Year 7 Science · Unit 2 · Lesson 7
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Learning Goals
Compare two
Complete the table to compare a compound and a mixture. Fill in both columns for each feature.
| Feature | Compound (e.g. NaCl) | Mixture (e.g. saltwater) |
|---|---|---|
| Are the parts chemically bonded? | ||
| Is the ratio of parts fixed? | ||
| Can it be separated by physical methods? | ||
| What does the particle diagram look like? | ||
| One everyday example |
Real-world context
Australia's water treatment industry uses chemistry every day. Drinking water is treated with compounds like calcium hypochlorite (Ca(ClO)₂) to kill bacteria. Desalination plants along the south-east coast process seawater — a mixture of water, salt (NaCl), magnesium compounds and dissolved gases — to produce safe drinking water. The Port Stanvac desalination plant in South Australia can produce 100 billion litres of drinking water per year.
(a) Seawater is described above as a "mixture." Give two pieces of evidence from the passage or your lesson that support this classification.
(b) Calcium hypochlorite Ca(ClO)₂ is a compound. Explain what this tells you about the ratio of its atoms and whether it could be separated by simply filtering or evaporating.
1. Brass is an alloy made of copper (Cu) and zinc (Zn). The percentage of zinc can range from 5% to 45% depending on the intended use. Is brass an element, compound or mixture? Justify your answer with two reasons.
2. Carbon dioxide (CO₂) has 1 carbon atom bonded to 2 oxygen atoms. Explain why CO₂ is a compound, not a mixture of carbon and oxygen.
Wrap Up
In one sentence, what was the main idea of this lesson?