HSC 2012-2015 Chemistry Marathon (archive) (3 Viewers)

[zhertec]

re: HSC Chemistry Marathon Archive

Ummm, no.

What part of it is wrong?

P.S. For some reason I feel that half the questions drscoccerball gives for acidic environment are like made up questions (by him) due to the incomplete nature of them...

But Soccer if you really want to answer an Acidic Question: Explain how buffer system works, specifically referencing to a natural (buffer) system (4 marks)

For all the other 2015'ers out there a POM question: Assess the impacts of TWO uses of ethanol in society (5 marks, was originally 7 but lets not make this one too long to answer).

 

[Librah]

re: HSC Chemistry Marathon Archive

What part of it is wrong?

P.S. For some reason I feel that half the questions drscoccerball gives for acidic environment are like made up questions (by him) due to the incomplete nature of them...

But Soccer if you really want to answer an Acidic Question: Explain how buffer system works, specifically referencing to a natural (buffer) system (4 marks)

For all the other 2015'ers out there a POM question: Assess the impacts of TWO uses of ethanol in society (5 marks, was originally 7 but lets not make this one too long to answer).

Was that the one asked this year?

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

Was that the one asked this year?

Yeah I think so, hilarious shit storm entailed on BoS as to whether or not you absolutely had to talk about ethanol as a fuel and a solvent (asked my teacher after he marked our year's HSC paper, you didn't)

 

[zhertec]

re: HSC Chemistry Marathon Archive

In 1884 Arrhenius proposed the notion that acids were substances which produced hydrogen ions in solution while bases were substances which formed hydroxide ions in solution. This theory however does not recognise the role the solvent plays as it is only applicable to solvents such as water, which can react with acids to form hydronium ions.

Furthermore, acid-base reactions are able to occur outside solutions, which Arrhenius's theory does not recognise. This can be see in reactions such as HCl(g) + NH3(g) -> NH4CL (g)

The Bronsted-Lowry definition is able to overcome the shortocmings of the Arrhenius definition as it stipulates that all acids are proton donors and bases are proton acceptors, e.g HCl (aq) + H20 (l) --> H30+ + Cl- The water acts as a base hence identifies the role of the solvent. The bronsted-lowry definition is furthermore not restricted to acids and bases only acting in a solution.

Sorry for the double post but also don't forget this point: Arrhenius also believed that H+ and OH- neutralised each other to become water, however his theory could not explain why carbonates were able to neutralise acid, producing water, even though there was no hydroxide ions present.

 

[enigma_1]

Chemistry marathon 2015

Yeah I think so, hilarious shit storm entailed on BoS as to whether or not you absolutely had to talk about ethanol as a fuel and a solvent (asked my teacher after he marked our year's HSC paper, you didn't)

Oh my god this was the worst

Lol thank gosh

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

Oh my gosh this was the worst

Lol we didn't end up finding out what was correct haha

I did, it's in the brackets. You could talk about any legitimate use, which is what I was saying for like five pages of fighting haha

 

[zhertec]

re: HSC Chemistry Marathon Archive

Yeah I think so, hilarious shit storm entailed on BoS as to whether or not you absolutely had to talk about ethanol as a fuel and a solvent (asked my teacher after he marked our year's HSC paper, you didn't)

Hahaha I remember that, one of the BOSer's was like: I'm pretty sure you are going to lose marks for not mentioning it being a solvent, like he was pretty adamant on this and started to tell other people they got it wrong for not writing solvent.

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

Hahaha I remember that, one of the BOSer's was like: I'm pretty sure you are going to lose marks for not mentioning it being a solvent, like he was pretty adamant on this and started to tell other people they got it wrong for not writing solvent.

Lol yes, and then other people joined them and they terrified people who had talked about dehydration to ethene haha

 

[Librah]

re: HSC Chemistry Marathon Archive

Yeah I think so, hilarious shit storm entailed on BoS as to whether or not you absolutely had to talk about ethanol as a fuel and a solvent (asked my teacher after he marked our year's HSC paper, you didn't)

Did not mention solvent at all lmfao, everyone in my class was like "solvent, solvent" including my teacher, thought i was gonna get like a 2/7. INB4 7/7 lololol. I'll give my response word for word if any1 decides to pst their response for 7 marks.

With reference to the underlying chemistry and with relevant equations, assess the impacts on society of TWO uses of ethanol.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

What part of it is wrong?

P.S. For some reason I feel that half the questions drscoccerball gives for acidic environment are like made up questions (by him) due to the incomplete nature of them...

But Soccer if you really want to answer an Acidic Question: Explain how buffer system works, specifically referencing to a natural (buffer) system (4 marks)

For all the other 2015'ers out there a POM question: Assess the impacts of TWO uses of ethanol in society (5 marks, was originally 7 but lets not make this one too long to answer).

Yeah im making them up and havnt done buffers yet

 

[SuchSmallHands]

re: HSC Chemistry Marathon Archive

Did not mention solvent at all lmfao, everyone in my class was like "solvent, solvent" including my teacher, thought i was gonna get like a 2/7. INB4 7/7 lololol. I'll give my response word for word if any1 decides to pst their response for 7 marks.

With reference to the underlying chemistry and with relevant equations, assess the impacts on society of TWO uses of ethanol.

I'm too terrified to buy my raw marks and responses. I'd pick them apart and hate myself over every tiny mistake. But it's great that you have yours for reference purposes here.

