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A1.5 · Conduct inquiries safely while controlling relevant variables

Learn to conduct inquiries safely while controlling relevant variables through clear examples and targeted practice.

Ontario Grade 12 Chemistry

Scientific Investigation Skills and Career Exploration

Planning investigations by controlling relevant variables

In chemistry, an inquiry is a planned investigation used to answer a question with observations or measurements. A safe inquiry protects people, equipment, and the environment. A fair inquiry changes the factor being tested while keeping other relevant conditions consistent. These are connected skills: a poorly controlled test may not answer its question, and an unsafe method should not be carried out. This lesson focuses on planning and conducting inquiries safely while controlling relevant variables.

What you will learn

Identify the question an inquiry is designed to answer.
Distinguish the variable changed, the outcome measured, and the conditions kept constant.
Choose practical safety steps that match the materials and procedure.
Plan a fair test and record observations without inventing or altering results.

1. From an observation to a testable question

A useful inquiry begins with something that can be observed. For example, a solid may appear to disappear more quickly in warm water than in cool water. The observation gives a reason to ask a question, but it does not prove why the difference occurred. A testable question identifies what will be changed and what will be observed or measured.

A variable is a condition or feature that can take different values. The independent variable is the one deliberately changed. The dependent variable is the outcome observed or measured. Controlled variables are the other relevant conditions kept the same so that the comparison is fair. These names describe roles in a particular inquiry; a variable is not always independent or dependent in every investigation.

Before planning, review the difference between an observation and an explanation. An observation is recorded evidence, such as a measured time or a visible change. An explanation is an idea about what caused the observation. Record observations carefully first. Do not report an expected result as if it had been measured.

Make the question specific enough to guide a method.
Name the factor you will change and the outcome you will measure.
Treat a prediction as a prediction, not as a result.

2. Control relevant variables

A fair test changes the independent variable while keeping relevant controlled variables as consistent as practical. If several conditions change at once, an observed difference cannot be linked clearly to just one of them. A controlled variable is relevant when changing it could also affect the measured outcome.

For a dissolving investigation, relevant conditions might include the mass and type of solid, the volume of water, the container, and the stirring method. If the question concerns water temperature, keep those other conditions consistent. The temperature is the independent variable, and the time taken for the solid to dissolve completely could be the dependent variable.

Decide in advance how each quantity will be measured. Use the same measuring equipment and the same endpoint rule for each trial. For instance, define what counts as fully dissolved before collecting data. This reduces differences caused by personal judgment. If a condition cannot be held perfectly constant, record what happened and consider how it may affect the comparison.

Repeated trials can help show whether a result is consistent, but they do not fix a poorly designed comparison. Plan the number of trials before beginning, when time and materials allow. Record each observation as it is made, including units for measured quantities. Do not remove a result simply because it differs from the others; discuss a result only using evidence and a clear reason.

Keep conditions that could affect the outcome consistent.
Use clear measurement rules and units.
Record actual observations, including unexpected ones.

3. Plan for safety before beginning

Safety is part of the method, not an extra step after the experiment. Before handling materials, identify possible hazards from the chemical label, teacher instructions, and the planned procedure. A hazard is a source of possible harm. Risk is the chance that harm could occur under the planned conditions. Students should follow the teacher’s directions and the school’s laboratory rules.

Choose precautions that match the materials and actions involved. Wear required protective equipment, such as safety goggles, and use other protective equipment when directed. Keep chemicals away from food and drink. Never taste a laboratory substance. Avoid direct contact and do not smell a substance unless the teacher has explicitly instructed a safe method. Keep containers identified, use only the amount directed, and do not return unused material to its original container unless instructed.

Check where the safety equipment is and how to get help before starting. Report spills, breakage, unexpected reactions, or contact with a chemical to the teacher promptly. Do not clean up an unfamiliar spill or continue an investigation after an unexpected hazard appears unless the teacher directs you. Dispose of materials as instructed; do not assume that every substance belongs in the sink.

A safe plan also considers how the investigation will stop. Use only teacher-approved equipment and conditions. Avoid unnecessary heating or handling. Keep the work area clear, and wash hands as directed after the activity. If the proposed method cannot be made safe with available instructions and equipment, pause and ask the teacher to revise it.

Follow teacher and school instructions before, during, and after the inquiry.
Match protective steps to the materials and procedure.
Stop and report unexpected hazards rather than improvising.

4. Connect the method to the evidence

A method should make clear what will be changed, what will be measured, and what will be held constant. It should also state how measurements will be taken, how many trials are planned, and what safety precautions apply. Another student should be able to understand the plan without guessing about important details.

When the inquiry is complete, organize observations so that comparisons are clear. Include units with measurements, label conditions, and preserve the original recorded values. Describe patterns only when the data support them. If the outcome is unclear, identify possible limitations, such as difficulty judging an endpoint or an uncontrolled condition. A limitation is a feature of the method that may affect how confidently the question can be answered.

