A mixture of iron and sulpher. Image credit MediaWiki

A mixture of iron and sulpher. Image credit MediaWiki

ZIMSEC O Level Combined Science Notes: Mixtures and compounds

  • When two or more elements are brought together they may either form:
  • a compound
  • or a mixture
  • The table below shows the differences between a compound and a mixture
Is formed by a physical changeIs formed by a chemical change
The components of the mixture can be separated easily by physical changes/means e.g. using a magnet or sieveThe parts of the compound cannot be separated by physical means such as using a sieve
The mixture has the properties of the added substances for example iron fillings are still magneticThe properties of the compound are different from those of the original reagents
They are neither endothermic nor exothermicThey are usually either endothermic or exothermic
No new substance is formedA new substance is formed
  • An example of a compound and a mixture can be demonstrated using iron fillings and sulphur
  • If the two are mixed they form a mixture
  • In the mixture the iron which is black and magnetic retains its properties
  • The sulphur which is a yellow solid retains its solid
  • Sulphur dissolves in toluene
  • The mixture can be separated by
  • physically picking out the iron fillings
  • picking them using a magnet
  • Pouring toluene on the mixture and filtering it since the iron fillings will not be able to pass through the filter
  • If however the mixture is heated in a test tube
  • A new substance known as iron sulphide┬áis formed
  • This substance is a compound
  • You cannot see the iron fillings or the powdered sulphur
  • A exothermic chemical reaction occurs and a new compound is formed
  • Heat is given out even when the burner is removed
  • The mixture continues to glow due to the chemical reaction
  • The resultant compound is not magnetic
  • The mixture changes colour and the ingredient elements can no longer be observed

To access more topics go to the Combined Science Notes page.

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