Year 8 Science · Unit 2 · Lesson 3
Foundation Worksheet
Learning Goals
Fill the gap
Choose the correct word from the word bank. Two words will not be used.
An element contains only one type of . In a compound, atoms of different elements are chemically together in a fixed . A mixture contains more than one , not bonded to each other, so it can often be separated by methods such as filtering.
Read the particle diagram
Each row describes a particle diagram. Write element, compound or mixture, then the clue you used.
| What the diagram shows | Element, compound or mixture? | Clue you used |
|---|---|---|
| (a) Every particle is one black circle joined to two white circles. All the particles are identical. | ||
| (b) Every particle is a pair of two identical blue circles joined together. | ||
| (c) Some particles are pairs of white circles; others are single black circles. They are not joined to each other. | ||
| (d) Every particle is a single grey circle. All the circles are the same. |
Sort it
Write each substance in the correct box. Each box gets exactly three substances.
Element
Compound
Mixture
Read the data
A separation test
A class poured four samples through filter paper, then heated the liquid that came through until all the water had evaporated. They recorded what was left each time.
| Sample | Left on the filter paper | Left after evaporating |
|---|---|---|
| A. Sand and water | sand | nothing |
| B. Salt water | nothing | white salt crystals |
| C. Pure (distilled) water | nothing | nothing |
| D. Muddy salt water | mud | white salt crystals |
Source: sample class results.
1. Which samples were shown to be mixtures? For one of them, name the method that separated it and what it separated out.
2. Sample C left nothing behind at either step. A student says: “So water must be an element.” Explain why the student is wrong, and why filtering and evaporating could never split water into hydrogen and oxygen.
3. A student writes: “A compound is just a mixture that has been stirred really well.” Explain why the student is wrong. Use iron(III) oxide (Fe₂O₃) as your example: iron is a strong grey metal, oxygen is a colourless gas, and iron(III) oxide is a reddish-brown solid.
Fill the gap
atom; bonded; ratio; substance; physical. Not used: colour, mass.
Read the particle diagram
(a) Compound: two different atoms joined in identical repeating units (a fixed 1 : 2 ratio). (b) Element: only one type of atom, even though the atoms are joined in pairs (like O₂ or H₂). (c) Mixture: two different substances present together, not joined to each other. (d) Element: only one type of atom.
Sort it
Element: copper, gold, oxygen gas (O₂). Compound: carbon dioxide (CO₂), water (H₂O), sodium chloride (NaCl). Mixture: salt water, air, sand and iron filings.
Read the data
1. A, B and D. Any one of: A, filtering separated out the sand; B, evaporating separated out the salt; D, filtering separated out the mud and evaporating separated out the salt. [3 marks: 1 all three samples, 1 method, 1 what it separated]
2. Nothing was left because pure water is one substance, not a mixture; that does not make it an element. Water contains two types of atom (hydrogen and oxygen), so it is a compound. Filtering and evaporating are physical methods that only separate substances that are mixed; the hydrogen and oxygen atoms in water are chemically bonded, so a chemical reaction (such as electrolysis) is needed to split them. [3 marks: one substance, not a mixture; two types of atom so compound; bonded atoms need a chemical reaction]
Show What You Know
3. Marking guide: 1 in iron(III) oxide (Fe₂O₃), iron and oxygen atoms are chemically bonded in a fixed 2:3 ratio, while a mixture has no bonds and no fixed ratio; 1 iron(III) oxide is a new substance with new properties (a reddish-brown solid, unlike strong grey iron or a colourless gas); 1 in a mixture each substance keeps its own properties; 1 a mixture can be separated by physical means, but getting iron back from iron(III) oxide needs a chemical reaction, so stirring can never make a compound. [4 marks]
Common error to watch for: in the particle diagram task, calling (b) a compound because the atoms are joined. Joined atoms of only one element still make an element.