Water

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What is formed with soft water and soap?
A lather
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What is formed with hard water and soap?
Scum
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What do you have to use to avoid getting scum?
Soapless detergent
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What does hard water contain that makes it hard?
Dissolved calcium ions and magnesium ions
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Is scum soluble soluble or insoluble?
Insoluble
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What do you need to do to get a lather with hard soap?
Use more soap
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Why is hard water more expensive?
You need more soap to form a lather with hard water, so it costs more to buy
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When hard water is heated, what does it form?
Scale
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What is scale mostly made out of?
Calcium carbonate
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What does scale do that makes it an expensive drawback?
Clogs up pipes and boilers, which reduces efficiency of heating systems
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What does rain falling on some types of rock do?
Can dissolve compounds
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Give two examples of soluble compounds that are dissolved by water
Magnesium sulfate and calcium sulfate
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What does hard water contain that makes it good for you?
Calcium ions, as they are good for healthy teeth and bones
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What does drinking hard water also decrease your risk of?
Heart disease
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What is temporary hardness caused by?
Hydrocarbonate ions (HCO-)
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What is permanent hardness caused by?
Dissolved calcium sulfate
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How is temporary harness removed?
By boiling
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Explain the process of removing temporary hardness
When heated, the calcium hydrocarbonate decomposes to form calcium carbonate which is insoluble. This is limescale and is solid
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How is hard water softened?
By adding washing soda (sodium carbonate)
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Explain the process of softening hard water by using washing soda
The added carbonate ions react with the calcium and magnesium ions to make an insoluble precipitate of calcium carbonate and magnesium carbonate. The Ca and Mg ions are no longer dissolved in the water so they can't make it hard
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What is the second way of softening hard water?
By running water through 'ion exchange columns'
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Explain the process of softening hard water by an ion exchange column
The columns have lots of sodium ions and 'exchange' them for calcium or magnesium ions in the water that runs through them
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Where does most of our drinking water come from?
Reservoirs
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What is the first stage of treating water?
The water passes through a mesh screen to remove big objects like twigs
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What is the second stage of treating water?
Chemicals are added to make solids and microbes stick together and fall to the bottom
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What is the third stage of treating water?
The water is filtered through gravel beds to remove all the solids
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What is the fourth stage of treating water?
Water is chlorinated to kill of any harmful microbes left
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What can people do to remove even more substances from their tap water?
Buy filters that contain carbon or silver
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What does carbon in filters do?
It removes the chlorine taste
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What is silver supposed to do in filters?
Kill any bacteria
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What do water softeners contain?
Ion exchange resins
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What is the method of getting totally pure water?
Distillation
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How can water be distilled?
By boiling water to make steam and condensing the steam
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Why is distillation inappropriate to produce tap water
It is too expensive, as so much energy would be needed to boil all the water we use
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Why is fluorine added to water in some parts of the country?
It helps to prevent tooth decay
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Why is chlorine added to water?
It helps to prevent disease as it kills off harmful microbes
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What is a risk of adding chorine that evidence suggests?
It could increase the risk of developing certain types of cancer
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Why do some people think that there is a link between chlorine in water and cancer?
Chlorine can react with other substances in water to produce toxic by-products which some people think could cause cancer
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What is the problem with high doses of fluorine?
It can cause cancer and bone problems
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In water, what needs to be carefully monitored and why?
Levels of chemicals need to be carefully monitored as too much of, for example, fluorine could be added to make it harmful
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Other cards in this set

Card 2

Front

What is formed with hard water and soap?

Back

Scum

Card 3

Front

What do you have to use to avoid getting scum?

Back

Preview of the front of card 3

Card 4

Front

What does hard water contain that makes it hard?

Back

Preview of the front of card 4

Card 5

Front

Is scum soluble soluble or insoluble?

Back

Preview of the front of card 5
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