Post by Admin on Nov 24, 2016 10:09:37 GMT
Water
Water is a compound made up of hydrogen and oxygen.
Water is tested for using cobalt chloride paper. It turns from blue to pink in the presence of water.
Water freezes at 0 degrees Celsius.
Water boils at 100 degrees Celsius.
Ice floats on water because it is less dense than water.
Water is an excellent solvent, and therefore it is very rarely pure because substances dissolve in it.
Water Treatment
Water treatment has five stages - screening, settling, filtration, chlorination, fluoridation.
Screening involves using a wire mesh to filter out large, insoluble particles (e.g. twigs/branches).
Settling involves using settling beds to remove smaller insoluble particles.
Filtration involves filtering the water through beds of sand & gravel to remove small insoluble particles.
Chlorination involves adding chlorine to kill bacteria.
Fluoridation involves adding fluoride for healthy teeth.
Hardness in Water
Soft water is water that forms a lather easily with soap.
Hard water does not form a lather easily with soap.
Water hardness is caused by the presence of dissolved calcium ions.
Hardness in water is removed by distillation or using an ion exchange resin.
Ion exchange resin works by exchanging the calcium ions which cause hardness with hydrogen ions.
Advantages of hard water include that it tastes better, and provides calcium.
Disadvantages of hard water include that it causes limescale, and wastes soap.
Electrolysis
Water can be broken down into hydrogen and oxygen by electrolysis. Hydrogen is formed at the negative electrode, oxygen is formed at the positive electrode.
Electrolysis of water produces twice as much hydrogen as oxygen because in water (H2O), there are 2 H atoms for every O atom.
A Hoffman voltameter is used in electrolysis of water.
Water is a compound made up of hydrogen and oxygen.
Water is tested for using cobalt chloride paper. It turns from blue to pink in the presence of water.
Water freezes at 0 degrees Celsius.
Water boils at 100 degrees Celsius.
Ice floats on water because it is less dense than water.
Water is an excellent solvent, and therefore it is very rarely pure because substances dissolve in it.
Water Treatment
Water treatment has five stages - screening, settling, filtration, chlorination, fluoridation.
Screening involves using a wire mesh to filter out large, insoluble particles (e.g. twigs/branches).
Settling involves using settling beds to remove smaller insoluble particles.
Filtration involves filtering the water through beds of sand & gravel to remove small insoluble particles.
Chlorination involves adding chlorine to kill bacteria.
Fluoridation involves adding fluoride for healthy teeth.
Hardness in Water
Soft water is water that forms a lather easily with soap.
Hard water does not form a lather easily with soap.
Water hardness is caused by the presence of dissolved calcium ions.
Hardness in water is removed by distillation or using an ion exchange resin.
Ion exchange resin works by exchanging the calcium ions which cause hardness with hydrogen ions.
Advantages of hard water include that it tastes better, and provides calcium.
Disadvantages of hard water include that it causes limescale, and wastes soap.
Electrolysis
Water can be broken down into hydrogen and oxygen by electrolysis. Hydrogen is formed at the negative electrode, oxygen is formed at the positive electrode.
Electrolysis of water produces twice as much hydrogen as oxygen because in water (H2O), there are 2 H atoms for every O atom.
A Hoffman voltameter is used in electrolysis of water.