igcse chemistry practicals

A Guide to IGCSE Alternative to Practical Chemistry

This is a complete guide to IGCSE alternative to practical chemistry and I have broken it down into several sections just to help us understand what is required in this section.

Please remember in IGCSE Olevel chemistry, there are three sections. We have the essay(theory), objectives, and alternative to practical or Practical.

The mark distribution is 50% for theory, 25% for objectives, and 25% for practical or alternative to practical.













Basic Facts in IGCSE Chemistry Practicals

The modules are arranged in hints as we discuss some salient key points needed to excel in IGCSE chemistry.

Hint 1:Methods of Preparing Gases in IGCSE Alternative to Practical Chemistry

The following gases are commonly prepared in the laboratory:

Carbon dioxide, chlorine, hydrogen, and oxygen

GasHow to prepare gasesEquation
CO2Add dilute HCl to marble chipsCaCO3 + HCl    CaCl+ H
Cl2Add conc. HCl to Manganese iv oxide4HCl + MnO2à MnCl2 + 2HCl +O2
H2Add dilute HCl to zinc granulesZn + HCl à ZnCl2 + H2
O2Add hydrogen peroxide to manganese IV oxide as catalyst2H2O2   à H2O2 + O2

Hint 2: Methods of Collecting Gases

There are two factors considered in collecting gases, solubility, and density.

  • There are four ways to collect gases produced in a chemical process.
  • Each method is different and depends on the nature of the gas and experiment.
  • Downward delivery is used when the gas being collected is denser than air(Note: the mass of air is 28.8g, any gas heavier than this is collected by downward delivery of the gas)
  • The opposite method is called upward delivery and is used when the gas is less dense than air.
  • gas syringe can be used to collect and measure the volume of a gas.
  • Collection over water is used when the gas being collected is insoluble in water.

Hint 3: Methods of drying gases

  • In many cases the gas we are collecting needs to be dried.
  • This can be done by passing the gas through a drying agent which removes any water present.
  • Depending on the gas being collected, a different drying agent may be used.
  • Three common drying agents are:
    • Concentrated sulfuric acid which can dry all gases except ammonia as neutralisation occurs.
    • Anhydrous calcium chloride can dry all gases except for ammonia as it forms calcium chloride complex
    • For ammonia and neutral gases, calcium oxide is the preferred drying agent

Hint 4: Methods of Separation and Purification

Mixtures are usually separated using various separation techniques through IGCSE chemistry focuses on a few of these methods of purification.

The few methods of purification discussed fully in IGCSE Chemistry are Filtration, Decantation, Centrifugation, Crystallization, Solvent Extraction, and Distillation.

Though I have written a thorough post on these methods of separation where I explained all the various separation methods with examples, I will still talk a little about them before I move on.

Filtration; An undissolved solid can be separated from solution or liquid by simply passing through a piece of paper in a filter funnel. The process is called filtration and the liquid that passed through the filter paper called filtrate while the solid that that stays on the filter paper is called the residue.

Decanting: This is a simple method of purification that is suitable for solids that have very heavy particles e.g sand and water.

Centrifugation: Centrifugation involves using a machine called a centrifuge to spin test tubes round and round at very high speeds.

Crystallization: Crystallization is a method of purification used to obtain solids from a solution. The solution is gently heated in an evaporating basin to concentrate it. Heat is applied to the solution until the crystallization point is reached.

If two dissolved substances have different solubilities at different temperatures, fractional crystallization can be used to separate them.

Solvent Extraction: Solvent extraction can be used to separate two solutes dissolved in a solvent. This works perfectly well if one of the solutes is volatile. A second solvent is used to extract one of the solids from the first solvent.

The second solvent must not be able to mix with the second i.e must not be miscible.

Simple Distillation: Simple distillation is used to obtain a solvent from a solution. When a solution of salt in water is heated, the water boils and escapes as steam. Simple distillation can be used to separate liquids of different boiling points and also recover water from salt.

Fractional Distillation: Fractional distillation is used to separate a mixture of liquids with close different boiling points that are miscible.

