Year 9 Science · Unit 2 · Lesson 05
Challenge Worksheet
Learning Goals
1. Name the organic compound that is (a) the main energy molecule in your cells and (b) the plastic in thin shopping bags.
Plan a short investigation
Plan a heating test to sort four white powders (table sugar, table salt, baking soda and citric acid) into organic and inorganic. Hint: black carbon left after strong heating is a clue.
Prediction
If a powder is organic, then when it is heated strongly it will …, because …
Variables
What result would show your prediction is wrong?
Another class’s results
Each powder (2.00 g) was heated strongly in an open crucible for five minutes, then cooled and weighed.
| Powder | Mass before (g) | Mass after (g) | Observations |
|---|---|---|---|
| Table salt | 2.00 | 2.00 | No change |
| Citric acid | 2.00 | 0.35 | Melted, bubbled, turned black |
| Baking soda (NaHCO₃) | 2.00 | 1.26 | Gave off steam and a gas; white solid left |
| Table sugar | 2.00 | 0.62 | Melted, went brown then black; smoked |
Source: sample class results. The baking soda value matches the known breakdown of NaHCO₃ on heating.
2. Calculate the percentage of its mass that baking soda lost.
Answer %
3. “Baking soda lost mass, so it must be organic, like sugar.” Use all the results and the C–H rule to evaluate this conclusion.
4. A classmate argues that one heating test is not enough to prove a compound is organic. Evaluate this argument, say what extra evidence you would want, and name a substance that could mislead the test.
5. A science vlogger with 2 million subscribers posts: “All natural materials are organic compounds and all synthetic (human-made) materials are inorganic. That’s why natural products are always safer.” Using named chemical examples from this lesson, respond to each part.