Year 8 Science · Unit 2 · Lesson 3
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Learning Goals
Compare two
Complete the table to compare a compound and a mixture. Fill in both cells for each feature.
| Feature | Compound | Mixture |
|---|---|---|
| Are the atoms/particles chemically bonded? | ||
| Ratio of components (fixed or variable?) | ||
| Can it be physically separated? (yes/no + method) | ||
| What does its particle diagram look like? | ||
| Give one example substance |
Read the graph
The bar chart below shows the percentage composition of air by volume. Study the graph carefully, then answer the questions.
Data: Bureau of Meteorology / Standard atmosphere composition (dry air), NOAA 2022
(a) Which gas makes up the greatest percentage of air by volume?
(b) Using the data in the graph, explain why air is classified as a mixture and not a compound.
(c) If argon were chemically bonded to nitrogen in a fixed ratio, what type of substance would form? Explain.
1. Seawater contains dissolved salt, water, gases and other minerals. Explain why seawater is classified as a mixture, referring to bonding and the ratio of components.
2. A student wants to separate salt from seawater. Suggest a suitable physical separation method and explain why it works for a mixture but would not work to separate the elements from salt (NaCl).
Wrap Up
In one sentence, what is the most important difference between a compound and a mixture?