HSC 2012-2015 Chemistry Marathon (archive) (7 Viewers)

[HeroicPandas]

re: HSC Chemistry Marathon Archive

ahh my bad, i discussed both, must I explicitly say the difference?

yeh

 

[Menomaths]

re: HSC Chemistry Marathon Archive

(unsure can someone mark this please )

a & b) CFC's are chloro fluro carbons and are harmful to the ozone layer due to their ability to break their c-cl bonds in the stratosphere (due to UV a and UV b radiation), they make it up to the stratosphere due to their low reactivity, potentially depleting the ozone layer. HCFCs are hydro chloro fluoro carbons and are more reactive than CFCs thus are broken down earlier and don't reach the stratosphere, thus help get rid of bad ozone, ie trophospheric ozone.

b) lol whoops answered a and b at once.

Discuss how a biopolymer you have studied is synthesised and compare it's uses to polyethylene (4 marks)

What do you mean by the bolded part? They have less depleting potential as they get broken down earlier and aren't able to get to the stratosphere whereas CFCs are inert so they can easily get to the stratosphere

 

[hayabusaboston]

re: HSC Chemistry Marathon Archive

a) HCFC = Hydrogenchlorofluorocarbon and CFC= Chlorofluorocarbon. The difference is HCFC contain Hydrogen while CFCs don't.
b) HCFCs are broken down in the troposphere due to the high reactivity of their bonds. Only a small percentage of HCFCs reach the stratosphere, but once they do, ozone destruction rapidly occurs. So they have much less ozone depletion potential than CFCs (CFCs are inert, so they stay can stay in the troposphere). Shouldn't this be like 2 marks, I could've written much more but 1 mark...

wOULD be better to use more technical language, like "Oxidised in troposphere to form water and halides" etc. Lacking appropriate terminology loses marks.

 

[Menomaths]

re: HSC Chemistry Marathon Archive

Question 1: In a nuclear fission reactor iron-58 is bombarded with neutrons. Iron-58 forms a new isotope of iron. This new isotope then undergoes beta decay. Identify the new product after this beta decay (1 mark)

^58₂₆Fe + ^1₀n -> ^59₂₆Fe
^59₂₆Fe-> ^59₂₇Co+e^-+ ^0₀ν(with small line on top)
Can someone check this and tell me the correct method if this is wrong(highly likely)

 

[AnimeX]

re: HSC Chemistry Marathon Archive

What do you mean by the bolded part? They have less depleting potential as they get broken down earlier and aren't able to get to the stratosphere whereas CFCs are inert so they can easily get to the stratosphere

I'm unsure if this is correct but since the c-cl bonds are broken in the trophosphere I assumed that they would do the ozone depletion process to the bad ozone (ie ozone formed in trophosphere as it is toxic and a pungent gas), thus would be beneficial due to getting rid of the bad ozone for us.

wOULD be better to use more technical language, like "Oxidised in troposphere to form water and halides" etc. Lacking appropriate terminology loses marks.

Ahh yeah, fair enough. Will do in future, I haven't really done many practice questions so I'm thinking up answers from the top of my head haha.

^58₂₆Fe + ^1₀n -> ^59₂₆Fe
^59₂₆Fe-> ^59₂₇Co+e^-
Can someone check this and tell me the correct method if this is wrong(highly likely)

Hmm, this looks good to me.

 

[Menomaths]

re: HSC Chemistry Marathon Archive

I'm unsure if this is correct but since the c-cl bonds are broken in the trophosphere I assumed that they would do the ozone depletion process to the bad ozone (ie ozone formed in trophosphere as it is toxic and a pungent gas), thus would be beneficial due to getting rid of the bad ozone for us.
Hmm, this looks good to me.

Ah, I see your point.
Cool, I just learnt this in Physics ahaha

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

^58₂₆Fe + ^1₀n -> ^59₂₆Fe
^59₂₆Fe-> ^59₂₇Co+e^-+ ^0₀ν(with small line on top)
Can someone check this and tell me the correct method if this is wrong(highly likely)

Correct, this was a multiple choice question (but if it was a short answer question, idk about the gamma radiation, it is right but not everyone will know it)


The question was "Explain why HCFCs have a lower ozone depletion potential compared to CFCs" so he would get no marks for mentioning the positives of using HCFCs

Question: Tony performed an experiment to ferment 12g of glucose with 1 g of yeast along with 50ml of water at 37 degrees Celsius. He left this for 1 days and recorded a mass change of 1.44 grams.
a) Calculate the mass of ethanol produced and compare this to the theoretical mass of ethanol. Explain the difference in masses (4 marks)

^question from before, its a good question that many got wrong in school's trial

 

[Menomaths]

re: HSC Chemistry Marathon Archive

I don't know how to do the maths questions of Chem, need to practice more.

 

[AnimeX]

re: HSC Chemistry Marathon Archive

Correct, this was a multiple choice question (but if it was a short answer question, idk about the [U]gamma[/U] radiation, it is right but not everyone will know it)


The question was "Explain why HCFCs have a lower ozone depletion potential compared to CFCs" so he would get no marks for mentioning the positives of using HCFCs

Question: Tony performed an experiment to ferment 12g of glucose with 1 g of yeast along with 50ml of water at 37 degrees Celsius. He left this for 1 days and recorded a mass change of 1.44 grams.
a) Calculate the mass of ethanol produced and compare this to the theoretical mass of ethanol. Explain the difference in masses (4 marks)

^question from before, its a good question that many got wrong in school's trial

Don't think it's gamma radiation (correct me if I'm wrong pls).

