HSC 2012-2015 Chemistry Marathon (archive) (8 Viewers)

[porcupinetree]

re: HSC Chemistry Marathon Archive

Lets get the ball rolling again:
Outline the industrial process of the production of ethanol from the fermentation of sugar cane. 2 marks LOL in the exam only one person got 2 i think

I studied this today actually, what a coincidence.

Sugar cane is crushed and grinded to a pulp, and then heated to 100 degrees C, when dilute sulfuric acid is added, which hydrolyses the cellulose and starch in the sugar cane into glucose molecules. This mixture is then filtered to remove unwanted residues of lignin. Then, calcium hydroxide is added which neutralises the acid and precipitates the sulfate out as gypsum (CaSO4), which is then filtered out.
Then, the remaining glucose solution is heated to 37C in anaerobic conditions with a catalyst of yeast to ferment into ethanol:
C6H12O6 (aq) --> 2CO2 (g) + 2C2H5OH (aq)

Next Q:

Discuss how manufactured products have had a damaging impact on the composition of the atmosphere and evaluate the measures being taken to decrease the damage. 6 Marks

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

I studied this today actually, what a coincidence.

Sugar cane is crushed and grinded to a pulp, and then heated to 100 degrees C, when dilute sulfuric acid is added, which hydrolyses the cellulose and starch in the sugar cane into glucose molecules. This mixture is then filtered to remove unwanted residues of lignin. Then, calcium hydroxide is added which neutralises the acid and precipitates the sulfate out as gypsum (CaSO4), which is then filtered out.
Then, the remaining glucose solution is heated to 37C in anaerobic conditions with a catalyst of yeast to ferment into ethanol:
C6H12O6 (aq) --> 2CO2 (g) + 2C2H5OH (aq)

Next Q:

Discuss how manufactured products have had a damaging impact on the composition of the atmosphere and evaluate the measures being taken to decrease the damage. 6 Marks

Apparently you have to mention that they recycle the waste and convert them into ethanol aswell. Good answer though
------------------------------------------------------------------------------------------------------------------------------

 

[pomsky]

re: HSC Chemistry Marathon Archive

Guys,
If you were to write an equation to dissociate acetic acid, how would you do it? Because I thought that most acids and bases (all of the HSC prescribed) were aqueous, but isn't it redundant to say:
? (yes, this is Arrhenius' definition)

considering that the definition of 'aqueous' is that it can dissociate? I'm asking cos I was marked down during half-yearlies for doing this (admittedly in a different question) but I can't see any other ways to dissociate something in this question.

Maybe it's just paranoia lol

 

[Kaido]

re: HSC Chemistry Marathon Archive

No, it's not 'redundant', you should def write that equation to show the dynamic EQUILIBRIUM of acetic acid (aq). Your arrow is single sided, perhaps thats how you lost the mark?

 

[Ekman]

re: HSC Chemistry Marathon Archive

Guys,
If you were to write an equation to dissociate acetic acid, how would you do it? Because I thought that most acids and bases (all of the HSC prescribed) were aqueous, but isn't it redundant to say:
? (yes, this is Arrhenius' definition)

considering that the definition of 'aqueous' is that it can dissociate? I'm asking cos I was marked down during half-yearlies for doing this (admittedly in a different question) but I can't see any other ways to dissociate something in this question.

Maybe it's just paranoia lol

You should always write aq, unless you are doing Industrial Chemistry, then you need to pay attention to whether the acid (usually sulphuric acid) is concentrated or not. If it was concentrated then you use l instead of aq, but this is only for industrial chemistry topic, not for the acidic environment topic.

 

[rand_althor]

re: HSC Chemistry Marathon Archive

the definition of 'aqueous' is that it can dissociate

That's not the definition of aqueous. An aqueous solution is one in which water is the solvent.

Did your teacher say you lost marks for not including the (aq) subscript?

