Chemistry Unit 3.2 - Water

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What dissolved ions does hard water contain?
Magnesium, and sodium ions.
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What are the two types of hard water?
Temporary (boil it to remove H((hydrogen carbonates), and permanent (sulfate).
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What two things does hard water produce?
Scum, and scale.
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What happens when hard/soft water, and soap react?
Soft water and soap creates a lather. Hard water and soap creates scum.
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Why does hard water create scum?
The dissolved Mg, and Ca ions, withing the react react with soap to produce scum - which is insoluble.
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What is formed when (temporary) hard water is heated? And what does it affect?
It produces scum, which affects kettles, pipes and boilers.
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What does scum do?
It decreases effiency of appliances, so money is needed to replace the old equipment.
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What are some positives of hard water?
Calcium is good for teeth, and bone development, and has links to reduced heart disease. Prevents tooth decay.
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What causes temporary, or permanent hardness?
Hydrocarbonate causes temporary, whilst hard water is caused by dissolved calcium sulfate.
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How do you remove temporary hardness?
Boiling. When heated, the calcium hydrogencarbonate decomposes to form calcium carbonate which is insoluble. The solid formed is 'limescale'. This won't work for permanent hardness, however. Heating a sulfate ion does not do anything!
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What is the equation for removing temporary hardness?
calcium hydrogencarbonate --> calcium carbonate + water + carbon dioxide
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How do you soften both types of hardness?
Add washing soda (sodium carbonate) to it. The added carbonate ions react with the calcium and magnesium ions to make an insoluble precipitate of calcium carbonate and magnesium carbonate. Another way is by running it through an ion-exchange column.
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What is an ion-exchange column?
Contains a resin packed with sodium/hydrogen ions, which are exchanged for Ca2+ or Mg2+ ions in hard water.
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How can you compare the hardness of water samples?
Titration.
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What are negatives of flouridation?
Leads to fluorosis - No significant benefits - Excess fluoride affects the brain, which could lead to learning difficulties. - You can't contol your intakes
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Card 2

Front

What are the two types of hard water?

Back

Temporary (boil it to remove H((hydrogen carbonates), and permanent (sulfate).

Card 3

Front

What two things does hard water produce?

Back

Preview of the front of card 3

Card 4

Front

What happens when hard/soft water, and soap react?

Back

Preview of the front of card 4

Card 5

Front

Why does hard water create scum?

Back

Preview of the front of card 5
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