Hsc Marathon 2009 - Chemistry (2 Viewers)

[jediloc]

firstly..

Fossil fuels may be used as fuels for combustion engines or to manufacture ethylene by fractional distillation and "cracking". Therefore it can be tranformed into many useful industrial and commercial products.

Biomass, for example, cellulose... a main consituent of biomass,
can be converted into ethanol to be used as a fuel in combustion engines and which can be further processed to derive ethylene. Cellulose is broken down by bacteria to it's constituent glucose molecules, which can be fermented to ethanol and used as a fuel. Ethanol can be prodused by alkanes in the petrochemcial industry by first deriving ethylene from petroleum, which is then dehydrated to ethanol. From biomass, Ethanol can be dehydrated to ethylene.
Using biomass as an alternative to fossil fuels is much more eco and envir friendly.

not sure if i structured that right?!?

ok


what are the factors which may effect a chemical system at equilibrium and what processes occur to restore the equilibrium for each of the imposed changes?? :rofl:

 

[hermand]

FACTORS;
- change in temperature.
- change in pressure. [gases]
- change in concentration.

PROCESSES;
one. if exothermic, and the equilibrium is heated, reaction moves to the left.
if endothermic, and equilibrium is heated, reaction moves to the right.
both of these happen to use up the excess heat. reverse happens if equilibrium is chilled.
two. eg, CO2(aq)<-->CO2(g), if the pressure on the CO2 gas is increased, [or more CO2 gas is added], it will drive the equilibrium to the left, to use up the excess CO2 gas.
three. if a chemical on the left is added, it will drive the equilibrium to the right, and vice versa. provided that there are still chemicals for it to react with.

is the production of ethanol carbon neutral? use equations to support your answer.

 

[kwabon]

is the production of ethanol carbon neutral? use equations to support your answer.

yes the production of ethanol is carbon neutral.
C2H5OH + 2O2 ---> 2CO2 + 3H2O

sorry hermand, thats a really funny question, could u please tell me whether the answer i have given to you is right or not . So i am not gonna put up a question.

 

[hermand]

yes the production of ethanol is carbon neutral.
C2H5OH + 2O2 ---> 2CO2 + 3H2O

sorry hermand, thats a really funny question, could u please tell me whether the answer i have given to you is right or not . So i am not gonna put up a question.

ah, sorry, i worded it wrong, so correction;

is the use of ethanol as a fuel carbon neutral? compare to octane & use equations to support your answer.
hint; think of photosynthesis & the burning of ethanol, but also the production.

i think that makes more sense. sorry i don't know what i was thinking when i wrote out that question haha.

 

[study-freak]

ah, sorry, i worded it wrong, so correction;

is the use of ethanol as a fuel carbon neutral? compare to octane & use equations to support your answer.
hint; think of photosynthesis & the burning of ethanol, but also the production.

i think that makes more sense. sorry i don't know what i was thinking when i wrote out that question haha.

I'm pretty sure you're looking for something about distillation.

My Answer:
It is argued that ethanol is carbon neutral since its combustion releases carbon dioxide that was originally used by plants in photosynthesis. Hence, no more carbon dioxide than how much originally existed is added to the atmosphere whereas the use of fossil fuels involves digging up those fuels and burning it, releaseing extra carbon dioxide that was not originally part of the air.
However, the production of ethanol involves distillation after fermentation. This distillation requires a heat source, which often is the combustion of fossil fuels. This is clearly an addition of extra carbon dioxide to the atmosphere. Hence, it cannot be said that the production of ethanol is completely carbon neutral, although if ethanol is used to power distillation, then it truly is carbon neutral.


Q: Discuss the potential of cellulose as a raw material to produce petrochemicals and explain its benefits and problems.

 

[hermand]

I'm pretty sure you're looking for something about distillation.

My Answer:
It is argued that ethanol is carbon neutral since its combustion releases carbon dioxide that was originally used by plants in photosynthesis. Hence, no more carbon dioxide than how much originally existed is added to the atmosphere whereas the use of fossil fuels involves digging up those fuels and burning it, releaseing extra carbon dioxide that was not originally part of the air.
However, the production of ethanol involves distillation after fermentation. This distillation requires a heat source, which often is the combustion of fossil fuels. This is clearly an addition of extra carbon dioxide to the atmosphere. Hence, it cannot be said that the production of ethanol is completely carbon neutral, although if ethanol is used to power distillation, then it truly is carbon neutral.


Q: Discuss the potential of cellulose as a raw material to produce petrochemicals and explain its benefits and problems.

*smiles and nods head*

haha i couldn't figure out if the question was worded properly.

