Question Chain Thread !!! (2 Viewers)

[SkimDawg]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

The Haber process is the process of producing ammonia from gaseous hydrogen and nitrogen.
3H2(g) + N2(g) ----> 2NH3(g)
Because the system can come to equilibrium and is exothermic, conditions need to be monitored and kept at levels that favour the formation of ammonia.
Temperature needs monitoring to maintain it at about 500 degrees C. If it falls below this the reaction rate becomes too low and if it rises above this the equilibrium shifts in reverse and the yield of ammonia drops. A iron oxide catalyst is used to raise the reaction rate at this moderate temperature.
A high pressure of 350 atmospheres is used to optimise the yield of ammonia because its production is accompanied by a decrease in the number of gaseous molecules. Pressure needs monitoring because if it drops, the yield of ammonia will also drop but if rises, the reaction vessel may not withstand the pressure.
The ratio of reactant gases must be monitored to keep it at 3:1 H2, N2 because this is the ratio at which these gases react. If this ratio is not adhered to, excess reactant will slow down the reaction and be costly.
For these reasons, it is extremely important to monitor the conditions used in the Haber process. If any of these conditions change the yield of ammonia will not be optimal.

Not quite what you asked, but something along the lines, a generic response i guess you could say ha.

Next qu:
Describe the process of eutrophication, and assess the suitability of water quality tests used to monitor it. (4 marks)

 

[danz90]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

The Haber process is the process of producing ammonia from gaseous hydrogen and nitrogen.
3H2(g) + N2(g) ----> 2NH3(g)
Because the system can come to equilibrium and is exothermic, conditions need to be monitored and kept at levels that favour the formation of ammonia.
Temperature needs monitoring to maintain it at about 500 degrees C. If it falls below this the reaction rate becomes too low and if it rises above this the equilibrium shifts in reverse and the yield of ammonia drops. A iron oxide catalyst is used to raise the reaction rate at this moderate temperature.
A high pressure of 350 atmospheres is used to optimise the yield of ammonia because its production is accompanied by a decrease in the number of gaseous molecules. Pressure needs monitoring because if it drops, the yield of ammonia will also drop but if rises, the reaction vessel may not withstand the pressure.
The ratio of reactant gases must be monitored to keep it at 3:1 H2, N2 because this is the ratio at which these gases react. If this ratio is not adhered to, excess reactant will slow down the reaction and be costly.
For these reasons, it is extremely important to monitor the conditions used in the Haber process. If any of these conditions change the yield of ammonia will not be optimal.

Not quite what you asked, but something along the lines, a generic response i guess you could say ha.

Next qu:
Describe the process of eutrophication, and assess the suitability of water quality tests used to monitor it. (4 marks)

Eutrophication involves the addition of nutrients, such as phosphates and nitrates, to waterways. This leads to the thriving/growth of algal blooms. Subsequently, these algal blooms at the water surface block the penetration of sunlight to photosynthetic aquatic plants in the waterway. This ultimately leads to a drop in [O_{2 (aq)}], which causes the death of aquatic organisms (such as fish). The establishment of anaerobic conditions allows for anaerobic bacteria to thrive and decompose organic matter of dead aquatic organisms. Respiration of anaerobic bacteria produces noxious gases such as CH₄ , NH₃ and H₂S. These gases further degrade the waterway.

Tests used to assess the impact of eutrophication, measure levels of DO (dissolved oxygen), and BOD (biochemical oxygen demand).
DO can be tested via the Chemical winkler method (which is a fairly inaccurate method, due to the multiple chemical procedural steps involved), or using an Oxygen sensor, a much more accurate and suitable method of measuring dissolved oxygen. An oxygen sensor uses an electrolytic sensor, which measures the rate of reduction of O_{2 (aq)} , which is proportional to[O_{2 (aq)}].

BOD can be measured using the Five Day Standard. This involves placing 1L of a water sample in complete darkness, for five days, at 20degrees. The difference in readings of [O_{2 (aq)}] before and after the test period, indicates the BOD.

