Chemical Monitoring and Management Flashcards
1
Q
what is collaboration?
A
the sharing of findings, information and research methods between scientisists in different sub disciplines
2
Q
why is collaboration important?
A
- collaboration reduces the work load for chemists, thus relieving stress and thus increasing efficiency. this reduces the time taken to complete a given project and reduces cost
- the communication of ideas to share knowledge allows for the advancment of research and personal growth and collective chemists can bounce ideas off eachother and learn new skills and develop more as a person
- different chemists specialise in different fields and hence some problems are better soled with the assistance of specialist chemists. Also, most real world problems occuring today require a broad range of chemical knowledge which only a selectiv few specialise in
- reliablity and validity are strengthened by peer crtiquing
3
Q
what is an example of a chemical reaction which needs monitoring?
A
combustion of petrol
4
Q
why does the combustion of petrol need monitoring?
A
the combustion of petrol results in the formation of different products depending on the conditions involved. some of these products are powerful pollutants such as carbon dioxide and soot
5
Q
what happens when oxygen is in plentiful supply in combustion?
A
complete combustion occurs! this means that the byproducts of the reaction are water and carbon dioxide
6
Q
why is complete combustion often unlikely in regards to the combustion of petrol?
A
assuming octane is petrol, for every one mole of petrol that is burnt, an incredible 12.5 mol of oxygen is required for complete combustion. often in small and confined systems, such as in the engines of cars, complete combustion rarely occurs due to this large oxygen supply
7
Q
what are the usual products of incomplete combustion?
A
soot, carbon dioxide and/or carbon monoxide
8
Q
why is carbon monoxide bad?
A
-disrupts the human bodys ability to transport oxygen by displacing oxygen in the blood by affecting haemoglobin molecules. this deprives the heart, brain and other vital organs of oxygen
9
Q
why is soot bad?
A
- when breathed in can cause respiratory conditions such as coronary heart disease, ashma, bronchitis and even cancer.
- soot build up in car engines can cause more engine wear and tear
10
Q
at high temperatures, what else do combustion reactions form and why are these products bad?
A
nitrogen gas and oxygen gas can react to form the famous nitrous oxides such as nitrogen dioxide and nitrogen monoxide
these oxides not only can cause acid rain but, in particular nitrogen dioxide, can produce photochemical smog, leaving ozone, which is a powerful lung irritant and oxidising agent even in small conentations which is extremely toxic to humans
11
Q
because petrol contains impurities, what else can be indirectly formed in combustion reactions and why are these products bad?
A
sulfur impurities in petrol can react with oxygen gas in the air at high temp and form sulfur dioxide. sulfur dioxide can cause a multitude of respiratory conditions such as bronchitis and can form acid rain
12
Q
carbon dioxide is often released as a by product during combustion. why isnt it as bad as a pollutant than other combustion pollutants?
A
carbon dioxide can be harmful, but it is mostly absorbed into the environment
13
Q
what are some chemist faculties?
A
- analytical chemistry
- Nuclear Chemistry
- Industrial chemistry
- forensic chemistry
14
Q
what is ammonia used to make?
A
- cleaning products on both an industrial and domestic level
- Fertilisers such as ammonium phosphate, sulfate and nitrate
- Nitric acid
15
Q
why is ammonia used to make cleaning products?
A
acqueous ammonia solution is used as a cleaning agent because of its basic nature, allowing it to emulsify grease stains and other unwanted marks.
it also leaves no residue behind because the water and ammonia in the solution evaporates into the air
16
Q
why is ammonia used to make fertilisers?
A
ammonia is a source of fixed nitrogen, an element which is essential in the growth of plants
17
Q
why are fertilisers and thus ammonia important?
A
fertilisers are used to satisfy the demands of farmers growing food crops
18
Q
how are most fertilisers made?
A
by reacting ammonia with some common acids including HNO3, H2SO4, and H3PO4
19
Q
how is ammonia made to produce nitric acid?
A
through the oswald process
20
Q
what can be made with nitric acid?
A
- fertilisers
- can produce gunpowder and explosives
21
Q
why are nitrogen compounds used to make explosives? give examples
A
some nitrogen compounds or mixtures have the ability to decompose suddenly and produce large volumes of gas at extreme pressure, making them the perfect explosive
examples include TNT (trinitrotoluene), gunpowder (potassium nitrate) and dynamite (nitroglycerin)
22
Q
what is the haber process?
A
the industrial process used to make ammonia from its constituent gases nitrogen and hydrogen
23
Q
what are some characteristics of the haber process reaction?
A
- its reversible (le chateliers principle oh boy!)
- its exothermic
- involves the elements nitrogen and hydrogen
- proceeds very slowly at atmospheric temp and pressure
24
Q
how can nitrogen be obtained for the haber process?
A
- via fractional distillation of liquefied air
- when methane reacts with air over a nickel catalyst to remove oxygen, which would form an explosive mixture with hydrogen if it were allowed to remain. in the process, hydrogen and nitrogen are formed
2CH4(g) + O2(g) + 4N2(g) –> 2CO(g) + 4H2(g) + 4N2(g)
25
how can hydrogen be obtained for the haber process?
- most common method is the hydrolysis of water, seperating the constituents oxygen and hydrogen. except where electricity is plentiful and inexpensive, hydrogen is not obtained in this way
- hydrogen can be made inexpensively by re-forming light petroleum fractions or natural gas by reacting it with steam
- carbon monoxide can be converted into carbon dioxide in a reaction resulting in more hydrogen
26
for every mole of ammonia produced,...
