7.1Reactivity 3 — What are the mechanisms of chemical change?

Tool 1: Experimental Techniques — IB Chemistry SL Revision Notes & Topical Questions

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7.1 Tool 1: Experimental Techniques — IB SL Notes — IB CHEMISTRY SL notes: Manage hazards, ethics and environmental impact, measure variables with suitable apparatus, and choose separation, purification and other techniques.Hazard = the potential of a substance to cause harm beca…

Symbol format
Control measures
Safety data sheets
Justified precautions
Handling and storage
Green chemistry

Part 1 of 9Hazards and risks

Hazard

Hazard the potential of a substance to cause harm because of its properties, e.g. concentrated HCl is corrosive, mildly concentrated is an irritant and dilute is not classed hazardous.

Risk

Risk the likelihood that harm occurs in a specific situation, depending on the amount used and how it is used.

Control

Control eye protection reduces the risk of harm without changing the hazard.

Hazard symbol	Meaning	Example precaution
Health hazard	Skin rashes, eye damage, harm if swallowed	Gloves and eye protection
Corrosive	Skin burns and permanent eye damage	Splash goggles, gloves
Flammable	Catches fire if heated or near a flame	Water bath or mantle, no flames
Acute toxicity	Life-threatening in small quantities	Fume cupboard
Hazardous to the environment	Threat to aquatic life	Collect waste, do not pour down sinks
Oxidising	Can cause fire or explosions	Store away from combustible reducing agents

Symbol format
- nine standard symbols, shown in a red diamond on a white background.

Part 2 of 9Risk assessment and control

Identify the hazards by listing the chemicals used and their dangers.

Assess the risks from the amount used, whether it is heated, the product given off and the experience of the user.

Rate each risk as low, medium or high.

Implement control measures.

Plan for emergencies such as spills or contact with skin.

Control measures

Control measures elimination, substitution with a less hazardous substance, good practice such as capping bottles, safety equipment such as fume hoods and personal protective equipment.

Safety data sheets

Safety data sheets give information on safe handling and use.

Justified precautions

Justified precautions say what the hazard is and why the precaution is taken, e.g. HCl gas is toxic and corrosive so the step is done in a fume cupboard.

Handling and storage

Handling and storage label containers with the chemical name, concentration and hazard symbols.

Part 3 of 9Environmental and ethical issues

Waste

Waste dispose of unused reactants and products correctly.

Green chemistry

Green chemistry reduce volumes and concentrations, use micro-scale work and reuse excess materials.

Solvents

Solvents choose aqueous solutions or simple alcohols and alkanes where possible.

Catalysis

Catalysis a catalyst minimises waste and energy.

Atom economy

Atom economy determine it and look for ways to increase it.

Microscale

Microscale cuts reagent volumes from 50–100 cm³ to 1–2 cm³, reducing toxic waste.

Ethics

Ethics human subjects require consent and animal work must follow ethical guidelines.

Part 4 of 9Measuring mass, volume and gas volume

Mass

Mass a digital balance, tared before use; the SI unit is the kilogram and 1 kg = 1000 g,
- and warm objects should not be weighed because convection currents change the reading.

Measuring cylinder

Measuring cylinder approximate volumes only.

Volumetric pipette

Volumetric pipette the most accurate for a fixed volume, e.g. 25.00 cm³.

Burette

Burette the most accurate for a variable volume, with the scale running from 0.00 at the top, so read from the top down.

Volumetric flask

Volumetric flask calibrated for one precise volume when making standard solutions.

Meniscus

Meniscus read with the eye level with the bottom of the curve to avoid parallax.

Gas volume

Gas volume a gas syringe, or an inverted cylinder or burette over water if the gas is insoluble.

Part 5 of 9Measuring time, temperature and length

Time

Time a stopwatch in seconds or minutes, and human reaction time matters for very short intervals.

Recording time

Recording time do not mix seconds and minutes, e.g. 1.30 on the display is 90 s, not 1.30 min.

Liquid thermometer

Liquid thermometer reads to the nearest 1 °C or 0.5 °C, is robust and cheap, but slower and less precise.

Digital probe

Digital probe reads to ±0.1 °C or better, gives fast readings and suits data logging.