This method is used to separate even petroleum fractions, the more volatile liquid evaporates and moves very fast while the less volatile liquid does not move as fast as the other one.

Hint 5: Preparation of salts   


There are five methods employed in preparing salts

Preparation of soluble saltsPreparation of insoluble salts
1. Action of metals with acids                                 
Use MAZIT =Mg,Al,Zn,Fe,Sn                             Zn + HCl à ZnCl2 + H2 2.

2. Action of carbonate with acids                               
ZnCO3 +2HCl à ZnCl2 + H2O + CO2  
3. Action of insoluble base with acids              
Use CuO or PbO                                               
CuO +2HCl à CuCl2 +H2O PbO + 2HNO3  à Pb(NO3)2 + H2O  

PROCEDURES –steps taken to prepare the soluble salts
1. Add the (metal, carbonate ,insoluble base) to the acid in the flask till it is in excess
2. Warm the flask gently to complete the reaction 3.filter off the excess metal, carbonate, insoluble base
4. Put the filtrate in the evaporating dish and heat to crystallization point
5. Filter off the crystals and allow to cool
6. Dry the crystals on a filter paper
1. Precipitation or double decomposition soluble salt
+ soluble salt à insoluble salt + soluble salt AgNO3+NaCl à AgCl + NaNO3 PROCEDURES                                                  
1. Mix the two soluble salts                                                                             2. Filter off the precipitate formed                                        
3. Rinse the precipitate with little water                             
4. Dry the residue                                                                  
4. Action of soluble base(Alkali) and acid PROCEDURES                                                 
1. First rinse the pipette with water and use it to pipette a known volume of the alkali onto the conical flask                                                                     2.Add a few drops of the indicator to the alkali in the flask                                                                            
3. Rinse the burette with little acid and then fill the burette with acid                                                   
4. open the burette tap and let the acid onto the alkali until you notice the first permanent color change                                                               
5. Record the burette reading and repeat the experiment up to 3 times                                           
6. Take the average of the titre values                                                        

Hint 6: Colours of common salts in IGCSE Chemistry

MetalsGenerally, the salts of metals like Na, Ca, Mg, Al, k are white                                          
Example KCl, MgCl2, CaCl2 etc.                                                                                                 
Transition metals form coloured compounds/ions except for zinc and scandium
Iron (Fe)FeO  black  Fe2O3 reddish-brownFe(OH)2 green Fe(OH)3 reddish-brownGenerally, iron ii compounds are green while iron ii compounds are red-brown
Copper (Cu)CuO-black, Cu2O-redCuCl2, CuCO3 Blue-greenCuSO4, white                                CuSO4.5H2O Blue 
Silver (Ag)AgCl –whiteAgBr –creamyAgi-yellow 

Hint 7: Solubility rule

SaltsSoluble ruleExceptions
NitratesAll nitrates are solubleNil
SulfatesAll sulfates are solubleBaSO4, PbSO4, CaSO4
ChloridesAll chlorides are solubleAgCl, PbCl2
IodidesAll iodides are solubleAgI, PbI
BromidesAll bromides are solubleAgBr,PbBr
CarbonatesAll carbonates are insolubleK2CO3,Na2CO3, (NH4)2CO3
HydroxidesAll hydroxides are insolubleKOH, NaOH, (NH4OH
*All salts of potassium,sodium, and ammonium are soluble

Hint 5: Common Pieces of Apparatus used in Chemistry

  • I will update the post with diagrams of the pieces of apparatus

Uses of pieces of apparatus

1. Pipette: A volumetric pipette is used to measure out or transfer very accurately single fixed volumes of liquids like 5 cm3, 10cm3 or 25cm3.

2.Burette: A burette is used to accurately measure the volume of liquids up to 50 cm3. It an also be used for measuring the volume of gases but when doing so, it is always turned upside down.