46kJ of energy is released
27
why is the rate of reaction increased with higher temperatures?
as temp increases within a system, the particles in that system gain more and more kinetic energy, beginning to move more frequently and eradicably. this increases the frequency of collisions between these particles, breaking their intramolecular bonds in the process.
therefore, there is more of a likelihood for successful collisions , collisions which must satisfy correct speeds and orientations, increasing the rate of reaction in accordance with collision theory
28
what happens to the yield of ammonia in the haber process at high temperatures and why does this occur?
the yield of ammonia is reduced because the reaction is exothermic (it releases heat). therefore when temp is increased, effectively their becomes an excess amount of heat which the system begins to reduce by shifting to favour the reactants, hence ammonia product is reduced
29
well, if high temps means less product but faster reaction rates, what does this mean for the hater process reaction?
compromise conditions of 450 degrees must be established to strike the perfect balance between efficiency and amount of ammonia
30
what is the equilibrium like at atmospheric temperature and pressure in the haver process?
the reaction proceeds very slowly and the equilibrium lies very much to the left favouring the reactants. in theres conditions, the triple bond in nitrogen and the single bond in hydrogen are reasonably strong and resist breaking to make ammonia
31
what does a catalyst to in the haber process?
a catalyst used in the haver process has no effect on the equilibrium position, but only provides an alternative reaction pathway that has a lower activation energy, and, in turn, increasing the rate of reaction
allows the nitrogen and hydrogen bonds to be more easily broken
32
why is using a catalyst in the haber process advantageous?
because using a catalyst permits the process to be operated at lower temperatures, temperatures which previously fostered a slow reaction rate in accordance with the collision theory but favours the forward reaction and thus produces a high yield of Ammonia
low operating temperatures reduce the cost of production, improving economic viability
33
whats the common catalyst used in the haber process and why?
it is common for magnetite iron oxide to be used as the catalyst. this is because the substance is highly porous and provides a large surface area for the reaction to take place
34
what other compounds can be added to the catalyst and why?
minor components called promoters such as calcium and aluminium oxides may also be added to support the structure of the catalyst and maintains its high surface area
potassium can increase the electron density of the catalyst, thereby improving its reactivity
35
what happens in the haber process when pressure increases?
when the pressure of the equilibrium increases, the equilibrium will shift in the forward direction according to Le Chateliers principle. hence the forward reaction is favoured and a higher yield of ammonia is produced
36
why is the forward reaction favoured when pressure in the haver process is increased?
in the haber process, for every 4 moles of gas which reacts, two moles of product is produced.
increasing the pressure forces the reaction mixture into a smaller volume, pushing each molecule closer together and increasing their chance of colliding and sticking to the catalysed used. via the collision theory, this increases the reaction rate
37
so, does increasing pressure in the haber process have a small or large impact?
a significantly large impact
38
what other concerns arise from the use of high pressure in the haber process?
- operating at higher pressures increases the rick of an accident as equipment is placed under extreme strain. this means that extremely strong, reinforced pipes and containment vessels must be made to withstand these pressures. this increases the production costs
- high pressures cost a lot to produce and maintain. therefore, running costs are very high
- monitoring and maintaining high pressure increases job opportunities for society which is good
- occupational safety issues need to be considered
39
what are the compromise conditions of the haber process?
temperature: 450 degrees Celsius
pressure: 250 atmospheres
40
in the end, what is the main and absolute goal for the haber process?
to make a profit.
41
why is monitoring in the haber process CRUCIAL?
producing ammonia in this process is an around the clock process. all components of the process must be monitored and managed for the effective and optimal production of ammonia. monitoring also ensures safety and efficiency
42
what list of things need to be monitored in the haber process?
- temp and pressure
- the feedstock nitrogen and hydrogen gas
- the presence of contaminants
- movement of the products through the reaction vessels
- the structural integrity of the reaction vessels
43
why are compromise conditions needed in the haber process?
to strike the perfect balance between effectiveness, safety and cost
44
describe the monitoring required for temp and pressure in the haber process?
-temp and pressure must be maintained within acceptable limits for optimal production of ammonia.
but, too high a temp can damage the catalyst and damage other components of the reaction vessel.
the pressure of the reaction vessel should also be maintained at a high level to promote a high level of ammonia production. but to high a pressure may cause the containing vessels to rupture, proving to be a major safety hazard.
maintaining high temp and pressure is also costly
45
describe the monitoring of the feedstock mixture of nitrogen and hydrogen gas fed into the reaction chamber?
the nitrogen and hydrogen that is fed into the containing vessels must be in a stoichemetric ratio of N:H 3:1, and must be pure and free of contaminants
the ratio should be maintained in this way to ensure no build up of any one reactant, thereby decreasing optimum efficiency
46
what contaminants can enter the reaction vessel in the haber process and what are their effects?
- oxygen, can react with flammable hydrogen and or nitrogen to produce a very damaging explosion
- argon(and any other noble gas), lowers the efficiency of the ammonia production
- sulfur compounds, can damage the expensive catalyst
- carbon dioxide, can damage the expensive catalyst
- methane, lowers the efficiency of the process and risks explosion
47
describe the monitoring involved in the movement of materials in the process
products must also be monitored to ensure they are continually condensed and removal from the reaction vessel so as to drive the equilibrium forward. this must be done at regular intervals and must be monitored to ensure no impurities contaminate the product
unreacted gases must also be fed back into the reacting vessel an recycled
48
describe the monitoring involved in the structural integrity of the equipment in the haber process?
the structural integrity of the reaction vessel and seals must be maintained to ensure safety and proper functioning of equipment
49
in what significant period did haber fabricate his ingenious process of ammonia production?
during the first world war
50
why was something like the haber process required during the first world war?
agriculture and industry were competing for the dwindling supplies of nitrogenous materials. Peruvian guano was exhausted by 1900 and sodium nitrate from Chile was also coming to an end.
as well as the above, an allied embargo strangled germanys overseas supply of raw materials from the rest of the world. this stopped Germany importing nitrates from Chile for use in agriculture and as well as in the manufacture of gunpowder and explosives
German industry therefore needed to be able to meet the country requirements for fertilisers and the tremendous demands for explosives
51
how significant was the haber process in its time of world history?
