Chemical Analysis

Pure Substances and Formulations

In chemistry, a pure substance is a single element or compound, not mixed with any other substance.
In everyday language, a pure substance can mean a substance that has had nothing added to it
Pure substances have specific melting and boiling points
Impure substances melt and boil over a range of different temperatures
A formulation is a mixture that has been designed as a useful product.
In formulations, the quantity of each component is carefully measured to ensure that the product has the required properties.
Examples include: fuels, cleaning agents, paints, medicines, alloys, fertilisers, and foods.

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This is a physical process, which means no chemical reactions take place and no new substances are made
It allows us to separate substances based on their solubilities
Stationary Phase: The paper, Mobile Phase: Solvent
Method:
Use a ruler to draw a horizontal line on the chromatography paper using a pencil
Use a capillary tube to put a small spot of each food colouring (A-D) and the unknown
Pour water (solvent) into a beaker to a depth of 1cm.
Attach the paper to a glass rod using tape and place it in the beaker
Pencil line must be above the water so the ink does not wash off
Put a lid over the beaker to reduce evaporation of the solvent
Water will travel up the paper and we should mark where it stops
Calculate the Rf = Distance moved by the chemical / Distance moved by the solvent
Rf tells us the identity of the chemical
Chemicals strongly attracted to the stationary phase will not move very far

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To test for hydrogen, we insert a burning splint and should hear a squeaky pop, because of hydrogen burning quickly
To test for oxygen, we insert a glowing splint and should see the splint relight
To test for carbon dioxide, we use limewater (an aqueous solution of calcium hydroxide) and should see it turn cloudy
To test for chlorine, we insert damp litmus paper into the tube and should see it bleached and turn white

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First, place a small amount of our chemical onto a nichrome wire
Place the end of this into a blue bunsen burner flame
The colour of the flame can show us the metal ion that is present
Lithium produces a crimson flame
Sodium produces a yellow flame
Potassium produces a lilac flame
Calcium produces an orange-red flame
Copper produces a green flame
Colour of the flame test can be difficult to distinguish if there's a low concentration of it
A sample can contain a mixture of metal ions that can mask the colour of the flame
We can use flame emission spectroscopy ( instrumental method) instead, which can tell us the concentration of the ion as well
A sample of the metal ion in solution is placed into a flame and the light it gives out can be seen through the spectroscope
The spectroscope can convert the light into a line spectrum
Instrumental methods are rapid, sensitive and accurate

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If we add sodium hydroxide solution to calcium, aluminium and magnesium ions they will all produce white precipitates
We can't distinguish between these, so we add excess sodium hydroxide the aluminium precipitate redissolves
We then use a flame test to work out which one is calcium
Copper II ions react with sodium hydroxide to form a blue precipitate of copper (II) hydroxide
Iron II ions react with sodium hydroxide to form a green precipitate iron (II) hydroxide
Iron III ions react with sodium hydroxide to form a brown precipitate iron (III) hydroxide

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Testing for Carbonate Ions:
Add dilute acid to the sample
If the carbonate is present, the acid will react with the carbonate to make carbon dioxide
We should see fizzing
Bubble the gas through limewater, if it turns cloudy the carbonate is present
Testing for Halide Ions:
Add dilute nitric acid to the sample
Add dilute silver nitrate solution
They should produce a precipitate of the silver halide. Chlorine: White, Iodine: Yellow, Bromide: Cream
Testing for Sulfate Ions:
Add dilute hydrochloric acid to our sample
Add barium chloride solution
If sulfate ions are present, we should see a white precipitate formed

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