The BOD five day standard, and Oxygen sensor, used to measure BOD and DO, are very suitable methods of assessing the impact of eutrophication upon water quality.

Next: Perform a first-hand investigation to carry out the fermentation of glucose and monitor mass changes.

 

[liamh16]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

Eutrophication involves the addition of nutrients, such as phosphates and nitrates, to waterways. This leads to the thriving/growth of algal blooms. Subsequently, these algal blooms at the water surface block the penetration of sunlight to photosynthetic aquatic plants in the waterway. This ultimately leads to a drop in [O_{2 (aq)}], which causes the death of aquatic organisms (such as fish). The establishment of anaerobic conditions allows for anaerobic bacteria to thrive and decompose organic matter of dead aquatic organisms. Respiration of anaerobic bacteria produces noxious gases such as CH₄ , NH₃ and H₂S. These gases further degrade the waterway.

Tests used to assess the impact of eutrophication, measure levels of DO (dissolved oxygen), and BOD (biochemical oxygen demand).
DO can be tested via the Chemical winkler method (which is a fairly inaccurate method, due to the multiple chemical procedural steps involved), or using an Oxygen sensor, a much more accurate and suitable method of measuring dissolved oxygen. An oxygen sensor uses an electrolytic sensor, which measures the rate of reduction of O_{2 (aq)} , which is proportional to[O_{2 (aq)}].

BOD can be measured using the Five Day Standard. This involves placing 1L of a water sample in complete darkness, for five days, at 20degrees. The difference in readings of [O_{2 (aq)}] before and after the test period, indicates the BOD.

The BOD five day standard, and Oxygen sensor, used to measure BOD and DO, are very suitable methods of assessing the impact of eutrophication upon water quality.

Next: Perform a first-hand investigation to carry out the fermentation of glucose and monitor mass changes.

I don't actually know what you're asking me to do, but i'll just sorta justify/outline the method.

Weigh 1g of yeast onto a square of paper, and add it to a 100mL conical flask.
Measure 200mL glucose solution using a 250mL measuring cylinder, and add the solution into the flask carefully. Insert the stopper and bent glass tube. Dry the outside of the flask with paper towel. Weigh the apparatus on a calibrated set of electronic scales. Record the initial mass of the flask and it's contents. Place the reaction apparatus is a 500mL beaker containing 300mL water. Place this beaker on a hotplate to heat the water to a constant temperature of 35*C. Ensure the temperature of this water bath is kept constant throughout the experiment. This is done to accelerate the fermentation process.
After 30 minutes, carefully remove the conical flask from the beaker and dry the outside with paper towel. Weigh the conical flask and it's contents on the same set of scales used prior, and record the weight. Return the flask to the water bath. Connect the rubber hose to the glass tube connected to the flask, and place the other end of the rubber hose submerged in a 200ml beaker containing 150mL of limewater. Observe the initial colour of the limewater. If the limewater goes milky this means CO2 has been produced by the reaction, thus the reaction is taking place sucessfully. Leave the experiment overnight. The next day, observe the colour changes of the limewater, and dry the conical flask and reweigh it with the same scales used before. Record the mass changed. Repeat the steps with a control containing only glucose.




I think that's alright. Correct me if im wrong.



Assess the evidence which indicates increases in atmospheric concentration of oxides of sulfur and nitrogen.

 

[friction]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

All 3 of those first 3 questions were from the 2003 paper lol.

 

[JasonNg1025]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

Assess the evidence which indicates increases in atmospheric concentration of oxides of sulfur and nitrogen.

1) Decrease in pH of water bodies. As we all know, these gases produce acid rain in the atmosphere, so increased levels of acid rain indicate increases in atmospheric concentrations of oxides of sulfur and nitrogen. Include equations if you want, I'm sick of typing those

2) Analysis of air bubbles trapped inside Antarctic ice. Holes are drilled into the ice to check, the deeper down they go, the older it is. Hence, by analysing concentrations in order of depth, trends can be taken. This shows that levels have indeed increased.

I'm pretty sure there was one more, just not coming to mind somehow.

