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Chemistry Leaving Cert > Water* > Flashcards

Water* Flashcards

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1
Q

What is hard water?

A

Water that will not EASILY form a lather with soap due to the presence of Ca 2+ or Mg 2+ ions in solution. (2+ is small like a power)

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2
Q

Why does hard water not easily form a lather?

A

Due to the presence of Ca 2+ or Mg 2+ ions in solution.

2+ is small like a power

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3
Q

What is temporary hardness?

A

Water hardness that can be removed by boiling the water.

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4
Q

What is temporary hardness caused by?

A

Ca(HCO3)2 (numbers small)

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5
Q

What does Ca(HCO3)2 become after heating?

A

CaCO3 (limescale) (numbers small)

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6
Q

What does CaCO3 lead to?

A

Blocked pipes etc.

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7
Q

What is permanent hardness?

A

Permanent hardness is not removed by boiling the water

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8
Q

What is permanent hardness caused by?

A

CaSO4 or MgSO4 (numbers small)

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9
Q

What are some methods of removing hardness?

A

Boiling (only works for temp. hardness)
Distillation
Washing Soda
Ion Exchange

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10
Q

What is distillation?

A

Distillation is a process that can be used to separate a pure liquid from a mixture of liquids. It works when the liquids have different boiling points.

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11
Q

What is ion exchange?

A

In an ion exchange system, undesirable ions in the water supply are replaced with more acceptable ions.

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12
Q

Which type of water is purer, distilled or deionised?

A

deionised

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13
Q

What are the steps in water treatment?

A

Screening, flocculation, sedimentation, filtration, chlorination, fluoridation, pH adjustment.

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14
Q

What does B.O.D stand for?

A

Biochemical Oxygen Demand

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15
Q

What is biochemical oxygen demand?

A 
The amount of dissolved oxygen consumed by biological action when a sample of water is...
kept at 20 degrees celsius
in the dark
for five days
(know reason for each of 3 conditions)
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16
Q

When finding out the biochemical oxygen demand why is the sample kept in the dark?

A

.To prevent photosynthesis taking place which creates oxygen

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17
Q

When calcium and magnesium ions mix with soap, what do they form?

A

a scum

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18
Q

Do modern detergents contain soap? What does this mean?

A

No so it will form a lather even with hard water

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19
Q

What will form a lather even with hard water?

A

Modern detergents which do not contain soap

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20
Q

What to types of hard water can in be?

A

Water with temporary hardness and permanent hardness

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21
Q

What is temporary hard water?

A

Hardness that can be removed by boiling the water

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22
Q

What is permanent hard water?

A

Hardness that cannot be removed by boiling the water

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23
Q

What are the advantages of hard water?

A

Provides calcium for teeth and bones
Nicer taste
Good for brewing, and for tanning

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24
Q

What are the disadvantages of hard water?

A

Blocks pipes, leaves scale on kettles
Wastes soap
Produces scum

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25
Q

What are three methods of removing water hardness?

A

Distillation, using ion exchange resin or using washing soda

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26
Q

How do you remove water hardness by distillation?

A

Evaporating of the water leaves the dissolved salts behind. The condensed water will no longer contain the salts and be “soft”.

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27
Q

How do you remove water hardness be using washing soda? (include formula)

A

Hydrated sodium carbonate Na2Co3.10H2O (washing soda) removes hardness from water and allows it to lather more easily with soap.
Ca2+ + Na2CO3 -> CaCO3 (soluble in water) + 2Na+

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28
Q

How do you remove water hardness by using ion exchange resin?

A

Pass water through ion exchange resin.
Cation exchange swaps ions that cause hardness (Ca2+ and Mg 2+) for ions that do not
Ca2+ + 2RNa -> R2Ca + 2Na+
(R in RNa represents the resin)

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29
Q

Draw the use of a cation exchange resin fig. 19.5 302

A

go

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30
Q

Draw the use of a mixed-bed ion-exchange resin fig 19.7 pg 302

A

go

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31
Q

What are the two types of ion exchange resin?

A

Mixed-bed ion exchange resin and ion exchange resin

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32
Q

What do mixed-bed ion-exchange resins do? (with formula)

A 
Mixed-bed ion-exchange resin removes ALL ions from water (water is deionised and cannot be hard)
Cation exchange (to remove + ions) and RH + Na+ -> RNa + H+
Anion exchange (to remove - ions) ROH +Cl- -> RCl + OH-
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33
Q

Where is mixed-bed ion exchange resin typically used?

