• Best of luck to the class of 2024 for their HSC exams. You got this!
    Let us know your thoughts on the HSC exams here
  • YOU can help the next generation of students in the community!
    Share your trial papers and notes on our Notes & Resources page
MedVision ad

HSC 2012-2015 Chemistry Marathon (archive) (2 Viewers)

Status
Not open for further replies.

Fizzy_Cyst

Well-Known Member
Joined
Jan 14, 2011
Messages
1,209
Location
Parramatta, NSW
Gender
Male
HSC
2001
Uni Grad
2005
re: HSC Chemistry Marathon Archive

New Question: (Industrial Chem) (5-6 marks)

In class, you performed an experiment to model an equilibrium reaction.

Outline your experiment and discuss the validity of the model.
 

Crisium

Pew Pew
Joined
Feb 17, 2014
Messages
2,009
Location
Australia
Gender
Male
HSC
2015
re: HSC Chemistry Marathon Archive

Method:

1) Label the two measuring cylinders; one marked “A” and the other “B”.

2) Place 100 ml of water in “A” and 0 ml of water in “B”.

3) Place the larger pipette upside down into “A” so that it rests vertically on the bottom, seal it tightly by finger pressure and transfer its contents to “B” without spillage. Place the smaller pipette upside down into “B”, seal and transfer the contents to “A”. This is one complete transfer cycle, and the volumes present in both “A” and “B” must be recorded.

4) Continue with a series of transfer cycles until a state of equilibrium is achieved (i.e. There is no further change in the volumes in “A” and “B”).

The experiment began with all the water in “A”, but at a point in time, both water levels were constant despite water still being transferred back and forth, which is representative of the concept of dynamic equilibrium. In this experiment the measuring cylinders A and B acted as the reactants and products respectively, whilst the large and small pipettes represented the reaction rates. Increasing the rate at which the water was transferred from one measuring cylinder to another via the pipettes, models the action of a catalyst. The transfer of liquid from “A” to “B” modelled the forward reaction, whilst the transfer of liquid from “B” to “A” modelled the reverse reaction. Therefore, this modelling investigation was valid as it applied accepted laws and all variables were controlled, baring the dependent and independent variables.

However, it did not show the reality of equilibrium systems, such as the reactants becoming products. Furthermore, the modelling of chemical equilibrium only allows for simplified representations of chemical processes that are based on assumptions, such as there being a closed-system at equilibrium when in reality there are minor inevitable spillages from the transfer cycles. Therefore, this experiment lacked validity in that, despite testing the aim, it was not entirely scientifically valid.

Overall, this experiment was a successful model for an equilibrium reaction.

~~~

I'm not expecting too much from this and since Fizzycyst asked it I wouldn't be surprised if I got 1 / 5-6
 

Drsoccerball

Well-Known Member
Joined
May 28, 2014
Messages
3,650
Gender
Undisclosed
HSC
2015
re: HSC Chemistry Marathon Archive

Method:

1) Label the two measuring cylinders; one marked “A” and the other “B”.

2) Place 100 ml of water in “A” and 0 ml of water in “B”.

3) Place the larger pipette upside down into “A” so that it rests vertically on the bottom, seal it tightly by finger pressure and transfer its contents to “B” without spillage. Place the smaller pipette upside down into “B”, seal and transfer the contents to “A”. This is one complete transfer cycle, and the volumes present in both “A” and “B” must be recorded.

4) Continue with a series of transfer cycles until a state of equilibrium is achieved (i.e. There is no further change in the volumes in “A” and “B”).

The experiment began with all the water in “A”, but at a point in time, both water levels were constant despite water still being transferred back and forth, which is representative of the concept of dynamic equilibrium. In this experiment the measuring cylinders A and B acted as the reactants and products respectively, whilst the large and small pipettes represented the reaction rates. Increasing the rate at which the water was transferred from one measuring cylinder to another via the pipettes, models the action of a catalyst. The transfer of liquid from “A” to “B” modelled the forward reaction, whilst the transfer of liquid from “B” to “A” modelled the reverse reaction. Therefore, this modelling investigation was valid as it applied accepted laws and all variables were controlled, baring the dependent and independent variables.

However, it did not show the reality of equilibrium systems, such as the reactants becoming products. Furthermore, the modelling of chemical equilibrium only allows for simplified representations of chemical processes that are based on assumptions, such as there being a closed-system at equilibrium when in reality there are minor inevitable spillages from the transfer cycles. Therefore, this experiment lacked validity in that, despite testing the aim, it was not entirely scientifically valid.

Overall, this experiment was a successful model for an equilibrium reaction.

~~~

I'm not expecting too much from this and since Fizzycyst asked it I wouldn't be surprised if I got 1 / 5-6
I thought you were going to do something with KSCN or dichromate or something D:
 

Crisium

Pew Pew
Joined
Feb 17, 2014
Messages
2,009
Location
Australia
Gender
Male
HSC
2015
re: HSC Chemistry Marathon Archive

This is the method I did for that experiment you're talking about jono. Do you want the results as well?

Method:

1) Pour 50 ml of distilled water into a 100 ml beaker.

2) Using a clean pipette for each, add to the beaker 2 ml of both Iron (III) Nitrate (Fe(NO3)3) Solution and Potassium Thiocyanate (KSCN) Solution. This should then be mixed thoroughly until the solution turns into a blood red coloured solution; Iron (III) Thiocyanate (FeSCN2+) Solution.

