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Lesson 16: Identifying Pure Substances Melting point (intro) Boiling point (intro) Simple observations
Year 8 • Chemistry
Identifying Pure Substances
In this lesson, students learn how pure substances can be identified using melting point and boiling point observations, and how these properties differ from those of mixtures.
Lesson Objectives
- Understand what a pure substance is.
- Learn what melting point and boiling point mean.
- Use simple observations to identify purity.
- Compare pure substances and mixtures.
1. What Is a Pure Substance?
A pure substance contains only one type of particle.
It can be a single element or a single compound.
[ Image Placeholder – Pure Substance vs Mixture ]
Examples of pure substances:
• Distilled water
• Pure copper
• Pure sodium chloride
• Distilled water
• Pure copper
• Pure sodium chloride
2. Melting Point (Intro)
The melting point is the temperature at which a solid changes into a liquid.
[ Image Placeholder – Melting Ice Experiment ]
Key idea:
• A pure substance melts at a fixed temperature
• A mixture melts over a range
• A pure substance melts at a fixed temperature
• A mixture melts over a range
3. Boiling Point (Intro)
The boiling point is the temperature at which a liquid changes into a gas.
[ Image Placeholder – Boiling Water ]
Key idea:
• Pure liquids boil at a fixed temperature
• Mixtures boil over a range of temperatures
• Pure liquids boil at a fixed temperature
• Mixtures boil over a range of temperatures
4. Simple Observations to Identify Purity
Scientists use simple observations to decide whether a substance is pure.
[ Image Placeholder – Laboratory Observations ]
Signs of a pure substance:
• Sharp melting point
• Sharp boiling point
• Same result every time
• Sharp melting point
• Sharp boiling point
• Same result every time
Practice Questions
A. Fill in the Blanks
- A pure substance contains only __________ type of particle.
- The melting point is when a solid turns into a __________.
- Pure substances melt at a __________ temperature.
- The boiling point is when a liquid turns into a __________.
- Mixtures boil over a __________ of temperatures.
B. True or False
- Distilled water is a pure substance.
- Pure substances have sharp melting points.
- Mixtures have fixed boiling points.
- Melting and boiling points help identify purity.
- All liquids boil at the same temperature.
C. Short Answer
- What is a pure substance?
- What does melting point mean?
- What does boiling point mean?
- Why do mixtures melt over a range?
- Name one way to identify a pure substance.
✅ Show Answer Key
A. Fill in the Blanks
- one
- liquid
- fixed
- gas
- range
B. True or False
- True
- True
- False
- True
- False
C. Short Answer
- A substance with only one type of particle.
- The temperature where solid becomes liquid.
- The temperature where liquid becomes gas.
- Because they contain different substances.
- Sharp melting or boiling point.
© Aviate Learning – Identifying Pure Substances (Year 8)
🌡️ Interactive Melting & Boiling Point Tester
Heat the substance and observe when it melts and boils.
Use the observations to decide if it is pure or a mixture.
Temperature: Low | State: Solid