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GCSE Chemistry > C3 - Water > Flashcards

C3 - Water Flashcards

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1
Q

What is hard water?

A

Water that contains dissolved compounds such as calcium and magnesium salts.

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2
Q

What does hard water cause?

A

Scum

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3
Q

How does scum form?

A

Soap reacts with dissolved salts.

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4
Q

Why isn’t scum a problem when washing clothes?

A

Modern detergents are soapless.

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5
Q

How is hard water formed?

A

When streams or rivers flow over rocks containing calcium or magnesium compounds, the compounds dissolve in the water.

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6
Q

How does limestone produce hard water?

A
  • As rain falls, carbon dioxide dissolves in the water making the water in rivers slightly acidic.
  • CaCO3 reacts with the acidic solution forming calcium hydrogencarbonate.
  • Ca2+ ions get into the water making it hard.
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7
Q

What is the equation for forming hard water with limestone?

A

CaCO3 + H2O + CO2(aq) —-> Ca2+ + 2HCO3-

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8
Q

What is the equation for calcium reacting with soap?

A

sodium stearate + Ca2+ —-> calcium stearate precipitate + Na+ ions

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9
Q

Why is using hard water expensive?

A

More soap is needed since some is wasted reacting with the ions in the water.

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10
Q

How is limescale formed?

A

When water containing calcium ions is heated.

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11
Q

Give two advantages of hard water.

A
  • Calcium ions help in the development of strong bones.

- Hard water could help reduce heart disease.

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12
Q

What is soft water?

A

Water that does not contain ions that produce scum or scale.

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13
Q

What is temporary hard water?

A

Water that can have its hardness removed by heating.

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14
Q

What is permanent hard water?

A

Water that remains hard after boiling.

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15
Q

What types salts produce permanent hard water?

A

Sulfates

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16
Q

What is the equation for heating temporary hard water?

A

Ca2+ 2HCO- —-> CaCO3 + H2O + CO2

17
Q

What are the two methods for softening water?

A
  • Washing Soda

- Ion Exchange System

18
Q

What does washing soda contain?

A

Sodium Carbonate

19
Q

How does washing soda soften water?

A

The soluble carbonate ions precipitate out calcium and magnesium ions.

20
Q

How do ion-exchange columns work?

A

The sodium ions replace the magnesium or calcium ions when hard water passes through a resin.

21
Q

How can ion-exchange systems be recharged?

A

Washing with sodium chloride solution.

22
Q

What does chlorine do in water treatment?

A

Kill microbes

23
Q

What does a water filter usually contain?

A
  • Carbon
  • Ion exchange resin
  • Silver
24
Q

What does the carbon in a water filter do?

A
  • Reduces the levels of chlorine

- Reduces amounts of pesticides and other impurities.

25
Q

What does the ion-exchange resin in a water filter do?

A

Removes calcium, magnesium, lead, copper and aluminium ions.

26
Q

What does the silver in a water filter do?

A

Discourages growth of bacteria.

27
Q

What is the process for supplying water once collected in a reservoir?

A
  • The water passes through a fine sand filter to remove grit and mud.
  • Large objects are trapped by metal screens.
  • A settlement tank allows sand and soil to settle out.
  • Aluminium sulfate and lime are added to make small particles of dirt clump together making them fall to the bottom.
  • Chlorine is added to kill bacteria.
  • The pH is checked to be neutral.
28
Q

Give an advantage of softening water.

A
  • Scale isn’t produced.

- Less soap needs to be used.

29
Q

Give three advantages of hard water.

A
  • Hard water is good for bones and teeth.
  • Hard water can prevent high blood pressure.
  • Softening can cost money.
30
Q

Give an alternative to chlorine for killing microbes in water.

A

Ozone

31
Q

Give five advantages of fluoridation.

A
  • There are no obvious health risks.
  • It can reduce tooth cavities.
  • It can protect people who don’t visit the dentist.
  • It can kill bacteria that can cause heart disease.
  • Fluoride is added in very small quantities.
32
Q

Give five disadvantages of fluoridation.

A
  • Fluorosis can cause bones to weaken.
  • The benefit of fluoridation isn’t considered to be significant.
  • People should have a right to choose treatments.
  • Excess fluoride can affect the brain.
  • Safe limits of fluoride can’t be set without controlling intake.

GCSE Chemistry (19 decks)

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