A

labs

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34
Q

What is distilled water?

A

Water which has had all the dissolved solids removed as well as the gases and is much purer than deionised water (only has ions removed)

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35
Q

Which is purer, distilled water or deionised water?

A

distilled water

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36
Q

What needs to be done to maintain ion exchange resin?

A

replace it after a certain amount of time

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37
Q

draw figure 19.3 mixed bed ion exchange resin

A

now

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38
Q

how much water does an average household use in a day

A

300 litres

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39
Q

what are the criteria expected of the water that reaches your house?

A

colourless
odourless
safe to drink (no active bacteria)
flourinated

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40
Q

when is water safe to drink? (brief explanation)

A

when there is no active bacteria present

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41
Q

how must we ensure that water is of an adequate standard for drinking?

A

It must be treated

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42
Q

What are the 7 stages of water purification?

A

Screening, Flocculation, Settlement, Filtration, Chlorination, Flouridation, pH adjustment

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43
Q

What does screening involve?

A

The water is passed through a wire mesh which removes large solids and floating debris like twigs, plastics etc.

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44
Q

What does flocculation involve?

A

Flocculating agent (or flocculant) usually aluminium sulphate (alum) is added. This makes smaller suspended solids coagulated or stick together in large clumps, so they are easier to remove in the next stage.

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45
Q

What does settlement involve?

A

Large tanks where water goes to the bottom and rises slowly to the top, at < 2m/hr particles settle to the bottom. Over 90% of suspended solids are removed at this stage.

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46
Q

What does filtration involve?

A

Large beds of sand which remove remaining susp solids. Sand supported on a layer of gravel and sand is cleaned regularly. Water is now clear, but may contain harmful bacteria.

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47
Q

What does chlorination involve?

A

Cl2 gas is added which sterilises the water. Very small quantities 0.2 - 0.5 ppm is added. It is controlled carefully and monitored by a bacteriological exam of the water.

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48
Q

What does flouridation involve?

A

NaF or H2SiF6 added. (Hexafluorosilicic acid). Added by law as helps to reduce dental decay by strengthening the enamel. Small quantities - 1 ppm, are used.

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49
Q

What does pH adjustment involve?

A

Optimum level is between 7 - 9. Too acidic may cause damage to pipes. May be corrected by addition of Ca(OH)2 (calcium hydroxide) (lime) to raise the pH. If very hard water, might be softened by addition of NaCO3 (sodium carbonate) which is a base. Too basic may be corrected by addition of dilute H2SO4 (sulfuric acid) to lower the pH.

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50
Q

Where does water come from and where does it end up?

A

Lakes and rivers to homes and industry where it is ready for consumption and use.

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51
Q

What is the optimum level for water pH?

A

Between 7 - 9

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52
Q

If water is too acidic, what might happen?

A

It may cause damage to the pipes.

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53
Q

How do you correct water which is too acidic?

A

by adding Ca(OH)2 (calcium hydroxide) (lime) to raise the pH.

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54
Q

If water is very hard, what might you soften it with?

A

NaCO3 (sodium carbonate) which is a base

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55
Q

If water is too basic, what might you soften it with?

A

dilute H2SO4 (sulfuric acid) to lower the pH

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56
Q

How does oxygen get into water?

A

It dissolves from air into water

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57
Q

What solubility does oxygen have in water?

A

low solubility

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58
Q

How does temperature affect the solubility of oxygen in water?

A

inversely

e. g. Temperature Solubility of O2
11. 3mg/L @ 10 degrees celsius
9. 2mg/L @ 20 degrees celsius

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59
Q

What is water pollution?

A

The release of substances into the environment that damage the environment is called pollution.

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60
Q

What are the three main types of water pollution?

A

Eutrophication (also found in biology)
Organic Waste
Heavy metals

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61
Q

What is eutrophication?

A

Enrichment with nutrients (fertilisers / nitrates / phosphates) due to run off from land, pollution, dispersion in water and/or absorption by plants

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62
Q

How is eutrophication caused?

A

Due to run off from land (erosion from land) / due to pollution / dispersion in water / absorption by plants

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63
Q

What happens on the surface of the water due to eutrophication?

A

Rapid growth of plants (algae) on surface/ algal blooms formed

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64
Q

How does eutrophication and algal bloom affect the water?

A

Light is blocked from (photosynthesis reduced in) plants below surface

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65
Q

What happens after the light is blocked due to eutrophication and algal bloom?

