Chemistry - purity, formulations and chromatography

what is a pure substance

a pure substance is a single element or compound, not mixed with any other substance

what can be used to distinguish between pure substances and mixtures

melting and boiling points for pure elements and compounds are very specific temperatures. melting and boiling data can be used to distinguish.

what is a formulation

a mixture that has been designed as a useful product. many products are complex mixtures in which each chemical has a particular purpose.

how are formulations made

they are made by mixing the components in carefully measured quantities to ensure that the product has the required properties

examples of formulations

fuels, cleaning agents, paints, medicines, fertilisers and foods.

what is chromatography used for

it can be used to separate mixtures and can give information to help identify substances. it is a physical process - no chemical reactions and no new compounds or anything are made

hat is R_f value

the ratio of the distance moved by a compound ti the distance moved by the solvent

R_f value equation

R_f = distance moved by substance/distance moved by solvent

paper chromatography

1. take a piece of chromatography paper and draw a pencil line near the bottom of the paper.

2. put a dot of your first colour on the pencil line and do the same with your second colour.

3. place the bottom of the paper into a solvent (a liquid that will dissolve substances)

4. the solvent makes its way up the paper and dissolves the ink in the two coloured dots, so the ink is carried up the paper dissolved in the solvent

5. if there is only one spot of colour, we can determine that that colour is a single, pure colour. However, if the colour has separated into two or more different colours, we can see that the colour is a mixture of two or more different colours

stationary and mobile phase

paper - stanionary phase because it does not move

solvent - mobile phase, because it does move

why does paper chromatography work

because different substances have different solubilities. a more soluble substance is more attracted to the mobile phase (the solvent) than a less soluble substance, so a more soluble substance travels further along the paper than a less soluble substance,

what is the result of chromatography analysis called

a chromatogram

test for hydrogen

the test for hydrogen is using a burning splint help at the open end of a test tube of the gas. Hydrogen burns rapidly with a pop sound

AKA SQUEEKY POP TEST

test for oxygen

the test for oxygen uses a glowing splint inserted into a test tube of the gas. The splint relights in oxygen.

test for carbon dioxide

the test for carbon dioxide uses an aqueous solution of calcium hydroxide (lime water). When carbon dioxide is shaken with or bubbled through limewater the limewater turns milky (cloudy)

test for chlorine

the test for chlorine uses litmus paper. When damp litmus paper is put into chlorine gas the litmus paper is bleached and turns white.