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A1.1 · Form scientific questions, predictions, and testable hypotheses

Learn to form scientific questions, predictions, and testable hypotheses through clear examples and targeted practice.

Ontario Grade 12 Chemistry

Scientific Investigation Skills and Career Exploration

SCH4U study topic A1.1: Form scientific questions, predictions, and testable hypotheses

A student notices that a sugar cube seems to disappear more quickly in warm tea than in iced tea. That is an observation: a description of something noticed. It may lead to a scientific question, but it is not yet an explanation. In chemistry, careful questions help us decide what evidence to collect. A prediction says what we expect to observe. A hypothesis gives a testable proposed answer, often including a reason. This lesson focuses on forming those three kinds of statements. It does not assume that an investigation has already been done.

What you will learn

Distinguish an observation from a scientific question, prediction, and hypothesis.
Write a focused question that can be investigated with evidence.
Identify the variables in a proposed investigation and state how they could be measured.
Write a testable hypothesis that gives a reasoned prediction about a relationship.

1. From an observation to a focused question

A scientific investigation often begins with an observation. An observation is information gathered using the senses or a measuring tool. For example, a student might observe that two sugar cubes placed in different cups appear to dissolve at different speeds. The observation describes what happened; it does not yet explain why.

A scientific question narrows an observation into something that evidence could help answer. A useful question names the factor being changed and the result being observed. For example: “How does the temperature of water affect the time needed for a sugar cube to dissolve?” This is more focused than “Why does sugar dissolve?” because it identifies a factor and a measurable result.

A variable is a factor that can take different values. The independent variable is the factor deliberately changed. The dependent variable is the result measured or observed. In the example, water temperature is the independent variable, and dissolving time is the dependent variable. Naming these variables helps show what evidence would answer the question.

A question is testable when a suitable investigation could provide evidence relevant to it. The result must be observable or measurable, and the investigation must be practical and safe. “Which cup of water feels nicer?” depends on personal preference, so it is not a clear testable chemistry question. “How does water temperature affect the time for a sugar cube to dissolve?” can be investigated by measuring temperature and time.

A focused question should avoid changing several factors at once. If the water temperature, cube size, stirring, and water volume all differ between trials, it will be difficult to tell which factor is connected to a difference in dissolving time. Factors kept the same are controlled variables. They make the comparison more useful, although no investigation can guarantee perfect control.

An observation describes evidence already noticed; a question identifies what to investigate.
A testable question points to an observable or measurable result.
State the independent variable, dependent variable, and relevant controlled variables.

2. Predictions and hypotheses

A prediction states what you expect to happen in a particular investigation. It should connect the factor being changed to the result being observed. A prediction may be written as an “If …, then …” statement: “If the water is warmer, then the sugar cube will dissolve in less time.” That statement tells the reader what result to look for, but it does not yet explain the expectation.

A hypothesis is a proposed, testable answer to a scientific question. It usually includes both a prediction and a reason. For example: “If the water temperature is increased, then a sugar cube will dissolve in less time because the water particles move more quickly and interact with the sugar more often.” The particle-level reason is a model-based explanation, not a claim that the investigation has confirmed it.

A model is a simplified way to describe or explain something that cannot be seen directly. Here, the particle model represents liquid water as particles in motion and sugar as particles that can spread through the water. This gives a possible reason for the prediction. The model helps form the hypothesis; evidence is still needed to evaluate it.

A useful hypothesis can be checked against evidence. It should not depend on a result that cannot be observed, or on a vague phrase such as “the change will be better.” It should state the direction or nature of the expected change and identify the conditions being compared. A hypothesis is not a guaranteed fact. If results do not match the prediction, the evidence can lead to a revised explanation or a better question.

A prediction and a hypothesis are related, but they are not identical. The prediction describes an expected observation. The hypothesis proposes why that observation may occur. Keeping these roles separate makes scientific thinking clearer.