 

[study-freak]

is the production of ethanol carbon neutral? use equations to support your answer.

*smiles and nods head*

haha i couldn't figure out if the question was worded properly.

I think what you initially posted is better worded than the corrected version. But I would have said "Is the production of ethanol as a fuel carbon neutral coz then it includes distillation as well as fermentation.

Btw, I just realised that I didn't use equations in my answer above lol.. And also didn't compare to octane, although I've said "fossil fuels."

 

[hermand]

I think what you initially posted is better worded than the corrected version. But I would have said "Is the production of ethanol as a fuel carbon neutral coz then it includes distillation as well as fermentation.

Btw, I just realised that I didn't use equations in my answer above lol.. And also didn't compare to octane, although I've said "fossil fuels."

yeah, was the general gist i was going for. it was a question in one of our exams but couldn't remember the wording.

 

[kwabon]

Q: Discuss the potential of cellulose as a raw material to produce petrochemicals and explain its benefits and problems.

wow this thread has been dead for a while ...lemme get the ball rolling once again

Cellulose has a great potential as a raw material to produce petrochemicals. Glucose is made from cellulose through acid hydrolysis, and then glucose is fermented into ethanol and carbon dioxide, and hence ethanol could be used as a very useful fuel. (show equations, but cannot be bothered, sorry), Cellulose is a major component of biomass and hence is a renewable resource and is biodegradable. disadvantages of cellulose include it not being economical, since acid hydrolysis is not very efficient and also leads to the production of greenhouse gases, land is also cleared to grow cellulose might lead to land degradation and land clearing.
Unfortunately, at the present time there is no easy process to break cellulose down into simple carbon chains, nor is there a micro-organism that can perform this function. This has been a barrier for the widespread use of cellulose as a raw material for petrochemicals. Although some progress is being made in the production of polymers from biological materials, cellulose has not been the focal point. Nonetheless considerable scientific effort and financial backing is being directed into methods of exploiting cellulose as an alternative source of chemical we currently obtain from crude oil. Whilst, the process is currently expensive, the diminishing world supplies of crude oil may eventually make it financially feasible.

 

[study-freak]

wow this thread has been dead for a while ...lemme get the ball rolling once again

Cellulose has a great potential as a raw material to produce petrochemicals. Glucose is made from cellulose through acid hydrolysis, and then glucose is fermented into ethanol and carbon dioxide, and hence ethanol could be used as a very useful fuel. (show equations, but cannot be bothered, sorry), Cellulose is a major component of biomass and hence is a renewable resource and is biodegradable. disadvantages of cellulose include it not being economical, since acid hydrolysis is not very efficient and also leads to the production of greenhouse gases, land is also cleared to grow cellulose might lead to land degradation and land clearing.
Hence Cellulose has a huge potential to produce petrochemicals since celluloses advantages outweigh its disadvantages.


Q: Another part of swimming maintenance is adjusting chlorine levels in the pool, 'liquid chlorine' is a solution of sodium hypochlorite (NaOCl) which can be used to do this. Upon the addition of sodium hypochlorite to the pool, the following equilibrium reaction occurs:

OCl minus (its an ion) + H2O <----> HOCl + OH minus (its an ion)

1)state reason for the chlorination of swimming pool. (1 mark)
2)explain how the addition of sodium hypochlorite will affect the pH of water in the pool. (2 marks)

yes i noe only equilibrium questions for me since its my weakest topic

You talked about how cellulose can be used as a raw material for the production of ethanol as a fuel. However, the word "petrochemical" suggests that it isn't enough.....

 

[kwabon]

Q: Discuss the potential of cellulose as a raw material to produce petrochemicals and explain its benefits and problems.

You talked about how cellulose can be used as a raw material for the production of ethanol as a fuel. However, the word "petrochemical" suggests that it isn't enough.....

righty i get what u mean, i have changed my answer

 

[kwabon]

Q: Another part of swimming maintenance is adjusting chlorine levels in the pool, 'liquid chlorine' is a solution of sodium hypochlorite (NaOCl) which can be used to do this. Upon the addition of sodium hypochlorite to the pool, the following equilibrium reaction occurs:

OCl minus (its an ion) + H2O <----> HOCl + OH minus (its an ion)

1)state reason for the chlorination of swimming pool. (1 mark)
2)explain how the addition of sodium hypochlorite will affect the pH of water in the pool. (2 marks)

yes i noe only equilibrium questions for me since its my weakest topic

 

[gigglinJess]

Okay I'll give this a go.

