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Pure Chemistry 6092 Practical - Olevel Cheat Sheet by

A summary of elaborate procedures to be carried out during the examination.Past year papers will be reviewed here


Thymol­pht­alein: deep blue (bases) to colourless (neutral) [Bases are Blue]
Methyl Orange : yellow (bases) to orange (neutr­al)/red (acidic) ROY
Screened methyl orange : green (bases) to grey (neutr­al)­/purple (acidic) [Purple is Poision]
Universal Indicator: blue/p­urple (bases) to green (neutral) / red (acidic)


Metal A is more reactive than Metal B. Hence Metal A is able to displace Metal B from its [aqueous salt] to form Metal B and Metal A salt
Remember to be specific about colour. Take note of the colours of the reagents and the products respec­tively and identify colour change if necessary
Remember to identify if the reaction is exothermic or endoth­ermic (if needed)
Remember to mention changes observed in Metal A as well as the changes observed in the Metal B salt solution.
Use nitric acid when possible

Qualit­ative Analysis

Cation Test: Use NaOH and NH4OH, Observ­ations to be taken note of is the colour of ppt after 2/3 drops of reagent as well as the solubility of that ppt in excess reagent (Ampho­teric hydroxides are soluble in ex NaOH/ Zn and Cu precip­itates are soluble in NH4Cl/ Ca forms no precip­itate in NH4Cl/ NH4+ ion test in NaOH, need to test for NH3 gas upon heating
Anion Test: Carbonate ion tested through presence of carbon dioxide/ Sulfate with barium nitrat­e/C­hloride and iodide with silver nitrat­e/N­itrate with NaOH, aluminum foil and heating
Use of HNO3 in anion tests: To remove any interf­ering ions that can form precip­itate with the added reagent and produce a false positive result
Describing efferv­esc­ence: Colour­/odour of gas


Burette: 2dp/ Pipette: 25.0 cm3 (Remember to rinse both with respective reagents before starting titration) Conical Flask (parti­cular about shape as conical shape is optimal to prevent spillage of reagen­ts-­->p­ossible SOE if beaker was asked to be used) Wash conical flask with distilled water
Final burette readin­g/cm3, Initial burette readin­g/cm3, Volume of (solution of unknown concen­tra­tion) used/cm3, Best Titration results (tick the ones within approp­riate range and use only these readings when calcul­ating average volume)
Write complete steps when doing mole calcul­ations
Iodometric titration: Burette filled with sodium thiosu­lfa­te/­pipette with iodine­-->­titrate until solution in conical flask turns yellow, then add starch indica­tor­(so­lution turns grey colour) continue titration until solution becomes colour­less)
Redox titration: Burette contains KMnO4/ Pipette contains reducing agent-­-> solution in conical flask will turn pale pink (if its the other way round end point should be colour­less)
Titrate A against B: B has unknown concen­tration (burette), A will have known concen­tration (pipette)

Speed of reaction

Concen­tra­tion: Experiment number, Volume of (solut­ion), volume of distilled water, time for reaction to stop
Mass change: Mass of empty vessel, mass of vessel + powder before heating, mass of powder before heating, mass of vessel + powder after heating, mass of powder after heating, change in mass of powder
When using stopwatch, always round to 2dp unless otherwise stated
Always make reference to frequency of effective collisions between reactant molecules to form products at a faster­/slower rate
Analyze chemical equation and identify limiting reactant. If increasing volume­/co­nce­ntr­ati­on/mass of a limiting reactant, more/less products may be formed (If question specify amount then use that data in your answering rather than more/l­ess­-->use terms like 2 times greater/smaller than
In planning questions, state the end points of reactions (ppt no longer dissolves/ all the ppt has dissolved to form a solution/ no more efferv­escence being produced/ 2 consistent mass readings)

Gas collection

Insoluble gases collected through displa­cement in water method (H2,CO2, O2)
Soluble gases: Delivery method (Upward when Mr<29/ Downward when Mr>29)
Drying agent: Conc. H2SO4 (dry acidic gases) Fused calcium chloride (neutral) Calcium oxide (basic gases)
Gas syringe is used to collect accurate amount of gas (Connect delivery tube to nozzle of syringe)
Deliver desired gas into the gas syringe and wait until there is no further change in gas volume in the syringe

Separation Techniques

Crysta­lli­zat­ion:For thermally unstable compounds (sugar) Saturation point-­->when solid no longer dissolves, the moment saturation point is reached, allow the solution to cool and form crystals (more time taken to cool down--> larger crystals)
Evapor­ation to drynes­s--­>th­ermally stable compou­nds­/salt (do not use glassware, instead use a crucible or an evapor­ating dish)
Filter­ation: clean residue with cool distilled water and dry in between sheets of dry filter paper/ filtrate collected can be used to crysta­llize
Paper chroma­tog­raphy: Draw line in pencil/ solvent level below start line/ dot substance with toothpick/ do a cylind­rical shape
Simple distil­lation: Solution in distil­lation flask heated with marble­/bo­iling chips to allow smooth boiling, at boiling point vapour will rise and flow into condenser where it cools to form pure liquid
Condenser: Provides a constant cool enviro­nment for vapour to condense into liquid (water in at bottom, water out at top)
Bulb of thermo­meter placed at top of distil­lation near conden­ser­-->­acc­urately measure temper­ature of vapour entering the condenser

Organic reactions

Bubbling gaseous alkene into aqueous bromin­e--> discol­oration of aqueous bromine
Carboxylic acid reactions: with base/ metal/ metal carbonate/ with alcohol to form sweet smelling esters

Salt Prepar­ation

Precip­ita­tion: soluble reagent + soluble reagent = insoluble salt (X nitrate + sodium Y), mix both soluble reagents, filter off, obtain residue, clean residue with cool distilled water and dry between sheets of dry filter paper
Excess insoluble compound + acid = soluble salt (not SPA salt) Mix until no more dissol­ving, heat till saturation point, allow to cool slowly to form crystals, wash crystals in cold distilled water and dry between sheets of dry filter paper
Acid + Alkali = soluble salt (SPA salt), titrate acid against alkali until endpoint with suitable indicator, repeat without indicator, obtain the aqueous salt,heat till saturation point, allow to cool slowly to form crystals, wash crystals in cold distilled water and dry between sheets of dry filter paper

Approp­riate Gas Tests

Hydrogen: Acid with metal reaction (test with lighted splint)
Ammonia: Nitrate and Ammonium ion test (damp red litmus turn blue)
Chlorine: red litmus bleached (Chlorine compound)
SO2: Potassium manganate turn colour­less/ potassium dichromate turn green
Oxygen: rekindle glowing splint (decom­posing metal oxides)
Describe colour and odour of the efferv­escence if its a known gas
CO2: carbonate test, decomp­osition --> Bubble gas into test tube of limewater (shake test tube to allow continuous bubbling)

Bunsen Burner

Close the airhole to produce luminous flame
Hold boiling tube containing reaction mixtur­e/w­ooden splint at 45 degree angle from the flame
Gentle heatin­g--­>Slowly remove reaction mixture near and far away from the flame
Strong heatin­g--­>hold the reaction mixture at hottest part of flame


As the reactivity of the metal increases, the more stable the metal carbonate, more harder to decompose it to consti­tuent substance
Metal Carbonate + heat -->­metal oxide +carbon dioxide
Use a crucible as strong heating is required
Take note of colours of substances provided and formed after the decomp­osition


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