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GCSE Chemistry > Water > Flashcards

Water Flashcards

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1
Q

What is a solvent

A

A thing that does the dissolving

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2
Q

What is a solute

A

Something that gets dissolved

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3
Q

What is a solution

A

Mixture of a solute dissolved in a solvent

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4
Q

What is the composition of water

A

Dissolved gases, mineral ions, bacteria and pollutants

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5
Q

Potable water

A

suitable for human consumption

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6
Q

What are the processes of water treatment

A
  • sedimentation
  • filtration
  • chlorination
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7
Q

What is sedimentation

A

Large insoluble particles fall to the bottom of water due to gravity

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8
Q

What is filtration

A

Removal of smaller, insoluble particles with a filter.

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9
Q

What is chlorination

A

Bubbled through water to kill all bacteria. Chlorine is toxic to all living things.

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10
Q

Why is fluoridation good (4)

A
  • decreases tooth decay
  • makes teeth stronger
  • some people are too poor to buy good toothpaste
  • many people don’t follow dentist’s advice on brushing
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11
Q

Why is fluoridation bad? (4)

A
  • fluorosis - brown mottling of teeth
  • infertility, stomach and bone cancers
  • toxic in high concentrations
  • unethical (mass medication)
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12
Q

How can pure water be collected from salty

A

distillation

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13
Q

What is osmosis

A

Movement of water through a semi permeable membrane from a low solute concentration to a high solute concentration.

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14
Q

Hypertonic

A

High concentration of solute

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15
Q

Hypotonic

A

Low concentration of solute

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16
Q

Reverse Osmosis

A

Forcing water across the semipermeable membrane in the opposite direction it would normally flow.

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17
Q

Name for hard water

A

Calcium sulfate

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18
Q

How can temporary hard water be made soft

A

Boil it

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19
Q

How does boiling calcium hydrogen carbonate affect it

A

It decomposes to form (insoluble) calcium carbonate, water and carbon dioxide

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20
Q

What is the effect of boiling calcium sulfate

A

There is none. It does not decompose

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21
Q

What is limescale

A

Insoluble calcium carbonate

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22
Q

How can hard water be softened

A

Adding sodium carbonate (washing powder) or using an ion exchange column.

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23
Q

What are the benefits of hard water

A
  • Calcium strengthens teeth and bones
  • Helps to reduce heart disease
24
Q

What are the disadvantages of hard water

A
  • Hot water pipes ‘fur up’ becoming blocked.
  • Limescale form (e.g. kettles become more inefficient)
  • soap scum wastes soap
25
Q

How does washing powder react with hard water

A

Adding sodium carbonate (washing powder) reacts with calcium from hard water forming calcium carbonate precipitate (limescale)

26
Q

Where is an ion exchange column used

A

Dishwashers

27
Q

If water lathers easily before and after being boiled what is it

A

Soft

28
Q

If water takes along time to lather before and after boiling what is it

A

Permanent hard water

29
Q

If water takes a long time to lather before boiling but lathers quickly after what is it

A

Temporary hard water

30
Q

How do you test water hardness

A

Tests how much soap is needs to make it lather before and after boiling.

31
Q

Sources for public water

A
  • reservoirs
  • lakes
  • rivers
32
Q

What does rainwater contain

A

Dissolved CO2 and O2

33
Q

What are the effects of dissolved CO2 in rainwater

A

Lowers the pH

34
Q

Why is water in increasing demand (2)

A
  • population increase
  • industrialisation
35
Q

How else can water be desalinated other than by distillation

A

Use of membrane systems

36
Q

Boiling point of water

A

100°C

37
Q

Why is it not possible to obtain pure ethanol (bp 78°C)

A

Some water evaporates at temperature below its boiling point

38
Q

Solubility

A

Amount of solute able to dissolve in a solvent

39
Q

Units for solubility

A

g/100cm3

40
Q

Saturated solution

A

No more solute is able to dissolve

41
Q

What methods can be used to measure solubility (2)

A
  • add mass of solute to a volume of water that dissolves some of it. Filter, dry and weigh the excess solute. Determine solubility.
  • add weighed solute that dissolves in volume of water at room temperature. Heat solution so all solute dissolves. Allow to cool and record when crystals first appear. Repeat with increasing volume of water, determine solubility at each temperature and plot solubility curve
42
Q

Why does boiling remove temporary water hardness

A

It thermally decomposes hydrogen carbonate ions to precipitate insoluble calcium carbonate (limescale)

43
Q

Disadvantage of ion exchange column

A

Expensive

44
Q

What causes water hardness

A

Dissolved calcium and magnesium ions

45
Q

Natural water pollutants (2)

A
  • bacteria
  • viruses
46
Q

Man- made water pollutants

A
  • fertilisers
  • pesticides
  • household and industrial waste (sewage)
47
Q

Can fluoride ions naturally be found in water

A

yes

48
Q

Why is desalination by distillation not viable across many parts of the world

A

It uses large amounts of costly energy to boil water

49
Q

Advantages of softening water using a kettle

A

No need for expensive equipment

50
Q

Disadvantages of using a kettle to soften water (2)

A
  • Does not remove permanent hardness
  • Only useful for small volumes
51
Q

Advantages of softening water using sodium carbonate (washing powder)

A
  • removes temporary and permanent hardness
52
Q

Disadvantages of softening water using sodium carbonate (washing powder)

A
  • limescale is formed which can block washing machine pipes
53
Q

Advantages of using an ion exchange column to soften water (2)

A
  • uses concentrated sodium chloride that is cheap and easily available
  • removes temporary and permanent hardness and is a continuous process
54
Q

What is the ratio of calcium ions to sodium ions in an ion exchange column

A

1:2

55
Q

How can the resin be regenerated in ion exchange

A

by being rinsed in concentrated sodium chloride solution

56
Q

How does an ion exchange column remove water hardness

A

Calcium ( and magnesium) ions are exchanged for sodium ions as the water passes through an ion exchange resin

GCSE Chemistry (6 decks)

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