More soap needed to produce a lather - more money going down the drain, Hard water forms scale when heated - blocks pipes and reduces efficiency of heating systems
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What causes hard water?
Calcium and magnesium ions - dissolved into the water when rain falls on some types of rock
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Name two benefits of hard water.
The calcium ions are good for teeth and bones - Those living in hard water areas are at less risk of developing heart disease
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What causes temporary hardness?
The hydro-carbonate ion HCO3
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What causes permanent hardness?
Dissolved calcium sulfate CaSO4
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How is temporary hardness removed?
By boiling - when heated calcium hydrogen-carbonate decomposes to form insoluble calcium carbonate (limescale)
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What is the word equation of the decomposition of calcium hydrogen carbonate?
calcium hydrogen-carbonate - calcium carbonate + water + carbon dioxide
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Name two ways of removing both temporary and permanent hardness.
adding washing soda - ion exchange columns
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How does washing soda soften water?
The carbonate ions in the sodium carbonate (washing soda) reach with magnesium and calcium ions to form an insoluble precipitate of calcium carbonate and magnesium carbonate
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How do ion exchange columns work?
The columns are made of resin containing sodium/hydrogen ions - hard water is run through and the calcium or magnesium ions are 'exchanged' for the ions in the resin
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What is clean drinking water?
Water that is free of poisonous salts (phosphates and nitrates) and harmful microbes
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Explain the stages of purification of water from reservoirs. 1
1 - water passes through a mesh screen to remove large solids e.g. stick
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2
2 - Chemicals are added to make smaller solids and microbes stick together and fall to the bottom
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3
3 - The water is filtered through gravel beds to remove all the solids
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4
4 - Water if chlorinated to kill off any remaining harmful microbes
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How is pure water produced?
Distillation - Boiling water to make steam and the condensing the steam - expensive
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Where is pure water used?
In chemistry labs - for making solutions
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Why is Fluorine added to drinking water in some parts of the country?
It is believed to reduce tooth decay
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What are the disadvantages of adding fluorine to water?
High doses of fluorine can cause cancer and bone problems - is it ethically right to 'mass medicate', no choice?
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Why is chlorine added to water?
It kills harmful microbes - preventing infection of water-borne diseases
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What are the disadvantages of adding chlorine to water?
Some studies have linked water containing chlorine with an increase in certain cancers - chlorine can react with substances in water to produce potentially cancer causing toxic by-products
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Other cards in this set
Card 2
Front
What causes hard water?
Back
Calcium and magnesium ions - dissolved into the water when rain falls on some types of rock
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