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gcse science C4 - H

specific for ocr gateway additonal science B.

QuestionAnswer
what are 4 different water sources? -rivers -lakes -bore holes -reservoirs
what are the 3 ways in which water is used? -coolant -valuable solvent -cheap raw material
what are 4 substances which pollute water and how do they get to the water supply? -nitrate residues, nitrates from fertiliser -lead compounds, older houses have lead water pipes, lead dissolved into water -pesticide residues, spraying near to water sources
how is clean water made? its passed through a water purification works
what are the tree main stages to water purification? 1. sedimentation. larger solid particles settle out 2. filtration. sand used to filter out fine particles 3. chlorination. chlorine added to kill microbes
what poisonous soluble substances can still remain in the water? pesticides and nitrates
how can these poisonous soluble substances be removed? extra processes e.g. distillation
why would distillation of sea water be impractical? uses huge amounts of energy, making it very expensive
why is clean water important? saves more lives than medicine
why will a dry winter result in water shortages? reservoirs don't fill up properly for the rest of the year
why is there an increase in demand for water? more homes are being built
why can saving tap water reduce carbon dioxide emissions? takes energy to pump and purify it
water tests: sulphate lead nitrate + sodium sulphate - lead sulphate (white precipitate) + sodium nitrate Pb(NO3)2 + Na2SO4 - PbSO4 + 2NaNo3
water tests: chloride silver nitrate + sodium chloride - silver chloride (white precipitate) + sodium nitrate AgNO3 + NaCl - AgCl + NaNO3
water tests: bromide silver nitrate + sodium bromide - silver bromide (cream precipitate) + sodium nitrate AgNo3 + NaBr - AgBr + NaNO3
water tests: iodide silver nitrate + sodium iodide - silver iodide (yellow precipitate) + sodium nitrate AgNO3 + NaI - AgI + NaNO3
Created by: jirwin