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Whats in the water we drink?
Description
Chemistry (Further) Mind Map on Whats in the water we drink?, created by ryangriscti on 14/11/2013.
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chemistry
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Resource summary
Whats in the water we drink?
Hard water
Disadvantages
Difficult to form lather with soap
Scum fomshich wastes soap
Scale (a hard crust) forms inside kettles wasting energy
Hot water pipes 'fur up' which can block them completely
Advantages
Preffered taste
Calciumin the water is good for strong teeth and bones
Reduces heart illnesses
Good for making beer
Stops poisonous salts dissolving in water
What makes it hard?
If the water supply has flowed through chalk or limestone (calcium carbonate) it will be hard
The chemistry of scum
Calcium and magnesium ions that cause hard water are not removed when water is purified at the water works, so they're found in tap water
calcium ions from water(soluble) + stearate ions from soap(soluble) = calcium stearate (scum) (insoluble)
Water softening
All rain is acidic due to co2 dissolving in water to form a weak solution of carbonic acid
Dissolving the rocks
When rain falls onto rocks, this weak acidity sets off the slow chemical reactions that cause chemical weathering
Some of the minerals in igneuos rocks are slowly turned to clay
The weak carbonic acid has a more direct effect on rocks such as limestone that are made of calcium carbonate
These rocks are slowly dissolved away as soluble calcium hydrogencarbonate froms
Limescale problems
As hard water evaporates (or heated) some co2 is lost with the water, and calcium carbonate reforms
Enhanced if heated meaning kettles, hot water pipes etc all suffer from limescale
Can be easily removed by dissolving it in a weak acid
Temporary and permanent hardness
By boiling hard water, you can reverse the reaction driving off the co2 and precipitating all of the calcium ions as calcium carbonate.
Temporary hardness
Water softening
Bath salts soften the water immediately by precipitating the calcium and magnesium ions in a double decomposition reaction
Sodium carbonate+calcium ions = calcium carbonate+sodium ions
An expensive option is a ion-exchange column
contains sodium ions (provided by common salts) or hydrogen ions, which can swap places with calcium or magnesium ions in the hard water
It can run continuously for a long time, removing the magnesium and calcium ions from the water.
Dishwashers have this which is why salts is added regularly
The water that comes out now however contains sodium ions which are not good for heath
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