IGCSE Chemistry Revision

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Key points for Cambridge IGCSE Chemistry Paper 6

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1 Precautions
1.1 For poisonous gases (toxicity of gas)
1.1.1 Fume cuboard
1.1.2 Well ventilated room Prevents burning of a substance
1.1.3 e.g. Nitrogen Dioxide, Ammonia, Bromine
1.2 Repeat and take averages
1.3 Wear goggles, lab coat and tie hair back
1.4 When heating alcohol, a water bath should be used because fire will be produced if touched by a lighted splint
2 Common Variables
2.1 Concentration
2.2 Volume
2.3 Surface Area
2.4 Mass
2.5 Temperature
3 Exam Technique
3.1 Independent variable (the one you change) goes on x-axis and the dependent on y-axis
3.2 For manufacturing errors, look carefully at apparatus (e.g. burettes without taps)
3.3 Don't round values in titration or mole questions
4 Tests
4.1 For water
4.1.1 Add anhydrous Copper(II) Sulphate (white to blue)
4.1.2 Add anhydrous Cobalt(II) Chloride (blue to pink)
4.2 For alkenes and alkanes
4.2.1 Alkenes: Add (if liquid) or pass through (if gas) bromine water and shake (brown to colourless)
4.2.2 Alkanes: (remain orange/brown)
4.3 For purity of substance
4.3.1 Test melting/boiling point and compare to correct value
4.4 Cation/Anion Tests (link)


4.5 For hydrochloric acid
4.5.1 Add silver nitrate (white ppt. formed)
5 Gas Collection
5.1 Upward delivery
5.1.1 Gases less dense than air
5.1.2 e.g. Hydrogen, Ammonia
5.2 Downward delivery
5.2.1 Gases more dense than air
5.2.2 e.g. Carbon Dioxide
5.3 Displacement of water method
5.3.1 Insoluble gases
5.3.2 e.g. Methane
6 Experiments
6.1 Crystallisation
6.1.1 Heat till point of crystallisation, allow to cool slowly, filter and dry Place a stirring rod in solution and if crystals form on it, it's the point of crystallisation
6.1.2 Crystallisation is the formation of solid crystals of a substance by precipitating it out from a staurated solution
6.2 Fermentation
6.2.1 Glucose and yeast used (yeast contains enzymes) 37 degrees is optimum for enzymes Reaction might stop due to an excess in conc. of alcohol, the yeast dies or Glucose finishes up
6.2.2 Bung is used to let Carbon Dioxide out and prevent entry of Oxygen Oxygen would oxidise the alcohol to Carboxylic Acid and affect anaerobic respiration
6.3 Chromotography
6.3.1 Spray locating agent if colourless dye (such as amino acids and sugars) RF = distance moved by dye/distance moved by solvent
6.4 Electrolysis
6.4.1 Concentration promotes the discharge of ions further down the reactivity series because their compounds are stable
6.4.2 Suitable electrodes: Graphite/Carbon/Steel
6.5 If on heating condensation occurs, the solid is hydrated
7 Agents
7.1 Oxidising
7.1.1 Acidified Potassium Manganate(VII) (purple to colourless)
7.1.2 Acidified Potassium Dichromate(VI) (orange to green)
7.2 Reducing
7.2.1 All metals (mention Group 1 when asked)
7.2.2 Aqueous Potassium Iodide (colourless to brown)
7.2.3 Sulphur Dioxide
7.3 Drying
7.3.1 Concentrated Sulphuric Acid (all gases except Ammonia)
7.3.2 Calcium Oxide (for Ammonia and neutral gases)
7.3.3 Anhydrous Calcium Chloride (all gases except Ammonia)
7.4 Locating
7.4.1 Ninhydrin
8 Universal Indicators
8.1 Methyl orange (red, orange, yellow)
8.2 Phenolphtalein (colourless, pink)
8.3 Bromothymol (yellow, dark green, blue)
9 Apparatus
9.1 Condenser
9.1.1 To liquify vapour in distillation and returning unreacted vapour back to the solution
9.2 Glass beads
9.2.1 To cool the gases in fractional distillation by absorbing heat from them
9.3 Fractionating column
9.3.1 To separate various liquids using their boiling points
9.4 Safety bulb
9.4.1 In pipettes to prevent liquid from entering mouth
9.5 Cover ethanol with a lid because it's volatile
9.6 Crush a solid to increase surface area (use a pestle and mortar)
9.7 Purpose of mineral wool is to absorb and hold liquid
10 Colours
10.1 Metals
10.1.1 Zinc is a grey solid (white compounds)
10.1.2 Lead is a shiny bluish metal
10.1.3 Iron is a shiny blackish solid Iron (II) salts are grey-green. Iron (III) salts are reddish-brown.
10.1.4 Group 1, 2 metals are white/silvery white
10.1.5 Group 3 metals are shiny grey
10.1.6 Copper is a pinkish solid Copper(II) sulphate/hydroxide/nitrate are blue. Copper(II) chloride/carbonate are green.
10.2 Non-metals
10.2.1 Iodine is a black solid Its vapours are purple. Silver iodide and Lead iodide are yellow.
10.2.2 Chlorine is a green gas Silver chloride and Lead chloride are white
10.2.3 Bromine is a red-brown gas Silver bromide and Lead bromide are cream
10.2.4 Nitrogen dioxide is a brown gas.
10.2.5 Sulphur and Phosphorus are yellow solids
11 Important reactions
11.1 Metal + Water → Metal hydroxide + Hydrogen Metal + Acid → Salt + Hydrogen
11.2 Acid + Carbonate → Salt + Water + Carbon Dioxide
11.3 Acid + Base → Salt + Water
11.4 Metal Hydroxide + Ammonia Salts → Salt + Ammonia + Water
11.5 Acidic Oxide + Water → Acid Neutral Oxide + Air → Acid Basic Oxide + Acid → Salt + Water
11.6 Alkene + Steam → Alcohol
11.7 Glucose + Yeast → Ethanol + Carbon Dioxide
11.8 Acid + Alcohol → Ester + Water
11.9 Alcohol (when oxidised) → Organic Acids + Water
11.10 Potassium, Sodium, Calcium, react with water to form hydroxides and metals below (till Copper) react with steam to form metal oxides
11.11 Water and oxygen is needed for rusting - water level increases as oxygen is used up
11.12 Copper oxide and hydrogen make copper (black to brown)
12 Acids and Bases
12.1 A concentrated acid contains a large number of H+, hydrogen ions and a concentrated base contains a large number of OH-, hydroxide ions
12.2 A strong acid ionizes completely giving H+ in solutions and a strong base ionizes completely gived OH- in solutions