 

[Librah]

re: HSC Chemistry Marathon Archive

I'm too terrified to buy my raw marks and responses. I'd pick them apart and hate myself over every tiny mistake. But it's great that you have yours for reference purposes here.

All my mistakes were silly tbh, besides maybe 1-3 marks lol.

Everyone should remember, that every mistake, is an avoidable mistake.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

The answers here are succinct and detailed.. How do i achieve such responses?

 

[Fiction]

re: HSC Chemistry Marathon Archive

What part of it is wrong?

P.S. For some reason I feel that half the questions drscoccerball gives for acidic environment are like made up questions (by him) due to the incomplete nature of them...

But Soccer if you really want to answer an Acidic Question: Explain how buffer system works, specifically referencing to a natural (buffer) system (4 marks)

For all the other 2015'ers out there a POM question: Assess the impacts of TWO uses of ethanol in society (5 marks, was originally 7 but lets not make this one too long to answer).

Not Soccer, but
Buffer systems are solutions which contain a weak acid and its conjugate base, or vice versa (weak base and conjugate acid) in equilibrium. As the system is in equilibrium, it is able to moderate pH. An example is the natural buffer system which exists in marine bodies.(where the system <----> means equilibrium~)

H2CO3 (aq) + H20 (l) <-- --> H30+ (aq) + HCO3- (aq)


If there is an increase of acid, such as acid rain acting on aquatic environments, the buffer system above will shift to the left according to Le Chatiler's Principle which denotes that is a system is in equilibrium and encounters a disturbance, then the system will shift in the direction to minimise the disturbance. By shifting to the left, the concentration of hydronium decreases, hence nullifies the addition of an acid.

Buffer systems can although moderate small changes in pH, upon reaching it's breaking point - the point where it is unable to counteract any further additional changes to the pH, the pH (of in this example, freshwater lakes and rivers) will rise regardless.

 

[Kaido]

re: HSC Chemistry Marathon Archive

This is a general tip, try and include at least one chemical equation in each answer, because marking criteria can say you need chemical equation(s) in your answer even if it's not explicitly stated in the question. (This is because there's a syllabus dot point in the start of Production of Materials I think that says students learn to apply chemical equations wherever appropriate, or something like that.)

So spam equations. And if they say explicitly to include one, but you can't remember the states of matter, just guess the states, since it can be mathematically proven that this is on average the best thing to do (assuming you don't lose marks for incorrect states if the marking criteria says you need a chemical equation but no states required).

I still remember that proof :3

 

[hawkrider]

re: HSC Chemistry Marathon Archive

I still remember that proof :3

I was like "wtf did I just read"

 

[Librah]

re: HSC Chemistry Marathon Archive

Buffer systems are solutions which contain a weak acid and its conjugate base, or vice versa (weak base and conjugate acid) in equilibrium. As the system is in equilibrium, it is able to moderate pH. An example is the natural buffer system which exists in marine bodies.(where the system <----> means equilibrium~)

Might want to refine your definition of a buffer.

 

[siggy]

re: HSC Chemistry Marathon Archive

Could anyone skim over my answer to those 2 questions on the last page and just see if I would get full marks for that?
Thanks!

 

[Fiction]

re: HSC Chemistry Marathon Archive

What part of it is wrong?

P.S. For some reason I feel that half the questions drscoccerball gives for acidic environment are like made up questions (by him) due to the incomplete nature of them...

But Soccer if you really want to answer an Acidic Question: Explain how buffer system works, specifically referencing to a natural (buffer) system (4 marks)

For all the other 2015'ers out there a POM question: Assess the impacts of TWO uses of ethanol in society (5 marks, was originally 7 but lets not make this one too long to answer).

I've kind of forgotten POM because of the holidays


Ethanol has many uses in society, among those include acting as a solvent and as a replacement for petrol-based fuels hence impacting society commercially and industrially.

Structurally ethanol's hydroxyl functional group enables it to be polar As it's hydrocarbons, the ethyl functional group is non-polar. This means it has two very different ends, which allows it to form intermolecular forces with other molecules, both polar and non-polar, hence allowing ethanol to dissolve both polar and non-polar substances. It is hence used in industrial applications as a solvent, such as in cosmetics, antiseptics/other cleaning agents and food colouring. It's impact is hence a social one - it is prevalent in our daily lifestyles, where as a cleaning agent, ethanol can provides medical aid.

As ethanol is liquid at room temperature which allows for easy transportation, a renewable resource and contains hydrocarbons it is able to be used in internal combustion engines, hence substituting current fuels which are hydrocarbons derived from crude oil, a non-renewable resource. As a fuel ethanol has several advantages including
- renewability
- more likely to undergo complete combustion (as it has an oxygen in it's structure)
- able to be used in bybrid fuels, hence extending the remaining petroleum resource life

However, it has several disadvantages including
- Not easily able to be extracted, where it's industrial processes require large amount of energy
- lower heat of combustion than octane, hence meaning that more ethanol is required to give the same amount of energy that a smaller amount of octane can give
- requires large agricultural land to produce (as it can be produced from fermentation)
- since only 14% of ethanol can be mixed into hybrid fuels, anymore than 14% would require a change in engine

 

[Fiction]

re: HSC Chemistry Marathon Archive

Might want to refine your definition of a buffer.

haha learnt it a week ago, not too keen to revise with the amount of english homework I have

Would appreciate it if you can help improve it