A prediction states an expected result.
A hypothesis gives a testable proposed answer, often with a reason.
A hypothesis can be supported or not supported by evidence; it is not proven in advance.

3. Make the question measurable and fair

Before writing a final question, decide what the result will mean in measurable terms. An operational definition is a clear description of how a quantity will be measured or judged. For dissolving time, one operational definition might be “the time from placing the cube in the water until no solid pieces are visible.” This makes the endpoint clearer, even though different observers may still judge it slightly differently.

The question should also identify a sensible range of conditions. “How does temperature affect dissolving time?” is a start, but it leaves the temperatures and measurement method unspecified. A more useful investigation plan could compare several recorded water temperatures while using the same water volume and sugar-cube size. The question itself need not list every procedure detail, but it should be precise enough to guide one.

A fair comparison changes the independent variable while keeping important other conditions as similar as possible. For the sugar example, those conditions could include the mass and shape of the sugar, the volume of water, and whether the water is stirred. If a controlled variable changes unexpectedly, record it; do not pretend the comparison was perfect.

Use precise language. Replace “a lot faster” with a measurable quantity such as elapsed time. Replace “hot” and “cold” with recorded temperatures if a thermometer is available. Units belong with measured values: temperature may be recorded in degrees Celsius, and time in seconds. A question does not need numerical data before the investigation; it needs a plan for obtaining relevant data.

Do not write a hypothesis as if results are already known. “The warm-water trial took 20 seconds” is a result claim and would be inappropriate before collecting data. A proposal should use language such as “I predict” or “If …, then …, because …”. This keeps a prediction distinct from an observation.

An operational definition states exactly how an observation or measurement will be made.
A fair comparison changes the planned factor and keeps relevant conditions similar.
Use measurable descriptions and suitable units rather than vague wording.

4. Check the quality of a proposed investigation

Use a short review before accepting a question or hypothesis. First, ask whether the question names a factor that can be changed and an outcome that can be observed or measured. Second, ask whether the outcome has a clear measurement method. Third, ask whether relevant conditions can be kept similar. Finally, check that the hypothesis predicts a result and offers a reason that can be considered in light of evidence.

A strong proposal is not the same as a successful result. At this stage, you are designing a way to ask and answer a question. You should not invent data, describe a trial as completed, or claim that the hypothesis is confirmed. The quality of the proposal depends on clarity and testability, not on whether its prediction later turns out to be correct.

The same structure can guide questions about many chemical observations. Begin with what can be observed. Choose one factor to investigate. Decide what result could be measured. Then write a prediction and a reasoned hypothesis. Keep the chemistry within what you understand, and make sure the proposed evidence could actually address the question.

Check focus, measurability, relevant controls, and a reasoned prediction.
A well-formed hypothesis is testable even if its prediction may be wrong.
Do not report proposed or imagined results as collected evidence.

Worked example

Turning a classroom observation into an investigation proposal

A learner notices that a sugar cube appears to disappear sooner in warm water than in cool water. Form a testable scientific question, identify the variables, write a prediction, and write a hypothesis. Do not claim that any trials have been performed.

Separate observation from explanation
The observation is that the cube appears to disappear sooner in warm water. It describes what the learner noticed. It does not establish the cause, and it is not a measured result because no times have been recorded.
Choose measurable variables
Water temperature can be changed and measured, so it is the independent variable. The time until no solid pieces are visible can be measured, so it is the dependent variable. Using cubes of similar size, equal water volumes, and the same stirring condition would help make the comparison fair.
Write a focused scientific question
The question names both the factor being changed and the outcome being measured. Defining the endpoint as the time until no solid pieces are visible makes “dissolve time” more consistent to judge. How does water temperature affect the time until no solid sugar is visible?
State a prediction
The prediction says what result is expected, without claiming that it has occurred. It gives a direction that can be compared with measured times. If water temperature increases, then the time until no solid sugar is visible will decrease.
Write a reasoned hypothesis
The hypothesis combines a testable prediction with a particle-model reason. The reason is a proposed explanation, not proof. An investigation could compare measured times under the planned conditions and assess whether the evidence is consistent with the prediction. If water temperature increases, then a sugar cube will dissolve in less time because the water particles move more quickly and interact with the sugar more often.

