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Chemistry (Tara) > Environmental Chemistry - Water > Flashcards

Environmental Chemistry - Water Flashcards

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1
Q

what is produced with hard water and soap

A

scum

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2
Q

what causes the hardness in water

A

Ca 2+ and Mg 2+ ions

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3
Q

equation to represent the formation of scum

A

2C17H35COONa + Ca+2 -> (C17H35OO)2Ca (↓) + 2Na+

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4
Q

C17H35COONa

A

sodium stearate (soap)

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5
Q

(C17H35OO)2Ca

A

calcium stearate (scum)

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6
Q

do Na+ ions cause hardness

A

no

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7
Q

hard water

A

water that does not form a lather easily with soap

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8
Q

2 types of hardness

A

temporary hardness

permanent hardness

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9
Q

what causes temporary hardness

A

the presence of calcium hydrogen carbonate

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10
Q

how does calcium hydrogen carbonate enter the water?

A

when carbonic acid (acid rain) reacts with limestone in the ground

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11
Q

formula for when carbonic acid (acid rain) reacts with limestone

A

H2CO3 + CaCO3 -> Ca(HCO3)2

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12
Q

how do you remove temporary hardness

A

by boiling

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13
Q

why can you boil off the temporary hardness

A

soluble normally, but when heated it forms insoluble calcium carbonate

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14
Q

what is the insoluble calcium carbonate responsible for?

A

the insoluble scale in kettles, washing machines, dish washers

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15
Q

equation for boiling temporarily hard water

A

Ca(HCO3)2 –> CaCO3 (↓) + H2O +CO2

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16
Q

what causes permanent hardness

A

the presence of calcium sulfate (CaSO4) or magnesium sulfate (MgSO4)

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17
Q

why can you not remove permanent hard water by boiling

A

as sulfates do not decompose on heating

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18
Q

3 methods for removing both types of hardness

A

distillation
addition of washing soda crystals
ion exchange resins

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19
Q

describe distillation

A

the water is boiled of through a Liebig Condenser and the hydrogen carbonates and sulfates remain in the flask

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20
Q

problem with distillation

A

too expensive on a large scale

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21
Q

washing soda crystals formula

A

Na2CO3.10H2O

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22
Q

describe how addition of washing soda crystals would work

A

the carbonate ions in the washing soda crystals react with calcium ions that cause the hardness (temp and perm) and thus remove them

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23
Q

formula for adding washing soda crystals

A

Na2CO3 + Ca+2 -> CaCO3 +2NA+

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24
Q

Ion exchange resins type 1

how do you denote it

A

Na2R

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25
Q

Ion exchange resins type 1

when the hard water passes through the resins

A

the calcium ions are ‘swapped’ with the sodium ions in the resin, removing the hardness as calcium ions stay in resin

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26
Q

Ion exchange resins type 1

formula

A

Na2R + Ca+2 -> CaR + 2Na+

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27
Q

Ion exchange resins type 1

what eventually happens to the resin

A

it becomes full of calcium ions and must be soaked in concentrated solution of sodium chloride to replace Ca2+ with Na+

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28
Q

Ion exchange resins type 2

what does this do?

A

will remove all the ions in water (not just the calcium/magnesium ones) to produce ‘deionised water’

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29
Q

Ion exchange resins type 2

the 2 resins involved

A

a cation exchange resin and an anion exchange resin

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30
Q

Ion exchange resins type 2

what does the cation exchange resin do

A

contains H+ ions which will swap with any positive ions in water

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31
Q

Ion exchange resins type 2

what does the anion exchange resin do

A

contains OH- ions which will swap with any negative ions in water

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32
Q

Ion exchange resins type 2

what happens at the end

A

the H+ and OH- form water

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33
Q

Ion exchange resins type 2

cation exchange resin equation

A

RH + cation -> H+ + spent resin

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34
Q

Ion exchange resins type 2

Anion exchange resin

A

ROH + anion -> OH- + spent resin

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35
Q

Ion exchange resins type 2

final equation

A

H+ + OH- -> H2O

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36
Q

2 properties of deionised water

A

no ions

has dissolved gases and organic material

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37
Q

2 properties of distilled water

A

no ions

no dissolved gases and organic material

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38
Q

3 advantages of hard water

A

tastes better
contains calcium for bones and teeth
good for brewing industry

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39
Q

3 disadvantages of hard water

A
  • dirty looking scum produced with soap
  • wastes soap
  • produces scale that can block pipes and break heating elements
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40
Q

what happens when organic waste is added to a water supply

A

it puts a demand on the dissolved oxygen

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41
Q

BOD

A

Biochemical oxygen demand

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42
Q

TEST FOR BOD IN A WATER SUPPLY

first step

A

water taken into 2 containers

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43
Q

TEST FOR BOD IN A WATER SUPPLY

2 things that must be done when filling container

A

filled under water

filled to the brim

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44
Q

TEST FOR BOD IN A WATER SUPPLY

why must be filled under water

A

to stop atmospheric oxygen from being trapped and affecting the result

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45
Q

TEST FOR BOD IN A WATER SUPPLY

why filled to brim?