It has been difficult to recognise trends which indicate increases in atmospheric concentrations of these gases. This is because the equipment necessary has only been available since the 1970s, and so clear and long trends have not been taken. Concentrations of these are also very small, being 0.001ppm at highly populated areas.

Err, my question is the one from the other chain thread. Not too sure about that one either.

EDIT: Okey, got it.

"There are many benefits and problems associated with the use of radioisotopes in industry and medicine. Evaluate the impact on society of the use of radioisotopes in both industry and medicine. In your answer, give examples of specific radioisotopes, making reference to their chemical properties. (7 marks)."

 

[yorkstanham]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

There are many benefits and problems associated with the use of radioisotopes in industry and medicine.<?xml:namespace prefix = o ns = "urn:schemas-microsoft-comfficeffice" /><o></o>
Evaluate the impact on society of the use of radioisotopes in both industry and medicine. In your answer, give examples of specific radioisotopes, making reference to their chemical properties. (7 marks) <o></o>
The use of radioisotopes in both medicine and industry has had significant impact on society. They have allowed for cheaper and quicker methods in both medicine and industry.
Medicine: Technetium-99m is a radioisotope widely used in medicine to evaluate the damage after a heart attack, to check for blockages as well as monitoring the functioning of the brain. The benefits associated with the used of Tc-99m in this case far outweigh the problems encountered. Tc-99m’s short half-life of around 6 hours allows the isotope to give off a sufficient amount of radiation to be imaged yet does not cause damage to the patient or build up in the patient. Tc-99m, once tagged, does not react with any cellular components within the body, this is beneficial as it will not cause unwanted hard to the patient. The choice to use Tc-99m has created many benefits with little problems.
Industry: Americium-241 is used in smoke alarms. It long half-life of 432 years ensures that it will outlast the life time of the smoke alarm system. This is extremely beneficial as it will not require replacement which will ensure the safety of the building. Americium-241 decays via alpha decay, alpha particle are only able to travel about 10cm in air, this allows the smoke alarm to be used in houses as it will not pose any radiation threats. Once again the benefits associated with the use of this radioisotope far outweigh the problems. The use of smoke alarms has no doubt saves 1000’s of lives.


NEXT QUESTION:
Discuss the problems with the use of CFC’s, and assess the suitability of alternative chemicals as replacement products. (7 marks)<o></o>

 

[JasonNg1025]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

Ok thanks a lot. Just need to talk about functions

Payback time.
Discuss the problems with the use of CFC’s, and assess the suitability of alternative chemicals as replacement products. (7 marks)

CFCs have been used in the past as aerosol propellants and refrigerants. Their use, however, has led to the decrease in ozone levels in the stratosphere. Ozone is an important as it blocks out harmful UV radiation. Increased exposure causes mutation in cells, leading to cancer.

When a CFC such as CCl<SUB>3</SUB>F gets into the stratosphere:

1) UV breaks it down:

CCl<SUB>3</SUB>F <SUB>(g)</SUB> --> CCl<SUB>2</SUB>F <SUB>(g)</SUB>+ Cl•

2) The Cl• attacks the ozone:

Cl• + O<SUB>3 (g)</SUB> --> ClO<SUB> (g)</SUB> + O<SUB>2 (g)</SUB>

3) The ClO then decomposes:

2ClO <SUB>(g)</SUB> --> 2Cl• + O<SUB>2 (g)</SUB>

Due to the fact that the chlorine free radical regenerates, one CFC molecule can take out thousands of ozone molecules. This process only stops when the Cl• reacts with another substance to produce a stable substance.

Alternative chemicals include hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs). HCFCs were used first. They worked quite well as the relatively unstable C-H bond allowed it to decompose in the troposphere, meaning it did not have the chance to decompose ozone in the stratosphere. However, some inevitably got past the troposphere, so some ozone was still depleted.

HFCs were then used. Again, these had the C-H bond decreasing their exposure to ozone in the stratosphere. Even if HFCs managed to get to the stratosphere, however, they did not contain Cl and so could not deplete ozone in that manner.