the haber process was very significant, allowing Germany to stay clinger to the war effort, without it the war effort could not have been sustained for long as food could not have been produced at a rate to feed the population
despite many labelling him as a war criminal, his contribution to the war effort was so significant that Haber was awarded the Nobel prize in chemistry in 1918.
haber also improved the nutrition of humanity by providing the world with a reliable source of synthetic fertilisers
52
whats the first test performed to identify cations in a sample?
adding HCl until a precipitate forms
53
after adding HCl, what is the precipitate and what colour is it?
the precipitate is white and it is lead chloride
54
after the first test for cations, what do you do next?
filter the sample and add H2SO4 until a precipitate forms
55
whats the issue when you add H2SO4 to a sample and a precipitate forms?
the precipitate could be one of two things, calcium sulphate or barium sulphate
56
what tests can be done to distinguish between barium sulphate and calcium sulphate?
flame tests
or
adding sodium fluoride, if a precipitate indicates calcium and no precipitate indicate barium
57
after adding H2SO4, whats the next test?
filter the sample and add sodium hydroxide
58
whats the issue with adding sodium hydroxide and a precipitate forms?
the precipitate could be one of two things, iron(II) hydroxide or iron (iii) hydroxide
59
what test can be done to distinguish between the two iron hydroxides?
add KSCN, potassium thiocyanate
if a red solution forms, iron(III) is present
if a clear solution forms, iron(II) is present
60
if a precipitate doesn't form when sodium hydroxide is added, what else does it indicate?
a blue solution forming indicates the presence of copper (II)
ammonia can be added to confirm that the colour is blue
61
what is the flame colour for barium?
light green
62
what is the flame colour for calcium?
brick red
63
what is the flame colour for lead?
blue-tinged white
64
what is the flame colour for copper?
blue green
65
what is the flame colour for iron?
yellow
66
in testing for any ion, why must you test in order using a flowchart etc?
ensures that there is no other ions present which can intefere with the one you are trying to find. for instance, in testing for calcium, you must first test for lead or else the precipitate formed could be lead sulphate instead of calcium sulphate. this is why you add HCl first to precipitate out the lead as lead chloride
67
what is the first test in identifying anions in a sample and what are the results?
add HNO3
if efference is observed, carbonate ion is present
68
what next after adding nitric acid to test for cations and what are the results?
add barium nitrate
| precipitate indicates the presence of sulphate as barium sulphate precipitates out
69
whats the next test after adding barium nitrate and what are the results?
adding ammonia to the sample until the ph is around 8-10
| if a precipate forms, phosphate is present as barium phosphate will precipitate out
70
why do you need to increase the ph when testing for phosphate ions?
barium phosphate increases decreases in solubility as the sample is more alkali
71
whats next after adding ammonia to increase the ph of the sample?
adding more barium ions to make sure definitely that a precipitate is not formed that indicates phosphate
72
whats next after adding more barium to make sure no phosphate is present and what are the results
add HNO3 to make solution acidic and then add silver nitrate
precipite forming indicates the presence of chloride ions as silver chloride precipitates out
73
what is atomic absorption spectroscopy?
a quantitative test for the concentration of metal ions in solution which can measure concentrations below 1ppm
74
what principle does AAS use ?
it works on the selective light absorption of metal ions
different metals have a specific set of wavelengths of light energy that it will absorb or emit which is characteristic of that element
75
what equipment is used in AAS and what are their roles?
- hollow cathode lamp: this lamp emits a particular wavelength of light that the metal being tested will absorb. as such each metal has its own unique cathode lamp
- nebuliser: this is attached to the test solution via a capillary tube which produces a fine mist or vapour. this vapour is then heated in a flame to obtain free atoms
- monochromator: this device ensures the same wavelength of light emitted from the lamp gets fed and analysed by the detector. this is needed as other elements which may be in the flame will also emit light at different wavelengths, which can cause false hight readings of absorption
- detector: measures the amount of light that has been absorbed. the amount of light absorbed is proportional to the concentration of the metal in the nebuliser, which can be compared to the absorption of known concentrations of standard solutions of that metal
- data processor/computer: analyses the data to determine the concentration of metal ions in the sample
76
what are the steps involved in AAS?
1. a calibration curve MUST be made. this is done by testing several standard solutions of a given metal and then plotting concentration to absorption on a graph. this curve will then be compared with the absorption of the unknown sample to achieve an accurate measure of the concentration of a particular metal in the sample
2. the unknown solution is connected to the nebuliser via a capillary tube and forms a mist which becomes heated into a flame. the substances in the sample have now been made into free atoms
3. a light source in the form of a hollow cathode lamp is shone at the flame. atoms in the flame absorb this light as their electrons move up to higher energy levels.
4. the light shines through the vapour into a monochromator, which isolates the particular wavelength of light that was emitted by the hollow cathode lamp in order to measure the difference in the amount of light that had been emitted initially to the amount that had reached the detector. there will be a diff because some of the light had been absorbed by the metal atoms in the flame
5. the light then reaches the detector (photomultiplier) which determine the amount of light absorbed by the tested sample
6. the absorbance value is then compared to a calibration curve to determine the concentration of metal ions in the sample
77
what are trace elements?
elements that are required by living organisms in very small amounts.
78
what impact has AAS had on the scientific understanding of trace elements?
- prior to AAS, wet methods such as gravimetric analysis and volumetric analysis were too insensitive to detect such low concentrations of metal ions, and were Laos very time consuming to do. hence the existence of trace elements and their importance when unnoticed until AAS
- AAS provided a way to test small quantities of metal ions quickly, reliably and very accurately
- AAS has increased our understanding of the necessity of these trace elements in organisms and the health problems associated with deficiencies or excessive amounts of these trace elements
- provided specitfic concentrations required for healthy development of crops, livestock and even humans
79
what are the uses of AAS?
