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

[leehuan]

re: HSC Chemistry Marathon Archive

a) Fractional Distillation of Petroleum ---> Catalytic and Thermal Cracking of higher chained hydrocarbons to obtain ethylene (as not enough is 'produced' from fractional distillation) ----> Substition reaction of ethylene with Benzene??? (i don't have a clue how the benzene ring is swapped for a hydrogen in ethylene) ----> This produces styrene ----> Styrene monomers are joined together in an addition reaction involving steps of initiation, propagation, termination -----> This produces polystyrene

For the bolded part, I don't either. I was just reading my textbook.

Edit:

Ethylene reacts with benzene (C6H6) to produce ethylbenzene. The reaction requires an aluminium catalyst at high temperature and pressure (80–100°C/0.1 MPa). This product then undergoes catalytic dehydrogenation in the presence of sulfur to produce styrene. The styrene that is formed is used as the monomer for the production of polystyrene.
C6H6 + CH2CH2 -> C6H5(C2H5)
C6H5(C2H5) + S -> C6H5(CHCH2) + H2S

(Thickett, 2006)

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

for part b) is this alright?

A biopolymer which can be synthesised is PHB. It is produced by feeding bacteria such as Alcigenes Eutrophus or E.Coli on a nurient rich diet until large colonies of the bacteria begin to form, and at this point, glucose is added and the nutrients such as nitrates removed from the diet. This unnatural high energy, low nutrient diet, makes the bacteria automatically secrete PHB as an energy store (similar to fat of humans). PHB is naturally occuring which means it is non toxic and renewable. It is also biodegrable as it decomposes into CO2 and H20, reducing landfill. PHB is also biocompatible hence can be used in medical sutures that don't need removal and decompose over time, hence removing the need or follow up appointments. Finally, it has physical properties similar to propylene meaning it can be used readily as a substiture for polypropylene.

 

[leehuan]

re: HSC Chemistry Marathon Archive

for part b) is this alright?

A biopolymer which can be synthesised is PHB. It is produced by feeding bacteria such as Alcigenes Eutrophus or E.Coli on a nurient rich diet until large colonies of the bacteria begin to form, and at this point, glucose is added and the nutrients such as nitrates removed from the diet. This unnatural high energy, low nutrient diet, makes the bacteria automatically secrete PHB as an energy store (similar to fat of humans). PHB is naturally occuring which means it is non toxic and renewable. It is also biodegrable as it decomposes into CO2 and H20, reducing landfill. PHB is also biocompatible hence can be used in medical sutures that don't need removal and decompose over time, hence removing the need or follow up appointments. Finally, it has physical properties similar to propylene meaning it can be used readily as a substiture for polypropylene.

Looks good. I actually didn't study PHB unlike the most of the chemistry cohort but everything seems to be there. I'll get someone else to comment if they think you missed anything

 

[BlueGas]

re: HSC Chemistry Marathon Archive

for part b) is this alright?

A biopolymer which can be synthesised is PHB. It is produced by feeding bacteria such as Alcigenes Eutrophus or E.Coli on a nurient rich diet until large colonies of the bacteria begin to form, and at this point, glucose is added and the nutrients such as nitrates removed from the diet. This unnatural high energy, low nutrient diet, makes the bacteria automatically secrete PHB as an energy store (similar to fat of humans). PHB is naturally occuring which means it is non toxic and renewable. It is also biodegrable as it decomposes into CO2 and H20, reducing landfill. PHB is also biocompatible hence can be used in medical sutures that don't need removal and decompose over time, hence removing the need or follow up appointments. Finally, it has physical properties similar to propylene meaning it can be used readily as a substiture for polypropylene.

How come you didn't mention that sugar is withdrawn once large colonies start to form?

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

How come you didn't mention that sugar is withdrawn once large colonies start to form?

I thought sugar was added, and nutrients (such as nitrates) removed. The students guide to hsc chemistry got it wrong...they say sugars are removed

I remember posting and askin if the student's guide was correct in this and everyone said it was wrong.

 

[leehuan]

re: HSC Chemistry Marathon Archive

NEXT QUESTION
Describe the method you used to prepare and test a natural indicator. (Whatever amount of marks you feel like it should be worth.)

