These are detailed Revision Notes for Topic Eight (Chemical Analysis) of AQA GCSE Chemistry. They are written by me, using a combination of class notes, text books and revision guides. I have also uploaded the other chapters in my store.
Chemical Analysis
Pure substances:
• A pure substance is a single element or compound that is not mixed with any other substances.
• Pure substances melt and boil at specific temperatures, however mixtures change state over a range of
temperatures.
• Salt water ~ freezes below 0⁰C depending how much salt is dissolved. This is used to stop ice forming on
roads in winter.
• Antifreeze ~ is mixed with water in car radiators to stop the water freezing in car radiators.
Formulations:
• A formulation is a mixture that has been designed as a useful product. It is made by mixing together
several different substances in carefully measured quantities to ensure the product has the required
properties.
Chromatography:
• Mobile phase is the solvent, stationary phase is the paper
• Substances more soluble in the solvent will move further up the paper.
• Substances more attracted to the paper will move a shorter distance
• Chromatography separates mixtures into their constituent components. It can be used to identify
artificial colours by comparing them to the results obtained from known substance.
"#$ &'(")*+$ "#$ (,-" ".)/$00$&
• 𝑅! = "#$ &'(")*+$ "#$ (-0/$*" ".)/$00$&
• An 𝑅! value is the ratio between the distance travelled by the dissolved substance and the distance
travelled by the solvent.
Gas Tests:
• Oxygen, O₂
o If you put a glowing splint inside a test tube containing oxygen, the glowing splint will relight.
• Chlorine Cl₂
o Chlorine turns damp litmus paper white.
• Carbon Dioxide, CO₂
o Bubbling carbon dioxide through a solution of limewater causes the solution to turn cloudy
• Hydrogen, H₂
o If you hold a lit splint at the end of a test tube of hydrogen you will get a squeaky pop sound.
Test for positive ions (cations):
Flame test:
• Some positive ions give distinctive colours in flame tests. A simple way to do a flame test is to dip a
damp splint into the compound and then put the splint into a roaring Bunsen flame.
o Lithium, 𝐿𝑖 1 - crimson-red flame
o Sodium, 𝑁𝑎1 - yellow-orange flame
o Potassium, 𝐾 1 - lilac flame
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