Part 1: Understanding Changes

Physical change: a change in which no new substance is formed. The change may be reversible.

Chemical change: a change in which one or more new substances are formed. The change is often difficult to reverse.

1. Complete the sentences using physical or chemical.

a) Melting ice is a __________ change.

b) Burning wood is a __________ change.

c) A change that forms a new substance is a __________ change.

d) A change in shape or state, without forming a new substance, is a __________ change.

2. Match each vocabulary word with its correct description.

1. Reactant

2. Product

3. Reversible

4. Evidence

A. A sign that something has happened

B. A starting substance in a reaction

C. Able to be changed back

D. A substance made in a reaction

3. Classify each example as a physical or chemical change. Circle one answer for each.

a) Cutting paper

Physical

Chemical

b) Rusting iron

Physical

Chemical

c) Dissolving sugar in water

Physical

Chemical

d) Cooking an egg

Physical

Chemical

e) Crushing a soft drink can

Physical

Chemical

f) A candle burning

Physical

Chemical

4. Name two observations that may provide evidence that a chemical reaction has occurred.

Part 2: Practical Activity — Vinegar and Bicarbonate

Aim: To observe the reaction between vinegar and sodium bicarbonate and identify evidence of a chemical change.

Equipment: Small plastic cup, 50 mL vinegar, 2 teaspoons sodium bicarbonate, balloon, funnel, measuring cylinder, safety glasses and tray.

Safety: Wear safety glasses. Do not taste the materials. Keep the mixture away from eyes and skin. Do not seal the cup with a rigid lid. Wash hands after the activity.

Method:

1. Place the cup on a tray and measure 50 mL of vinegar into it.

2. Use a funnel to place 2 teaspoons of sodium bicarbonate into the balloon.

3. Carefully fit the balloon over the cup without tipping in the powder.

4. Lift the balloon so the sodium bicarbonate falls into the vinegar. Observe carefully.

5. Predict what you think will happen when the two substances are mixed. Explain your prediction.

6. Complete the observation table.

Before mixing

Vinegar appearance:

Sodium bicarbonate appearance:

Balloon size:

After mixing

Bubbles or gas:

Temperature change:

Balloon size:

7. Write a conclusion. Was this mainly a physical or chemical change? Use evidence from your observations.

8. Higher-order question: How could you investigate whether the amount of vinegar affects the amount of gas produced? Identify the variable you would change and one variable you would measure.

Teacher Answer Key

1. a) physical b) chemical c) chemical d) physical

2. 1–B, 2–D, 3–C, 4–A

3. a) Physical b) Chemical c) Physical d) Chemical e) Physical f) Chemical

4. Accept: bubbles or gas produced, colour change, temperature change, light produced, sound produced, a new solid or precipitate, or a new smell.

5. Answers will vary. A suitable prediction is that bubbles will form, the mixture may become cooler, and the balloon may inflate.

6. Before mixing: vinegar is a liquid, sodium bicarbonate is a white powder, and the balloon is flat. After mixing: bubbles or fizzing occur, the mixture may cool, and the balloon inflates as gas is produced.

7. This is a chemical change because bubbles show that a gas was produced, indicating that new substances formed.

8. Change the volume of vinegar while keeping the amount of sodium bicarbonate and other conditions the same. Measure balloon circumference or the volume of gas produced.