3.Measuring cylinder: Measuring is only used to estimate the volume of liquids and not for accurate measurements because it is only calibrated to 1 or 2cm3

4. Gas syringe: The gas syringe is used to accurately measure volume of gases liberated during reactions.

Hint 6: Test for ions and gases

*Test for gases

OxygenGlowing splint testRelight the glowing splint
HydrogenLighted splint testBurns with a (squeaky) pop sound
Carbon iv oxideLime water testTurns lime water milky
AmmoniaLitmus paper testTurns damp red litmus paper blue
ChlorineLitmus paper testBleaches damp litmus paper
Sulphur iv oxidePotassium dichromate paper test       Aqueous potassium manganate VI testTurns paper green                                           Decolourises it

*Test for Cations

CationsTest 1 Add a few drops of sodium hydroxide(NaOH) in drops then in excessTest 2 Add a few drops of aqueous ammonia (NH4OH) in drops then in excess
Aluminium ion   (Al3+)White precipitate dissolves in excess NaOH forming a colourless solutionWhite precipitate insoluble in excess NH4OH
Zinc ion (Zn2+)White precipitate dissolves in excess NaOH forming a colourless solutionThe white precipitate dissolves in excess NH4OH
Calcium ion (Ca2+)White precipitate insoluble in excess NaOHNo precipitate or very slight(faint) precipitate
Copper ion (Cu2+)Light blue or pale blue precipitate formed insoluble in excess NaOHThe light blue precipitate dissolves in excess NH4OH to form a deep blue solution
Iron II ion (fe2+)Green precipitate insoluble in excess NaOHGreen precipitate insoluble in excess NH4OH
Iron iii ion(Fe3+)Red-brown precipitate insoluble on excess NaOHRed-brown precipitate insoluble on excess NH4OH

*Test for Anions

Carbonate ion (CO32-)Add dilute hydrochloric acidEffervescence, carbon dioxide given off turns lime water milky
Chloride ion (Cl)Add excess dilute nitric acid and then aqueous silver nitrateWhite precipitate
Bromide ion(Br)Add excess dilute nitric acid and then aqueous silver nitrateCream precipitate
Iodide ion (I)Add excess dilute nitric acid and then aqueous silver nitrateYellow precipitate
Nitrate ion (NO3)Warm with aqueous sodium hydroxide and aluminums foilAmmonia gas is given off, pungent-smelling gas turns red litmus paper blue
Sulphate ion (SO42-)Add excess hydrochloric acid followed by barium chlorideWhite precipitate

*Flame test  

*the ions in bold are commonly asked so commit to memory

Metallic groupMetalFlame colour
Group 1Lithium                        Sodium                                 Potassium                      Rubidium                             CaesiumCrimson                                       Golden yellow                                 Lilac                                          Red                                                            Blue  
Group 2Calcium                     Strontium                     BariumBrick red                               Crimson                                    Apple green
OthersLead                                        CopperBlue –white                               green

Hint 7: Salt Analysis

Hint 8: Skills needed in investigating experiments

                  Reading the thermometer 

                  Reading the stop clock

                  Reading the volume of liquids in measuring cylinders

Hint 9: Planning an investigation

I have solved many papers on IGCSE broken down in an easy way to understand. I will update the post once i have permission from Cambridge


1. Why is the burette rinsed with water any acid-base reaction?                                                                  To remove traces of acid / clean / remove impurities

2. Why is recommended before titration to rinse again acid after rinsing with water?                               To remove traces of water

3. When doing experiments especially on rates of reactions, what would be the advantage of taking the temperature readings every 15 seconds?                                                                                 

To get more readings and to get a better graph

4. If the pipette is very accurate in measuring out or transferring volumes/, why can’t it be used for any volume like 13.5cm3, 14.8cm3, etc?                                                                              

Pipette is not calibrated and thus only measures specific volumes

5. Why would measuring the volume of dilute sulfuric acid with a burette rather than a measuring cylinder be an improvement?                                                                                                

More accurate

6. Why is it not recommended to heat the round bottom flask containing organic solvents directly?                                                                                                                                          

Organic solvents are flammable

I could go on and on but there are several planning investigation examples on IGCSE chemistry and we just need to practice past papers on IGCSE to be able

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