 

[pomsky]

re: HSC Chemistry Marathon Archive

No, it's not 'redundant', you should def write that equation to show the dynamic EQUILIBRIUM of acetic acid (aq). Your arrow is single sided, perhaps thats how you lost the mark?

http://imgur.com/RjSSKRJ

Marking criteria said it is a forward reaction- but I completely agree with you. Aren't weak acids always in equilibrium? Or did Arrhenius say something about this?

 

[pomsky]

re: HSC Chemistry Marathon Archive

That's not the definition of aqueous. An aqueous solution is one in which water is the solvent.

Did your teacher say you lost marks for not including the (aq) subscript?

No, I lost a mark because I included the (aq) subscript. They said the equation wasn't necessary. And yes, but by extension, the solute will be able to dissociate into free ions.

"An aqueous solution is one that is occurring in water. What makes water significant is that it can allow for substances to dissolve and/or be dissociated into ions within it." -http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Reactions_in_Aqueous_Solutions/Unique_Features_of_Aqueous_Solutions

 

[Fizzy_Cyst]

re: HSC Chemistry Marathon Archive

No, I lost a mark because I included the (aq) subscript. They said the equation wasn't necessary. And yes, but by extension, the solute will be able to dissociate into free ions.

"An aqueous solution is one that is occurring in water. What makes water significant is that it can allow for substances to dissolve and/or be dissociated into ions within it." -http://chemwiki.ucdavis.edu/Inorganic_Chemistry/Reactions_in_Aqueous_Solutions/Unique_Features_of_Aqueous_Solutions

Notice the AND/OR

The solute does not always dissociate. What about glucose? Urea?

Sounds a bit dodge that you lost marks for including the aq subscript. Whilst they are not required in the HSC, you should not LOSE marks for writing them, assuming it is correct.

 

[turntaker]

re: HSC Chemistry Marathon Archive

Anyone doing Chemistry of Art for option topic. lel

 

[porcupinetree]

re: HSC Chemistry Marathon Archive

Anyone doing Chemistry of Art for option topic. lel

I'm doing Industrial because my class is doing it, and I know it's stupid to not do the option that you do in class. However, if I had complete control over which option my class and I did, I would have seriously considered doing Chemistry of Art - it looks much more interesting than industrial and has some similarities to the Physics option Quanta to Quarks.

Anyway, here's a new question:

Discuss the need for monitoring and management of the release of soaps and detergents into the environment. 4 marks

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

I'm doing Industrial because my class is doing it, and I know it's stupid to not do the option that you do in class. However, if I had complete control over which option my class and I did, I would have seriously considered doing Chemistry of Art - it looks much more interesting than industrial and has some similarities to the Physics option Quanta to Quarks.

Anyway, here's a new question:

Discuss the need for monitoring and management of the release of soaps and detergents into the environment. 4 marks

This might be a bit dodge:
Soaps and detergents all have the ability to lather in water(bubble). This can be a catastrophic environmental impacts as the long non-polar chain causes organisms to detach from their safe environment and ultimately kills them. By adding alot of soaps and detergents to the waterways this not only kills organisms but also changes the pH of the water. Some species cant survive at the change of pH and they again will ultimately die. Phosphate based detergents cause eutrophication in the waterways making water undrinkable and inhabitable. The fact that they most soaps and detergents (disregarding new developments) stay in the water ways for a long time and are not biodegradable also contribute to these catastrophes. Ultimately, the release of soaps and detergents need to be monitored and managed in the environment due to its potential destruction it can cause.

 

[Crisium]

re: HSC Chemistry Marathon Archive

This might be a bit dodge:
Soaps and detergents all have the ability to lather in water(bubble). This can be a catastrophic environmental impacts as the long non-polar chain causes organisms to detach from their safe environment and ultimately kills them. By adding alot of soaps and detergents to the waterways this not only kills organisms but also changes the pH of the water. Some species cant survive at the change of pH and they again will ultimately die. Phosphate based detergents cause eutrophication in the waterways making water undrinkable and inhabitable. The fact that they most soaps and detergents (disregarding new developments) stay in the water ways for a long time and are not biodegradable also contribute to these catastrophes. Ultimately, the release of soaps and detergents need to be monitored and managed in the environment due to its potential destruction it can cause.

