# Ch 1 Introducing Science · Supplementary Exercises

F.1 Integrated Science · Chapter 1 revision (1.1–1.4) · Lesson 3

The whole chapter in practice: working like a scientist, fair tests, lab safety, the Bunsen burner and careful measuring.

## Key points

- Scientists work like detectives: careful **observation**, **experiments** to collect **evidence**, then **conclusions** drawn from the results.
- Research steps: observe, identify the problem, **predict**, carry out experiments, **measure accurately**, record in detail, **analyse**, discuss, **draw conclusions**.
- An **observation** is what you see or measure (ice floats on water). A **hypothesis ／ 假設** is a guess made to explain an observation.
- **Fair test**: change only the **independent** variable, measure the **dependent** variable, keep the **controlled** variables constant.
- **Safety**: goggles for everyone, glasses or not; tie long hair back; never run or stand on stools; never point a heated test tube at anyone. Every school lab keeps a fire blanket, fire extinguisher and sand bucket.
- **Fires and burns**: never use water on an electrical fire; a burning liquid fuel is put out with sand or a wet towel; a chemical burn goes under slow running water for at least 10 minutes.
- **Bunsen burner**: close the air hole, strike a match, hold it above the chimney, turn on the gas tap. Opening the air hole slowly turns the flame from yellow and irregular to **blue and regular**; the blue flame is hotter.
- **Striking back ／ 回火** (a loud sound from the burner): turn off the gas tap immediately.
- **Volume**: read with your eyes level with the bottom of the **meniscus ／ 彎月面**; an irregular object's volume = rise in the water level (or use a displacement can and measuring cylinder). 1 mL = 1 cm^3^.
- **Too thin to measure?** Measure many and divide: 500 sheets are 5 cm thick, so one is 0.01 cm. Thermometers use **mercury** or **coloured alcohol**.

## Must know

| Investigation | Independent variable (change) | Dependent variable (measure) | Controlled variables (keep the same) |
|---|---|---|---|
| Does food wrap slow ice melting? | Number of layers of food wrap | Time for the ice to melt completely | Size of the ice cubes, room temperature |
| Which tissue paper is strongest? | Brand of tissue paper | Number of weights needed to break the strip | Length and width of the strip |

Only one independent variable at a time, or you cannot tell which change caused the result.

## Common mistakes

- ✗ "I wear glasses, so I don't need goggles." ✓ Everyone wears **safety goggles** during experiments; glasses do not protect the eyes.
- ✗ Pouring water on an electrical fire. ✓ **Never water**: use a fire blanket, sand or a carbon dioxide fire extinguisher.
- ✗ Loud sound from the burner? Open the air hole fully. ✓ That is striking back: **turn off the gas tap** at once.
- ✗ "In a fair test, the independent variable is kept constant." ✓ You **change** the independent variable; the **controlled** variables are kept constant.
- ✗ Taking the final reading as the object's volume. ✓ Subtract the **starting** water level: volume = final reading − initial reading.

## Quick check

1. Water in a measuring cylinder rises from 43 cm^3^ to 71 cm^3^ when 7 equal iron cubes are added. What is the volume of each cube?
2. Put these in order to light a Bunsen burner: turn on the gas tap; close the air hole; strike a match; hold the match above the chimney.
3. Two cards are heated for 5 seconds: the one in the blue flame gets a hole, the one in the yellow flame does not. Why?
4. Which two liquids are commonly used in thermometers?
5. June compares ice cubes of different sizes, one wrapped in food wrap and one not. Is this a fair test? Why?

## Answers

1. (71 − 43) ÷ 7 = 4 cm^3^.
2. Close the air hole, strike a match, hold it above the chimney, turn on the gas tap.
3. The blue non-luminous flame is hotter than the yellow luminous one, so it burns through the card.
4. Mercury and coloured alcohol.
5. No: the ice cubes are not the same size; only the food wrap should differ.

## Did you know?

The word "meniscus" comes from a Greek word meaning "little moon" or "crescent", because of its curved shape.