| What is potable water? | Water that is safe to drink, its impure as it has sufficiently low levels of dissolved impurities: salt and microbes |
| Why does potable water have low salt and microbe levels? | dissolved salts can sometimes be harmful to humans
microbes can cause illness |
| How is most potable water in the UK produced? | 1)passing the water through filter beds to remove insoluble particles
2)sterilising the water to kill microbes (the methods used for sterilisation include chlorine, ozone and ultraviolet light) |
| How is desalination carried out? | Desalination can be done by distillation and by reverse osmosis (Water is put under high pressure and passed through a membrane which has tiny pores (holes) in it. The pores allow water molecules through, but prevent most ions and molecules from passing through.) |
| What are the 3 main problems with desalination? | 1)requires a lot of energy to boil the water, and also to cool the steam down to condense it.
2)The waste water is very salty and can be difficult to dispose of in a sustainable way which does not harm marine ecosystems
3)Reverse osmosis requires expensive membranes and also produces a large volume of waste water, so its efficiency is often quite low |
| What are the processes of sewage treatment? | 1)screening and grit removal to remove large particles
2)sedimentation allows tiny particles to settle out from still water, which produces sewage sludge and effluent (the liquid which remains on top)
3)the sewage sludge is digested anaerobically by specific bacteria
4)the effluent is treated with aerobic bacteria to reduce the volume of solid waste |
| Required practical for analysis and purification of water? | 1)For each sample of water you are given, test the pH using either a pH meter or universal indicator and an appropriate colour chart. Record your observations carefully.
2)For each sample of water, pour 50 cm3 into a clean pre-weighed evaporating basin. Heat gently over a Bunsen burner, tripod and gauze until no liquid remains. Allow to cool, then weigh the evaporating basin again and calculate the mass of solid that remains in the evaporating basin. |
