Year 7 Science · Unit 2 · Lesson 9
Challenge Worksheet
Learning Goals
Design a mini-experiment
The Reserve Bank of Australia wants to test whether a suspicious $50 note is authentic or counterfeit. One approach is to compare the ink used in the printing. An authentic $50 note uses a specific combination of security inks with known Rf values. A forensic scientist suggests using paper chromatography to compare the printing ink from the suspicious note with a confirmed genuine note. Plan the investigation below.
| What I will change (independent variable) | |
| What I will keep the same (controlled variables — list at least 3) | |
| What I will measure (dependent variable) | |
| My prediction — what result would tell me the note is genuine? | |
| My prediction — what result would tell me the note is counterfeit? | |
| One limitation of this experiment |
1. Two pens produce the same black ink when writing, but a forensic scientist says they are different brands. Explain how paper chromatography could prove this, even if the inks look identical to the eye. Include the term "Rf value" in your answer.
2. Crude oil from Bass Strait (Victoria) is a complex mixture of hundreds of different hydrocarbon liquids, each with a different boiling point. Australia's Kwinana refinery in Western Australia uses fractional distillation to separate crude oil into useful products such as petrol (boiling range 35–75 °C), kerosene (150–250 °C), and diesel (250–350 °C). Explain why fractional distillation — rather than filtration or chromatography — is the correct technique for separating crude oil, and how it separates the fractions.
Wrap Up
In one sentence, what was the main idea of this lesson?