- to test the purity of metallic samples in the mining industry
- to monitor pollution levels in waste waters, particularly heavy metals
- to detect harmful levels of metals in organisms, such as inc in oysters and mercury in fish
- to monitor dangerous airborne metallic particles, such as lead
- for quality control of alloys
- to detect minute concentrations in foods, especially processed foods
- analysing blood samples or urine in the diagnosis of particular conditions
80
overall, what has been the impact of AAS on the scientific understanding of trace elements?
AAS has had a significant impact on the scientific understanding of the effects of trace elements
81
whats so significant about lead?
lead is a cumulative poison which is toxic to humans, animals and some plants. hence because of this, lead concentrations in the environment must be constantly monitored
82
what are some sources of lead?
- burning of leaded petrol
- pigment in paint, potentially making its way into the air when it flakes off, or waterways when dumped
- from infrastructure such as pipes
- dust
- soil
- old toys and jewellery
83
what are some problems that arise through lead poisoning?
-lead affects the brain: causes brain damage, retards brain development, schizophrenia, deafness, speech impediments, learning disabilities, seizures, decreased bone and muscle growth
- lead affects the kidney: can cause kidney damage
- lead affects the nervous system: damages the nervous system
- lead affects the blood: inhibits the growth of haemoglobin, a protein responsible for transporting oxygen throughout the body. this causes anaemia and reduces the ability of the blood to carry oxygen needed for cellular respiration
84
where must lead concentrations be monitored?
- in the air and surface soils near highly populated areas, such as highways
- must also be monitored in water ways, soils and the atmosphere as the bioaccumulation of lead in plants and animals can lead to biomagnification whereby concentrations increase as lead moves up the food chain. the lead then reaches humans though consumption of meat and animal products
85
what is a big use of AAS in pollution control?
to monitor high concentrations of heavy metals in the oyster industry
86
what are the advantages of using AAS in pollution control?
- trace amounts of a metal can be measured with a high degree of accuracy
- the results can be analysed without waiting for a long time
- results are not affected by the presence of other ions, this is very advantageous since heavily polluted areas have a range of pollutants present
87
what are the disadvantages of using AAS in pollution control?
- only one species can be tested for at a time, so multiple tests are required which slows the process down
- can only be used to test for metal ions
- the equipment used in AAS is extremely expensive, so start up fees are normally rather high
- machine must be calibrated, inconvenience which slows the process down
88
what is my assessment of the effectiveness of AAS in pollution control in the seafood industry?
very effective means of pollution control for fish. from these results, necessary action can be taken, such as quarantine of fish as a food source, and similar testing with water samples from where the fish come from can allow for appropriate action to take place
HOWEVER
AAS cannot measure the concentration of non metal pollutants, and therefore alternative quantitative methods must be used if measuring the concentration of non metal pollutants is required
89
what are some sources of error encountered in the sulphate in fertiliser practical and what are the proposed solutions to these problems?
- measurement errors: use a large amount of fertiliser and use an electronic balance to weight
- water remaining, influencing the total wight of the sintered glass crucible: use acetone to seperate any water from the precipitate and dry effectively over an extended period of time
- barium sulphate that has been lost dissolved in solution: cool the solution with ice before filtering, as reducing the temp with decrease the solubility of the barium sulphate even more
- carbonates present in solution results in the precipitation of barium carbonate, when combined with barium sulphate, the precipitate is not purely barium sulphate: add a concentrated HCl to neutralise the carbonate ions while increasing the solubility of phosphate compounds
90
what are the four main layers of the atmosphere starting from the ground to space?
thermosphere
mesosphere
Stratosphere
troposphere
91
what are some of the features of the troposphere?
- lowest layer that extends from 10km above sea level to 15km above sea level
- contains 75% of the atmospheres mass
- filled with nitrogen (78%) and oxygen (20%), as well as carbon dioxide and inert gases to a lesser degree
- gases are well mixed due to the transfer of heat energy via convection currents that circulate the gases and particles
- temp in this sphere decreases with increasing altitude, warmest at the surface(15 degrees) and coldest near the tropopause( -50 to -60) ... tropopause is oen of the several punctuated boundaries which seperate the layers
- the weather comes from this sphere and aircraft fly in this sphere
92
what are some of the features of the stratosphere?
- next after the troposphere, spanning from 15km to 50km
- contains most of the ozone layer
- contains 25% of the atmospheres mass
- temp increases with altitude because the ozone layer is absorbing uv radiation. this prevents convection currents from forming, meaning there is little vertical mixing of gases
- air is very dry and stable, ozone layer also doesn't migrate into the troposphere. hence pollutants often remain for a very long time.
93
what are some of the features of the mesosphere?
- next following the stratosphere, spanning from 50km to 85km
- the temp in this layer decreases with altitude from 0 to -90
- contains many gas particles and gas ions that could not normally exist at lower altitudes, some of these include oxygen free radical as well as metal atoms present in the meters which burn up as a result of colliding with the gas particles present
94
what are some of the features of the mesosphere?