Length

Length a ruler to the nearest mm, and a tape measure for larger distances.

Part 6 of 9Measuring pH, current and potential difference

pH meter

pH meter a glass membrane electrode gives precise pH, often to two decimal places.

Indicators

Indicators natural ones give approximate values and synthetic ones (phenolphthalein, methyl orange) have sharp colour changes for titrations.
- (litmus, red cabbage)

Universal indicator

Universal indicator a blend giving approximate pH 1–14 read against a colour chart.

Ammeter

Ammeter connected in series.

Voltmeter

Voltmeter connected in parallel across the component.

Zero errors

Zero errors analogue and digital meters should be checked for zero error and the zero value subtracted.

Parallax

Parallax analogue meters should be read perpendicular to the scale.

Part 7 of 9Volumetric analysis and titration protocol

1Standard solution

Standard solution made with a three-decimal-place balance and a volumetric flask, then inverted to mix.

2Primary standard

Primary standard high purity, high molar mass, low hygroscopicity and stable in air, e.g. anhydrous Na₂CO₃.

3Burette

Burette read to two decimal places with uncertainty ±0.05 cm³, with the tip filled and free of air bubbles.

4Rough titre

Rough titre an initial pilot titre is excluded from the average.

5Concordant

Concordant titres within ±0.10 cm³, and only concordant titres are averaged.

6End point versus equivalence point

End point versus equivalence point the equivalence point is stoichiometric equivalence and the end point is the observed colour change.

Part 8 of 9Separation, purification and other techniques

Separation

Separation filtration, crystallisation, simple and fractional distillation, and paper or thin-layer chromatography.

Purification

Purification recrystallisation and melting point determination.

Other techniques

Other techniques calorimetry, electrochemical cells, drying to constant mass, reflux, colorimetry or spectrophotometry,
- and physical or digital molecular modelling.

Reflux

Reflux heats a mixture to boiling for a long time without losing volatile material, using a vertical condenser and anti-bumping granules.

Distillation

Distillation simple distillation separates liquids with very different boiling points,
while fractional distillation uses a column for close boiling points such as ethanol and water.

Part 9 of 9More from the specification

1Volumetric analysis

Volumetric analysis titration uses a burette and pipette to find an unknown concentration from the volume of a reacting solution.

2Hazard warning symbols

Hazard warning symbols pictograms indicate toxic, corrosive, flammable or oxidising substances and guide safe handling.

3Environmental issues

Environmental issues green chemistry reduces waste and hazardous solvents, and waste must be disposed of correctly.

4Applying techniques

Applying techniques choose heating methods, measure temperature accurately, and repeat to obtain concordant results.

5Results and uncertainty

Results and uncertainty record data with appropriate precision and calculate the average of consistent trials.

6Volumetric analysis

Volumetric analysis titration uses a burette and pipette to find an unknown concentration from the volume of a reacting solution.

7Hazard warning symbols

Hazard warning symbols pictograms indicate toxic, corrosive, flammable or oxidising substances and guide safe handling.

8Environmental issues

Environmental issues green chemistry reduces waste and hazardous solvents, and waste must be disposed of correctly.

9Applying techniques

Applying techniques choose heating methods, measure temperature accurately, and repeat to obtain concordant results.

10Results and uncertainty

Results and uncertainty record data with appropriate precision and calculate the average of consistent trials.

11Temperature

A measure of the average kinetic energy of the particles.

12Volumetric analysis

Quantitative analysis by measuring volumes of solutions.

Key terms

Term	Meaning
Hazard	The potential of a substance to cause harm.
Risk	The likelihood that harm will occur in a specific situation.
Primary standard	A pure, stable, high-molar-mass substance used to make a standard solution.
Concordant titres	Titres that agree within 0.10 cm³.
Reflux	Heating with a vertical condenser so vapour returns to the flask.
Green chemistry	The design of processes that reduce waste and hazards.

Avoid these mistakes

Saying wearing eye protection removes the hazard — it only reduces the risk.

Giving a vague precaution like wear a lab coat — name the hazard and justify the precaution.

Including the rough titre in the mean — average only concordant titres.

Mixing seconds and minutes in a table — use one unit throughout.

Last updated: 15 October 2026