7.4Reactivity 3 — What are the mechanisms of chemical change?

Inquiry 1: Exploring and Designing — IB Chemistry SL Revision Notes & Topical Questions

15 min read 26 parts Lesson 8 of 12 1 quiz

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Lesson summary

7.4 Inquiry 1: Exploring and Designing — IB SL Notes — IB CHEMISTRY SL notes: Explore a topic, formulate a focused research question and hypothesis, design a valid methodology and control variables.Exploring — uses curiosity and chemical knowledge to form a focused research quest…

Independent thinking
Single relationship
Good starting points
Feasibility
Focused versus general
Measurable

Part 1 of 9Developing an investigation

1Exploring

Exploring uses curiosity and chemical knowledge to form a focused research question and a testable hypothesis.

2Independent thinking

Independent thinking start from a standard experiment and add insight, e.g. comparing propan-1-ol and propan-2-ol to link structure to enthalpy of combustion.

3Single relationship

Single relationship investigate one independent and one dependent variable in depth, rather than several factors at once.

4Sources

Sources textbook, notes, the IB data booklet and reliable databases such as the NIST Chemistry WebBook or PubChem,
giving theory, accepted values for comparison and a method.

5Good starting points

Good starting points an unexplained class result, a different catalyst or acid in a standard practical, or a real-world product.

6Feasibility

Feasibility check equipment, chemicals and time first, and be ready to refine the question.

Part 2 of 9Research question

Qualities

Qualities focused, specific, and clearly linking the independent variable to the dependent variable.

Focused versus general

"how does temperature affect reaction rate" is too general, whereas naming the reaction, range and quantities is focused.

Measurable

Measurable involves quantities that can be measured rather than vague descriptions.

Theory

Theory should be supported by relevant syllabus concepts such as kinetic, thermodynamic or equilibrium ideas.

Part 3 of 9Hypothesis

Hypothesis

Definition

Definition a clear, testable statement predicting the outcome with a scientific justification, not a guess.

Structure

"If ..., then ..., because ...".

Justification

Justification the "because" uses established principles such as collision theory, intermolecular forces or thermodynamics.

Prediction only

Prediction only a statement like "if concentration increases, rate increases" needs the justification, e.g. a higher frequency of effective collisions.

Part 4 of 9Variables

Independent variable

Independent variable the single factor deliberately changed, with at least five values across a justified range.

Dependent variable

Dependent variable the quantity measured, with units and instrument uncertainty.

Controlled variables

Controlled variables all other factors that could affect the result, each with an explanation of its effect and the method used to keep it constant.

Range justification

Range justification explain why a range was chosen, e.g. low temperatures give too slow a reaction and high temperatures cause significant evaporation.

Repeats

Repeats at least three trials per value, to calculate a mean, reduce random error and identify anomalous results.

Part 5 of 9Designing the methodology

Replicability

Replicability a logical, step-by-step procedure that another chemist can repeat exactly.

Specific detail

Specific detail name apparatus and quantities, e.g. a 50.0 cm³ burette, not "add some solution".

Apparatus choice

Apparatus choice choose for sensitivity and justify it, e.g. a gas syringe instead of an inverted cylinder,
- or a colorimeter instead of timing a colour by eye.

Sample size

Sample size large enough that measurement uncertainties are small.

Report layout

Report layout materials and apparatus with concentrations and precision, a safety/ethical/environmental section, then numbered procedure steps.

Other data sources

Other data sources databases such as NIST or simulations such as PhET can supply data for processing.

Part 6 of 9Safety, environmental and ethical considerations

Risk assessment

Risk assessment list the hazards of each reagent and product, the risks in the procedure and specific precautions.

Specific precautions

Specific precautions name the hazard and the response, e.g. 1.0 M HCl is a corrosive irritant, so handle with gloves in a well-ventilated area.

Emergency measures

Emergency measures eye-wash station, rinsing skin and neutralising acid spills with sodium hydrogencarbonate.

Environmental plan

Environmental plan minimise waste and dispose of toxic by-products correctly in the right waste container.

Ethics

Ethics consent for human participants and animal guidelines where relevant.

Part 7 of 9Pilot testing

Definition

Definition a small-scale trial run to check the planned method works.

Checks

Checks the chosen concentrations and temperatures give measurable reaction times, and the gas volume does not exceed the syringe capacity.

Rough titration

Rough titration shows the approximate volume needed so that the recorded titrations can slow down near the end point.

Calibration

Calibration probes such as pH meters, colorimeters and temperature probes can be checked.

Refinement

Refinement document how the method was changed after the pilot.

Part 8 of 9Controlling variables

Controlling variables

Aim

Aim minimise systematic errors so the results are valid and the test is fair.

Calibration

Calibration pH meters with at least two buffers, digital thermometers against boiling water (100.0 °C) and crushed ice (0.0 °C),
- and balances tared before use.
- (e.g. pH 4.00 and 7.00)

Temperature

Temperature use a thermostatically controlled water bath and hold all solutions in it for 5–10 minutes before mixing.

Draughts

Draughts close windows or use a draught shield, especially in calorimetry.

Uncontrollable factors

Uncontrollable factors monitor and record them, then discuss their impact in the evaluation.

Heat loss

Heat loss use a polystyrene cup inside a glass beaker with a lid.

Consistency

Consistency use the same apparatus and the same person reading measurements.

Good control statements

Good control statements give the method and justify it, e.g. a 2.0 cm length of polished Mg ribbon from one roll keeps surface area constant.

Priority

Priority focus on the variables that affect results most, such as heat loss in calorimetry.

Part 9 of 9More from the specification

Key terms

Term	Meaning
Research question	A focused question linking an independent variable to a dependent variable.
Hypothesis	A testable prediction with a scientific explanation.
Independent variable	The factor deliberately changed.
Dependent variable	The quantity measured in response.
Controlled variable	A factor kept constant to ensure a fair test.
Pilot study	A small-scale trial used to check and refine the method.
Calibration	Checking an instrument against a known standard and adjusting it.

Avoid these mistakes

Investigating several variables at once — vary one independent variable only.

Writing a vague method such as add some acid — give exact quantities and apparatus.

Stating control the temperature without a method — name the water bath and its temperature.

Treating safety as an afterthought — include a dedicated, specific risk assessment.

Last updated: 15 October 2026