- comes after the mesosphere spanning from 85km to as high as 600km
- very few gas particles present, which therefore implies low air density
-major temp fluctuations occur in this sphere, but vernally temp increases rapidly with altitude, reaching up to 1700 degrees
this temp gradient is as a result of the gas particles absorbing the most energy from sunlight in this layer
95
what are some of the main pollutants found in the lower atmosphere and their sources?
carbon dioxide:
- combustion of fossil fuels in combustion engines and factories
- deforestation and decomposition of organic matter
- released as a byproduct from repairing organisms
carbon monoxide:
- incomplete combustion of fossil fuels
- forest fires
nitrogenous oxides:
- combustion in motor vehicles and in power stations
- forest fires, combustion of organic matter
- from lightning
sulfur oxides:
- internal combustion engines(from fuel impurities)
- sulfide ore smelting
- volcanic gases and geothermal hot springs
- power stations
ozone:
- photochemical smog, caused by nitrogen dioxide destruction under UV light
chlorofluorocarbons:
-manufactured chemicals used in aerosols, refrigerants, foams and air conditioners, fire extinguishers
96
what is ozone and what is its chemical formula?
ozone, O3, is a pale blue, highly reactive toxic gas with a pungent odour
97
what is ozone in the stratosphere?
a blanket against UV
98
what is ozone in the troposphere?
lower atompshere pollutant
99
how does ozone act as a UV sheild in the stratosphere?
ozone acts as a UV shild by absorbing the short UV radiation nd using its energy to decompose into oxygen gas and an oxygen free radical
O3 ---> O2 + O
simultanously, oxygen free radicals combine to form oxygen gas, which subsequently absorbs UV radiation when it breaks back into its component oxygen free radicals
O + O --> O2
O2 --> 2O
these radicals then react with oxygen gas to reform the decomposed ozone, completing the cycle
O + O2 -->O3
100
because of the cycle of the ozone reactions, what happens to the supply of ozone in the stratsphere?
there is a constant supply of it. winds then transfer it within the stratosphere around the earth
101
what health conditions can ozone cause when it is found in the lower atmosphere?
-causes respiratory illness in humans, increases symptoms with asmatics
- can induce fatigue
- can cause headaches
- readily oxidises organic tissue
- irritates the eyes
102
how is ozone formed in the lower atmosphere?
-formed durig electrical discharge from high voltage devices, such as sparks from photocopiers, overhead power lines and lightning
O2--> 2O
O2 + O --> O3
-also forms in the lower atmosphere when there is abundant sunlight and nitrogen dioxide levels are above average (as happens with many large indutrial cities around the world). nitrogen dioxide and nitrogen monomide are produced in high temps of internal combustion engines and from certain industrial chimney stacks
NO2 --> NO + O
O2 + O --> O3
103
what can happen to ozone in the presence of nitrogen monoxide?
it can be destroyed
| NO + O3--> NO2 + O2
104
whats good about ozone in the lower atmosphere despite its toxicity?
its pretty reactive and only remains in the troposphere for a relatively short time
105
what is a coordinate covalent bond?
forms when one of the species provides all the electrons necessary for that bond rather than one each in a normal covalent bond
106
any compound that contains a lone pair of electrons is capable....
of forming a coordinate covalent bond
107
what are some examples of molecules which have a coordinate covalent bond?
- ammonium
- hydronium
- ozone
108
describe the formation of the ozone molecule?
with an atomic number of 16, oxygen has an outer shell of 6, and can combine with two other oxygen atoms to for ozone
the third oxygen atom is unable to form a double covalent bond with one of the now bonded oxygen atoms, as both that atom and the middle atom would then have 10 electrons in their outer valence shells. as such, the middle oxygen atom provides both of the electrons necessary to fill the outer valence shells on both oxygen atoms. this is done through a coordinate covalent bond
thus ozone is formed through one double covalent bond and one coordinate covalent bond
109
compare the molecular shape of ozone and oxygen?
oxygen: linear
ozone: bent
110
which is more dense, oxygen and ozone and what are their amounts? ALSO
explain why they are different in terms of bonding and structure
ozone (2g/L) is more dense than oxygen (1.3g/L)
density is mass/vol, and equal volumes of gas contain the same number of molecules. O3 is denser because it has 3 oxygen atoms instead of 2, and hence has more mass per unit volume
111
compare the reactivity of ozone to oxygen and explain why they are different in terms of chemical structure and bonding
oxygen is very stable while ozone is much more reactive and can easily decompose in the presence of UV radiation
unlike O2 which has a very strong covalent bond, O3 has a single bond, which is much easier to break. hence there bond energy in ozone is much less than the bond energy in O2, hence O3 is more reactive and less stable
112
compare the solubility of oxygen and ozone and exlpain why they are different in terms of chemical structure and bonding
oxygen is sparingly soluble (about 4.9ml of oxygen per 100ml of water) compred to ozone which is considerably more soluble. its also soluble in turpentine, cinnamon oil and mnay other organic compounds containing onre or more ethylene linkages
O2 has a linear structure, making it non-polar, and as such does not form strong intrermolecular bonds with polar water molecules. O3 on the flip side has a bent assymetrical structure and is polar, and thus has a greater solubility in polar water
113
compare the BP and MP of oxygen and ozone and explain the difference in terms of chemical structure and bonding
ozone has a higher BP and MP than oxygen
this reflects the presence of stronger intermolecular forces due to the bent structure of the O3 molecule. as O2 is non-polar, it posseses only disperson forces which are weaker and require less energy to break
114
whats the boiling point of the oxygen free radical?
cannot be accurately measured
115
whats the reactivity of the oxygen free radical?
highly unstable as it attempts to fill the outer most shell
they react readily with most organic compounds at room temp
116
what are chloroflurocarbons?
compounds containing only chlorine, fluorine and carbon. they are alkanes in which all hydrogen atoms are replaced by fluoro or chloro functional groups
117
what were the origins of chloroflurocarbons?
originally introduced as a replacement for ammonia in 1930's refrigeration( and air conditioners). this was because CFCs are odourless, non toxi, chemically inert, non flammable which had ideal boiling points and were readily liquified upon compression. they were also non corrosive and moderate thermal conductivity
after WW2, they were used as
- aerosal spray cans/propellants
- forming agents in the manufacture of foam plastics( polystyrene)
- a solvent in cirtuit board cleaning used from 1960s onwards
118
what are halons?
similar to CFCs, but with the addition of bromine atoms. again, no hydrogen atoms present
119
what are the uses of halons?
they are dense, non flammable liquids found use in fire extinguishers, especially those used where there is electrical equipment. also used for cars, boats, automatic fire extinguishers
120
what is a haloalkane?
a regular alkane where at least one hydrogen atom has been replaced by a halogen
121
whats an isomer?
when a molecule that has the same atoms as another molecule, but an enirely different structure(atoms are arranged differently), then we say that these two molecules are isomers
122
what are the rules for naming haloalkanes?
