A mixture of two substances with differences in physical properties can be separated by physical means.
E.g. Salt and stones can be separated by adding to water, as the salt will dissolve, but the stones will not. Water can be separated from sea water by heating, as the water will boil at 100°C, but the salt and other dissolved minerals will not.
A compound can only be separated into its constituent elements by a chemical reaction. E.g. Iron can be extracted from iron oxide by reacting with carbon. Th e iron could not be extracted from the iron oxide by physical means such as heating, dissolving or with a magnet.
Physical and chemical change
Physical change:
• Does not involve changing substances into different substances, and
• An element stays as an element when heated, although its shape or state may change.
Examples of physical changes
• Crumpling a sheet or paper
• Breaking a pane of glass
• Freezing water into ice
• Chopping vegetables
• Tempering steel
Chemical change:
• Involves changing one or more substances into different substances, and
• A compound might break apart (decompose) into its elements, or into different compounds.
Examples of chemical changes
• Combustion (burning) of wood
• The metabolism of food in the body
• Electroplating a metal
• Rotting bananas
