2713782
Descripción
Fichas por Kelly Jowett, actualizado hace más de 1 año
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Creado por Kelly Jowett
hace más de 9 años
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| Pregunta | Respuesta |
| what does hard water form? | scum |
| what can soft water do easier than hard water? | lather |
| what can form when hard water is heated? | limescale (CaCO3) |
| how is scum formed? | ions react with soap |
| what ions cause hard water? | Ca2+ and Mg2+ |
| what is Ca2+ good for in hard water? | good for teeth and bones |
| what is Mg2+ good for in hard water? | reducing the risk of heart disease |
| what is temporary hardness caused by? | the hydrogen carbonate (HCO3-) ion in calcium hydrogencarbonate Ca(HCO3)2 |
| how can temporary hardness be removed? | boiling |
| what is the equation for temporary hardness? | calcium hydrogencarbonate -> calcium carbonate + water + carbon dioxide |
| what is permanent hardness caused by? | dissolved calcium sulphate |
| how can permanent hardness not be removed? | by boiling |
| how can permanent hardness be removed using washing soda? | *adding sodium carbonate (Na2CO3) *the CO32- ions react with the Ca2+ and Mg2+ ions in the hard water *forms insoluble precipitate of calcium carbonate and magnesium carbonate which can be filtered out |
| how does an ion exchange column work? | *sodium ions on resin beads *exchange sodium ions for the calcium and magnesium ions *adds the sodium ions to the water and takes out the calcium and magnesium |
| why is ok for the sodium ions to be in the water? | doesn't make the water hard |
| how can the ion exchange column be reused? | running salt water through to replace the calcium and magnesium ions with the sodium ions |
| how is water treated to be safe for drinking? | *rainwater collected in reservoirs *aluminium sulphate and calcium oxide added to remove dirt *precipitate allowed to settle out *water filtered through sand *chlorine added to kill bacteria *water quality tested before piped to customers |
| why does the use of chlorine have to be carefully controlled when killing microbes? | it is toxic and can be used to make more toxic products |
| why is fluoride compounds added to the water supplies and toothpaste? | it prevents tooth decay |
| what are one of the arguments against adding fluoride to water? | people feel they should be able to choose if they have extra fluoride |
| how is pure water made? | distillation |
| why is pure water not made very often? | it needs a large amount of energy to boil so is expensive to produce on a large scale |
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