- bromo, fluoro, chloro are used as prefixes to the hydrocarbon name
- if more than one of these halogens is present in the molecule, precede the prefix with di-, tri- or tetra-
- if more than one halogen is present, list them alphabetically, ignoring any die, tri, tetra
- number the chain (left to right or right to left) so as to give to lowest set of numbers of the halogen group
- halogen atoms are givenn before any alkyl group chains
123
whats the big problem with CFCs when they are released into the atomosphere?
they deplete the ozone layer
124
descibe the process of ozone depletion with a CFC
in the stratosphere, short wavelength UV radiation decomposes CFCs, splitting a chlorine free radical off the CFC molecule.
the chlorine free radical can then react with ozone, forming back oxygen as well as chlorine monoxide
Cl. + O3 --> ClO. +O2
ClO. + O. --> Cl. + O2
thus the overall reaction is O. + O2 --> O3
the chlorine free radical is free to continue this loop many tens of thoasands of times over before it meets some otehr species that will remove it from the loop. some of these include reacting with methan or nitrogen dioxide
125
what are the dangers of UV exposure and hence the depletion of the ozone layer?
-danger of global warming as temps increase
-prolonged exposure to UV radiation can lead to
cell tissue damage leading to tumours and cancers, damage to certain plants and organisms dependant on sunlight but vunlnerable to UV including forms of plankton
- damage to synthetic materials such as polymers like PVC
- lowering peoples immune response
126
what is the montreal protocol and when was it introduced?
an international treaty designed to protect the ozone layer by phasing out the production of numerous substances that are responsoble for ozone depletion. these substances are CFCs and halons.
introduced in 1987, ammended in 1992, and aimed to fully phase out ozone depleting chemicals by 2000. financial support and extra dealines were handed out to less developed countries to help them phase out these ozone depleteing chemicals. by 2007, 191 had signed
127
what other things have been introduced other than the protocol to help alleviate the issues of CFCs ?
- trade agreements have been created for the purpose of restricting trade in susbances which are dangerous to the ozone layer
- research being undertken to establish alternatice chemicals to replace CFCs, including hydrochlorofluorocarbons and hydroflurocarbons
HCFCS are a moderately effective as replacements for CFCs. HCFCs replace the role of CFCs in plastic production and refrigertation well, and their ozone capacity is much lower than CFCs. however the damage they cause to the ozone layer is still signficant, and HCFCs are only seen as a temporary sub before better compoudnds are put to use
HFCS are very effective replacements
they contain no bromine or chlorine atoms and hence have zero ozone destroying capacity. they are now wdiely used in refrigeration and airconditioning. they are however more expensive and less efficient than CFCs
128
whats my assessment of the effectiveness of the steps undertaken to alleviate the problems of CFCs?
these steps have had a significant effect on slowing the increasing trend of problems caused by ozone depletion. although these is no doubt that the ozone layer was damaged immensly through years of thourghtless use of synthetic chemicals such as CFCs, the damage us not irrepable, and steps such as the montreal protocol will see that the problem is not made worse. with time, the ozone layer will replenish
129
what is a total ozone mapping spectromometer?
a sattelite instrument used to map global ozone levels. these devices are orbiting the earth in several US satellites
130
how do the TOMS measure global ozone levels?
measures the intensity of light recieved at wavelengths equal to, lower, and greater to what ozone absobrs. this data is then compared to calcualte ozone conentrations as a function of altitude and geographical position
131
what can TOMS be used to make?
used to produce ozone profiles and contour maps. these maps were especially useful during the 1980s showing the extent of the ozone holes
132
how have TOMS been useful to scientists?
TOMS ozone data has helped scientists in detecting small, but steady, long-term damage to the ozone layer over several parts of the globe, including most of the heavily populated regions in the northern mid latitudes
133
what is the dobson ozone spectrometer?
ground based instrument used to measure total column ozone in the atomosphere
134
how does the dobson measure total column ozone?
measures column ozone by the technique of differential absorption of ultraviolet light with the sun (or moon) as a light source. by comparing the uv light intensity at wavelengths that are strongly absorbed and weakly aborbed by ozone, the total column ozone content of the atmosphere can be accurately determined
135
when was the dobson first made and by who?
made during the mid 1920s by Gordon Dobson
136
what are some of the changes in ozone concentrations which have been measured over the years?
- globally CFCs have caused a 3-8% decrease in ozone in the strataopshere annually. however more recently they have caused a 50-90% decrease over antarctica during spring
- by 1985, measurements over antarctica showed at least 50% decrease in atmospheric ozone conentration. evidence has also indicated a 12% thnning of the ozone layer over australia and New Zealand in 1987
- further decreases in ozone have been reported in 2003, 2000 and 1998.
- due to the recent decrease in the use of CFCs, there has been an observable decrease in the rate at which ozone is being depleted in recent yrs
137
why does ozone depletion increase rapidly during spring?
rare clouds form in the winters of antarctica, forming a surface upon which various oxides of nitrogen can combine with chlorine monoxide to form ClONO2 inside ice crystals
in spring, temps increase and these crystals metl, releasing the accumilated ozone-destroying molecules and causing weakening in the ozone layer above antarctica
138
overall, what have instruments detected in regards to ozone in the atmosphere?
that the ozone layer has indeed diminsihed in thickness. although the use of synthetic substances which damage the ozone layer, such as CFCs, have been greatly reduced, these substances have rather long lifetimes.
