Physical vs. Chemical Properties — Drills · Grade 8 Science

Chapter: Properties of Matter

What these drills covers

By the end of Physical vs. Chemical Properties you should be able to:

8 questions, multiple choice, numeric and written answer, each with a worked explanation.

Vocabulary used: physical property, chemical property, physical change, chemical change, density, model, evidence, system boundary, assumption.

Problem 1

Which is a chemical property?
  1. Melting point
  2. Density
  3. Flammability
  4. Colour
Answer and explanation

Flammability

Flammability describes how a substance reacts to form something new; the others can be measured without changing what it is.

Problem 2

Cutting a sheet of aluminium in half is
  1. a chemical change
  2. a physical change
  3. a nuclear change
  4. a reaction
Answer and explanation

a physical change

The pieces are still aluminium, so only the shape has changed.

Problem 3

Which observation is the strongest evidence that a chemical change occurred?
  1. The sample got smaller
  2. A new substance with different properties formed
  3. The sample changed shape
  4. The sample was warmed
Answer and explanation

A new substance with different properties formed

A new substance is the defining outcome; size, shape and warming can all accompany physical changes.

Problem 4

A 25.0 g sample of ice melts completely. What is the mass of the water produced, in grams?
Answer and explanation

25 g

Melting is a physical change and conserves mass, so 25.0 g.

Problem 5

Which pair are both physical properties?
  1. Density and boiling point
  2. Flammability and reactivity
  3. Rusting and burning
  4. Acidity and toxicity
Answer and explanation

Density and boiling point

Density and boiling point can be measured without changing the substance's identity.

Problem 6

Dissolving sugar in water looks like a change. Explain why it is classified as physical.
Answer and explanation

The sugar particles spread out among the water particles but keep their own identity, which is why the water tastes sweet and why evaporating the water leaves the sugar behind unchanged. No new substance has formed, so the change is physical even though the sugar is no longer visible.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 7

A student says a change must be chemical because it gave off heat. Correct this.
Answer and explanation

Giving off heat is a clue, not proof. Physical changes also release or absorb energy — water freezing releases heat, and ice melting absorbs it — without forming any new substance. Deciding requires evidence that the material afterwards is a different substance, such as a new colour, gas, precipitate, or a change in properties that cannot be reversed by a physical means.

Response criteria

  • State a scientifically accurate conclusion.
  • Show the data, mechanism, or calculation that supports it.
  • Include units, conditions, or limits where relevant.

Problem 8

Iron rusting in damp air is a chemical change because
  1. the iron changes shape
  2. a new substance, iron oxide, forms
  3. the iron gets heavier only
  4. the colour is reddish
Answer and explanation

a new substance, iron oxide, forms

Rust is a different compound with different properties; the mass increase and colour are consequences of that.

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