3) Pour 5 ml of this mixture into each “spot” on the spot test plate and label them from A to E, where;

- Spot A: The Control

- Spot B: Add 10 Drops of The Iron (III) Nitrate Solution

- Spot C: Add 10 Drops of The Potassium Thiocyanate Solution

- Spot D: Add 10 Drops of The Sodium Hydroxide Solution

- Spot E: Add 1 g of The Solid Potassium Nitrate

4) Record any observations based on any colour changes in the four spots by comparing each spot with the control. To sharpen the colour, place the spot test plate over a piece of white paper.
 
Joined
Mar 9, 2014
Messages
101
Gender
Female
HSC
2015
re: HSC Chemistry Marathon Archive

Explain the importance of ammonia in the Solvay Process. Include a chemical equation to support your answer (3 marks)
 
Joined
Mar 9, 2014
Messages
101
Gender
Female
HSC
2015
re: HSC Chemistry Marathon Archive

Compare and contrast the structure and cleaning action of anionic, cationic, and non-ionic detergents, including how they are affected by hard water. (4 marks)
 

Drsoccerball

Well-Known Member
Joined
May 28, 2014
Messages
3,650
Gender
Undisclosed
HSC
2015
re: HSC Chemistry Marathon Archive

Explain the importance of ammonia in the Solvay Process. Include a chemical equation to support your answer (3 marks)
Ammonia in the Solvay process is an example of the utilisation of Le chateliers principle.
Adding a basic substance such as ammonia would cause the equlibrium to shift to the right. This maximises the production of carbonic acid due to le chateliers principle. That is the main purpose of Ammonia. Without this the potential yield produced would be much smaller.
Very dodge
 

jono_jonoson

Member
Joined
Aug 14, 2015
Messages
95
Gender
Male
HSC
2015
re: HSC Chemistry Marathon Archive

Ammonia in the Solvay process is an example of the utilisation of Le chateliers principle.
Adding a basic substance such as ammonia would cause the equlibrium to shift to the right. This maximises the production of carbonic acid due to le chateliers principle. That is the main purpose of Ammonia. Without this the potential yield produced would be much smaller.
Very dodge
Yeh like maybe 2/3 haha
 
Joined
Mar 9, 2014
Messages
101
Gender
Female
HSC
2015
re: HSC Chemistry Marathon Archive

Ammonia in the Solvay process is an example of the utilisation of Le chateliers principle.
Adding a basic substance such as ammonia would cause the equlibrium to shift to the right. This maximises the production of carbonic acid due to le chateliers principle. That is the main purpose of Ammonia. Without this the potential yield produced would be much smaller.
Very dodge

I dont think the question meant "adding extra ammonia." I think they meant explain why the ammonia in the process itself is important. So I was thinking that since ammonia reacts with water and NaCl to form sodium hydrogen carbonate which then produces sodium carbonate, it is important. But I didnt think that was sufficient for 3 marks...
 

Ekman

Well-Known Member
Joined
Oct 23, 2014
Messages
1,615
Gender
Male
HSC
2015
re: HSC Chemistry Marathon Archive

I dont think the question meant "adding extra ammonia." I think they meant explain why the ammonia in the process itself is important. So I was thinking that since ammonia reacts with water and NaCl to form sodium hydrogen carbonate which then produces sodium carbonate, it is important. But I didnt think that was sufficient for 3 marks...
Well my response to the question would be:

Ammonia is a material (I wouldn't classify it as raw, as it is recycled) that is used in the Solvay Process, allowing the carbonation of brine in the carbonator tower. The reaction is as follows: NH3 + H2O + CO2 + NaCl -> NH4Cl + NaHCO3. The importance of ammonia is due to its capacity to provide the ability of brine to react with carbonic acid in the low temperatures inside the carbonating tower, forming ammonium chloride and sodium bicarb. Due to the acid-base reaction that occurs between ammonia and the dissolved carbon dioxide in water (forming carbonic acid), ammonium and bicarb ions are formed; NH3 + H2CO3 -> NH4+ + HCO3-, which effectively bonds with the Na+ and Cl- ions, to produce the products mentioned before, which is further calcinated to produce Na2CO3, and recycled in order to preserve the amount of ammonia due to its high prices, hence allowing ammonia to be classified as a 'catalyst'.
 
Last edited:
Joined
Mar 9, 2014
Messages
101
Gender
Female
HSC
2015
re: HSC Chemistry Marathon Archive

Equal volumes of four 0.1 mol L−1 acids were titrated with the same sodium hydroxide
solution.
Which one requires the greatest volume of base to change the colour of the indicator?
(A) Citric acid
(B) Acetic acid
(C) Sulfuric acid
(D) Hydrochloric acid
 

lpodtouch

Active Member
Joined
Jan 3, 2014
Messages
143
Gender
Female
HSC
2015
re: HSC Chemistry Marathon Archive

Equal volumes of four 0.1 mol L−1 acids were titrated with the same sodium hydroxide
solution.
Which one requires the greatest volume of base to change the colour of the indicator?
(A) Citric acid
(B) Acetic acid
(C) Sulfuric acid
(D) Hydrochloric acid
A) Citric acid
 

Drsoccerball

Well-Known Member
Joined
May 28, 2014
Messages
3,650
Gender
Undisclosed
HSC
2015
re: HSC Chemistry Marathon Archive

I wouldve said acetic acid ? is the answer citric ?
 

Drsoccerball

Well-Known Member
Joined
May 28, 2014
Messages
3,650
Gender
Undisclosed
HSC
2015
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 ?
 

Ekman

Well-Known Member
Joined
Oct 23, 2014
Messages
1,615
Gender
Male
HSC
2015
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
 
Status
Not open for further replies.

Users Who Are Viewing This Thread (Users: 0, Guests: 2)

Top