HSC 2012-2015 Chemistry Marathon (archive) (1 Viewer)

[BlueGas]

re: HSC Chemistry Marathon Archive

For those that do Industrial Chemistry, can you answer HSC 2010 Q32 (d) (ii)? The sample answer is too long for a 3 mark question like this...

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

For those that do Industrial Chemistry, can you answer HSC 2010 Q32 (d) (ii)? The sample answer is too long for a 3 mark question like this...

post the qustion

 

[Mr_Kap]

re: HSC Chemistry Marathon Archive

We learnt that if you replace a strong acid into a weaker one it will require the same amount of volume to reach the equivalence point therefore the questions broken ?

No it isn't, you will need 3 times more of the base in order to neutralise the 3 protons from the citric acid, in comparison to hydrochloric acid, which only requires enough base to neutralise the one proton donated. Remember, [HCl] = [H+] but 3x[C6H8O7] = [H+], when it is added to a base, such that all acid go through complete ionisation/donation of protons

Are you sure. I learnt the same as Drsoccerball

 

[BlueGas]

re: HSC Chemistry Marathon Archive

post the qustion

 

[Ekman]

re: HSC Chemistry Marathon Archive

Are you sure. I learnt the same as Drsoccerball

Im not saying he is wrong, here are a few equations to illustrate my point:

Citric Acid: C6H8O7 + 3NaOH -> (C6H5O7)3- + 3Na+ + 3H2O (This is because citric acid is a triprotic acid, and the addition of a base shifts the equilibrium for all 3 levels of disassociation)

Hydrochloric Acid: HCl + NaOH -> H2O + Na+ + Cl-

See how you require 3 moles of NaOH with citric acid, in comparison to hydrochloric acid. Plus the strength doesn't matter when it comes down to adding a base.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Im not saying he is wrong, here are a few equations to illustrate my point:

Citric Acid: C6H8O7 + 3NaOH -> (C6H5O7)3- + 3Na+ + 3H2O (This is because citric acid is a triprotic acid, and the addition of a base shifts the equilibrium for all 3 levels of disassociation)

Hydrochloric Acid: HCl + NaOH -> H2O + Na+ + Cl-

See how you require 3 moles of NaOH with citric acid, in comparison to hydrochloric acid. Plus the strength doesn't matter when it comes down to adding a base.

So what does the amount of moles have to do with the total volume. We learnt that in titration replacing a strong acid with a weaker one would require the same volume ? IF its what you say theres a contradiction

 

[lpodtouch]

re: HSC Chemistry Marathon Archive

So what does the amount of moles have to do with the total volume. We learnt that in titration replacing a strong acid with a weaker one would require the same volume ? IF its what you say theres a contradiction

This is only applicable if both acids are monoprotic or diprotic etc.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

This is only applicable if both acids are monoprotic or diprotic etc.

Yeah someone explained that to me thanks

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Quick question, in the reaction, should it be 4e- or 2e-?

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

Its 4

 

[Study_like_a_nerd]

re: HSC Chemistry Marathon Archive

Justify the continued use of the Arrhenius definition of acids and bases, despite the development of the more sophisticated Bronsted Lowry definition. (4 marks)

 

[Ekman]

re: HSC Chemistry Marathon Archive

Justify the continued use of the Arrhenius definition of acids and bases, despite the development of the more sophisticated Bronsted Lowry definition. (4 marks)

My answer would be that:

The reason behind the continued use of the Arrhenius definition is because Arrhenius's theory described the disassociation of acids in water producing aqueous solutions. His theory also explained why these solutions were able to conduct electricity, because of the disassociation of the H+ ions, allowing for a medium of electricity to flow through. In comparison to the Bronsted and Lowry definition, which only describes acids and bases as proton donors and proton acceptors and neutralisation reactions as proton transfer reactions, Arrhenius was able to describe neutralisation reactions through the disassociation of H+ from acids, and OH- from bases and their reaction together to form water.

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Industrial Chem question: Assess both the importance and resulting environmental impacts of using limestone in the Solvay Process. (7 marks)

 

[porcupinetree]

re: HSC Chemistry Marathon Archive

Industrial Chem question: Assess both the importance and resulting environmental impacts of using limestone in the Solvay Process. (7 marks)

I've only learnt the Solvay process recently, but I'll have a go:

Importance
Limestone (calcium carbonate, CaCO3) is an essential raw material for the production of sodium carbonate via the Solvay method. It is burnt/heated in a kiln in order to produce carbon dioxide gas and calcium oxide (lime), both of which are key elements in the Solvay process. Carbon dioxide gas is bubbled through ammoniated brine, participating in the reaction:
H2O(l) + CO2(g) + NH3(aq) + NaCl(aq) ---> NaHCO3(s) + NH4Cl(aq)
The sodium hydrogen carbonate is then heated to produce sodium carbonate (Na2CO3); thus carbon dioxide from limestone is an integral factor in allowing the production of Na2CO3. In addition, the lime produced by the limestone after heating is used to convert the left over ammonium chloride solution to more useful products (namely more ammonia).