A

Decay by bacteria of algae, algal blooms / increase in bacteria

66
Q

What happens after the light is blocked due to eutrophication and algal bloom and there is decay by bacteria?

A

Dissolved oxygen depleted (lowered, used up) / oxygen level falls

67
Q

When the oxygen level in the water falls what happens?

A

Fish levels reduced or killed off

68
Q

What are examples of organic waste?

A

Domestic sewage, slurry, silage effluent, effluent from food processing factories, milk, industrial waste, etc.

69
Q

What feeds on organic waste?

A

Bacteria and other micro-organisms

70
Q

When bacteria and other micro-organisms feed on organic waste what happens? (plus equation)

A

Waste is broken down, O2 used up

Organic matter + O2 -> CO2 + H2O

71
Q

What happens when waste is broken down by bacteria and other micro-organisms?

A

O2 used up, reducing levels of fish and possibly killing off fish life.

72
Q

What happens when the oxygen is gone from the water?

A

O2 gone, anaerobic bacteria take over, river will smell due to presence of by product, Hydrogen Sulphide, H2S

73
Q

Why will a river smell after the O2 is gone and the anaerobic bacteria take over?

A

Due to presence of by product, Hydrogen Sulphide, H2S

74
Q

What are some heavy metal ions known to be?

A

Cumulative poisons (can build up in the tissue and be harmful to our health)

75
Q

What are cumulative poisons?

A

Poisons which can build up in the tissue and be harmful to our health

76
Q

Name some metal ions where they are found and their harmful effects.

A

Lead (Pb 2+) Old plumbing and paints Damage to
nervous system
Mercury (Hg2+) Industrial effluent Birth defects
Cadmium (Cd2+) Discarded batteries Carcinogenic

77
Q

How is the conc of heavy metal ions measured?

A

Using Atomic Absorption Spectrometry (AAS)

78
Q

How can heavy metals be removed from water?

A

By precipitation reactions e.g. lead reacts with HCl for form an insoluble precipitate that fall out of soln
Pb2+ + 2HCl -> PbCl2 + 2H+

79
Q

Who sets the limits on how much heavy metals should be in our water?

A

The EU sets limits on the conc of certain species in water

80
Q

Give an example and formula for a precipitation reaction?(for removing heavy metals)

A

lead reacts with HCl for form an insoluble precipitate that fall out of soln
Pb2+ + 2HCl -> PbCl2 + 2H+

81
Q

What is a colorimeter?

A

a device used to test the concentration of a solution by measuring its absorbance of a specific wavelength of light.

82
Q

How do you use a colorimeter?

A

To use this device, different solutions must be made, and a control (usually a mixture of distilled water and another solution) is first filled into a cuvette and placed inside a colorimeter to calibrate the machine. Only after the device has been calibrated can you use it to find the densities and/or concentrations of the other solutions.

83
Q

draw a diagram of colorimetry

A

but put in cuvette instead of test tube

84
Q

Give the principle of colorimetry

A

If a solution is coloured then the intensity of the colour is proportional to the concentration.
2. The percentage of light absorbed by the colured solution in the colorimeter is proportional to the concentration.

85
Q

Give the processes of colorimetry

A

Light of a particular wavelength is passed through a number of samples of known concentration. A graph of absorbance of the unknown is noted and using the graph the concentration of the unknown can be found.

86
Q

Give the uses of colorimetry

A

Uses
Analysis
1. Lead in water
2. Fertilisers in water e.g. nitrates and phosphates

87
Q

How does atomic absorption spectrometry work?

A

White light is passed through a gaseous sample of the element, and will have specific frequencies removed from it. Whereas emission spectrum is coloured lines on a black background, absorption spectrum is black lines on a coloured background. This technique is used to determine the concentration of elements.

88
Q

Uses of atomic absorption spectra

A

Identifying elements
Concentration of elements
concentration of heavy metals in water

89
Q

What happens in an atomic absorption spectrometer?

A

White light is passed through a sample (river water).
The elements in the water e.g. Pb, (lead) and Hg (Mercury) will absorb certain characteristic wavelengths of light.
The amount of light absorbed is directly proportional to the concentration of the element in the sample.

90
Q

On what principle does an atomic absorption spectrometer work?

A

Every element: 1) absorbs a particular wavelength of light.

2) amount of light absorbed is proportional to the concentration of the element.

91
Q

Draw a diagram of absorption versus concentration with regard to chlorine in swimming pool water or bleach

A

with correct graphing technique

92
Q

What are the three main stages of sewage treatment?

