GCSE AQA Chemistry Unit 3

The Water Cycle

• Hydrosphere - (Sea, rivers , lakes etc.)
• Evaporation - (The water evaporates into the atmosphere)
• Condensation - (The water condeses in the atomsphere and forms clouds)
• Precipitation - (Hey presto...Rain!)

The Purification process

• The water is filtered through screens to rid of large solids
• Ozone is added to kill off algae, bacteria and pesticides
• Refiltering takes place through sand
• The water is then passed through active carbon atoms
• Cholrine is used to rid of excess bacteria
• Stored with cholrine to ensure cleaniness

Remember: Filteration, Sedimentation, Chlorination!

Hard Water

• Hard Water is basically a stupid name for normal water with Magnesium and Calcium ions dissolved in it.
• AQA tell us that "Hard Water is high in dissolved minerals".
• These minerals often dissolve in rain water from the soil and rocks
• Hard water does NOT lather well with soap (Why that is on the sylabus i don't know?)
• The opposite of HardWater is Soft Water!

Remember: The bigger the mineral concentration, the hard the water is!

Removing the minerals

• Distilation removes the minerals in hard water but it's too expensive to use on a large scale
• The cheapest method is to add a Sodium Carbonate solution which will react anf form a precipitate with the Magnesium and Calcium
• CALCIUM SULPHATE + SODIUM CARBONATE = SODIUM SULPHATE = CALCIUM CARBONATE
• Another method is an Ion-Exchange Column which is used in large scales

Remember: CALCIUM SULPHATE + SODIUM CARBONATE = SODIUM SULPHATE = CALCIUM CARBONATE

Removing the minerals

• Inside an Ion-Exchange column there is Hydrogen OR Sodium ions
• The Hydrogen or Sodium ions replace the Magnesium and Calcium in the hard
• When the hard water passes through the column, the Magnesium and Calcium is left behind and the Hydrogen or Sodium ions are taken away.
• It is because of this the the column has to be recharged and maintatined very often

Remember: The minerals in the hard water are replace by the ions in the Ion-Exchange column!

Developing the Periodic Table

• John Newlands 1864 - Knew of 63 elements, arranged them by atomic Mass
• Dimitri Mendeleev 1869 - Used Newlands' table but left space for undiscovered elements
• Mendeleed predicted what the uniscovered elements were going to be like from the patterns he saw in the periodic table...his predictions were right
• The discovery of subatomic particles (electrons, protons) meant the periodic table was more useful

Remember: Groups = columns, Periods = rows!

Properties of Alkali Metals

• There are 6 Alkali metals: Lithium (Li), Sodium (Na), Potassium (K)...
• Situated in group 1 of the periodic table meaning there is 1 electron in their outer shell
• The reactivity of the metals increase as the column goes down - this is because the metals are proton donors meaning they get rid of an electron during a reaction. Since the single electron in their outer shell is further away as the period number increases there is less attraction from the metals nucleus meaning it is eaiser to rid of that electron therefore meaning it is an eaiser for a reaction to occcur.
• The melting points decrease as the column goes down - for the same reason as an increase in reactivty: the outer shell electron is further is further away from the nucleus atrraction.
• Alkali Metals are stored under oil so they do not react with the oxygen in the air

Reactions with Water

• Lithium - fizzes
• Sodium -
• Potassium - melts and catches fire

Remember: The test for Hydrogen is the "Squeaky Pop"!