The purpose is not to force data to match a prediction. A careful inquiry may produce an unexpected or unclear outcome. Reporting that honestly is part of scientific practice. Safety and variable control make the evidence more useful, but they do not guarantee a particular result.

Write enough method detail to make the comparison understandable.
Keep original measurements and state units.
Separate what the data show from possible explanations.

Worked example

Planning a dissolving inquiry

Plan a safe, fair inquiry to investigate whether water temperature affects the time required for a fixed amount of a solid to dissolve. Do not assume or report any results.

Frame the question
Ask how changing water temperature affects the time for a chosen solid to dissolve. The question names a factor to change and an outcome to measure. Use only a material and procedure approved by the teacher.
Identify the variables
Water temperature is the independent variable because it is deliberately changed. Dissolving time is the dependent variable because it is measured. Keep the solid’s identity and mass, water volume, container, and stirring method consistent. These conditions could otherwise affect the comparison.
Set a consistent measurement rule
Use the same timing method for each trial and define the endpoint before starting, such as the point at which no solid remains visible. Use the same observer or a clearly agreed rule where possible. Record time in seconds and record the temperature with its unit. Do not insert values until they have actually been measured.
Apply safety steps
Wear the protective equipment required by the teacher. Use teacher-approved water temperatures and equipment; avoid hot water that could cause a burn. Keep materials out of the mouth, clean the workspace as directed, and report spills or breakage. Follow the teacher’s disposal instructions.
Record and interpret evidence
Plan repeated trials if materials and class time allow, and record each result rather than choosing only the values that fit a prediction. Compare the recorded times across the planned temperatures. If another condition changed, note that the comparison may be less fair. No outcome can be claimed until the inquiry has been carried out.

Answer: A suitable plan changes water temperature, measures dissolving time, and keeps the solid, its amount, water volume, container, stirring method, and endpoint rule consistent. The plan includes teacher-approved temperatures, required protective equipment, and clear reporting and disposal steps.

Check: The plan tests one intended factor and specifies both safety actions and consistent measurement conditions. It does not invent results.

Common mistakes and how to avoid them

Changing temperature, water volume, and stirring at the same time, then attributing a difference to temperature.

Correction: Change the factor named in the question and keep other relevant conditions consistent.

Writing a predicted outcome as if it were measured evidence.

Correction: Label predictions clearly and record results only after making observations.

Assuming familiar or small quantities of chemicals need no precautions.

Correction: Follow the teacher’s safety directions and check the hazards and procedure before handling materials.

Leaving units or endpoint rules out of the method.

Correction: State the units and explain how the measured outcome will be judged in every trial.

Lesson summary

A testable inquiry connects a specific question to observable or measurable evidence.
The independent variable is changed, the dependent variable is measured, and relevant controlled variables are kept consistent.
Safety steps must match the materials and procedure and must follow teacher and school directions.
Record actual observations honestly, with units, and distinguish evidence from prediction or explanation.

Check your understanding

Question 1

A student changes the water temperature and the amount of solid in each trial. What is the main problem?

The student has changed more than one relevant condition, so the cause of a difference is unclear.
The student has measured too many dependent variables.
The student has kept every condition constant.
The student has proved the prediction before collecting data.

Show answer and explanation

The student has changed more than one relevant condition, so the cause of a difference is unclear.

Changing both temperature and the amount of solid makes it difficult to link a difference in dissolving time to temperature alone.

Question 2

Which statement is an observation rather than a prediction?

The solid will dissolve sooner in warm water.
Warm water should make the solid dissolve sooner.
The measured dissolving time was recorded as 42 s.
The solid must dissolve sooner because the water is warm.

Show answer and explanation

The measured dissolving time was recorded as 42 s.

A recorded time is an observation if it was actually measured. The other statements predict or explain an outcome.

Question 3

A student notices a spill during an inquiry. What should the student do?

Wipe it up immediately without telling anyone.
Continue the trial and report it at the end.
Report it promptly and follow the teacher’s directions.
Pour water over it and put the container away.

Show answer and explanation

Report it promptly and follow the teacher’s directions.

The student should alert the teacher and follow the school’s spill procedure rather than improvising or continuing.

Key terms

Inquiry: A planned investigation that uses observations or measurements to answer a question.
Variable: A condition or feature that can take different values.
Independent variable: The variable deliberately changed in an inquiry.
Dependent variable: The outcome observed or measured in response to a change.
Controlled variable: A relevant condition kept consistent during a comparison.
Hazard: A source of possible harm.
Risk: The chance that harm could occur under particular conditions.
Limitation: A feature of a method that may affect how confidently it answers the question.

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About this lesson and its review

Published by DoAssignment. This reviewed lesson follows Ontario Grade 12 Chemistry (SCH4U), expectation A1.5. It is a study resource, not an official curriculum publication.

Before publication, content is checked for structure, mathematical or chemical notation, calculations, course boundaries, and readability. Errors can still occur, so corrections are welcomed.

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