1) Swimming pools are chlorinated, as the chlorine will kill harmful microorganisms that cause health issues (ie ear infections and athletes foot), also can control the growth of algae.

2) The equilibrium will move towards the RHS to balance out the excess OCl ions that would be found in the sodium hypochlorite solution. As the equilibrium shifts towards the right, the pH of the system will increase as the number of OH ions increase.

Q Identify the name of a radioisotope used for medicine and what it is used for, and describe the way in which it is used.

 

[kwabon]

Okay I'll give this a go.

1) Swimming pools are chlorinated, as the chlorine will kill harmful microorganisms that cause health issues (ie ear infections and athletes foot), also can control the growth of algae.

2) The equilibrium will move towards the RHS to balance out the excess OCl ions that would be found in the sodium hypochlorite solution. As the equilibrium shifts towards the right, the pH of the system will decrease as the number of OH ions increase.

Q Identify the name of a radioisotope used for medicine and what it is used for, and describe the way in which it is used.

you are contradicting yourself, if the number of OH ions increase then the pH of the system will increase as it becomes more basic.

A; One method of treating cancer patients is to irradicate the affected areas of the body with gamma rays. A common source for this radiation therapy is Cobalt 60. it emits high energy gamma radiation making it suitable to penetrate and destroy abnormal cells. cobalt 60 has a half life of 5 years which is sufficiently long enough for the radiation source to have reasonable life span, but short enough to emit a reasonable and consistent amount of radiation.


Q: define molar heat of combustion (2 marks).

 

[gigglinJess]

you are contradicting yourself, if the number of OH ions increase then the pH of the system will increase as it becomes more basic.

Sorry, i had it worked out in my head right. All fixed now

Q: define molar heat of combustion (2 marks).

AMolar heat of combustion is the heat produced when one mole of a substance is burned under standard temperature and pressure Not sure, is that enough?



Q Explain what is meant by a conjugate pair.

 

[study-freak]

A Molar heat of combustion is the heat produced when one mole of a substance is burned under standard temperature and pressure Not sure, is that enough?

With the product being carbon dioxide gas and liquid water. Plus you need to say COMPLETE combustion



Q Explain what is meant by a conjugate pair.

A conjugate pair refers to an acid and a conjugate base that is formed by donating a proton OR a base and a conjugate acid formed by accepting a proton.

Q Identify the temperature ranges that are suitable for the Haber process and account for the use of the particular temperature.(3 marks)

 

[ColdBuffet]

A Molar heat of combustion is the heat produced when one mole of a substance is burned under standard temperature and pressure Not sure, is that enough?

With the product being carbon dioxide gas and liquid water. Plus you need to say COMPLETE combustion



Q Explain what is meant by a conjugate pair.

A conjugate pair refers to an acid and a conjugate base that is formed by donating a proton OR a base and a conjugate acid formed by accepting a proton.

Q Identify the temperature ranges that are suitable for the Haber process and account for the use of the particular temperature.(3 marks)

Off the top of my head, I think it is 400-500 degrees celsius. If the temperature is too high, the equilibrium will shift to the left forming less yield and if the temperature is too low, the rate of reaction will be too slow. Therefore a moderate temperature of 400-500 degrees celsius is used.

How does AAS work?

 

[gifted:)]

it uses the spectrum of each individual atom, it has a detector which detects the change in light intensity caused by the excitement of the electrons within the target ion. Go to conquering chemistry text book for a good diagram

Q. Explain the process of esterification.

 

[bored of sc]

Q. Explain the process of esterification.

Esterification is production of an ester.

An alkanol and alkanoic acid are mixed together with a catalyst of concentrated sulphuric acid. Refluxing occurs - the reaction is takes place under indirect heat as the higher temperature increases the rate of reaction and helps the catalyst convert the reactants into product(s). This can be summarised by the equation:

Alkanol + Alkanoic acid <---> (conc. H₂SO₄) Ester (aq)

Finally the ester is decanted.


Someone else do a better response please.


In the meantime: Give two features of a reversible reaction, when a dynamic equilibrium has been set up.

 

[kwabon]

Esterification is production of an ester.

An alkanol and alkanoic acid are mixed together with a catalyst of concentrated sulphuric acid. Refluxing occurs - the reaction is takes place under indirect heat as the higher temperature increases the rate of reaction and helps the catalyst convert the reactants into product(s). This can be summarised by the equation:

Alkanol + Alkanoic acid <---> (conc. H₂SO₄) Ester (aq)

Finally the ester is decanted.


Someone else do a better response please.


In the meantime: Give two features of a reversible reaction, when a dynamic equilibrium has been set up.

woops, u forgot + water on the product side.