Year 8 Science · Unit 2 · Lesson 05
Apply Worksheet
Learning Goals
Match each word to its meaning
Write the matching letter in the middle column. Each letter is used once.
| Word | Letter | Meaning |
|---|---|---|
| Element | A. More than one substance present together, not bonded in a fixed ratio. | |
| Compound | B. A pure substance made of only one type of atom. | |
| Mixture | C. A picture that shows how the particles in a sample are arranged. | |
| Symbol | D. A simplified representation used to reason about something too small to see. | |
| Particle diagram | E. A pure substance made of different atoms chemically bonded in a fixed ratio. | |
| Model | F. A one- or two-letter shorthand for an element, such as Fe. |
1. Write the symbol for iron and for copper. Then state what the formula NaCl tells you about the atoms in table salt.
Odd one out
In each row, circle the one substance with a different classification (element, compound or mixture) from the other three. Give the reason.
| Row | Substances | Reason |
|---|---|---|
| (a) | O₂ H₂O N₂ Cl₂ | |
| (b) | salt water air muddy water carbon dioxide | |
| (c) | CO Co Cu Ca |
Cause and effect
Complete the chain to explain why salt water is a mixture. Each box follows from the box before it.
Four unlabelled jars
A lab technician finds four unlabelled jars. She records what each sample looks like, then uses a particle model of each sample to describe its particles.
| Jar | What it looks like | What the particles are like | Classification |
|---|---|---|---|
| P | Clear, colourless liquid | All particles identical; each is 2 hydrogen atoms bonded to 1 oxygen atom | |
| Q | Clear, colourless liquid | Water particles with sodium and chloride particles spread among them, not bonded to the water | |
| R | Shiny, grey solid | Only one type of atom, packed in regular rows | |
| S | Colourless gas | Pairs of bonded nitrogen atoms and pairs of bonded oxygen atoms, moving about separately |
Source: sample lab notes.
2. Complete the last column of Table 1. Then write the formula of the substance in jar P, and the two formulas of the substances in jar S.
3. Jars P and Q look exactly the same. Use the table to explain why the technician could not classify them by looking, and what evidence finally separated them.
Scenario: brass
Brass is a yellow metal made by melting copper and zinc together. Its particles are copper atoms and zinc atoms mixed in the solid, and makers can change how much zinc they add.
4. A student writes: “Brass is a compound because it is made of two elements.” Explain what the student has got wrong. Then write a stronger answer that uses all four tools: classification, symbols, a particle diagram (describe it in words) and a model.
Match each word to its meaning
Element → B; Compound → E; Mixture → A; Symbol → F; Particle diagram → C; Model → D.
1. Iron Fe; copper Cu. NaCl shows salt contains sodium and chlorine, bonded in a fixed 1:1 ratio. [2 marks: 1 both symbols, 1 elements and ratio]
Odd one out
(a) H₂O: a compound (hydrogen and oxygen bonded); the others are elements made of one type of atom. (b) carbon dioxide: a compound, a pure substance; the others are mixtures. (c) CO: carbon monoxide, a compound of carbon and oxygen; Co (cobalt), Cu (copper) and Ca (calcium) are elements. Reward noticing that a capital letter starts a new element symbol.
Cause and effect
Box 2: the salt splits up and its particles (Na⁺ and Cl⁻ ions) spread out among the H₂O molecules. Box 3: the salt particles are not bonded to the water in a fixed ratio; each substance keeps its own identity.
Go Deeper
2. P compound; Q mixture; R element; S mixture. P is H₂O; S contains N₂ and O₂. [3 marks: 2 column (all four correct, or 1 for three), 1 formulas]
3. Both are clear colourless liquids, so appearance gives no difference; particles are far too small to see. The particle evidence separated them: P has only one kind of particle, H₂O, so it is a pure compound; Q has sodium and chloride particles spread through the water but not bonded to it, so it is a mixture (salt water). [3 marks: 1 appearance identical, 1 P with evidence, 1 Q with evidence]
Show What You Know
4. Marking guide (points expected): 1 being made of two elements is not enough, a compound needs atoms chemically bonded in a fixed ratio; 1 brass is a mixture because the amount of zinc can change and the copper and zinc atoms are not bonded in a fixed ratio; 1 symbols Cu and Zn, and brass has no single formula; 1 particle diagram: two kinds of atom (drawn in two sizes or colours) packed together in rows, mixed unevenly; 1 model: a simplified picture of packed metal atoms explains why brass still behaves as a metal, for example it conducts electricity; 1 the model is useful even though it is not to scale or exact. [6 marks]
Common error to watch for: classifying by appearance, for example “it looks the same all the way through, so it is pure”. Salt water and brass both look uniform but are mixtures.