๐ฌ Core Techniques
Step-by-step guides to the techniques used in every chemistry lab - from GCSE through to university level.
Purpose: Separates an insoluble solid from a liquid (suspension).
Steps
1.Fold filter paper into a cone and place in a funnel.
2.Pour the mixture slowly down a glass rod into the funnel.
3.The liquid (filtrate) passes through; the solid residue remains on the paper.
4.Wash the residue with a small amount of distilled water to remove impurities.
Used for
Removing sand from waterCollecting a precipitateCoffee making
Always wet the filter paper first with solvent to help it seal against the funnel.
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Simple Distillation
Technique
Purpose: Separates a solvent from a dissolved solid, or liquids with widely different boiling points.
Steps
1.Heat the mixture in a round-bottom flask.
2.Vapour travels through a condenser (cold water jacket).
3.Vapour cools and condenses back to liquid in the collection flask.
4.Thermometer reads the boiling point of what is distilling over.
Used for
Purifying waterSeparating ethanol from water (whisky production)Obtaining distilled water for labs
The thermometer bulb must be at the side-arm junction, NOT in the liquid.
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Paper Chromatography
Technique
Purpose: Separates mixtures of soluble substances (dyes, inks, amino acids) based on how far they travel up paper.
Steps
1.Draw a pencil baseline on chromatography paper (not ink - it would move).
2.Spot the mixture and known samples on the baseline.
3.Place in a solvent (e.g. water or ethanol) below the baseline.
4.Allow solvent to rise, then remove and mark the solvent front.
5.Calculate Rf = distance moved by substance / distance moved by solvent.
Used for
Identifying food dyesForensic analysis of inksAmino acid identification in biology
Use pencil, not pen, for the baseline. Each substance has a fixed Rf value for a given solvent - use it to identify unknowns.
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Acid-Base Titration
Technique
Purpose: Determines the exact concentration of an acid or base by neutralising it with a solution of known concentration.
Steps
1.Fill burette with the standard solution (known concentration).
2.Pipette exact volume of unknown solution into a conical flask.
3.Add 2-3 drops of indicator (e.g. phenolphthalein or methyl orange).
4.Add standard solution dropwise until the indicator permanently changes colour (endpoint).
5.Record volume used. Repeat for concordant results (within 0.1 cmยณ).
6.Calculate: n = c ร v, then find unknown concentration.
Used for
Measuring acidity of vinegarQuality control of pharmaceuticalsWater treatment monitoring
Add solution slowly near the endpoint - dropwise. The colour change should persist for 30 seconds for a valid endpoint.
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Recrystallisation
Technique
Purpose: Purifies a solid by dissolving it in a hot solvent, then allowing it to slowly crystallise as the solution cools.
Steps
1.Dissolve the impure solid in the minimum volume of hot solvent.
2.Filter while hot to remove insoluble impurities.
3.Allow the filtrate to cool slowly (fast cooling gives small, less pure crystals).
4.Filter the crystals and wash with cold solvent.
5.Dry in an oven or desiccator.
Used for
Purifying aspirin after synthesisGrowing large crystals for X-ray analysisSugar refining
Slow, controlled cooling gives large, pure crystals. Scratching the inside of the flask with a glass rod encourages nucleation.
Purpose: Identifies metal ions in a sample by the characteristic colour they emit when heated in a flame.
Steps
1.Clean a nichrome or platinum wire by dipping in HCl and heating until no colour appears.
2.Dip the clean wire in the sample solution.
3.Hold in the edge of a blue Bunsen flame.
4.Observe the colour produced.
Flame Colours
IonMetalColour
Liโบ
Lithium
Crimson red
Naโบ
Sodium
Bright yellow
Kโบ
Potassium
Lilac/violet
Caยฒโบ
Calcium
Brick red
Srยฒโบ
Strontium
Scarlet red
Baยฒโบ
Barium
Apple green
Cuยฒโบ
Copper
Blue-green
Used for
Qualitative analysis of unknown saltsChecking purity of metal saltsUnderstanding why fireworks produce colours
Sodium is so sensitive that even a tiny contamination produces a yellow flash. Use a cobalt blue glass to filter it out when looking for potassium.
๐งช Lab Equipment
What every piece of glassware and apparatus is actually for.
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Burette
Measures and delivers exact, variable volumes of liquid. Used in titrations. Accurate to 0.05 cmยณ.
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Pipette
Delivers a single, fixed, accurate volume (10, 25, or 50 cmยณ). More accurate than a measuring cylinder.
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Conical Flask
Holds reaction mixtures during titrations and reactions. Easy to swirl without spilling.
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Round-Bottom Flask
Used for heating and distillation. Round shape distributes heat evenly.
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Condenser
Water-cooled glass tube that cools vapour back to liquid during distillation.
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Buchner Funnel
Used with suction filtration to collect precipitates faster than gravity filtration.
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Reflux Condenser
Allows reaction mixture to boil and condense continuously without losing vapour. Used for slow reactions needing heat.
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Separating Funnel
Separates two immiscible liquids (e.g. water and oil) based on density. Used in solvent extraction.
โ ๏ธ Safety Symbols
Every chemical hazard symbol you will encounter on labels and safety data sheets (COSHH/GHS system).
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Toxic
Can cause serious harm or death if inhaled, swallowed, or absorbed. Wear gloves and work in fume cupboard.
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Irritant/Harmful
Can cause irritation to skin, eyes, or respiratory system. Mild hazard but precautions needed.
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Flammable
Catches fire easily. Keep away from ignition sources. Examples: ethanol, acetone, diethyl ether.
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Explosive
Can explode under certain conditions. Examples: ammonium nitrate, concentrated peroxides.
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Corrosive
Destroys living tissue and many materials on contact. Examples: concentrated acids, sodium hydroxide.
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Oxidising
Provides oxygen to support combustion of other materials. Can intensify fires. Examples: hydrogen peroxide, KMnOโ.
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Environmental Hazard
Toxic to aquatic life or the environment. Dispose of properly - do not pour down the drain.