Properties of substances
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Why
Why are power cables made of copper and pots made of metal, but drinks made of liquids? Every substance has properties that help you recognise it and that show what it is good for.
Rule
Three properties help to sort substances:
- The state of matter at room temperature (20 °C): solid, liquid or gaseous.
- The melting point: from this temperature a solid becomes liquid.
- The boiling point: from this temperature a liquid becomes gaseous.
- Melting point
The temperature at which a solid becomes liquid. For a pure substance it is always the same.
- Boiling point
The temperature at which a liquid becomes gaseous. For a pure substance it is always the same.
Memory aid
If room temperature (20 °C) is below the melting point, the substance is solid. If it lies between the melting and the boiling point, it is liquid. If it is above, it is gaseous.
Example
Why is water liquid at 20 °C?
Water melts at 0 °C and boils at 100 °C. Room temperature (20 °C) lies in between. That is why water is liquid at 20 °C.
Practice
Exercise
Three worked tasks, each with its solution:
Task no. 1
Is Iron solid, liquid or gaseous at room temperature (20 °C)?
Hint
Compare 20 °C with the melting point and the boiling point of Iron.
Solution
- Iron melts at 1539 °C and boils at 3070 °C.
- So at 20 °C Iron is solid.
Right answer: solid
Task no. 2
Is Aluminium solid, liquid or gaseous at room temperature (20 °C)?
Hint
Compare 20 °C with the melting point and the boiling point of Aluminium.
Solution
- Aluminium melts at 660 °C and boils at 2470 °C.
- So at 20 °C Aluminium is solid.
Right answer: solid
Task no. 3
Is Copper solid, liquid or gaseous at room temperature (20 °C)?
Hint
Compare 20 °C with the melting point and the boiling point of Copper.
Solution
- Copper melts at 1085 °C and boils at 2595 °C.
- So at 20 °C Copper is solid.
Right answer: solid
Exercise
Three worked tasks, each with its solution:
Task no. 1
Put these substances in order of their boiling point, the lowest first: Ethanol, Water and Copper.
Hint
The substance that turns gaseous most easily has the lowest boiling point.
Solution
- Sort by boiling point, from low to high.
Right answer: 1. Ethanol, 2. Water, 3. Copper
Task no. 2
Put these substances in order of their boiling point, the lowest first: Ethanol, Aluminium and Mercury.
Hint
The substance that turns gaseous most easily has the lowest boiling point.
Solution
- Sort by boiling point, from low to high.
Right answer: 1. Ethanol, 2. Mercury, 3. Aluminium
Task no. 3
Put these substances in order of their boiling point, the lowest first: Oxygen, Nitrogen and Table salt (sodium chloride).
Hint
The substance that turns gaseous most easily has the lowest boiling point.
Solution
- Sort by boiling point, from low to high.
Right answer: 1. Nitrogen, 2. Oxygen, 3. Table salt (sodium chloride)
Exercise
Solution
Copper conducts electric current well. right answer
Copper is a metal that conducts current very well. That is why it is used in wires and cables.
Copper is liquid at room temperature.
Copper is solid at 20 °C. It only melts at about 1085 °C.
Copper has a very low boiling point.
Copper only boils at about 2595 °C. A low boiling point would be no advantage for a cable anyway.
You choose a substance for the property you need. A cable has to conduct current well, and copper does.
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