Environmental Chemistry - Water Flashcards
(117 cards)
1
Q
what is produced with hard water and soap
A
scum
2
Q
what causes the hardness in water
A
Ca 2+ and Mg 2+ ions
3
Q
equation to represent the formation of scum
A
2C17H35COONa + Ca+2 -> (C17H35OO)2Ca (↓) + 2Na+
4
Q
C17H35COONa
A
sodium stearate (soap)
5
Q
(C17H35OO)2Ca
A
calcium stearate (scum)
6
Q
do Na+ ions cause hardness
A
no
7
Q
hard water
A
water that does not form a lather easily with soap
8
Q
2 types of hardness
A
temporary hardness
permanent hardness
9
Q
what causes temporary hardness
A
the presence of calcium hydrogen carbonate
10
Q
how does calcium hydrogen carbonate enter the water?
A
when carbonic acid (acid rain) reacts with limestone in the ground
11
Q
formula for when carbonic acid (acid rain) reacts with limestone
A
H2CO3 + CaCO3 -> Ca(HCO3)2
12
Q
how do you remove temporary hardness
A
by boiling
13
Q
why can you boil off the temporary hardness
A
soluble normally, but when heated it forms insoluble calcium carbonate
14
Q
what is the insoluble calcium carbonate responsible for?
A
the insoluble scale in kettles, washing machines, dish washers
15
Q
equation for boiling temporarily hard water
A
Ca(HCO3)2 –> CaCO3 (↓) + H2O +CO2
16
Q
what causes permanent hardness
A
the presence of calcium sulfate (CaSO4) or magnesium sulfate (MgSO4)
17
Q
why can you not remove permanent hard water by boiling
A
as sulfates do not decompose on heating
18
Q
3 methods for removing both types of hardness
A
distillation
addition of washing soda crystals
ion exchange resins
19
Q
describe distillation
A
the water is boiled of through a Liebig Condenser and the hydrogen carbonates and sulfates remain in the flask
20
Q
problem with distillation
A
too expensive on a large scale
21
Q
washing soda crystals formula
A
Na2CO3.10H2O
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
23
Q
formula for adding washing soda crystals
A
Na2CO3 + Ca+2 -> CaCO3 +2NA+
24
Q
Ion exchange resins type 1
how do you denote it
A
Na2R
25
Ion exchange resins type 1
| when the hard water passes through the resins
the calcium ions are 'swapped' with the sodium ions in the resin, removing the hardness as calcium ions stay in resin
26
Ion exchange resins type 1
| formula
Na2R + Ca+2 -> CaR + 2Na+
27
Ion exchange resins type 1
| what eventually happens to the resin
it becomes full of calcium ions and must be soaked in concentrated solution of sodium chloride to replace Ca2+ with Na+
28
Ion exchange resins type 2
| what does this do?
will remove all the ions in water (not just the calcium/magnesium ones) to produce 'deionised water'
29
Ion exchange resins type 2
| the 2 resins involved
a cation exchange resin and an anion exchange resin
30
Ion exchange resins type 2
| what does the cation exchange resin do
contains H+ ions which will swap with any positive ions in water
31
Ion exchange resins type 2
| what does the anion exchange resin do
contains OH- ions which will swap with any negative ions in water
32
Ion exchange resins type 2
| what happens at the end
the H+ and OH- form water
33
Ion exchange resins type 2
| cation exchange resin equation
RH + cation -> H+ + spent resin
34
Ion exchange resins type 2
| Anion exchange resin
ROH + anion -> OH- + spent resin
35
Ion exchange resins type 2
| final equation
H+ + OH- -> H2O
36
2 properties of deionised water
no ions
| has dissolved gases and organic material
37
2 properties of distilled water
no ions
| no dissolved gases and organic material
38
3 advantages of hard water
tastes better
contains calcium for bones and teeth
good for brewing industry
39
3 disadvantages of hard water
- dirty looking scum produced with soap
- wastes soap
- produces scale that can block pipes and break heating elements
40
what happens when organic waste is added to a water supply
it puts a demand on the dissolved oxygen
41
BOD
Biochemical oxygen demand
42
TEST FOR BOD IN A WATER SUPPLY
| first step
water taken into 2 containers
43
TEST FOR BOD IN A WATER SUPPLY
| 2 things that must be done when filling container
filled under water
| filled to the brim
44
TEST FOR BOD IN A WATER SUPPLY
| why must be filled under water
to stop atmospheric oxygen from being trapped and affecting the result
45
TEST FOR BOD IN A WATER SUPPLY
| why filled to brim?
so no air is found between water and stopper
46
TEST FOR BOD IN A WATER SUPPLY
| what do you do to one sample
one has its dissolved oxygen content determined using a titration called the Winkler method
47
TEST FOR BOD IN A WATER SUPPLY
| what does the Winkler method give you
concentration of oxygen in parts per million
48
TEST FOR BOD IN A WATER SUPPLY
| where does the second container go?
in the dark at 20ºC for 5 days
49
TEST FOR BOD IN A WATER SUPPLY
| why is one in the dark
to prevent photosynthesis using the oxygen
50
TEST FOR BOD IN A WATER SUPPLY
| why 20ºC?
to validate the results so that conditions are kept constant
51
TEST FOR BOD IN A WATER SUPPLY
| why 5 days
allows enough time for consumption of oxygen to occur
52
TEST FOR BOD IN A WATER SUPPLY
| after 5 days is up
the second water sample is tested using the Winkler method and agin the amount of dissolved oxygen is in ppm
53
TEST FOR BOD IN A WATER SUPPLY
| to find BOD
the difference between the 2 dissolved oxygen levels as this indicates the amount of oxygen consumed by a biochemical reaction
54
BOD is a
rate
55
the rate at which the dissolved oxygen is used up is independent of what?