The use of alternative chemicals has been effective. These chemicals have similar properties to CFCs, but do not have the same problems. Ozone depletion has drastically decreased as a result, but unfortunately CFCs already in the atmosphere will continue to attack ozone.

 

[liamh16]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

NEXT QUESTION:
Discuss the problems with the use of CFC’s, and assess the suitability of alternative chemicals as replacement products. (7 marks)<O></O>

UMMMM

CFC's are used in the propellants of such products as aerosol cans. They are very dangerous for the environment because when they are exposed to ozone in the stratospheric ozone layer, they have the potential to destroy the Ozone molecule. They are problematic because not only do they destroy one ozone molecule, one Cl radical that came from CFC's has the ability to destroy hundreds of Ozone molecules. CFC's such as CCl2F2 are split into CClF2 and Cl when they are exposed to UV radiation
CCl2F2 -UV-> Cl + CClF2
This reactive chlorine radical then is exposed to an ozone molecule and splits it into an oxygen molecule and forms ClO with the other oxygen.
Cl + O3 -> ClO + O2
ClO then reacts with the reactive O radical to form O2 and Cl radical
ClO + O -> Cl + O2
Which starts the chain of events again.
This then means that the ozone layer is slowly being depleted, and when many CFC's are let into the atmosphere this causes holes in the ozone layer, which can destroy ecosystems on earth and give humans melanoma and various skin diseases by the dangerous UV-B rays emitted from the sun.
To counter this problem, alternative chemicals such as HFCF's and HFC's have been introduced, and have been very sucessful replacements. HCFC's are only a short term solution, because they still have ozone depleting potential. On the other hand, they have only cost a little more to produce and thus have not caused too much economic disadvantage to consumers. They do the same thing as CFC's, and therefore are sucessful alternative products, due to their comparitive environmentally friendly nature, and also because they do not cost a large amount more than CFC's.


That was shockingly answered. Oh well.




Qualitiativley describe the effect of buffers with reference to a specific example in a natural system.

 

[minijumbuk]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

3) The ClO then decomposes:

2ClO _(g) --> 2Cl• + O_{2 (g)}

ClO + O -> Cl + O2

I think liamh's equation is the correct one which demonstrates the decomposition of ClO. That's what Conquering Chemistry says anyway. I don't know if other textbooks say different or same things.

 

[JasonNg1025]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

Oh, ok
I'll check Dot Point (grr at that book, it's taken up at least 24 hours in total)

EDIT: Actually, I don't know how long. Just a lot of time.

Ok, Dot Point says my one, but I'd maybe trust something else. Going to google it xD

From minijumbuk, CC says liamh16.

Another edit - HSC online says liamh16's one.

Yet another - Australian Bureau of Meteorology says liamh16's one is good. I'm beginning to think so too.

Current score -

Me - liamh16
1 - 3

I guess it makes sense - 2 Cl• produced together would rather become Cl<SUB>2 (g)</SUB>

 

[SkimDawg]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

Qualitiativley describe the effect of buffers with reference to a specific example in a natural system.

A buffer is a solution that is able to maintain a constant pH; even the addition of a strong acid or base does not change its pH. The buffer solution contains approximately equal amounts of a weak acid and its conjugate base. The equilibrium involved can be represented as:
HA + H2O H3O+ + A-
‘HA’ is the weak acid, which protonates water, forming its conjugate base, ‘A-’. Using Le Chatelier’s principle, we can deduce why the pH remains constant: Addition of any acid (regardless of its strength) increases [H3O+]. However, this does not decrease the pH; the additional acid simply reacts with the conjugate base and forces the equilibrium to the left, forming more of the weak acid, and the pH returns to its original value. Addition of any base (that is OH- ions) does not increase the pH as expected; as the base reacts with the hydronium, [H3O+] decreases. This shifts the equilibrium to the right, and more H3O+ is produced through the forward reaction. The pH returns to its original value.
– An example of a NATURAL buffer system is the carbonic acid system:
This system occurs naturally in freshwater lakes and rivers, and it maintains the constant neutral pH needed for life to exist. Carbon dioxide from the air dissolves in the water, forming carbonic acid, while its conjugate base, hydrogen carbonate, is present as ions leeched out of rocks and minerals of the lake. Because there are comparable amounts of the acid and its conjugate base, it is considered a buffer:
Ø H2CO3 (aq) + H2O (l) H3O+ (aq) + HCO3־ (aq)
This natural system protects many water systems from the effects of acid rain.

