Reactions+and+mixtures

__**Targets for revision**__

Revision tip - There are several brain-pop videos which link well with this unit we've seen the atomic model and chemical bonds videos but you may also like to view the video on 'conservation of mass' and 'chemical equations' to support your revision.

__**Reactions and Mixtures**__

** Ideas about burning have changed greatly over the last 300 years. The Phlogiston Theory (‘flow-jis-ton’) was developed by Georg Stahl (1660–1734). It was shown to be incorrect by the work of Joseph Priestley (1733–1804) and Antoine Lavoisier (1743–1794) **

These websites may be a little hard to understand but they are a good starting place, find out about the life and theories of these scientists, what did they find out to disprove the phlogiston theory?

__**Phlogiston**__ http://www.jimloy.com/physics/phlogstn.htm __**Joseph Priestley on Phlogisto**__n __**http://web.lemoyne.edu/~giunta/phlogiston.html**__ __**Antoine Laurent Lavoisier**__ __**http://web.lemoyne.edu/~giunta/lavoisier.html**__

__**Additional information on Phlogiston theory!**__

The theory of phlogiston was German in origin, with much early work done in the town of Mainz. It was widely believed through much of the eighteenth century. Georg Ernst Stahl first used the name phlogiston in 1700. The theory became widespread and deep-seated. Eventually it gave way to the atomic theory, but only slowly. Phlogiston theorists identified three ‘essences’ which are found in all matter: ★ Sulphur or terra pinguis is the essence of inflammability. ★ Mercury or terra mercurialis is the essence of fluidity. ★ Salt or terra lapida is the essence of fixity (staying the same) and inertness.

This makes the phlogiston theory similar to the ancient alchemical idea of earth, air, fire and water. It was the ‘essence’ of inflammability that was renamed phlogiston. The idea was that substances such as metals were made of a ‘calx’ (or residue) combined with phlogiston. The phlogiston was liberated during combustion, leaving only the calx. Air, according to the theory, was merely the receptacle for phlogiston. All combustible substances, in fact, were not elements but compounds containing phlogiston. Rusting iron, for instance, was believed to be losing its phlogiston and thereby returning to its elemental state. The theory came under increasing attack as experiments pointed out its difficulties. When it was found that some metals actually gained mass when burnt, the people loyal to the theory explained this by saying phlogiston had negative mass. Even Joseph Priestley believed in the theory until his death, convinced that his discovery of oxygen was ‘dephlogisticated air’. It was Lavoisier who realised the significance of his discovery. Lavoisier made a symbolic break with phlogiston theory by burning all textbooks that supported the theory. His theory of oxidation soon replaced phlogiston theory, and remains a part of modern chemistry.

__**Peer Assessment**__ Draw a table with four columns

Teamworking Scientific content Interest levels TOTAL

give a mark out of 3, 1 is not good, 2 is good, 3 is excellent - we'll collate the class scores at the end and see who's presentation scores highest!!