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
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
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
More from the specification
Designing an investigation
- State a focused research question, identify independent, dependent and controlled variables, and justify the method chosen.
Consulting sources
- Gaining insight from literature gives scientific context and helps to refine the method.
Volumetric pipette
- Measures a fixed volume accurately, more precisely than a measuring cylinder,
- which is why it is used in titrations of strong and weak acids for neutralisation.
Percentage yield
- Actual yield divided by theoretical yield times 100, used to evaluate a synthesis; losses reduce the yield.
Potassium iodide
- Used in a kinetics investigation, e.g. iodide oxidation, where concentration is varied and the rate measured.
Designing an investigation
- State a focused research question, identify independent, dependent and controlled variables, and justify the method chosen.
Consulting sources
- Gaining insight from literature gives scientific context and helps to refine the method.
Volumetric pipette
- Measures a fixed volume accurately, more precisely than a measuring cylinder,
- which is why it is used in titrations of strong and weak acids for neutralisation.
Percentage yield
- Actual yield divided by theoretical yield times 100, used to evaluate a synthesis; losses reduce the yield.
Potassium iodide
- Used in a kinetics investigation, e.g. iodide oxidation, where concentration is varied and the rate measured.
Neutralisation
- The reaction of an acid with a base to form a salt and water.
Volumetric pipette
- Apparatus measuring one fixed volume accurately.
Percentage yield
- Actual yield divided by theoretical yield, times 100.
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
1
Investigating several variables at once — vary one independent variable only.
2
Writing a vague method such as add some acid — give exact quantities and apparatus.
3
Stating control the temperature without a method — name the water bath and its temperature.
4
Treating safety as an afterthought — include a dedicated, specific risk assessment.
Marked practiceQuizzes for this lesson
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