physics/Chem final prep (5 Viewers)

[HyperComplexxx]

i'm going for the khorne way tbh

i think strategically it's better and you sort of get the initial nerves out of the way which seem to stuff me up in *every* subject

is anyone willing to help me with the 2 dot points on AAS :s my knowledge is really limited AAS-wise

help with what , ask me some questions
FIRE AWAY

 

[abc123yoyo]

Idenpdent variable is what you are changing
Dependent is what you are measuring as a result of changing
So Independet would be different metal, iron and stainlesssteel

But isnt time always the indepedent variable? So if u drew a graph of the different metal and the amount of rust you would do the amount of rust on the y-axis and time for the metal to corrode on the x-axis wodnt u thats what confuses me :S

 

[HyperComplexxx]

But isnt time always the indepedent variable? So if u drew a graph of the different metal and the amount of rust you would do the amount of rust on the y-axis and time for the metal to corrode on the x-axis wodnt u thats what confuses me :S

I doubt you'd have to draw a corossion/time graph (i dont think it even exists O_O, dont take my word though lol)
Time is not always independent
If you measuring how long it takes to rust to a specific amount, time = dependent
If you measuring how much rust forms for a given time, time = control variable
If you are comparing the amount of rust for 2, 3, 4 days, time = independent
For that experiment, the time should be a controll variable (x days) as your comparing rate of corrosion, type of metal is indepdent, amount of rust is dependent

 

[Some Vunt]

You dont even do bio or chem ...

I did bio accelerated last year. I should probably add that to all my other subjects. That's why I failed Music 2 so hard and all my other subjects, and yeah I'm doing chem, but it probably won't count.

 

[abc123yoyo]

I doubt you'd have to draw a corossion/time graph (i dont think it even exists O_O, dont take my word though lol)
Time is not always independent
If you measuring how long it takes to rust to a specific amount, time = dependent
If you measuring how much rust forms for a given time, time = control variable
If you are comparing the amount of rust for 2, 3, 4 days, time = independent
For that experiment, the time should be a controll variable (x days) as your comparing rate of corrosion, type of metal is indepdent, amount of rust is dependent

That makes a lot of sense now thanks

 

[UnrealAnchovies]

help with what , ask me some questions
FIRE AWAY

Well just regarding the process of the whole aas thing (light beam atomised in fire specific hollow cathode lamp bla bla) and its effect on pollution control

 

[roryclifford]

Well just regarding the process of the whole aas thing (light beam atomised in fire specific hollow cathode lamp bla bla) and its effect on pollution control

Just to revise I will try and help haha. So each metal / ionic substance emits a characteristic light wavelength when electrons move up shells and then fall down right? When it moves up a shell, it absorbs the light energy of that particular wavelength, and when it 'falls' back down it emits it. So, the light source (cathode lamp) is set to emit the characteristic wavelength of light absorbed by the substance being analysed. The heat source / flame is fed a solution of the substance so it can give the electrons enough energy to jump up the shells, ready to absorb the light from the lamp, by being atomised in the flame.

As the light passes through, the amount absorbed by the substance is directly proportional to the concentration of the substance, so when it passes through it hits a prism and is refracted onto a reciever (photomultiplier). The intensity of the light is 'changed' into an electronic signal and logged in a graph of intensity to determine concentration. The measurements are compared against the intensity of light without any substance there, so therefore the substances concentration can be accurately determined in ppm.

Now AAS allows the determination of tiny concentrations of ions and trace elements (elements required by living things to function) in the environment. It has allowed scientists to monitor these ions and elements such as Lead in tiny concentrations, and determine whether parts of the environment are polluted or safe for humans to live etc. For Lead specifically they identified the toxic nature at certain concentrations and also its presence on highways and in water, and thus AAS has been used for pollution control.

Hope this helps, did that all off memory lol!!

 

[HyperComplexxx]

Well just regarding the process of the whole aas thing (light beam atomised in fire specific hollow cathode lamp bla bla) and its effect on pollution control

idk if this would suffice but
-AAS was developed by Alan Walsh to detect concentration of metallic elements in ppm and ppb range
-Function on fact that each metallic element absorbs a specific wavelength of visible light
-Test solution is fed into nebuliser and is atomised in flame
-Hollow cathode lamp produces a light with wavelneth known to be absorbed by the metallic element testing for
-Photomultiplier detects intensity of the light, and transfeered to a data processor where intial intensity of lamp is compared with its intensity after passing through the flame
the lower the intensity of light, the more the element

-Highly accurate, quick and reliable, small concentrations of metal, micronutrients in soils and contaminants in food can be found, leads to greater understanding on trace elements which causes deficiency disease when lacking (undetectable by traditional gravimetric/volumetric)
-with greater unerstanding, deficiency disease can be explained and treated for e.g. anaemia as a result of lacking red blood cells, more iron into diet = profit? etc...
-AAS also used to monitor heavy metals such as lead, mercury in environment (waterways, farmland, ) in rage of ppm to ppb
-Allows envirnomental chemists to devise methods to reduce amounts of heavy meta l? Keep public away from certain areas?
Maintain sfaety and health of public and also environment?

 

[CalumGemmell]

Just to revise I will try and help haha. So each metal / ionic substance emits a characteristic light wavelength when electrons move up shells and then fall down right? When it moves up a shell, it absorbs the light energy of that particular wavelength, and when it 'falls' back down it emits it. So, the light source (cathode lamp) is set to emit the characteristic wavelength of light absorbed by the substance being analysed. The heat source / flame is fed a solution of the substance so it can give the electrons enough energy to jump up the shells, ready to absorb the light from the lamp, by being atomised in the flame.

