Water Chemistry 3 AQA

Water

The water cycle:

1. The sun causes evaporation from the sea.

2. Water vapour is carried upwards because warm air rises.

3. As the water vapour gets higher it cools and condenses into clouds.

4. When this gets too heavy it falls as rain.

5. Eventually gets back to the sea.

Solvents:

• Water is a solvent.
• It dissolves many other chemicals.
• Dissolves most ionic compounds.
• Water molecules surround the ions and disrupt the ionic bonding.
• The ionic compound gradually falls apart.
• Water molecules are polar.
  • Positive hydrogen side.
  • negative oxygen side.
• The slightly negative side attracts the positive ions.
• The slightly positive side attracts the negative ions.

• All of these dissolve in water:
  • Salts of sodium (Na) Potassium (K) or Ammonium (NH4).
  • Nitrates (NO3)
  • Chlorides (Cl) except for silver and lead.
  • Sulfates (SO4) except for barium and lead.
  • Calcium sulfate is only slightly soluble.
• Many covalent compounds don't dissolve - they don't form ions and their molecules are too big.

Solubility:

• The solubility of a substance in a given solvent is the number of grams of the solute that dissolves in 100g of the solvent at a particular temperature.
• The solubility of a substance increases with increased temperature.
• A saturated solution is one that cannot hold any more solid at that temperature - and you have to be able to see solid on the bottom to be…