Page 9 - Curriculum Visions Dynamic Book

 Oxygen dissolves poorly in still water. It has to be mixed into the water physically. In the open oceans this mixing takes place through the action of waves. Lakes become aerated by the action of surface waves. Thus, oxygen is most abundant in
the upper levels of any body of water and this, therefore, is also where most life is found.
In rivers oxygen is mixed with the water as it tumbles over rocks, goes over waterfalls or flows in river channels.
dissolve: to break down a substance in a solution without a resultant reaction.
ionise: to break up neutral molecules into oppositely charged ions or to convert atoms into ions by the loss of electrons.
ionisation: a process that creates ions. molecule: a group of two or more
atoms held together by chemical bonds.
vapour: the gaseous form of a substance that is normally a liquid. For example, water vapour is the gaseous form of liquid water.
Also...
The chemical symbol for water is normally written H2O, meaning that water molecules contain three atoms: two hydrogen atoms bound to each oxygen atom. The bonds are very strong and rarely break. However, a few water molecules ionise, that is the neutral molecules break up into oppositely charged particles – hydrogen (H+(aq)) ions and hydroxide (OH-(aq)) ions.
The ions in a liquid allow it to behave
as an electrolyte – a carrier of electric current. Because water ionises so poorly
it is a poor conductor of electricity.
This is why, for example, pure water
cannot be used alone in a vehicle battery. Compounds that readily ionise (substances like dilute sulphuric acid) have to be added to improve the conductivity.
This part of the diagram represents a hydrogen ion associated with a water molecule.
This part of the diagram represents a hydroxide ion.
Oxygen
+ –
Hydrogen
Water molecules
Hydrogen ions
Hydroxide ions
➡
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