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Flashcards in C3 Water Deck (25)
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Is the water that we drink pure and safe? Explain your answer.

The water we drink is not pure because it contains dissolved substances. It should be safe to drink treated water as it does not contain anything that could harm us.


What is soft water?

Soft water readily forms lather with soap.


What is hard water?

Hard water reacts with soap to form scum and so more soap is needed to form lather.


What are soapless detergents?

Soapless detergents do not form scum.


What causes hard water?

Hard water contains dissolved compounds, usually of calcium or magnesium, from the rocks that the water comes into contact with.


What is the difference between permanent and temporary hard water?

Permanent hard water stays hard when it is boiled. Temporary hard water is softened by boiling.


What causes temporary hard water and why is it treatable?

It contains hydrogencarbonate ions (HCO3––). These decompose on heating to produce carbonate ions which react with Ca2+ and Mg2+ ions to form precipitates that remove the hardness as limescale.


What are the disadvantages of hard water?

Using it can increase costs because more soap is needed. When temporary hard water is heated it produces scale that coats heating elements and reduces the efficiency of heating systems and kettles.


What are the advantages of hard water?

Calcium cmpds are good for the growth and maintenance of bones and teeth; they help to reduce heart disease; it makes good tea!


How does sodium carbonate soften hard water?

It reacts with the Ca2+ and Mg2+ ions to form a precipitate of calcium or magnesium carbonate


How do ion exchange columns soften hard water?

Ion exchange columns contain sodium ions, which replace the calcium and magnesium ions when hard water passes through the column.


Why do you need to put salt into a dishwasher regularly?

The sodium ions in the salt exchange for the calcium ions that have built up in the dishwasher’s ion exchanger.


How would you compare the hardness of two water samples?

By titrating with soap solution. i.e. add soap solution from a burette and shake the water to see if forms a lasting lather.


How would you compare the effects of water softening by bath salts and ion exchange?

Take a water sample and separate it into three equal parts. Pass one through an ion exchange resin, add bath salts to the second and filter. Then compare the hardness of the three samples by titrating with soap solution.


When choosing water to make into drinking water, where do you start?

By choosing an appropriate source, drinking water should have sufficiently low levels of dissolved salts and microbes; start with clean water out in the country if you can.


How do you get rid of suspended solids in the water during treatment?

By passing the water through filter beds to remove any solids


How do you get rid of the microbes in water during water treatment?

By sterilising with chlorine.


Why is fluoride added to drinking water?

Fluoride may be added to improve dental health though this is controversial.


Why is chlorine added to drinking water?

To kill/sterilise the pathogens/microbes


Why is drinking water neutralised during treatment?

Acids taste sour; alkalis taste soapy, neutral water has no taste.


Some people use water filters on their tap water, what do they filter out?

They remove some dissolved substances from tap water to improve the taste and quality.


What is in commercial water filters?

They contain activated charcoal (carbon), silver and ion exchange resins


Some people make drinking water using distillation, what does this mean?

Water, even seawater, is boiled. The steam is condensed as pure water.


Explain why distillation is an expensive way to make drinking water.

A large amount of energy is needed to boil the water so high costs are involved.


Suggest an area of the world that might use distillation to make water.

Somewhere wealthy, The Gulf States.