Lesson 12 What is mixture

1
Lesson 12 What is mixture ?

• What is mixture ?
• Is a sugar solution a mixture ?
• How do we know whether a substance is pure ?
• Is mixture a macroscopic or microscopic concept ?
  
• Are there more elements, compounds or mixtures in
  the nature ?

2
What is mixture ?

• Mixture is an impure substance with two or more
  different substances physically placed together.
• Example sea water, air, rock

3
Is a sugar solution a mixture ?

• Sugar solution is a homogenous mixture of water
  and sugar.
• Homogenous different parts are the same.

4
How do we know whether a substance is pure ?

• A pure substance has a sharp melting point where
  an impure substance has a wide melting range.
• For a pure substance, solid state and liquid
  state only coexist at a single temperature.
• For an impure substance, solid state and liquid
  state coexist over a range of temperature.

5
How do we know whether a substance is pure ?
Pure ice
Frozen Sugar Solution
6
Is mixture a macroscopic or microscopic concept ?

• A mixture is usually a substance that can be
  seen. E.g. rock, sea water
• Therefore, the term mixture usually refers to a
  macroscopic concept.

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Are there more elements, compounds or mixtures in
the nature ?

• Rock, air, sea water, wood, human are all
  mixture.
• Free elements are very rare in nature. E.g. pure
  gold and mercury
• Pure compounds are also very rare in nature. E.g.
  Ice at the two poles

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Homework

• pg40 Q2.7, pg45 Q8,9,10,11,14,15,16,17,18
• Do them on your textbook