C3- What is hard and soft water?

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Hard water
Contains dissolved C2+ ions and/or Mg2+ ions
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Temporary hard water
Contains HC03- ions too
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Permanent hard water
Doesn't contain hydrogen carbonate ions
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Soft water
NO C2+ OR Mg2+ IONS. THERE CAN BE ANY COMBO OF OTHER IONS BUT IF THERE IS NO CALCIUM OR MAGNESIUM IONS PRESENT THEN IT'S SOFT WATER
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How does water become hard?
The water first comes from rain fall. the rain passes through rocks (CaC03) and gypsm (MgSO4) and because the water is slightly acidic, it dissolves the rocks and releases the ions
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What happens to temporary hard water when it's heated?
The hydrogen carbonate ions react with the calcium and/or the magnesium ions and you get either calcium carbonate/magnesium carbonate. Both of these are insoluble solids so they drop out of the solution (limescale) and soft water remains.
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Advantages of hard water
More calcium intake for people- good for teeth and bones. Decreases risk of heart disease
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Disadvantages
limescale- if appliances have limescale they don't work as effectively bc the heat has to travek through the warer AND the limscale. Limescale clogs up pipes, scum build up in sinks
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Scum is also known as
calcium/magnesium sterate
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2 methods of softening water
ion exchange column, adding washing soda
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Ion exchange columns work by
hard water gets poured into the column (contins a resin). Na+ ions from the water pass over the resin and the Ca2+/Mg2+ ions swap with the Na+ ions. Softened water comes out
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Water containing Na+ ions rather than Ca2+/Mg2+ ions is better because
it doesn't damage appliances
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However you can't
drink this water because the salt content will cause a high BP
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Adding washing soda
makes the Ca2+/Mg2+ ions form insoluble precipitates (calcium + sodium carbonate > calcium carbonate + sodium ions)
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The issue with this is..... so...
Calcium/ magnesium carbonate forms limescale which reduces the effiency of appliances, only to be used in particular cases eg washing clothes by hand
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How to remove temporary hardness
Boiling the water. When this happens, the soluble calcium hydrogencarbonate decomposes (breaks down) to form calcium carbonate (which is insoluble), water and carbon dioxide
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During the filtration stage...
water passes through layers of sand and gravel. This removes all solids.
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It also contains
carbon slurry which removes odours and tastes
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In the disinfection stage
chlorine is added (chlorination) which kills all the bacteria.
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The issue with this is
too much is poisonous but too little means there are still bacteria present
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You can purify water by desalination
the salty water is boiled then the water evaporates and is then condensed in the condenser. The cold water surrounding it cools it down and the water comes out in the beaker, you're left with the salt.
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The problem with this is
you can't just pout it back in the ocean (would ruin ecosystems) so it's difficult to get rid of. Plus the costs are high and it contributes to the greenhouse effect
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A domestic water filter contains 3 filters:
an ion exchange column (this one doesn't out the salt back in), activiated carbon-removes chlorine, pesticides and other organic compunds and silver- kills bacteria
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Adding floiurine to water is good because
improved dental care, prevents cavities
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However the disadvantages are
flourosis and weakening of the bones
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Other cards in this set

Card 2

Front

Temporary hard water

Back

Contains HC03- ions too

Card 3

Front

Permanent hard water

Back

Preview of the front of card 3

Card 4

Front

Soft water

Back

Preview of the front of card 4

Card 5

Front

How does water become hard?

Back

Preview of the front of card 5
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