A

Primary treatment - physical
Secondary treatment - biological
Tertiary treatment - chemical

93
Q

What type of treatment is primary sewage treatment?

A

physical stage

94
Q

What type of treatment is secondary sewage treatment?

A

biological stage

95
Q

What type of treatment is tertiary sewage treatment?

A

chemical stage

96
Q

Draw a diagram of sewage treatment

A

and label

97
Q

What are the two types of waste that enter sewage treatment?

A

Industrial waste and domestic waste

98
Q

How much B.O.D has been removed after the first stage of sewage treatment?

A

33% percent

99
Q

How much B.O.D has been removed after the second stage of sewage treatment?

A

95% B.O.D

100
Q

What are the two phases of the primary stage of sewage treatment?

A

Screening and settlement (sedimentation)

101
Q

What is another word for settlement with regard to sewage treatment?

A

sedimentation

102
Q

What are the two phases of the secondary stage of sewage treatment?

A

Aeration and settlement

103
Q

What are the two phases of the tertiary stage of sewage treatment?

A

removal of nitrates and removal of phosphates

104
Q

What is the first stage of the primary phase of sewage treatment?

A
  1. The incoming sewage is screened to remove debris and non-biodegradable material (screening)
105
Q

What is the second stage of the primary phase of sewage treatment?

A
  1. It passes into large deep sedimentation (settlement) tanks where about 50% of the suspended solids and about 33% of B.O.D are removed.
106
Q

What is the third stage of the primary phase of sewage treatment?

A
  1. Liquid on top is then passed onto to secondary treatment.
107
Q

How much of sewage passing into the second stage is suspended solids/B.O.D?

A

about 50% of the suspended solids and about 33% of B.O.D are removed.

108
Q

What is the first stage of the secondary phase of sewage treatment?

A

The incoming sewage from the first stage of treatment is passed into aeration tanks where the mechanical stirrers aerate it.

109
Q

What is the second stage of the secondary phase of sewage treatment?

A

The aeration allows aerobic bacteria and other micro-organisms to decompose the solid matter into a harmless sludge called Activated Sludge.

110
Q

What is activated sludge?

A

a harmless sludge made of solid matter decomposed by aerobic bacteria and other micro-organisms.

111
Q

What is the third stage of the secondary phase of sewage treatment?

A

Sewage then flows into settling tanks, sludge can be reused, or or recycled to make methane. About 95% of B.O.D is removed.

112
Q

How much B.O.D is removed during sewage treatment?

A

about 95%

113
Q

What can sewage sludge be recycled to make?

A

methane

114
Q

What is the first stage of the tertiary phase of sewage treatment?

A

When the liquid passes out of the second round of settling, it is clean and inoffensive, but it may contain compounds of nitrates and phosphates

115
Q

What is the second stage of the tertiary phase of sewage treatment? / What are the nitrates and phosphates found in?

A

Phosphates from washing powders and washing up liquids and nitrates from organic material in sewage

116
Q

What is the third stage of the tertiary phase of sewage treatment?

A

Phosphates and nitrates must be removed before water is discharged into river as could cause eutrophication.

117
Q

What is added to get rid of aluminium phosphate precipitates?

A

aluminium sulphate

118
Q

What is added to get rid of iron (III) phosphates precipitates?

A

Iron chloride

119
Q

What may also be used to get rid of phosphates?

A

Lime

120
Q

What happens to insoluble phosphate particles?

A

They are allowed to settle out before discharge into waterway

121
Q

why is nitrate removal difficult and expensive?

A

as nitrogen may be present in many forms, NH3, NO2-, NO3-, organic compounds containing N

122
Q

give examples of nitrogen forms

A

NH3, NO2-, NO3-, organic compounds containing N

123
Q

what is done to phosphates to get rid of them?

A

They are precipitated

124
Q

what is done to nitrates to get rid of them?

A

They are denitrified

125
Q

what are grit traps?

A

sewage is passed over grit channels to remove grit and pebbles.

126
Q

What does removing solid matter do?

A

It reduces the B.O.D

127
Q

what can sludge be used as?

A

a fertiliser

128
Q

where does the remaining water from stage 1 go to?

A

stage 2

129
Q

What is aeration?

A

sewage is churned to mix with air. Mixture of sewage and bacteria is called “activated sludge”.

130
Q

What is oxidative breakdown?

A

Micro-organisms aerobically breakdown the organic matter in the water, forming harmless products such as carbon dioxide.

131
Q

What may some sewage contain and what can this lead to?