A

so no air is found between water and stopper

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46
Q

TEST FOR BOD IN A WATER SUPPLY

what do you do to one sample

A

one has its dissolved oxygen content determined using a titration called the Winkler method

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47
Q

TEST FOR BOD IN A WATER SUPPLY

what does the Winkler method give you

A

concentration of oxygen in parts per million

48
Q

TEST FOR BOD IN A WATER SUPPLY

where does the second container go?

A

in the dark at 20ºC for 5 days

49
Q

TEST FOR BOD IN A WATER SUPPLY

why is one in the dark

A

to prevent photosynthesis using the oxygen

50
Q

TEST FOR BOD IN A WATER SUPPLY

why 20ºC?

A

to validate the results so that conditions are kept constant

51
Q

TEST FOR BOD IN A WATER SUPPLY

why 5 days

A

allows enough time for consumption of oxygen to occur

52
Q

TEST FOR BOD IN A WATER SUPPLY

after 5 days is up

A

the second water sample is tested using the Winkler method and agin the amount of dissolved oxygen is in ppm

53
Q

TEST FOR BOD IN A WATER SUPPLY

to find BOD

A

the difference between the 2 dissolved oxygen levels as this indicates the amount of oxygen consumed by a biochemical reaction

54
Q

BOD is a

A

rate

55
Q

the rate at which the dissolved oxygen is used up is independent of what?

A

the amount of dissolved oxygen in the water

56
Q

the higher the BOD

A

the more polluted the water is as more bacteria are present decomposing

57
Q

TEST FOR BOD IN A WATER SUPPLY

what is important to ensure

A

water is diluted to a known volume using well oxygenated water to ensure there is enough oxygen present for the 5-day period of the test

58
Q

TEST FOR BOD IN A WATER SUPPLY

if all the oxygen was used up before 5 days

A

a valid BOD would not be obtained

59
Q

TEST FOR BOD IN A WATER SUPPLY

would adding extra oxygen affect the rate at which micro-organisms use it up

A

no

60
Q

Biochemical Oxygen Demand Definition

A

the amount of dissolved oxygen consumed by biochemical action when a sample of water is kept in the dark at 20ºC for five days

61
Q

Eutrophication

A

the enrichment of a body of water with nutrients resulting in deoxygenation of the water

62
Q

What can cause eutrophication?

A

excessive amounts of nitrates and phosphates in water supply

63
Q

how can excessive amounts of nitrates and phosphates cause eutrophication in water supply?

A

cause increase in plant life, algal bloom, eventually die, decompose, bacteria use up the oxygen `

64
Q

artificial eutrophication

A

when artificial fertilisers leach into water supplies

65
Q

heavy metal pollution

A

when metals with a high atomic mass enter water supplies if industrial sewage enters water supply or old batteries dumped illegally

66
Q

3 heavy metals

A

lead (II) Pb2+ , mercury (II) Hg2+, cadmium (II) Cd 2+

67
Q

why do most heavy metals not build up to toxic levels in our body

A

they are excreted in urine

68
Q

problems with heavy metals

A

bio-accumulative and toxic at high concentrations
neurological impacts
some are carcinogenic

69
Q

how do heavy metals affect processing

A

can interfere with chemical processes by poisoning chemical catalysts
can impact on biochemical processes by interfering with enzyme action

70
Q

how are heavy metals ions removed

A

precipitation

71
Q

precipitation of lead equation

A

Pb 2+ + 2Cl- -> PbCl2 (↓)

72
Q

EU limits on nitrates

A

50 ppm

73
Q

EU limits on phosphates

A

2.2 ppm

74
Q

EU limits on mercury

A

1 ppm

75
Q

EU limits on lead

A

50 ppm

76
Q

EU limits on cadmium

A

5 ppm

77
Q

In Ireland, who carries out water treatment?