139
why do CFCs in the atmosphere have really long lifetimes?
due to the fact that they are repeatedly recycled through their ozone destroying processes, as such, it will take much time before the ozone layer is restored
140
what are some of the replacements for CFCs and evaluate their effectiveness as a replacement
-halons, nah soz bud, these bromine containing weapons are more of a detrimental impact to the ozone layer than CFCs given that they are more reactive under UV light than conventional CFCs
-hydrochlorofluorocarbons, HCFCs,
these bad boys are highly reactive and break down in the lower altitudes of the troposphere, and generally break down completely before entering the stratosphere which is nice. they decompose significantly in these areas as the CH bonds can react with atoms and free radicals in the troposphere. but chlorine atoms still manage to get into the upper atmosphere. despite them only contributing to 10% of the depleted ozone layer, they arent really effective and are only seen as temporary substitutes
-hydroflurocabons, HFCs
have no trace of chlorine or bromine, TICK
more expensive and less efficient than CFCs, damn
widely used in refirgeration and air conditioning, awesome
theyre greenhouse gases
hence, seen as viable subs , but they are expensive and are less efficient which limits their use
141
what are the factors that need to be considered when talking about water quality?
- concentration of common ions
- total dissolved salts
- tubidity
- dissolved oxygen
- biological oxygen demand
- acidity
- hardness
142
what are some ions found in water?
Na, K, SO4, PO3, Mg etc
143
what are some tests for common ion concentration?
- AAS, for metal ions in very small amounts
- gravimetric analysis, this can be used to measure the concentration of a moderate amount of a specific ion. acts as an alternative other than AAS when testing for anions
144
what is the general outline for gravimetric analysis?
1. water is added to sample
2. sample is then filtered
3. the remaining solid is dried and weighed and stoichemetric calculations can then be used to quantatively calculare the concentration fo the ion in question
145
what is total dissolved soils a measure of?
measure of the mass of dissolved solids per unit volume of water, measureable in ppm. most dissolved solids are salts
146
what is the value of tds that is good for drinking water?
below 100ppm is preferable. above 500ppm is a no go
147
what are the tests for tds ?
- gravimetric analysis--> used in the lab for coneentrations that are greater than 100ppm. this is not desirable if the ammount of solid is quite low, meaning an auccrate result is unlikely
- electrical conductivity is the preffered method. because the dissolved solids are often salts, they are able to carry electric charge. as such, a conductivity metre can be used to determine the tds of a sample
148
what is hardness a measure o?
hard water includes water that has a high conc of magnesium and calcium ions.
due to the presence of these ions, water is unabl to form a lather with soap. instead, a grey scum forms on the water surface( calcium and magnesium ions precipiate with soap)
149
what are the tests for hardness?
- AAS
- gravimetric analysis
- EDTA titrations, most accurate and prefferable method
- electronic probes
150
what is tubidity a measure of?
measure of the collodial matter suspended in water.
151
what are the problems with turbid water?
highly turbid water is a lot darker than normal water, because it is darker, it absorbs moree heat, and hence less oxygen is able to dissolve in the water
- suspended solids in water can clog fish gills, reduce growth rates, decrease resistance to disease, and prevent egg and larvael growth
- plants and otehr photosynthetic organisms in highly turbid water experience a reduced source of light, impeding on photosynthetic processes. thus they suffer from less chemical energy to operate off
152
what are the tests for turbidity and how do they work?
- turbidity tube--> water is poured into a calibrated tube, and the turbidity is measured by examining which lines marked on the tube can be seen, the units of measurement ar known as NTUs, or nphelometric turbidity untis
- turbidity meter--> measures the amount of light scattering
- secchi disc--> a secchi disc is a disc divided into four quandrants with alternative quandrants pained silver and black. this disc can be lowered into a body of water. the longer the length before the quandants become invisible, the lower the turbidity
153
what is acidity a measure of?
the concentration of hydronium ions in water. higher the concentration, lower the pH, higher the acidity
154
tests for acidity?
universal indicator
data logger and pH meter
155
what is dissolved oxygen a measure of?
simply the amount of dissolved oxygen per litre of water at a fixed temp
156
what are the suitable levels of oxygen concentration and why are these important?
too low DO promotes the growth of harmful bacteria which rely upon anaerobic respsiration
many species will also die and the water becomes smelly and unsightly
157
DO levels are highest in the...
afternoon and lowest at dawn
158
DO levels depend on other factors including.. .
```
temp
pressure
water movement
salinity
chemicals in water
```
159
what are the tests for dissolved oxygen?
- specific titration procedure known as the wrinkler method
- calibrated oxygen sensor probe = electronic device where oxygen diffuses across a membrane in a submerged probe to complete an electrical circuit
160
what is biological oygen demand a measure of?
measure of the concentration of dissolved oxygen required for the complete breakdown fo the organic matter in the water by anerobic bacteria
161
lower the BOD,...
the higher the quality of the water as their is more DO and there is less organic matter needed to be broken down
162
what is the accepted level of BOD and what is it measured in?
below 5ppm and it is measured in ppm
163
what are some tests for BOD?
a sample of water is divided into two. the DO content of one is then measured, while the other is placed in a location away from any source of light( eg a cupboard)
this is so photosynthesis cannot occur and hence DO levels do not change or increase
after 5 days the DO content of the 2nd sample is tested. the difference in DO betweem tje first and 2nd sample is the BOD
this means that BOD is essentially the amount of O2 consymed in a 5 day period for the complete breakdown of organic matter present within a water sample
164
what are some examples of human activity which affect the oncentration of ions in water?
-farming and agriculture
use of fertilisers or from faeces from livestock contain lots of nitrates, phosphates and sulfates
water may recieve salts from irrigation, where the water from rivers or rain are passed though soil before returning back to the river
-industrial activity
wastes often contain high amount of heavy metals
industrial activity produces acid rain, ph of water ways become more acidic. increases solubiluty of ions such as Mg, Ca, which are contained within rocks and soils, enters via leaching
activity also releases impurities into the air such as soot, can be collected via rainwater, others include sulfur, dust etc
-clearing of land
increases erosion and a raising of the underground water levels(because trees suck up water and hence it isnt used up), reuslting in more runoff and a higher concentration of ions, both cations and anions
-swerage waste
should the water combine with sewerage wastem the ionic conent will again differ. will result in an increase in the concetnrations of sulfates, nitrates, phosphates
165
what are some natural factors which affect the concentration of ions in water?