Try to use more scientific terms to make your response more succinct such as for "Phosphate Based Detergents" you could just say "Builders" - This also shows a greater understanding and gives you more space to write. Perhaps make reference to how there is a need for monitoring and management of detergents but not so much for soaps as they are biodegradable; I guess this is required seeing as this is a "Discuss" question. You can also talk about how linear chain anionic detergents were introduced to minimise the effects of branched chain anionic detergents (However they must be used carefully as their biocidal effects may kill bacteria essential to the degradation of sewage <-- This is just extra information, but I wouldn't mention it in a question like this)

I was just curious, what do you mean by the bolded part? I've never heard of that before I'm actually interested to know what it's about haha

I came across some information in regards to soaps lathering where the bubbles prevent sunlight from passing into the water and so this prevents water plants from undergoing photosynthesis to an appreciable extent which means less dissolved oxygen, etc.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Some microorganism are non-polar by nature and are attached to safe places where normal water wouldnt detach them but since detergents are highly non-polar it detaches them from their safe environment... In regards to the question why do i have to mention recent developments such as linear chains and biodegradability?

 

[Crisium]

re: HSC Chemistry Marathon Archive

Some microorganism are non-polar by nature and are attached to safe places where normal water wouldnt detach them but since detergents are highly non-polar it detaches them from their safe environment... In regards to the question why do i have to mention recent developments such as linear chains and biodegradability?

Since it's a discuss question you would usually have to "Identify issues and provide points for and/or against"

So it's good to acknowledge how detergents bring about these problems but how they have adopted new detergents to address this problem and thus reduce the effect on the environment

 

[Ununoctium]

re: HSC Chemistry Marathon Archive

Discuss how manufactured products have had a damaging impact on the composition of the atmosphere and evaluate the measures being taken to decrease the damage. 6 Marks

Discuss how manufactured products have had a damaging impact on the composition of the atmosphere and evaluate the measures being taken to decrease the damage. (6 Marks)

Many manufactured products, such as chloroflurocarbons (CFCs) which are used as refrigerants and in air conditioners, have adverse impacts on the composition of the atmosphere.
CFCs are inert molecules that are insoluble in water. As a result, they do not break down in the troposphere, and reach the ozone-rich stratosphere. UV radiation breaks the C-Cl bond in the molecule, releasing a chlorine free radical. This free radical reacts with ozone molecules:

CCl3F (g) + UV light --> CCl2F3· (g) + Cl· (g)
Cl· (g) + O3 --> ClO· (g) + O2 (g)
ClO· (g) + O· (g) --> O2 (g) + Cl· (g)

Ozone concentrations in the atmosphere are significantly reduced, and since Ozone absorbs UV-B and UV-c radiation, a lack of ozone means more of this harmful radiation reaches the biosphere. This results in an increased presence of skin cancers and reduced immunity in many land dwelling organisms.

Many measures are currently being taken to decrease the damage to the Ozone, such as introducing hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) and conducting international conventions. The 1987 Montreal Protocol and the Kyoto Convention aimed to completely phase out halons and CFCs by 1996.

HCFCs and HFCs have been introduced to also decrease the damage from CFCs. HCFCs can react with OH- free radicals in the lower troposphere and decompose to CO2, H2O and hydrogen halides due to their C-H bond. Significantly less chlorine reaches the stratosphere when compared to CFCs. Comparatively, HFCs do not have a chlorine atom, significantly lowering ozone depletion.