A

The EPA

78
Q

7 steps in water treatment

A 
screening 
flocculation
settlement (sedimentation)
filtration
chlorination
fluoridation
pH adjustment
79
Q

screening

A

water is passed through graded screens to remove debris

80
Q

flocculation

A

flocculating agent, Al2(SO4)3, aluminium sulfate is added to cause suspended particles to coagulate together

81
Q

settlement (sedimentation)

A

the water passes into settlement tanks so that coagulated particles can settle at the bottom

82
Q

filtration

A

water passes through filter beds (sand and gravel) and any remaining suspended particles can be removed

83
Q

chlorination

A

chlorine added in small quantities, as sodium hypochlorite (NaClO) to sterilise water

84
Q

why not add free chlorine

A

it is an oxidising agent and will oxidise the bacterial enzymes

85
Q

fluoridation

A

hexafluorosilicic acid is added (1 ppm) to prevent tooth decay

86
Q

pH adjustment

A

if too high, then dilute sulfuric acid added

if too low then calcium hydroxide added

87
Q

pH of drinking water should be

A

7-9

88
Q

acid pH would lead too

A

corrosion of pipes

89
Q

Primary treatment of sewage

this treatment is mainly

A

physical

90
Q

Primary treatment of sewage

how is large debris removed

A

it is screened

91
Q

Primary treatment of sewage

how is smaller debris rempved

A

passed through grit-traps

92
Q

Primary treatment of sewage

sedimentation

A

passed into settlement tanks to allow suspended particles to settle as sludge at the bottom

93
Q

Primary treatment of sewage

saponification

A

removes grease and oil floating on water

94
Q

Primary treatment of sewage

what moves to secondary stage

A

the liquid on top

95
Q

Secondary treatment of sewage

this treatment is mainly

A

biological

96
Q

Secondary treatment of sewage

first

A

liquid is passed into large aeration tanks that continuously churn the water around

97
Q

Secondary treatment of sewage

second step

A

micro-organisms in the tank break down organic and suspended particles to harmless substances

98
Q

Secondary treatment of sewage

churning

A

increase dissolved oxygen content of the water

99
Q

Secondary treatment of sewage

after churning

A

water passes into a settlement tank and some sludge is removed and can be used as fertiliser or anaerobically oxidised by bacteria to produce methane (fuel)

100
Q

Secondary treatment of sewage

by the end of this stage

A

about 95% of original sewage is removed so it can be let into rivers or lakes

101
Q

Secondary treatment of sewage

why may it undergo tertiary treatment

A

to remove chemicals containing nitrogen and phosphorous

102
Q

Tertiary treatment of sewage

this treatment is mainly

A

chemical

103
Q

Tertiary treatment of sewage

what does the water now contain

A

dissolved nitrates from organic waste

dissolved phosphates from washing powders

104
Q

Tertiary treatment of sewage

why remove the chemicals

A

they can cause eutrophication

105
Q

Tertiary treatment of sewage

removal of nitrogen 3 steps

A

biological oxidation of ammonia to nitrate (nitrification)
denitrification, reduction of nitrate to nitrogen gas
released into atmosphere

106
Q

Tertiary treatment of sewage

removal of phosphates

A

by precipitation;
calcium and/or aluminium ions added and they precipitate the phosphates out of solutionn
allowed to settle before the final effluent is let into waterways

107
Q

Tertiary treatment of sewage

sludge after removal of phosphates

A

this nutrient-rich sludge can be used as fertiliser

108
Q

instrumental methods of analysis 3

A

pH meter
atomic absorption spectrometry (AAS)
colorimetry

109
Q

use of a pH meter

A

to check the pH of the water
sensitive to hydrogen ion or hydroxide ion concentration
pH can be adjusted

110
Q

Atomic Absorption Spectrometry (AAS)

A

each element has its own unique absorption spectrum

used to identify and measure the concentrations of heavy metals in water

111
Q

colorimetry

A

white light passed through a coloured solution
amount of light energy that gets through is converted to electrical energy and shown on a meter
amount of light that passes through is dependent on the concentration, can measure concentration

112
Q

suspended solids

A

insoluble substances that are floating in the water and can be removed by filtering

113
Q

dissolved solids

A

soluble substances in solution in the water and can be measured by evaporating off the water leaving the dissolved solids behind

114
Q

Free chlorine

A

the chlorine in chloric (I) acid and hypochlorite ions is knows as free chlorine

115
Q

how is water in swimming pools kept sterile

A

addition of oxidising agents such as chlorine compounds kill bacteria by oxidising their enzymes
sterilised with chlorine compounds which produce chloric (I) acid when dissolved in water

116
Q

chloric (I) acid formula

A

HOCl

117
Q

2 chemicals that produce chloric (I) acid in water

A

sodium hypochlorite NaOCl

calcium hypochlorite Ca(OCl)2

Chemistry (Tara) (50 decks)

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