C4h-Purifying and testing water Flashcards
What are the different types of water resources found in the UK?
Lakes
Rivers
Aquifers
Reservoirs
Why is water an important resource for many important industrial chemical processes?
It is a cheap raw material, a coolant and a solvent
Why is it important to conserve water?
All these resources are limited and demand for water increases every year
What are some pollutants that may be found in domestic water supplies?
Nitrate residues
Lead compounds
Pesticide residues
Why might water contain nitrates?
From excess fertiliser ‘run off’ into rivers and lakes
Why might water contain lead compounds?
From old lead pipes
Why might water contain pesticide residues?
From spraying too near rivers and lakes
What are the substances present in water before its purified?
Dissolved salts and minerals
Microbes
Pollutants
Insoluble materials
What are the key steps in water purification?
Filtration
Sedimentaion
Chlorination
What happens in filtration?
A wire mesh screens out large twigs then gravel and sand beds filter out solid bits
What happens in sedimentation?
Iron sulfate or aluminium sulfate is added to the water which makes fine particles clump together and settle at the bottom
Why are some soluble substances not removed from water during purification?
They cant be filtered out
What is the disadvantage of using sea water to make large quantaties of fresh water?
It is really expensive as distillation needs lots of energy
What solution is used to test for sulfate ions?
Barium chloride solution
What kind of precipitate do sulfate ions give?
White precipitate
What solution is used to test for halide ions?
Silver nitrate solution
What colour precipitate do choride ions give?
White precipitate
What colour precipitate do bromide ions give?
Cream precipitate
What colour precipitate do iodide ions give?
A pale yellow precipitate
What is the symbol equation for the reaction between silver nitrate and sodium chloride?
AgNO3 + NaCl –> AgCl + NaNO3
What is the symbol equation for the reaction between silver nitrate and sodium bromide?
AgNO3 + NaBr –> AgBr + NaNO3
What is the symbol equation for the reaction between silver nitrate and sodium iodide?
AgNO3 + NaI –> Agl + NaNO3