-nearby geography and landmass
water contains concentrations ions depending on the composition of the landmass over which it flows. eg water going over limestone must have high concs of calcium bicarbonate
leaching of minerals and salts from soils and rock as the water goes underground
-pH
affects the solubility of certain ions, for instance, decreased pH increases the solubility of calcium and magnesium ions
-water temp
generally, increased temp increases in ion solubility
166
whats the first step in the method of the purifying of water?
collecting the water in the catchment area
this natural environment is preserved through: no logging, grazing, land clearing, no mining or other farming activities so that the water is relatively free of animal wastes, sediments, fertilisers and harmful ions
167
after the catchment area, whats next in purifying water?
screening!!!!!
water is passed through a series of large sieve screens in order to remove the larger foreign objects from the water supply
168
whats next in the purifing of water after screening?
COAGULATION, FLOCCULATION AND CLARIFICATION!!!!!!
coagulants such as potash alum, alum mied with lime, aluminium hydroxide or iron chloride are added to the water to cause the finer particles to clump together forming a floc. this then can be filtered out
clarification:
flocs are allowed to settle to the bottom,these clumps consits of solids, iron and bacteria present in the water that are absorbed into the coagulant
169
whats next after coagulation??????
FILTRATION!!!!!
remaining water is passed through another set of filters that are much finer then the ones used in screening
170
what are some common filters used in filtration?
- grains of sand
- gravel
- granular anthracite
or usually a mixture of the three
microscopic membrane filters are also used but because of their high cost, they arent used often
171
how do sand filters work?
sand filters remove fine, suspended solids and some larger micro-organisms. over time, these sand particles become covered in a slimy layer of micro-orgainisms (biofilm), which traps very small particles
172
what comes after filtration in the purification of water?
the use of ion exchange resins
these resins are used to remove the low concentrations of organic matter that can cause odour and taste problems that have not been dealt with through prior treatments
carbon and ion exchange resisn can be used as absorbants to remove soluble contaminents from the water, in exchange for ions found on the resin
after some time these resins can become saturated and require a costly replaceents, hence absorption is a very costly venture and one that isnt used often
173
what comes after the use of ion exchange resins?
oxidation using ozone or chlorine monoxide
each chemical is used as strong oxidants that can destroy contaminents such as algal toxins and taste and odour compounds
although considerably costly than compared with other standard techniques, it is still highly affective when odour and taste problems are severe
174
what comes after oxidation?
water stabilisation, where the water is made to have a pH of around 7
done by adding lime or sometimes carbon dioxide
175
what comes after water stabilisation?
chlorination
widely used disinfectant as it is cheap and easy to use (effective in small doses)
main downside is that chlorine can react with dissolved organic matter, forming chlorinated organic compounds
176
what comes after chlorination?
fluridation
| in accordance with dental safety regulations, the water is pumped with fluorine
177
what is my assessment of the methods used to purify mass water supplies?
while not perfect, still very effective for hygiene and portability
- vast majority of systems meet health standards with techniques used
- although membrane filters seem cool, their high cost and the fact that they will only provide small improvements limit its use
178
what makes a microscopic membrane filter?
water is filtered through tiny pores in a membrane wall or polymer sheet. the size of these holes are very tinty, as to trap very fine particles
membrane wall is a thin film of a synthetic polymer usually polypropylene and polytetrafluroethylene. these filters are often used with eachother in layers to provide an even finer level of filtration
usually, sheet of porous polymer that is folded around a central, rigid, porous core, held together by mesh, forming the filter catridge
a suitable housing in a water pipe is used to store the fulter catridge which filters the water as it flows through
179
how does a microscopic membrane filter work?
by using high levels of pressure:
- gravity, or a pump or vacuum forces the water through the filter. water is forced across the surface of the filter, not at right angles to ensure that the pores do not clog up.
- clean water penetrates the filter, and in so doing, all particles, including bacteria and even viruses greater than the size of the poeres are trapped outside the filter
180
how effective is a microscopic membrane filter?
-high level of filtration provided and the filter is reusuable
HOWEVER:
-due to high pressures used, their costs can be rather high
-if the filters get clogged due to large amounts of organic matter, it will require a rather expensive replacement
-the filters require constant flushing to ensure they/re working properly
181
what is eutrophicaiton?
Eutrophication is the enrichment of a body of water with nutrients (phosphates and nitrates) that causes uncontrolled
microbial growth, eg algal blooms, to occur
182
what are the problems associated with eutrophication?
- the algal blanket which forms prevents sunlight from reaching photosynthetic organisms lower down in the water. they die and no oxygen enters the water by photosynthesis. all available DO is used up to breakdown the dead organisms
- fish die due to the severely low DO
- algal blanket restricts oxygen from the air difusing into the water at the surface
- algal growth becomes a breeding ground for cyanobacteriadue to the low DO. these bacteria produce harmful toxins that can kill livestock and make humans sick
- decomposition of dead matter leads to the formation of putrid hydrogen sulfide
183
how can we measure eutrophication?
- perfoming a BOD test
- 1ml of sample heated gently under a fume cupboard with a copper strip and 3 drops of sulfuric acid. nitrogen dioxide will be released if nitrate if present
- sample with the addition of sodium molybdate solution and hydrazine sulfate should turn the solution blue if phosphate is present
184
what nitrate:phosphate ratio is considered healthy and what isnt when considering eutrophication?
20:1 is healthy
relatively clean has 10:1