As the light passes through, the amount absorbed by the substance is directly proportional to the concentration of the substance, so when it passes through it hits a prism and is refracted onto a reciever (photomultiplier). The intensity of the light is 'changed' into an electronic signal and logged in a graph of intensity to determine concentration. The measurements are compared against the intensity of light without any substance there, so therefore the substances concentration can be accurately determined in ppm.

Now AAS allows the determination of tiny concentrations of ions and trace elements (elements required by living things to function) in the environment. It has allowed scientists to monitor these ions and elements such as Lead in tiny concentrations, and determine whether parts of the environment are polluted or safe for humans to live etc. For Lead specifically they identified the toxic nature at certain concentrations and also its presence on highways and in water, and thus AAS has been used for pollution control.

Hope this helps, did that all off memory lol!!

+1, that helped me also! Nice and concise!

I have a question regarding exam technique. For the questions worth >3 marks, how can you be sure that what your saying is getting you the marks? I usually try and ask myself what the examiners would be looking for (ie 2 marks for an identification of something, and another 2 for societal impacts, or something like that), but struggle when it comes to the 6/7 markers. Is the trick planning your response according to the verb used?

 

[roryclifford]

+1, that helped me also! Nice and concise!

I have a question regarding exam technique. For the questions worth >3 marks, how can you be sure that what your saying is getting you the marks? I usually try and ask myself what the examiners would be looking for (ie 2 marks for an identification of something, and another 2 for societal impacts, or something like that), but struggle when it comes to the 6/7 markers. Is the trick planning your response according to the verb used?

For me any question = to or over 4 marks I plan out. So, say it's an 'Evaluate' question worth 6 marks, I try and think of at least 5 important pieces of information to answer the question, and a final evaluation. So say for Ethanol, if it said 'Evaluate its use as a fuel in the future' I would talk about its Combustion, Fermentation to produce it, the renewable nature of Cellulose, its use in engines (needing modification or whatever) and its replacement of oil currently sourced from non-renewable sources.

To finalise the question I would evaluate it by considering the environmental impact, the ease of use, and its contribution to petrochemicals and replacement of non-renewable sources.

Hope that helps

So definitely focus on answering the verb, that determines how much to put in, how to structure the answer and how they award marks

 

[Aindan]

Also regarding AAS, only talk about specific wavelengths of light being ABSORBED (and definitely not re-emitted) by the atomised sample. This is because AAS works by the principle of comparing the amount of light absorbed by the sample (the more absorbed the higher the concentration) in reference to a second ray of light that is shone when there is no sample - a measurement given as absorbance.

And on another note hsc marking is not as simple as one point for one mark. They have a marking criteria (go check board of studies for an example) that catagorise what you have written into bands. For example, in a 7 marker in chem and say you have no equations when the marking criteria says that a 2-3 marker must have at least 1 correct equation, regardless of what else you have written you will not get even reach this band.

 

[UnrealAnchovies]

thanks for the aas stuff guys

@ Aindin is that really how it works? O_O

 

[silence--]

yeah, that is true (well we go to the same school so ofc there is bias in me saying this but still...)

thats why b6 cutoffs are only like 70-75 despite HSC tests not really appearing to be that hard

edit: well ofc i dont KNOW that its true, i dont mark HSC haha. but the info comes from our science head who is a senior marker and has shown us examples of sample answers / guidelines for HSC's before 2009.

 

[UnrealAnchovies]

yeah, that is true (well we go to the same school so ofc there is bias in me saying this but still...)

thats why b6 cutoffs are only like 70-75 despite HSC tests not really appearing to be that hard

yeah i'd always wonder why cut-offs were so low, sorta makes sense now

that's insane, I guess it'll pay off to read some marking guidelines/ markers notes after finishing a past paper

 

[silence--]

lol its really not >that< scary :L

the important things are really just to use equations for stuff worth like 4+ marks, even if the question doesn't ask for them (you never know what the marking guidelines will want...) and to make sure to answer the question to the verb (e.g. providing a judgement for evaluate questions etc). especially the latter because then you will lose a shitload of marks, not just one or two.

 

[jamesfirst]

I just got fked by all the calculation questions (cept the titration one) in 2009 chem paper..


oh gawd

 

[roryclifford]

Also regarding AAS, only talk about specific wavelengths of light being ABSORBED (and definitely not re-emitted) by the atomised sample. This is because AAS works by the principle of comparing the amount of light absorbed by the sample (the more absorbed the higher the concentration) in reference to a second ray of light that is shone when there is no sample - a measurement given as absorbance.

And on another note hsc marking is not as simple as one point for one mark. They have a marking criteria (go check board of studies for an example) that catagorise what you have written into bands. For example, in a 7 marker in chem and say you have no equations when the marking criteria says that a 2-3 marker must have at least 1 correct equation, regardless of what else you have written you will not get even reach this band.

Ah yep, was just making sure he kinda knew why the electrons were pushed up in the first place, but yeah simpler just to mention absorption

And I had no idea, thanks for telling me that, that is actually scary, knowing that missing a singular piece of info can make me lose more than one mark :/ Better get reviewing content again tonight

 

[GypoGuirginator]

I do so many past papers that i get bored of them so i read over notes as sort of like a break but i am still learning. It helps

 

[jamesfirst]

I shall try 2010 paper tmr

 

[HyperComplexxx]

i have yet to do a chem/phys paper, feeling pretty confident with the measly calculation questions (Chem)
All I'm doing now is reading over content and memorising every single statistic and information I don't already know lolololol