next qu
Sodium hydrogen carbonate, NaHCO3, is commonly used to neutralise chemical spillsthat are a potential hazard to the environment. Assess the effectiveness of NaHCO3 in this role, with reference to its chemical properties.

ps: keep it up guys, this thread is excellent for others to understand stuff they are not sure about, or just the crammiesters haha

 

[liamh16]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

CCl2F2 -UV-> •Cl + •CClF2
This reactive chlorine radical then is exposed to an ozone molecule and splits it into an oxygen molecule and forms ClO with the other oxygen.
•Cl + O3 -> •ClO + O2
ClO then reacts with the reactive O radical to form O2 and Cl radical
•ClO + O -> •Cl + O2


just to throw a curveball in here and say that this is actually what i have and would do in the HSC, but i couldn't find the electron dot.
So yeah, what do you guys think about that? I'm so confused now...

 

[Zeber]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

Evaluate the significance of the Haber process whilst considering the context within it's invention.

 

[liamh16]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

Sodium hydrogen carbonate, NaHCO3, is commonly used to neutralise chemical spillsthat are a potential hazard to the environment. Assess the effectiveness of NaHCO3 in this role, with reference to its chemical properties.

NaHCO3 is very effective at neutralising potentially hazardous chemical spills in the environment, due to it's chemical properties.

NaHCO3 is an amphiprotic substance, which means it can act as an acid or a base depending on the chemicals present.

NaHCO3 + OH- --> NaCO3 + H2O
NaHCO3 is acting as an acid.

NaHCO3 + H3O+ --> NaH2CO3 + H2O
NaHCO3 is acting as a base.

This is very useful because it can be used to neutralise acidic or basic spills. NaHCO3 is also easy to transport, because it is a powder. This is also useful after the spill is neutralised, it can be easily mopped up and disposed of safely. NaHCO3 is also a weak substance, which will not harm the environment if an excess is left over from the reaction.

Therefore, due to it's chemical properties, NaHCO3 is very effective in the job of neutralising chemical spills that could be potentially hazardous.

Describe how commercial radioisotopes are produced, and how transuranic elements are produced.

 

[SkimDawg]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

Evaluate the significance of the Haber process whilst considering the context within it's invention.

Nice lets pretty much repeat questions, just with different wording....
Haber developed a method of porducing ammonia by reacting together hydrogen gas and nitrogen gas at 400 degrees C and 250 kPa with an Fe3O4 catalyst. This was significant because prior to his discovery the world relied on obtaining ammonia from natural sources of guano (isnt this batshit? lol), principally from Chile. When Haber made his discovery in 1908, his home country Germany was preparing to enter a war which would become WW1. Germany could not wage war without a reliable source of ammonia to fertilise crops to feed the German people and to produce nitric acid used to make explosives. Chile would cut off supply of guano as it was an ally of England. Haber's discovery allowed Germany to wage a war that they very nearly won; therefore his discovery was very significant in the timeframe of its context (Nazism Germany).

lol forgot next qu, Explain how the structure and properties of polyethylene and polystyrene relate to the way each is used.

 

[danz90]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

Nice lets pretty much repeat questions, just with different wording....
Haber developed a method of porducing ammonia by reacting together hydrogen gas and nitrogen gas at 400 degrees C and 250 kPa with an Fe3O4 catalyst. This was significant because prior to his discovery the world relied on obtaining ammonia from natural sources of guano (isnt this batshit? lol), principally from Chile. When Haber made his discovery in 1908, his home country Germany was preparing to enter a war which would become WW1. Germany could not wage war without a reliable source of ammonia to fertilise crops to feed the German people and to produce nitric acid used to make explosives. Chile would cut off supply of guano as it was an ally of England. Haber's discovery allowed Germany to wage a war that they very nearly won; therefore his discovery was very significant in the timeframe of its context (Nazism Germany).

lol forgot next qu, Explain how the structure and properties of polyethylene and polystyrene relate to the way each is used.

