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Chemistry > Water > Flashcards

Water Flashcards

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1
Q

What is hard water?

A

Hard water is when soap does not easily form a lather due to the presence of Ca and Mg.

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2
Q

How do you get rid of temporary hardness in water?

A

Temporary hardness can be removed by boiling.

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3
Q

What can temporary water hardness cause?

A

Blocked pipes

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4
Q

Give two ways of removing water hardness?

A
  • Distillation

- Ion exchange

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5
Q

Name the seven stages of water treatment.

A
  1. Screening
  2. Flocculation
  3. Sedimentation
  4. Filtration
  5. Chlorination
  6. Fluoridation
  7. pH adjustment
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6
Q

What is B.O.D?

A

It’s the amount of dissolved oxygen consumed by biological action in a sample of water.

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7
Q

What are the three requirements for B.O.D testing?

A
  1. 20 degrees
  2. 5 days
  3. In the dark
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8
Q

What is eutrophication?

A

It’s the enrichment of water with nutrients that leads to an excessive amount of algae growth.

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9
Q

What are the stages of sewage treatment?

A
  1. Primary (Physical)
  2. Secondary (Biological)
  3. Tertiary (Chemical)
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10
Q

What happens to the hard water when Ca and Mg mix?

A

It forms a scum.

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11
Q

Why can detergents lather easily with hard water?

A

Most modern soaps don’t contain soap.

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12
Q

What are some advantages of hard water?

A
  • Provides calcium for teeth and bones.

- Good for brewing.

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13
Q

What are some disadvantages of hard water?

A
  • Blocks pipes

- Wastes soap

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14
Q

What are the 4 criteria of water treatment?

A
  • Colourless
  • Odourless
  • Safe to drink
  • Fluorinated
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15
Q

How do they use screening and what does it do?

A

They use a wish mesh, to remove large solids and floating debris (twigs, plastics etc.).

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16
Q

What is Flocculation and how does it work?

A

Flocculent (or flocculating agent) usually aluminium sulphate (alum) is added and makes the smaller suspended solids coagulate in large chunks.

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17
Q

How does sedimentation work?

A

Sedimentation is a process using gravity to remove suspended solids from water in large tanks.

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18
Q

How does Filtration work?

A

Large beds of sand remove the remainder of suspended solids.

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19
Q

How does chlorination work?

A

A small amount of Cl2 gas is added and it sterilises the water, it’s monitored by preforming a bacteriological exam of the water.

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20
Q

What is fluoridation?

A

The addition of sodium fluoride (NaF), it is added by law in EU countries to help reduce dental decay and strengthening the enamel.

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21
Q

What is pH adjustment?

A

The addition of lime (Ca(OH)2) if the water is too acidic and the addition of H2SO4 if the water is too basic, the optimum level is between 7-9.

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22
Q

Talk about the factor of dissolved oxygen in terms of water treatment.

A

When waste from factories and farms enter waterways there is an increase in microbial activity. As the micro organisms break down the waste, the oxygen in the water is used up and after a while, eutrophication can occur.

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23
Q

How is dissolved oxygen in a water sample measured?

A

It’s measured by a B.O.D test

24
Q

How does oxygen get into water?

A

It dissolves into the water by air.

25
Q

Does water have a high or low solubility?

A

It has a low solubility

26
Q

How does temperature affect solubility?

A

It inversely affect solubility (the higher the temperature, the lower the solubility)

27
Q

How is the B.O.D test carried out?

A
  • The sample being tested is divided into two portions, the concentration of dissolved oxygen in one portion is measured.
  • The second portion is left in the dark, at 20*c, for 5 days and the concentration of dissolved oxygen is measured.
  • The test B.O.D is found by the subtraction of the two portions.
28
Q

What is sewage?

A

Sewage is the waste from homes, businesses, and factories.

29
Q

What are the three stages of sewage treatment?

A
  1. Primary
  2. Secondary
  3. Tertiary
30
Q

Explain the primary stage of sewage treatment.

A
  • The incoming sewage is screened to remove debris and non-biodegradable material.
  • It passes into large deep sedimentation tanks where about half of suspended solids and a third of B.O.D is removed.
  • The liquid on top is then passed on to the secondary stage.
31
Q

Explain the secondary stage of sewage treatment.