 

[Kaido]

re: HSC Chemistry Marathon Archive

NEXT QUESTION
Describe the method you used to prepare and test a natural indicator. (Whatever amount of marks you feel like it should be worth.)

Something along the lines:
Red Cabbage:
- Cut a red cabbage leaf into small pieces
- Half-fill a 250mL beaker with the red cabbage pieces. Add water until 200mL
- Heat and boil for about 10mins
- Allow to cool, then strain mixture. Purple juice obtained
- Turns yellow in strong bases; green in weak bases; purple in neutral; pink in acids

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

Something along the lines:
Red Cabbage:
- Cut a red cabbage leaf into small pieces
- Half-fill a 250mL beaker with the red cabbage pieces. Add water until 200mL
- Heat and boil for about 10mins
- Allow to cool, then strain mixture. Purple juice obtained
- Turns yellow in strong bases; green in weak bases; purple in neutral; pink in acids

Ahmad Shah notes say, Pink in Acid, Dark Purple Neutral, Yellow in Bases.

They don't mention weak base.

 

[BlueGas]

re: HSC Chemistry Marathon Archive

I thought sugar was added, and nutrients (such as nitrates) removed. The students guide to hsc chemistry got it wrong...they say sugars are removed

I remember posting and askin if the student's guide was correct in this and everyone said it was wrong.

So what's the right process?

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

So what's the right process?

let me check a 'valid source'

 

[Kaido]

re: HSC Chemistry Marathon Archive

Ahmad Shah notes say, Pink in Acid, Dark Purple Neutral, Yellow in Bases.

They don't mention weak base.

These were results I recorded during my own experiment. So yeah o.o

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

let me check a 'valid source'

"PHB production occurs maximally in A. eutrophus and Azotobacter beijerinckii during growth under nitrogen limitation and oxygen limitation respectively"

"Effect of nutrient limitation on PHB production A. eutrophus was grown in continuous culture at low dilution rate with glucose as the carbon source and either glucose, ammonia, potassium or oxygen as the growth-limiting nutrient.

In all of these cultures glucose was converted only into a mixture of PHB, non-PHB biomass and carbon dioxide.

The yield of PHB from glucose PHB were all highest in ammonia-limited cultures and decreased in the order: ammonia-limited cultures > potassium-limited/oxygen- limited cultures > glucose-limited cultures "

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

so i guess glucose can be limited (as well as being the carbon source), but it just isn't as efficient in production

 

[leehuan]

re: HSC Chemistry Marathon Archive

Something along the lines:
Red Cabbage:
- Cut a red cabbage leaf into small pieces
- Half-fill a 250mL beaker with the red cabbage pieces. Add water until 200mL
- Heat and boil for about 10mins
- Allow to cool, then strain mixture. Purple juice obtained
- Turns yellow in strong bases; green in weak bases; purple in neutral; pink in acids

Looks good. I reckon that's all the 4 marks attainable.
______________
https://www.google.com.au/search?q=...MgCFcMYlAod7kwFbQ&dpr=2#imgrc=wCtpyWmbKELpOM:
Red cabbage indicator.

When I did it, I had quite a fair few consistencies with that picture:
-Strong acid -> Red
-Weak acid -> Pink
-Neutral -> Purple
-Weak base -> Dark purple, it was 0.1 mol L^-1 ammonia
-Strong base -> Algae green (i.e. yellow was somewhat visible)
______________
NEXT QUESTION
Compare the effects of ozone in the troposphere and in the stratosphere. Include relevant equations. (4)

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Looks good. I reckon that's all the 4 marks attainable.
______________
https://www.google.com.au/search?q=...MgCFcMYlAod7kwFbQ&dpr=2#imgrc=wCtpyWmbKELpOM:
Red cabbage indicator.

When I did it, I had quite a fair few consistencies with that picture:
-Strong acid -> Red
-Weak acid -> Pink
-Neutral -> Purple
-Weak base -> Dark purple, it was 0.1 mol L^-1 ammonia
-Strong base -> Algae green (i.e. yellow was somewhat visible)
______________
NEXT QUESTION
Compare the effects of ozone in the troposphere and in the stratosphere. Include relevant equations. (4)

Damn I love this question, okay here goes nothing.