High-Density Polyethylene consists of long, unbranched and aligned molecules, thus making it a strong, sturdy and versatile material. Hence, since it is a dense plastic, HDPE is used in the manufacture of bottles (such as for shampoos) and sturdy electrical coating for wires.

Low-Density Polyethylene consists of short, branched and tangled molecules, which makes it a less-dense, more versatile and 'malleable' substance. Thus, LDPE is used in the manufacture of cling wrap and sandwich bags.


Polystyrene is a good sound and thermal insulator. Since it can be easily moulded, and can be expanded, polysterene is used in the manufacture of polystyrene foam, for packaging of a wide variety of goods. Polystyrene is also used in producing plastic drinking cups.

lol this is all I remember... mehh I've never liked this dot point, and plus it was asked last year, so I doubt it will be there this year.

Next: Explain the need for refluxing during esterification.

 

[SkimDawg]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

Next: Explain the need for refluxing during esterification.

The Reactants are volatile and yet need to be heated to reach their activation energy. Refluxing cools the reactant gases and condenses them returning them to the reaction mixture for continued heating. The gases would otherwise escape before they reacted.

sigh im running out of qu's, but i what this to keep rolling
Describe the physical and chemical processes needed to purify and sanitise a town water supply. (5 marks)
actually im sorry, if you dont like that qu (I guarantee everyone would hate it haha) this one is slightly better.
Assess the impact of atomic absorption spectroscopy (AAS) on the scientific
understanding of the effects of trace elements. (4 marks)

 

[Undermyskin]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

The Reactants are volatile and yet need to be heated to reach their activation energy. Refluxing cools the reactant gases and condenses them returning them to the reaction mixture for continued heating. The gases would otherwise escape before they reacted.

sigh im running out of qu's, but i what this to keep rolling
Describe the physical and chemical processes needed to purify and sanitise a town water supply. (5 marks)
actually im sorry, if you dont like that qu (I guarantee everyone would hate it haha) this one is slightly better.
Assess the impact of atomic absorption spectroscopy (AAS) on the scientific
understanding of the effects of trace elements. (4 marks)

Well done! I'm allergic to both of them!

1. Filtration is one of the physical steps that is expanded along the whole process. At the first place when water is drawn into the system, it goes through depth filters. They are a maze of flow channels in a thick mat that trap particles and other large load of suspended substances. Then a flocculant (commonly FeCl3) is added to help the other charged particles clump up, hence assist in the sedimentation step and again filtration. This flocculation step is another physical one, along with sedimentation. (nothing is chemically modified yeah? Correct if I'm wrong) Filtrations this time are into two steps: surface filtration and screen filtration. Surface filters consist of lots of layers and fibres that remove 99.9% suspended solids. Screen filters (genuine filters) are made up of thin membranes (polypropylene, PVC, nylon, glass fibre) acting like a sieve with pores of uniform size that remove inorganic and biological particles. In places where the latter two filters are not available, chemical processes involving the addition of chlorine and ammonia (to make chloramine disinfectant) is used, very effectively. Other chemicals are also added to adjust pH (Na2CO3), increase tooth hardness (F2) or remove excess fluorides (CaCl2).

2. AAS (finger cross I still remember) has signified the roles of trace elements on the health of human, especially and also mainly metals. Trace elements are acknowledged as vital to good being (Zn, Fe, Cu, Mg, Ca and so on). However, excessive amounts of them do more harms than good. Being present at very low concentrations down to ppm, any change in their concentrations take quick effects. For example, the lack of Fe in people, especially pregnant women is known to causes nausea and weakness due to a shortage of O2 delivered to body's organs. Lacking Mg (which assists the function of nuclease) prevents normal efficiency of cells. Talking about lead, a rather notorious poisonous chemical that was widely used without caution and in turn has caused several damages to human healthy and long-lasting detrimental impacts on the environment, monitoring of this element is crucial. The recommended level of lead in blood is below 10 microgram/dL (basically 0.1 ppm) and without AAS, such concentration is hard to manage. Other examples can include Hg bioaccumulating along the foodchain; As, Cd and so on.