A

nitrates and phosphates

eutrophication

132
Q

How can phosphates be removed? Give an example

A

Phosphates removed by precipitation reactions E.g. Al2SO4 (flocculating agent) can be added to convert phosphates to aluminium phosphate (insoluble)

133
Q

How are nitrates removed and why does it work?

A

By using denitrifying bacteria. Converts nitrates to N2 gas.

134
Q

Is oxygen soluble in water?

A

not very soluble

135
Q

What can happen to the amount of oxygen dissolved in the water? What can this cause?

A

it can be affected easily, possibly having serious implications for organisms living in water

136
Q

When organic waste from factories or farms is passed into waterways what can it cause?

A

an increase in microbial activity

137
Q

What happens as micro-organisms break down waste in water?

A

the oxygen in the water gets used up

138
Q

What is the amount of oxygen used to break down waste in the water an indication of?

A

the extent of which the water is polluted

139
Q

How is the amount of oxygen used up by micro-organisms measured?

A

a bio-chemical oxygen demand (B.O.D) test

140
Q

What is bio-chemical oxygen demand (B.O.D)?

A

The amount of dissolved O2 consumed by biological (biochemical) action when a sample of water is kept at 20 degrees celsius in the dark for five days.

141
Q

What is the first step in testing water B.O.D?

A

The sample being tested is divided into two portions. The concentration of the dissolved O2 in one portion is measured.

142
Q

What is done with the second portion of water being tested?

A

The second portion is left in the dark in the dark at 20 degrees celsius for 5 days and the concentration of dissolved O2 in the water is measured.

143
Q

How is the B.O.D of the sample being tested calculated?

A

The B.O.D is found by subtraction, taking into account any relevant dilution factor.

144
Q

What is the Winkler Method?

A

A method used to determine the amount of dissolved oxygen in a water sample

145
Q

How is the Winkler method carried out?

A

Sample is divided into two portions
1st portion is tested right away for the p.p.m of O2
2nd portion is tested after five days in the dark at 20 degrees celsius for the p.p.m of O2
Difference between the two readings is the B.O.D level, as this is the amount of oxygen used up.

146
Q

What is the B.O.D found by doing?

A

finding the difference between the two samples, as this is the amount of oxygen used up.

147
Q

What is added to the water during the Winkler Method?

A

1cm cubed of Manganese sulphate
1cm cubed of Alkaline potassium iodide solution (Kl)
1cm cubed of H2SO4

148
Q

Write out the formula of the Winkler Method.

A

Mn2+ + OH- ions react together
Mn(OH)2 (white precipitate) reacts with O2
Acid is added to Mn(OH)3 (brown precipitate)
Iodine is liberated from I- + Mn(OH)3
I2
Titrated against standard sodium thiosulphate
1O2 : 4S2O3 2- (2- is small)

149
Q

How many instrumental methods of water analysis are there? Name them

A

3
AAS (heavy metals)
pH sensor
Colorimetry

150
Q

What is the principle of colorimetry?

A

It is that the amount of light absorbed by a coloured solution is proportional to the concentration of the solution.

151
Q

How is colorimetry carried out?

A

DPD tablets added, reacts with chlorine in water
Compare colour with ones of known concentration
Comparator - disc of precalibrated solutions
or
Colorimeter - measure absorbance of known solutions and plot graph

152
Q

what do you add to solution in colorimetry and why?

A

DPD tablets added, reacts with chlorine in water

153
Q

What is a comparator?

A

Comparator - disc of precalibrated solutions

154
Q

What is a colorimeter?

A

Colorimeter - measure absorbance of known solutions

155
Q

What is the last step in colorimetry?

A

to plot a graph

156
Q

How are swimming pools disinfected?

A

by adding Ca(OCl)2 (chlorine)

157
Q

When chlorine dissolves in water what does it set up?

A

the equilibrium HOC (hypochlorous acid) H+ + OCl- (Hypochlorite ion)

158
Q

Which is better at disinfecting water, hypochlorous acid or hypochlorite ion

A

hypochlorous acid

159
Q

Why is it important to monitor the pH of the water?

A

Drop in the H+ ion concentration (water becomes more basic) will shift the reaction to the right.

160
Q

What are hypochlorous acid and hypochlorite ion known as? What is a feature of them?

A

Free chlorine (colourless)

161
Q

What happens when a compound known as DPD is added?

A

The solution turns pink

162
Q

How can the concentration of free chlorine be determined?

A

By measuring the intensity of the pink colour by colorimetry.

Chemistry Leaving Cert (10 decks)

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