Year 7 Science · Unit 2 · Lesson 1
Challenge Worksheet
Learning Goals
Odd one out
In each set, circle the odd one out and give the reason. The rule for each set is given in brackets. There is one best answer in each set.
| Set | Circle the odd one out | Reason |
|---|---|---|
| 1 | (Is it matter?) oxygen gas · eucalyptus oil · the sound of thunder · a lump of ice | |
| 2 | (State at room temperature) honey · milk · brake fluid · dry sand | |
| 3 | (What the unit measures) kilogram · gram · newton · milligram | |
| 4 | (Is it plasma?) the Sun · a lightning bolt · a neon sign that is switched on · the helium in a party balloon |
Find the error
Sam’s revision notes
(1) My weight is 45 kilograms. (2) The white cloud coming out of a kettle’s spout is steam, which is a gas. (3) A liquid is very nearly impossible to compress, because its particles are already touching. (4) Heat and light are matter, because you can feel heat and see light. (5) Plasma conducts electricity because it is made of charged bits that are free to move.
1. Three of Sam’s five sentences contain one error each. For each wrong sentence, give its number and rewrite it correctly.
Read the data: a litre of each
Scenario
A party balloon filled with helium floats up to the ceiling. The same balloon filled with air from your lungs falls to the floor. Table 1 gives the mass of 1 litre of four substances.
| Substance | State | Mass of 1 litre (g) |
|---|---|---|
| Helium | Gas | 0.17 |
| Air | Gas | 1.2 |
| Carbon dioxide | Gas | 1.8 |
| Water | Liquid | 1000 |
Source: rounded values at about 20 °C and sea-level air pressure.
2. How many times greater is the mass of 1 litre of air than the mass of 1 litre of helium? Round to the nearest whole number.
Answer times
3. A student says: “The helium balloon floats, so helium has no mass and is not matter.” Use Table 1 to evaluate this claim.
4. Over 99% of the matter we can see in the universe is plasma, yet we rarely meet plasma on Earth. Explain both parts of this statement.
5. A student argues: “Plasma is just a very hot gas. It has no fixed shape or volume, so there are really only three states of matter.” Evaluate this argument, using evidence from the lesson.
Odd one out
1. The sound of thunder: energy, not matter. 2. Dry sand: a solid (each grain keeps its shape) though it pours; the others are liquids. 3. Newton: it measures weight; the others measure mass. 4. The helium: an ordinary gas; the others are plasma. [4 marks]
Find the error
1. Sentence 1: my mass is 45 kg (my weight is about 450 N) (1). Sentence 2: the white cloud is tiny droplets of liquid water; steam (water vapour) is an invisible gas (1). Sentence 4: heat and light are energy, not matter; they have no mass or volume (1). Sentences 3 and 5 are correct. [3 marks]
Read the data: a litre of each
2. 1.2 ÷ 0.17 = 7.06 (1), so about 7 times (1). [2 marks]
3. The claim is wrong. Helium has mass (0.17 g per litre) and fills the balloon, so it is matter (1). It floats because 1 litre of helium has about 7 times less mass than 1 litre of the air around it (1). Floating shows helium is lighter than the same volume of air, not that it has no mass or weight (1). [3 marks]
Question 4
The Sun and every other star are made almost entirely of plasma, so most visible matter is plasma (1). Plasma forms only when a gas is hot enough to lose its electrons, and Earth is not hot enough (1). [2 marks]
Question 5
Marking guide: 1 clear judgement (the argument is wrong: plasma is a separate, fourth state); 1 plasma is matter because it has mass and volume; 1 a gas has whole, neutral particles; in plasma electrons are torn away, leaving charged bits free to move; 1 plasma conducts electricity because its charged bits move (a gas does not); 1 plasma glows because electrons dropping back onto atoms release light (a jar of air does not); 1 two correct examples (the Sun, lightning, a neon sign, the aurora). [6 marks]
Model answer: The argument is wrong. Plasma has mass and volume, so it is matter, and having no fixed shape does not make it a gas. In an ordinary gas the particles are whole and neutral. In plasma, the heat has torn electrons off the atoms, leaving charged bits that are free to move. So plasma conducts electricity, and it glows because electrons dropping back onto atoms give out light; a jar of air does neither. Lightning and the Sun are plasma. So plasma is a fourth state, not just a hot gas.
Common error: naming plasma a gas because both fill their container; test for conducting and glowing.