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Lesson 15: Pure Substances Definition of purity Pure elements vs pure compounds Why purity matters
Year 8 • Chemistry
Pure Substances
In this lesson, students learn what purity means in chemistry, understand the difference between pure elements and pure compounds, and explore why purity is important in everyday life and science.
Lesson Objectives
- Define what purity means in chemistry.
- Distinguish between pure elements and pure compounds.
- Identify examples of pure substances.
- Explain why purity is important.
1. What Is Purity?
In chemistry, purity means that a substance contains only one type of particle and nothing else mixed with it.
[ Image Placeholder – Pure Substance vs Mixture ]
A pure substance can be:
• A single element
• A single compound
• A single element
• A single compound
2. Pure Elements
A pure element contains only one type of atom.
All the particles are the same.
[ Image Placeholder – Pure Element Particles ]
Examples of pure elements:
• Oxygen (O₂)
• Copper (Cu)
• Gold (Au)
• Oxygen (O₂)
• Copper (Cu)
• Gold (Au)
3. Pure Compounds
A pure compound contains two or more different elements chemically bonded together in fixed proportions.
[ Image Placeholder – Pure Compound Particles ]
Examples of pure compounds:
• Water (H₂O)
• Carbon dioxide (CO₂)
• Sodium chloride (NaCl)
• Water (H₂O)
• Carbon dioxide (CO₂)
• Sodium chloride (NaCl)
4. Why Does Purity Matter?
Purity is important because substances behave differently when they are mixed with impurities.
[ Image Placeholder – Importance of Purity ]
Purity matters in:
• Medicines (correct dose)
• Food and drinking water
• Scientific experiments
• Manufacturing materials
• Medicines (correct dose)
• Food and drinking water
• Scientific experiments
• Manufacturing materials
Practice Questions
A. Fill in the Blanks
- Purity means only one type of __________.
- A pure element contains one type of __________.
- A pure compound contains elements __________ together.
- Water is a pure __________.
- Purity is important in making __________.
B. True or False
- A pure substance can be an element or a compound.
- Pure elements contain different atoms.
- Pure compounds have fixed compositions.
- Impurities can change properties.
- All mixtures are pure substances.
C. Short Answer
- What does purity mean?
- Give one example of a pure element.
- Give one example of a pure compound.
- Why is purity important in medicines?
- How are pure compounds different from mixtures?
✅ Show Answer Key
A. Fill in the Blanks
- particle
- atom
- bonded
- compound
- medicines
B. True or False
- True
- False
- True
- True
- False
C. Short Answer
- It contains only one type of particle.
- Oxygen / copper / gold.
- Water / carbon dioxide.
- Correct dose and safety.
- Compounds are chemically bonded; mixtures are not.
© Aviate Learning – Pure Substances (Year 8)
🧪 Pure Substance or Mixture?
Click on a substance, then decide whether it is a pure substance or a mixture.
Select a substance to begin.