Purifying and Testing Water Flashcards
What can enter water before and after treatment?
Before - pollutants such as nitrates from fertilisers and pesticides from crops
After - lead from old pipes
What are the three main stages of purification?
- Sedimentation: chemicals are added to make solid particles and bacteria settle out
- Filtration: a layer of sand on gravel filters out the remaining fine particles and some types of sand filter also remove microbes
- Chlorination: chlorine is added to kill microbes
What are the problems of water conservation?
- If there is not enough rain reservoirs don’t fill up
- The energy to pump and purify can lead to global warming
- More homes being built in the UK which increases the demand for water
What are the extra processes of purifying water for?
Soluble substances such as nitrates and pesticides that are not removed by standard purification methods because they are dissolved in water.
Why is sea water undrinkable?
It has so many dissolved substances it would have to be distilled which requires a lot of energy so it is expensive, therefore it is only used in emergency shortages.
How is water tested?
Precipitation reactions using aqueous silver nitrate and barium chloride.
What does barium chloride react with?
Barium chloride + magnesium sulphate —> barium sulphate (white precipitate) + magnesium chloride
BaCl2 + MgSO4 —> BaSO4 + MgCl2
What does silver nitrate react with to produce a cream precipitate?
Silver nitrate + sodium bromide —> silver bromide (cream precipitate) + sodium nitrate
AgNO3 + NaBr —> AgBr + NaNO3
What does silver nitrate react with to produce a yellow precipitate?
Silver nitrate + sodium iodide —> silver iodide (yellow precipitate) + sodium nitrate
AgNO3 + NaI —> AgI + NaNO3
What does silver nitrate react with to produce a white precipitate?
Silver nitrate + sodium chloride —> silver chloride (white precipitate) + sodium nitrate
AgNO3 + NaCl —> AgCl + NaNO3