Environmental impacts
Specifically, extraction of limestone from local deposits can alter the landscape from which it is taken, and may harm local ecosystems.
In addition, the Solvay process as a whole has several environmental impacts:
Calcium chloride (CaCl2) is a by-product and is not useful in the large quantities in which it is produced. Thus it is often disposed into waterways, which can greatly increase the concentration of chloride and calcium ions. This may disrupt marine ecosystems. In addition, the Solvay process is exothermic overall; this excess heat is released into the environment as thermal pollution and poses a real threat to ecosystems (particularly marine).
Moreover, while ammonia is theoretically completely recycled in the Solvay process, inevitably some of it is lost into the atmosphere where it acts as a pollutant.

Conclusion/Assessment
This, while limestone is a cheap raw material for the Solvay process, and is an important component in the process, its use does cause some environmental impacts, which can be minimised by careful monitoring and management and research into alternative methods of producing sodium carbonate.

 

[Ekman]

re: HSC Chemistry Marathon Archive

I've only learnt the Solvay process recently, but I'll have a go:

Importance
Limestone (calcium carbonate, CaCO3) is an essential raw material for the production of sodium carbonate via the Solvay method. It is burnt/heated in a kiln in order to produce carbon dioxide gas and calcium oxide (lime), both of which are key elements in the Solvay process. Carbon dioxide gas is bubbled through ammoniated brine, participating in the reaction:
H2O(l) + CO2(g) + NH3(aq) + NaCl(aq) ---> NaHCO3(s) + NH4Cl(aq)
The sodium hydrogen carbonate is then heated to produce sodium carbonate (Na2CO3); thus carbon dioxide from limestone is an integral factor in allowing the production of Na2CO3. In addition, the lime produced by the limestone after heating is used to convert the left over ammonium chloride solution to more useful products (namely more ammonia).

Environmental impacts
Specifically, extraction of limestone from local deposits can alter the landscape from which it is taken, and may harm local ecosystems.
In addition, the Solvay process as a whole has several environmental impacts:
Calcium chloride (CaCl2) is a by-product and is not useful in the large quantities in which it is produced. Thus it is often disposed into waterways, which can greatly increase the concentration of chloride and calcium ions. This may disrupt marine ecosystems. In addition, the Solvay process is exothermic overall; this excess heat is released into the environment as thermal pollution and poses a real threat to ecosystems (particularly marine).
Moreover, while ammonia is theoretically completely recycled in the Solvay process, inevitably some of it is lost into the atmosphere where it acts as a pollutant.

Conclusion/Assessment
This, while limestone is a cheap raw material for the Solvay process, and is an important component in the process, its use does cause some environmental impacts, which can be minimised by careful monitoring and management and research into alternative methods of producing sodium carbonate.

Just a few edits:

For the first bolded part, you can take it further by talking about how lime is used to recover ammonia which is essential because ammonia is really expensive and recovering it will reduce overall costs.

For the second bolded part, you can take it further and talk about increase in salinity in soil because of the presence of chloride ions, and the increase in hardness of water which effectively kills off the ecosystem, if and only if, the CaCl2 is disposed in riverways. That is something you have to mention because most Solvay plants don't care about the disposal of CaCl2 and the thermal pollution associated with the combustion of CaCO3 because they dump it in oceans which has no overall environmental impact, but it has detrimental impacts on river systems. Also when you are talking about thermal pollution, its good to mention that it reduces the overall DO levels, potentially causing hypoxia of water and the destruction to the ecosystem.

Also a final thing to add in, there tends to be unburnt CaCO3 in the kiln which is disposed of into oceans. However if it was to be disposed into river systems, it will cause turbidity and has the potential to cause blockages of river systems.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

1) In a 250 mL beaker mix 30 mL of NaOH and 10 mL of olive oil
2) Add boiling chips to the mixture and heat for 30 minutes while stirring until the oil layer disappeared
3) Once the mixture cools down add 40 mL of NaCl to "salt out" the solution.
4) Use a muslin cloth to separate the mixture and wash it with water and bang you have your soap
Safety: The NaOH is highly caustic and therefore safety glasses, goggles and lab coat must be worn.

 

[porcupinetree]

re: HSC Chemistry Marathon Archive

Just a few edits:

For the first bolded part, you can take it further by talking about how lime is used to recover ammonia which is essential because ammonia is really expensive and recovering it will reduce overall costs.

For the second bolded part, you can take it further and talk about increase in salinity in soil because of the presence of chloride ions, and the increase in hardness of water which effectively kills off the ecosystem, if and only if, the CaCl2 is disposed in riverways. That is something you have to mention because most Solvay plants don't care about the disposal of CaCl2 and the thermal pollution associated with the combustion of CaCO3 because they dump it in oceans which has no overall environmental impact, but it has detrimental impacts on river systems. Also when you are talking about thermal pollution, its good to mention that it reduces the overall DO levels, potentially causing hypoxia of water and the destruction to the ecosystem.

Also a final thing to add in, there tends to be unburnt CaCO3 in the kiln which is disposed of into oceans. However if it was to be disposed into river systems, it will cause turbidity and has the potential to cause blockages of river systems.

Cheers dude, that's super helpful

 

[Gabriel Moussa]

re: HSC Chemistry Marathon Archive

I am
Gabriel Moussa

 

[BlueGas]

re: HSC Chemistry Marathon Archive

Has anyone seen any HSC questions asking about an experiment of galvanic cells?

 

[Ekman]

re: HSC Chemistry Marathon Archive

Has anyone seen any HSC questions asking about an experiment of galvanic cells?

I got one in my chem trial, so I don't see any reason there shouldn't be one in the HSC