Answer: Question: How does water temperature affect the time until no solid sugar is visible? Independent variable: water temperature, measured in degrees Celsius. Dependent variable: dissolving time, measured in seconds. Prediction: increasing water temperature will decrease the time. Hypothesis: warmer water will dissolve the cube in less time because its particles move more quickly and interact with the sugar more often. Relevant conditions to keep similar include cube size, water volume, and stirring.

Check: The question is testable because it identifies a changeable factor and a measurable outcome. The proposal gives no invented results.

Common mistakes and how to avoid them

Writing “Sugar dissolves faster in warm water” as an observation before measuring it.

Correction: If it has only been noticed, describe it as an observation. If it is an expected outcome, label it as a prediction.

Writing a question such as “Why is chemistry interesting?” and treating it as a testable investigation question.

Correction: Choose a factor that can be changed and an outcome that can be observed or measured.

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

Correction: Change one planned factor at a time and keep relevant conditions similar so the comparison can address the question.

Treating a hypothesis as a proven fact or as a record of results.

Correction: A hypothesis is a proposed, testable answer. State it before testing and evaluate it using evidence.

Using a vague result such as “it dissolves better.”

Correction: Name an observable endpoint, such as the time until no solid pieces are visible.

Lesson summary

An observation describes what is noticed; a scientific question identifies something evidence could address.
A testable question names a changeable factor and an observable or measurable result.
A prediction states an expected result. A hypothesis adds a testable proposed reason.
Define how measurements will be made and keep relevant conditions similar.
A proposed investigation is not a completed experiment. Do not invent or assume results.

Check your understanding

Question 1

Which question is most clearly testable?

Why is warm water nicer?
How does water temperature affect the time for a sugar cube to disappear from view?
Is sugar the best substance?
correctIndex": 1,"explanation":"The second question names a factor that can be changed and an outcome that can be measured using a defined endpoint."}

Show answer and explanation

How does water temperature affect the time for a sugar cube to disappear from view?

The second question names a factor that can be changed and an outcome that can be measured using a defined endpoint.

Question 2

Which statement is a prediction rather than a hypothesis?

If the water is warmer, the cube will disappear from view in less time.
The cube will disappear in less time because warmer water particles move more quickly.
The learner observed that the cube disappeared.
correctIndex": 0,"explanation":"The first statement gives an expected result. The second adds a proposed reason, making it a hypothesis. The third describes an observation."}

Show answer and explanation

If the water is warmer, the cube will disappear from view in less time.

The first statement gives an expected result. The second adds a proposed reason, making it a hypothesis. The third describes an observation.

Question 3

A learner compares different water temperatures but also uses a different amount of water each time. What is the main problem?

The dependent variable cannot be measured.
More than one condition changes, so the comparison cannot isolate the effect of temperature.
A hypothesis cannot include a reason.
correctIndex": 1,"explanation":"Changing water volume as well as temperature makes it difficult to tell which factor is connected to any difference in dissolving time."}

Show answer and explanation

More than one condition changes, so the comparison cannot isolate the effect of temperature.

Changing water volume as well as temperature makes it difficult to tell which factor is connected to any difference in dissolving time.

Key terms

Observation: Information noticed or collected using the senses or a measuring tool.
Scientific question: A focused question that evidence from an investigation could help answer.
Variable: A factor that can take different values.
Independent variable: The factor deliberately changed in an investigation.
Dependent variable: The outcome measured or observed.
Controlled variable: A relevant condition kept similar during a comparison.
Prediction: A statement of what is expected to happen in an investigation.
Hypothesis: A testable proposed answer to a scientific question, often including a reason.

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Published by DoAssignment. This reviewed lesson follows Ontario Grade 12 Chemistry (SCH4U), expectation A1.1. 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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