PS: Question: How about: describe how a named device function to detect radioisotope? (It's quite short even tho you choose Geiger Muller counter)
Or you can choose: Describe how they monitor the concentration of ozone in the atmosphere. (I think we have to include how the spectrophotometer works as well)

 

[SkimDawg]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

PS: Question: How about: describe how a named device function to detect radioisotope? (It's quite short even tho you choose Geiger Muller counter)
Or you can choose: Describe how they monitor the concentration of ozone in the atmosphere. (I think we have to include how the spectrophotometer works as well)

Geiger-Muller Counter. This device also uses ionising properties of radiation. It is particularly good for measuring beta particles, thought it can be made to work for alpha and gamma rays too. The beta ray enters through the thin end window of the Geiger tube, hits a gas molecule (argon)) and ionises it by knocking an electron out of it. The high voltage accelerates this electron towards the central electrode and as it gains speed (energy) it ionises more argon atoms in its path, so that there is a cascade of electrons reaching that electrode. This constitutes an electrical pulse wich is amplified and measured either by generating clicks in an audio amplifier or by operating an electronic digital counter. The positive argon ions move more slowly towards the negative case to complete the circuit.

Now next question, as you answered both of mine
Information on the atmospheric concentration of ozone comes from three sources:
1 ground based spectophotometers pointing directly upwards.
2 spectophotometers on satellites scanning through the atmosphere
3 instruments on weather balloons.
The psychedelic pictures tha you usualy see of the earth are a result of measurements taken from the TOMS. Total Ozone Mapping Spectrometer, on board the Nimbus-7 ad Meteor-3 satellites. TOMS measures "total column zone", the total amount of ozone in a column of air from the Earth's surface to the upper atmosphere. It measures both the incoming solar energy directly from the Sun and the backscattered ultraviolet radiation at six wavelengths. Some of the backscattered radiation has been absorbed by ozone. The TOMS instrument can then compare the backscattered radiation to the incoming radiation which has not been absorbed, at identical wavelengths, and determine the amount of ozone about the Earths surface.

next qu
The following article was sourced from the internet.
In 2004, Australia’s Minister for the Environment announced that the allowableamounts of sulfur in unleaded petrol and diesel would be reduced over the next 5years. Currently sulfur in diesel is 500 parts per million (ppm) but it will be cut to 50ppm on 1 January 2006 and capped at 10 ppm from January 2009.
(a)Calculate the volume of sulfur dioxide produced when a full tank(capacity60kg) of diesel is consumed at 25°C and 100kPa in November 2007. (3 marks)
I need to top up on my numerical calculations for chem :rofl:

 

[midifile]

Re: [-- Official 2008 HSC Chemistry Pre-exam Study Thread --]

next qu
The following article was sourced from the internet.
In 2004, Australia’s Minister for the Environment announced that the allowableamounts of sulfur in unleaded petrol and diesel would be reduced over the next 5years. Currently sulfur in diesel is 500 parts per million (ppm) but it will be cut to 50ppm on 1 January 2006 and capped at 10 ppm from January 2009.
(a)Calculate the volume of sulfur dioxide produced when a full tank(capacity60kg) of diesel is consumed at 25°C and 100kPa in November 2007. (3 marks)
I need to top up on my numerical calculations for chem :rofl:

I just did this paper yesterday.

In 1 kg there is 0.05g sulfur --> therefore in 60 kg there is 3g

Equation of reaction: S + O₂ --> O₂
So 1 mole S reactions produces 1 mole SO₂

Moles (sulfur)= m/mm
= 3/32.07
= 0.0935...
Moles (SO₂) = 0.0935

Therefore V = 0.0935 x 24.70
= 2.32 L

Identify your local catchment area and discuss possible sources of contamination in this catchment