Carbonates and dilute acids
What is the test for carbonate ions?
Add dilute hydrochloric acid and take gas produced. Run through limewater to observe carbon dioxide production
What is the test for sulfate ions?
Adding dilute hydrochloric acid, removing carbonate and sulfite ions. Add barium chloride solution to produce a white precipitate
What is the test for halide ions?
Add dilute nitric acid to remove impurities. Add silver nitrate afterwards so that the silver can react with the halide ions, producing a precipitate
What colour is the precipitate from silver chloride?
White
What compound’s precipitate is cream?
Silver bromide
What colour is the precipitate from silver iodide?
Yellow
In paper chromatography, how would you know if any of the chemicals are soluble in the solvent?
Then they won’t be able to dissolve and move up the paper
What is the mobile phase?
The solvent used
What is the stationary phase?
The paper
How do impurities affect melting and boiling points?
They decrease MP but increase BP
What is the main advantage of flame emission spectroscopy?
The line spectrum shows lines for all elements of a compound
What are advantages of manual methods, i.e. flame tests?
Basic and cheap
What are advantages of instrumental methods?
Accurate, sensitive and very fast
