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Chemistry- C3 > C3.2 Water > Flashcards

C3.2 Water Flashcards

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1
Q

What happens when hard water reacts with soap?

A

scum is formed so more soap is needed to form lather

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2
Q

What type of soap does not form scum when it reacts with hard water?

A

soapless detergents

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3
Q

What does hard water contain?

A

dissolved compounds, usually of calcium or magnesium

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4
Q

When do compounds of calcium or magnesium become dissolved in water?

A

when water comes into contact with rocks

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5
Q

What are the 2 types of hard water?

A

temporary hard water

permanent hard water

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6
Q

What is the difference between temporary hard water and permanent hard water?

A

permanent hard water remains hard when it is boiled whereas temporary hard water is softened by boiling

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7
Q

Describe how temporary hard water is softened by boiling

A

temporary hard water contains HYDROGENCARBONATE IONS (HCO3-) that decompose on heating to produce carbonate ions which react with calcium or magnesium in the hard water to form precipitates- scale

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8
Q

What are some disadvantages of using hard water?

A

can increase costs because more soap is needed

When temporary hard water is heated it can produce scale that reduces the efficiency of heating systems and kettles

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9
Q

What are some advantages of using hard water?

A

calcium compounds are good for the development and maintenance of bones and teeth and can also help to reduce heart disease

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10
Q

How can hard water be made soft? (2 ways)

A

ADDING SODIUM CARBONATE- which reacts with the calcium and magnesium ions to form a precipitate of calcium carbonate and magnesium carbonate

USING COMMERCIAL WATER SOFTENERS- such as ion exchange columns containing hydrogen ions or sodium ions, which replace the calcium and magnesium ions when hard water passes through the column

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11
Q

How can the correct water quality be produced by?

A

by:

  • choosing an appropriate water source
  • passing the water through filter beds to remove any solids
  • Sterilising with chlorine
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12
Q

For humans, what should water have significantly low levels of?

A

dissolved salts and microbes

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13
Q

What do water filters contain?

A

carbon, silver and ion exchange resins

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14
Q

What do water filters do?

A

they remove some dissolved substances from tap water

to improve the taste and quality

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15
Q

How do water filters work?

A

carbon removes the chlorine taste and silver is suppose to kill bugs

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16
Q

Why may chlorine be added to water?

A

to reduce microbes

17
Q

Why may fluoride be added to water?

A

to improve dental health

18
Q

What are some arguments against the addition of fluoride to drinking water?

A

high doses can cause cancer and bone problems

people do not think it is right to ‘mass medicate’ so should be able to chose whether they want to be taking fluoride

19
Q

What are some arguments against the addition of chlorine to drinking water

A

toxic

no consumer choice

20
Q

Pure water can be produced by…….

A

distillation

21
Q

Why does the distillation of water cost a lot?

A

because of the large amount of energy needed

22
Q

Describe how pure water can be produced by distillation

A

heat and boil water to make steam.

cool steam and allow it to condense

23
Q

What is the word equation for when temporary hard water is heated?

A

calcium hydrogencarbonate—calcium carbonate + water + C02

24
Q

What is limescale?

A

calcium carbonate

25
Q

Describe how you can measure the hardness of water by titration with soap solution

A
  • Fill a burette with 50 cm3 of soap solution
  • Add 50cm3 of the first water sample into a flask
  • use the burette to add 1cm3 os soap solution into the flask
  • put a bung in the flask and shake for 10 seconds
  • repeat steps 1-4 until a good, lasting lather is formed (a lasting lather is one where bubbles cover the surface for at least 30 seconds)
  • record how much soap was needed to create a lasting lather
  • repeat all the steps with other water samples
  • repeat whole experiment again using boiled samples instead to see if the results change if the sample is temporary hard water
26
Q

What happens when soft water reacts with soap?

A

soft water readily forms a lather

27
Q

Describe how an ion exchange column softens water

A

the calcium ions in the water are replaced by sodium ions in the resin in ion exchange columns

28
Q

Explain why sodium chloride needs to be passed through an ion exchange column after the column has been used for a couple of weeks

A

to replenish sodium ions

29
Q

Suggests arguments for the addition of adding chlorine to sterilise water

A
  • kills microbes
  • prevents disease
  • only small amounts are needed
30
Q

Explain how scale forms on heating elements

A

on heating, the calcium hydrogencarbonate ions decompose

forming calcium carbonate which is insoluble

31
Q

Explain how adding sodium carbonate softens hard water

A

the carbonate ions react with calcium ions forming a precipitate of calcium carbonate

therefore the water is softened as this removes the calcium ions which caused the water to be hard

32
Q

Suggest why scale on heating elements causes problems

A

the scale reduces the efficiency of the heating element

this increases energy costs

33
Q

Explain how water filters containing carbon, silver and ion exchange resin softeners soften permanent hard water

A

sodium ions are present in the resin

these sodium ions replace the calcium ions, which caused the hardness of water

34
Q

How is hard water produced from rainwater?

A

calcium or magnesium ions causing water hardness are dissolved

from rocks

35
Q

What are some advantages and disadvantages of using an ion exchange column?

A

resin needs replenishment with sodium ions

increases sodium content of the water

easy/quick method

continuous process

36
Q

What are some advantages and disadvantages of using sodium carbonate to soften water?

A

batch process

leaves a residue of precipitated carbonate in the water

increases sodium content of the water

easy/cheap

Chemistry- C3 (6 decks)

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