The advantages of HCFCs and HFCs are that they lower the depletion of ozone in the atmosphere, while still being able to be used in refrigerants and air conditioners that CFCs are normally used for. They are non-toxic molecules. However, the disadvantages of HCFCs and HFCs are that they are more expensive, less efficient and are greenhouse gases.

The criteria for this evaluation are environmental benefits, uses, and cost.

The implementation of HCFCs and HCFs as measures being taken to decrease the damage caused by CFCs have been, overall, effective, since they decrease the depletion of ozone but still provide the same uses as CFCs. However, they are both expensive and are greenhouse gases. As a result, more research and development must continue.

---

Questions:

Shipwrecks: Assess the methods used to prevent the corrosion of steel. (4 marks)

Modules: A solution contains sulfate, phosphate, chlorine and carbonate anions. Describe a wet method test used to identify these anions. Your response should include equations and qualitative analysis of results. (4 marks)

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Discuss how manufactured products have had a damaging impact on the composition of the atmosphere and evaluate the measures being taken to decrease the damage. (6 Marks)

Many manufactured products, such as chloroflurocarbons (CFCs) which are used as refrigerants and in air conditioners, have adverse impacts on the composition of the atmosphere.
CFCs are inert molecules that are insoluble in water. As a result, they do not break down in the troposphere, and reach the ozone-rich stratosphere. UV radiation breaks the C-Cl bond in the molecule, releasing a chlorine free radical. This free radical reacts with ozone molecules:

CCl3F (g) + UV light --> CCl2F3· (g) + Cl· (g)
Cl· (g) + O3 --> ClO· (g) + O2 (g)
ClO· (g) + O· (g) --> O2 (g) + Cl· (g)

Ozone concentrations in the atmosphere are significantly reduced, and since Ozone absorbs UV-B and UV-c radiation, a lack of ozone means more of this harmful radiation reaches the biosphere. This results in an increased presence of skin cancers and reduced immunity in many land dwelling organisms.

Many measures are currently being taken to decrease the damage to the Ozone, such as introducing hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) and conducting international conventions. The 1987 Montreal Protocol and the Kyoto Convention aimed to completely phase out halons and CFCs by 1996.

HCFCs and HFCs have been introduced to also decrease the damage from CFCs. HCFCs can react with OH- free radicals in the lower troposphere and decompose to CO2, H2O and hydrogen halides due to their C-H bond. Significantly less chlorine reaches the stratosphere when compared to CFCs. Comparatively, HFCs do not have a chlorine atom, significantly lowering ozone depletion.

The advantages of HCFCs and HFCs are that they lower the depletion of ozone in the atmosphere, while still being able to be used in refrigerants and air conditioners that CFCs are normally used for. They are non-toxic molecules. However, the disadvantages of HCFCs and HFCs are that they are more expensive, less efficient and are greenhouse gases.

The criteria for this evaluation are environmental benefits, uses, and cost.

The implementation of HCFCs and HCFs as measures being taken to decrease the damage caused by CFCs have been, overall, effective, since they decrease the depletion of ozone but still provide the same uses as CFCs. However, they are both expensive and are greenhouse gases. As a result, more research and development must continue.

---

Questions:

Shipwrecks: Assess the methods used to prevent the corrosion of steel. (4 marks)

Modules: A solution contains sulfate, phosphate, chlorine and carbonate anions. Describe a wet method test used to identify these anions. Your response should include equations and qualitative analysis of results. (4 marks)

Why are you answering your own question?

 

[Ekman]

re: HSC Chemistry Marathon Archive

Why are you answering your own question?

 

[Kaido]

re: HSC Chemistry Marathon Archive

Why are you answering your own question?

The burns are real

 

[Ununoctium]

re: HSC Chemistry Marathon Archive

Why are you answering your own question?

Uhm, it was asked on the previous page...

Discuss how manufactured products have had a damaging impact on the composition of the atmosphere and evaluate the measures being taken to decrease the damage. 6 Marks