Ozone when in the troposphere is considered as a serious air pollutant, because when nitrogen dioxide is formed by high combustion reactions such as in power stations and in cars, it reacts with UV to form NO radical and an oxygen radical. This highly reactive oxygen radical then combines with molecular oxygen and forms oxygen which can cause breathing difficulties. Ozone in the stratosphere acts as a UV sheild rather than a pollutant and stops harmful UV-B and UV-C from entering while allowing UV-A to pass through for photosynthetic reactions. However ozone can be depleted by CFCs through the following reactions.
CFCs react with UV forming a Cl radical

CCl2F2 + UV ---------> CClF2 + Cl (radical)

This chlorine radical then reacts with ozone, breaking it down and forming oxygen and an oxygen radical

Cl(radical) + O3 -------> O2 + O(radical)

Ah my brain stopped working lol, I don't know what comes after this reaction.

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Mind helping me out here?

 

[leehuan]

re: HSC Chemistry Marathon Archive

Damn I love this question, okay here goes nothing.

Ozone when in the troposphere is considered as a serious air pollutant, because when nitrogen dioxide is formed by high combustion reactions such as in power stations and in cars, it reacts with UV to form NO radical and an oxygen radical. This highly reactive oxygen radical then combines with molecular oxygen and forms oxygen which can cause breathing difficulties. Ozone in the stratosphere acts as a UV sheild rather than a pollutant and stops harmful UV-B and UV-C from entering while allowing UV-A to pass through for photosynthetic reactions. However ozone can be depleted by CFCs through the following reactions.
CFCs react with UV forming a Cl radical

CCl2F2 + UV ---------> CClF2 + Cl (radical)

This chlorine radical then reacts with ozone, breaking it down and forming oxygen and an oxygen radical

Cl(radical) + O3 -------> O2 + O(radical)

Ah my brain stopped working lol, I don't know what comes after this reaction.

Eeeeeehhh wrong question in mind with the equations. The equations needed were only that of the ozone cycle! 3/4

O3 -(UV)-> O2 + O(radical)
O(radical) + O2 -> O3

 

[leehuan]

re: HSC Chemistry Marathon Archive

Mind helping me out here?

The CFC equations are

Cl(radical) + O3 -> O2 + ClO(radical)

ClO(radical) + O(radical) -> O2 + Cl(radical)

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

Looks good. I reckon that's all the 4 marks attainable.
______________
https://www.google.com.au/search?q=...MgCFcMYlAod7kwFbQ&dpr=2#imgrc=wCtpyWmbKELpOM:
Red cabbage indicator.

When I did it, I had quite a fair few consistencies with that picture:
-Strong acid -> Red
-Weak acid -> Pink
-Neutral -> Purple
-Weak base -> Dark purple, it was 0.1 mol L^-1 ammonia
-Strong base -> Algae green (i.e. yellow was somewhat visible)
______________
NEXT QUESTION
Compare the effects of ozone in the troposphere and in the stratosphere. Include relevant equations. (4)

In the troposphere ozone is an air pollutant, which can react with nitrogen oxide??? and cause photochemical smog. This is harmful to breathe in and can cause respiratory problems. In the stratosphere however, ozone is a very useful substance. The ozone in the stratosphere forms a ozone layer that absorbs most of the Sun's ultraviolet (UV) radiation. This prevents harmful UV rays (UV-B and UV-C) from entering earth and harming its inhabitants, while allowing UV-A for photosynthesis. It is able to do this because it uses up the UV radiation to decompose into oxygen and an oxygen radical as per the equation: O3(g) ----UV RADIATION---> O2(g) + O dot(g)
Hence it can be seen that in the troposphere ozone has a negative affect, while in the stratosphere it forms an essential 'ozone layer', which is essential in preventing harmful UV radiation.

This is pretty shit but can't be bothered looking at my notes.

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Eeeeeehhh wrong question in mind with the equations. The equations needed were only that of the ozone cycle! 3/4

O3 -(UV)-> O2 + O(radical)
O(radical) + O2 -> O3

Oh snap, didn't think of those equations lol.