B- decay (electron) is acompanied by an electron anti neutrino (it's just fundamental for this to occur, something to do with balancing and conserving energy or something =S, think it's anti matter.)

B+ decay (positron) is accompanied by an electron neutrino

Haha, just some background info I learnt from medphys.

 

[Menomaths]

re: HSC Chemistry Marathon Archive

Yep. It's not gamma radiation, it's something to do with anti-matter and matter

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

Discuss how a biopolymer you have studied is synthesised and compare it's uses to polyethylene (4 marks)

The biopolymer biopol can be produced from a culture of bacteria, namely Alcaligenes eutrophus or Ralstonia eutrophus, fed with high carbohydrates and valeric acid with restriction to nitrogen and phosphorus compounds. The polymer is stored as excess energy in the bacteria which is isolated, purified, dissolution with chloroform, (and something else...).
Biopol can be used for medical application such at suture and stiches. This is because it is biodegradable, having the ability to degrade into natural compounds, and also is biocompatible, meaning it is not recognised as foreign material in living organisms.
Polyethylene has 2 forms depending on the conditions it is produced, lo-density or high-density. High-density polyethylene (HDPE) contains unbranched chains accounting for its hgih rigidity, density and strength, therefore can be used as shampoo bottles, chemical containers, rubbish bins. LOw density polyethlyene can be used to make cling wrap and plastic cups.
Biopol can also be used as a replacement for some products made by HDPE such as shampoo bottles because of its non-toxic nature, high tensile strength, water resistant but vulnerable to chlorinated substances

This is a low-quality answer because it is produced on a computer by tpying, we know everyone writes more sophisticated and clearer answers on paper

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

Don't think it's gamma radiation (correct me if I'm wrong pls).

B- decay (electron) is acompanied by an electron anti neutrino (it's just fundamental for this to occur, something to do with balancing and conserving energy or something =S, think it's anti matter.)

B+ decay (positron) is accompanied by an electron neutrino

Haha, just some background info I learnt from medphys.

dont bring in physics...

 

[AnimeX]

re: HSC Chemistry Marathon Archive

Correct, this was a multiple choice question (but if it was a short answer question, idk about the gamma radiation, it is right but not everyone will know it)


The question was "Explain why HCFCs have a lower ozone depletion potential compared to CFCs" so he would get no marks for mentioning the positives of using HCFCs

Question: Tony performed an experiment to ferment 12g of glucose with 1 g of yeast along with 50ml of water at 37 degrees Celsius. He left this for 1 days and recorded a mass change of 1.44 grams.
a) Calculate the mass of ethanol produced and compare this to the theoretical mass of ethanol. Explain the difference in masses (4 marks)

^question from before, its a good question that many got wrong in school's trial

What trial is this from? I gave it a go but it's probably wrong... I'll scan it.

I assumed that there would be no change in mass from the yeast.

Can you PM me the paper and solutions please HeroicPandas?

edit: lol maybe due to my laziness and not using exact value may have caused me not to get exact answer...

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

What trial is this from? I gave it a go but it's probably wrong... I'll scan it

It my school's trial paper so where the question was from (either trial hsc or actual hsc or they made it)

post up ur working out! (i encourage others to try it aswell), who cares if its wrong, u will learn how to do it correctly anyways!

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

@AnimeX - well done on the solution, its correct!

oh dw about the trial, do actual HSC or something, its way better. The trial i did in school had like citric acid titration, arguments for and against for 'carbon neutral' of ethanol, and some other stuff (very low amount of rote learning question). Also the teacher didnt provide solutions (but they did have solutions...), we only went through the paper as a class

 

[Menomaths]

re: HSC Chemistry Marathon Archive

@AnimeX - well done on the solution, its correct!

oh dw about the trial, do actual HSC or something, its way better. The trial i did in school had like citric acid titration, arguments for and against for 'carbon neutral' of ethanol, and some other stuff (very low amount of rote learning question). Also the teacher didnt provide solutions (but they did have solutions...), we only went through the paper as a class

This was also in my trials.

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

This was also in my trials.

Mine said something like this: "Discuss the basis of the claim that ethanol can be a 'carbon neutral' fuel" (3 marks)
A lot of people got 1-2 marks

 

[hayabusaboston]

re: HSC Chemistry Marathon Archive

Mine said something like this: "Discuss the basis of the claim that ethanol can be a 'carbon neutral' fuel" (3 marks)
A lot of people got 1-2 marks

I had same queston. Hold up, did we all do independent trial here?

What'd u all get? I'm a tad unsure whether to say first cos u either all smashed me, or I got around the same as u, or I smashed u. Anythings possible lol.

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

I had same queston. Hold up, did we all do independent trial here?

What'd u all get? I'm a tad unsure whether to say first cos u either all smashed me, or I got around the same as u, or I smashed u. Anythings possible lol.

I THINK....... because my teacher usually buys trials.......................... let me see the question again.... (and then modifies the test by removing/adding questions)

 

[Menomaths]

re: HSC Chemistry Marathon Archive

Just to make sure we did different papers, did you guys have a question saying 'Draw the curve of the Haber Process when the pressure is lowered' That's horribly worded but it was something similar to that. My teacher said he bought the trials and changed it completely so there's a possibility