A
  • The incoming sewage is passed into aeration tanks where mechanical stirrers aerate it.
  • This allows for the aerobic bacteria and other micro organisms to decompose the solid matter into a harmless sludge called Activated Sludge.
  • Sewage is then put into settlement tanks and the sludge can be removed and or recycled to make methane.
32
Q

Explain the tertiary starve of sewage treatment.

A
  • When the liquid is passed onto this stage, it is clean and inoffensive but it may still contain nitrates and phosphates.
  • Nitrates are from organic material and phosphates are from washing powders and washing up liquids.
  • The nitrates and phosphates must be removed before being released into waterways in case it causes eutrophication.
33
Q

How do you remove phosphates from water?

A

There are two ways:
- If you add aluminium sulphate then aluminium phosphate will precipitate out.

  • If you add iron (III) chloride then iron (III) phosphate will precipitate out.
34
Q

Talk about nitrate removal.

A

Removing nitrates is difficult and expensive as nitrogen may be presented in many different forms (NH3, NO2, NO3 and organic compounds containing N).

35
Q

What is the definition of water pollution?

A

The release of substances into the environment that damage the environment.

36
Q

What are the three main types of pollution?

A
  1. Eutrophication
  2. Organic waste
  3. Heavy metals
37
Q

What are some instrumental methods of water analysis?

A
  • AAS (Heavy metals)
  • pH Sensor
  • Colorimetry
38
Q

What is the principle of colorimetry?

A

The principle of colorimetry is that the amount of light absorbed by a coloured solution is proportional to the concentration of the solution.

39
Q

What are some nutrients that can cause eutrophication?

A

Fertilisers, nitrates and phosphates.

40
Q

How do these nutrients get into the water?

A

They’re due to run off from land and or pollution.

41
Q

What happens on the water?

A

There is a rapid growth of algae on surface / algal blooms.

42
Q

Why is algal blooms bad?

A

The light from the sun is blocked from the underwater plants which produce oxygen for aquatic life.

43
Q

What are some examples of organic waste?

A
  • Domestic sewage
  • Slurry
  • Silage effluent
  • Effluent with food processing factories
  • Milk
  • industrial waste
44
Q

What feeds on this waste?

A

Bacteria and micro-organisms.

45
Q

What happens when organic waste is broken down?

A

O2 is used up

organic matter + O2 –> CO2 + H2O

46
Q

What is one effect of the oxygen being used up?

A

The reducing of fish life or killing off of fish life.

47
Q

What happens when all of the oxygen is used up?

A

When the oxygen is all used up, anaerobic bacteria take over. We know this because the river will start to smell due to the presence of H2S (hydrogen sulphide).

48
Q

Why are heavy metals dangerous?

A

They are known as cumulative poisons.

49
Q

What is the ion of lead from the example, what does it come from and what is a harmful effect?

A

Pb2+ is found in old paints and it causes damage to the nervous system.

50
Q

What is the ion of mercury from the example, what does it come from and what is a harmful effect?

A

Hg2+ is found in industrial effluent and it causes birth defects.

51
Q

What is the ion of cadmium from the example, what does it come from and what is a harmful effect?

A

Cd2+ is found in discarded batteries and is considered carcinogenic.

52
Q

How can the concentration of heavy metals be measured?

A

It can be measured by Atomic Absorption Spectrometry (Pb2+ + 2HCL –> PbCL2 + 2H+).

53
Q

How does the EU control the amount of heavy metals in water?

A

The EU sets limits on how concentrated certain species can be in water.

54
Q

What chemical is used in pools to disinfect them?

A

Swimming pools are disinfected by adding Ca(OCL)2 (Calcium hypochlorite).

55
Q

Which is better at disinfecting? (Hypochlorous acid or Hypochlorite Ions)

A

Hypochlorous acid (HOCl).

56
Q

What is free chlorine?

A

(HOCl) and ((H+) + (OCl-)) are known as free chlorine.

57
Q

What is the compound added to test the levels of chlorine called and colour does it turn?

A

When DPD is added, the solution turns pink.

Chemistry (11 decks)

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