Water in rivers, lakes and the oceans is evaporated by the heat of the Sun.
This forms water vapour that rises in the atmosphere and cools so that it condenses to form clouds.
The water droplets in the clouds join together to produce rain. It then falls as precipitation.
This is known as the water cycle.
Solubility of Compounds
Most ionic compounds are soluble in water.
Most Covalent compounds are insoluble in water. (some molecular substances are soluble in water)
Solubility is given in.. grams of solute per 100g of water at a given temperature.
A saturated solution in one in which no more solute will dissolve at that temperature. When a hot saturated solution cools, some of the solute will separate from the solution(crystallise).
Water of the correct quality is essential for life. For humans, drinking water should have sufficiently low levels of dissolved salts and microorganisms.
To produce good quality and safe water you...
- Pass the water through a filter bed to remove solid particles.
- Add chlorine gas to kill any harmful bacteria.
Solubility of Gases
Many Gases are soluble in water.
The solubilty of gases DECREASES as the TEMPERATURE INCREASES.
- dissolving carbon dioxide in water at high pressures produces carbonated water. It is used to make fizzy drinks.
- dissolved oxygen is essential for aquatic life.
Hard and Soft Water
Soft Water Doesn’t contain many dissolved particles
Hard Water Contains dissolved particles usually magnesium or calcium. (the compounds are dissolves when they come in contact with rocks.
- Reduces heart disease. It contains calcium compounds which are good for teeth and bones.
- Produces Scale (when heated) reduces efficiency of kettles.
- Reacts with soap to produce scum. (more soap needed so increases cost)
Water filters containing carbon, silver and ion exchange resins can remove some dissolved substances from tap water to improve the taste and quality.
Carbon absorbs organic compounds
Ion-exchange resins get rid of metal ions
Silver is a bactericide (has a anti-bacterial effect)
Add Sodium Carbonate
- It reacts with the calcium/magnesium ions to form calcium/magnesium carbonate which precipitates out of the solution.
Use an Ion Exchange Column
- The column contains a resin with sodium/ hydrogen ions. As the hard water passes through the column the calcium/magnesiun ions are replaced with the sodium/hydrogen ions.
Distillation - This produces pure water. This process involves boiling water to produce steam and condensing it to produce pure liquid water.
It uses alot of energy therefore it is expensive