the amount of dissolved oxygen in the water
56
the higher the BOD
the more polluted the water is as more bacteria are present decomposing
57
TEST FOR BOD IN A WATER SUPPLY
| what is important to ensure
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
TEST FOR BOD IN A WATER SUPPLY
| if all the oxygen was used up before 5 days
a valid BOD would not be obtained
59
TEST FOR BOD IN A WATER SUPPLY
| would adding extra oxygen affect the rate at which micro-organisms use it up
no
60
Biochemical Oxygen Demand Definition
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
Eutrophication
the enrichment of a body of water with nutrients resulting in deoxygenation of the water
62
What can cause eutrophication?
excessive amounts of nitrates and phosphates in water supply
63
how can excessive amounts of nitrates and phosphates cause eutrophication in water supply?
cause increase in plant life, algal bloom, eventually die, decompose, bacteria use up the oxygen `
64
artificial eutrophication
when artificial fertilisers leach into water supplies
65
heavy metal pollution
when metals with a high atomic mass enter water supplies if industrial sewage enters water supply or old batteries dumped illegally
66
3 heavy metals
lead (II) Pb2+ , mercury (II) Hg2+, cadmium (II) Cd 2+
67
why do most heavy metals not build up to toxic levels in our body
they are excreted in urine
68
problems with heavy metals
bio-accumulative and toxic at high concentrations
neurological impacts
some are carcinogenic
69
how do heavy metals affect processing
can interfere with chemical processes by poisoning chemical catalysts
can impact on biochemical processes by interfering with enzyme action
70
how are heavy metals ions removed
precipitation
71
precipitation of lead equation
Pb 2+ + 2Cl- -> PbCl2 (↓)
72
EU limits on nitrates
50 ppm
73
EU limits on phosphates
2.2 ppm
74
EU limits on mercury
1 ppm
75
EU limits on lead
50 ppm
76
EU limits on cadmium
5 ppm
77
In Ireland, who carries out water treatment?
The EPA
78
7 steps in water treatment
```
screening
flocculation
settlement (sedimentation)
filtration
chlorination
fluoridation
pH adjustment
```
79
screening
water is passed through graded screens to remove debris
80
flocculation
flocculating agent, Al2(SO4)3, aluminium sulfate is added to cause suspended particles to coagulate together
81
settlement (sedimentation)
the water passes into settlement tanks so that coagulated particles can settle at the bottom
82
filtration
water passes through filter beds (sand and gravel) and any remaining suspended particles can be removed
83
chlorination
chlorine added in small quantities, as sodium hypochlorite (NaClO) to sterilise water
84
why not add free chlorine
it is an oxidising agent and will oxidise the bacterial enzymes
85
fluoridation
hexafluorosilicic acid is added (1 ppm) to prevent tooth decay
86
pH adjustment
if too high, then dilute sulfuric acid added
| if too low then calcium hydroxide added
87
pH of drinking water should be
7-9
88
acid pH would lead too
corrosion of pipes
89
Primary treatment of sewage
| this treatment is mainly
physical
90
Primary treatment of sewage
| how is large debris removed
it is screened
91
Primary treatment of sewage
| how is smaller debris rempved
passed through grit-traps
92
Primary treatment of sewage
| sedimentation
passed into settlement tanks to allow suspended particles to settle as sludge at the bottom
93
Primary treatment of sewage
| saponification
removes grease and oil floating on water
94
Primary treatment of sewage
| what moves to secondary stage
the liquid on top
95
Secondary treatment of sewage
| this treatment is mainly
biological
96
Secondary treatment of sewage
| first
liquid is passed into large aeration tanks that continuously churn the water around
97
Secondary treatment of sewage
| second step
micro-organisms in the tank break down organic and suspended particles to harmless substances
98
Secondary treatment of sewage
| churning
increase dissolved oxygen content of the water
99
Secondary treatment of sewage
| after churning
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
Secondary treatment of sewage
| by the end of this stage
about 95% of original sewage is removed so it can be let into rivers or lakes
101
Secondary treatment of sewage
| why may it undergo tertiary treatment
to remove chemicals containing nitrogen and phosphorous
102
Tertiary treatment of sewage
| this treatment is mainly
chemical
103
Tertiary treatment of sewage
| what does the water now contain
dissolved nitrates from organic waste
| dissolved phosphates from washing powders
104
Tertiary treatment of sewage
| why remove the chemicals
they can cause eutrophication
105
Tertiary treatment of sewage
| removal of nitrogen 3 steps
biological oxidation of ammonia to nitrate (nitrification)
denitrification, reduction of nitrate to nitrogen gas
released into atmosphere
106
Tertiary treatment of sewage
| removal of phosphates
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
Tertiary treatment of sewage
| sludge after removal of phosphates
this nutrient-rich sludge can be used as fertiliser
108
instrumental methods of analysis 3
pH meter
atomic absorption spectrometry (AAS)
colorimetry
109
use of a pH meter
to check the pH of the water
sensitive to hydrogen ion or hydroxide ion concentration
pH can be adjusted
110
Atomic Absorption Spectrometry (AAS)
each element has its own unique absorption spectrum
| used to identify and measure the concentrations of heavy metals in water
111
colorimetry
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
suspended solids
insoluble substances that are floating in the water and can be removed by filtering
113
dissolved solids
soluble substances in solution in the water and can be measured by evaporating off the water leaving the dissolved solids behind
114
Free chlorine
the chlorine in chloric (I) acid and hypochlorite ions is knows as free chlorine
115
how is water in swimming pools kept sterile
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
chloric (I) acid formula
HOCl
117
2 chemicals that produce chloric (I) acid in water
sodium hypochlorite NaOCl
| calcium hypochlorite Ca(OCl)2
