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

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Crisium

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re: HSC Chemistry Marathon Archive

Sulphur Dioxide = Oxidation (You will therefore have to switch the sign from +0.16 V to -0.16 V)

Potassium Dichromate = Reduction (+1.36 V)

EMF = -0.16 + 1.36 = 1.2 V

Therefore is it A?
 
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Chris_S

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re: HSC Chemistry Marathon Archive

yeah thanx I just stuffed up the potassium dichromate
 

porcupinetree

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re: HSC Chemistry Marathon Archive

Next question:
(a) A solution containing an unknown cation is tested in a variety of ways. The results were as follows:
No ppt with dilute hydrochloric acid
No ppt with ammonia solution
Demonstrates a greenish flame test.

(i) Identify the unknown cation.
(ii) Propose a confirmatory test that would give you greater confidence in your identification.

(b) A solution is known to contain either Pb2+ or Ca2+ ions. Describe a procedure that would allow you to identify which ion is present.
 

BlueGas

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re: HSC Chemistry Marathon Archive

Next question:
(a) A solution containing an unknown cation is tested in a variety of ways. The results were as follows:
No ppt with dilute hydrochloric acid
No ppt with ammonia solution
Demonstrates a greenish flame test.

(i) Identify the unknown cation.
(ii) Propose a confirmatory test that would give you greater confidence in your identification.

(b) A solution is known to contain either Pb2+ or Ca2+ ions. Describe a procedure that would allow you to identify which ion is present.
a i) Barium
a ii) Add sulfate ions (barium sulfate) until a white precipitate forms, if a precipitate forms, then barium is present.

b) To test for Lead add iodide ions (lead iodide), if a yellow precipitate forms, then lead is present. Keep adding until there is no more lead present in the solution. To test for the presence of Calcium, conduct a flame test or add carbonate ions (calcium carbonate), if you conducted a flame test, then you should observe an orange/red flame, if you added carbonate ions, then a white precipitate should form. Sorry I couldn't include equations :)
 

porcupinetree

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re: HSC Chemistry Marathon Archive

a i) Barium
a ii) Add sulfate ions (barium sulfate) until a white precipitate forms, if a precipitate forms, then barium is present.

b) To test for Lead add iodide ions (lead iodide), if a yellow precipitate forms, then lead is present. Keep adding until there is no more lead present in the solution. To test for the presence of Calcium, conduct a flame test or add carbonate ions (calcium carbonate), if you conducted a flame test, then you should observe an orange/red flame, if you added carbonate ions, then a white precipitate should form. Sorry I couldn't include equations :)
Another good one to distinguish between Pb2+ and Ca2+ is to add hydroxide - if a (white) ppt forms, Pb2+ is present, if not, Ca2+ is present
 

porcupinetree

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re: HSC Chemistry Marathon Archive

Next Q:
Explain the optimal conditions for the production of ammonia in the Haber process and hence evaluate the importance of monitoring the reaction vessel for the Haber process (6 marks)
 

Drsoccerball

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re: HSC Chemistry Marathon Archive

a i) Barium
a ii) Add sulfate ions (barium sulfate) until a white precipitate forms, if a precipitate forms, then barium is present.

b) To test for Lead add iodide ions (lead iodide), if a yellow precipitate forms, then lead is present. Keep adding until there is no more lead present in the solution. To test for the presence of Calcium, conduct a flame test or add carbonate ions (calcium carbonate), if you conducted a flame test, then you should observe an orange/red flame, if you added carbonate ions, then a white precipitate should form. Sorry I couldn't include equations :)
Potasium iodide not lead iodide....
-------------------------------------------------------
How does one poison a catalyst ?
 

Drsoccerball

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re: HSC Chemistry Marathon Archive

Next Q:
Explain the optimal conditions for the production of ammonia in the Haber process and hence evaluate the importance of monitoring the reaction vessel for the Haber process (6 marks)
This questions been asked so many times look up for solutions
 

rand_althor

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How does one poison a catalyst ?
I think it refers to contaminants preventing the catalyst from functioning optimally. For the Haber process, the iron oxide catalyst uses adsorption. If the reaction vessel is contaminated, the catalyst cannot work properly as the reactants cannot interact with the catalyst to produce the products.

Not sure what reaction is happening in this picture, but it looks to be the same concept.
 
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Ekman

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re: HSC Chemistry Marathon Archive

Potasium iodide not lead iodide....
-------------------------------------------------------
How does one poison a catalyst ?
Actually it is lead iodide that forms a bright canary yellow, potassium iodide shouldn't form a precipitate, as potassium is a group 1 element.
 

Drsoccerball

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Actually it is lead iodide that forms a bright canary yellow, potassium iodide shouldn't form a precipitate, as potassium is a group 1 element.
You mix potassium iodide in the solution and if it turns yellow it confirms lead precipitate.
 

Drsoccerball

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I think it refers to contaminants preventing the catalyst from functioning optimally. For the Haber process, the iron oxide catalyst uses adsorption. If the reaction vessel is contaminated, the catalyst cannot work properly as the reactants cannot interact with the catalyst to produce the products.

Not sure what reaction is happening in this picture, but it looks to be the same concept.
Poisoning refers to heating im pretty sure youre talking about contamination
 

Ekman

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You mix potassium iodide in the solution and if it turns yellow it confirms lead precipitate.
But he didn't say add lead iodide, nor did he say add potassium iodide. All he said was add iodide ions, which is enough as he is just explaining the process of identification of lead ions in solution.
 

Drsoccerball

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re: HSC Chemistry Marathon Archive

a i) Barium
a ii) Add sulfate ions (barium sulfate) until a white precipitate forms, if a precipitate forms, then barium is present.

b) To test for Lead add iodide ions (lead iodide), if a yellow precipitate forms, then lead is present. Keep adding until there is no more lead present in the solution. To test for the presence of Calcium, conduct a flame test or add carbonate ions (calcium carbonate), if you conducted a flame test, then you should observe an orange/red flame, if you added carbonate ions, then a white precipitate should form. Sorry I couldn't include equations :)
This wouldnt get him the marks
 

Ekman

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re: HSC Chemistry Marathon Archive

This wouldnt get him the marks
He just put the brackets in to show the product forming... He did the same thing for the previous part with barium sulphate.

I am pretty sure no hsc marker will identify iodide ions as lead iodide...
 

Drsoccerball

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re: HSC Chemistry Marathon Archive

He just put the brackets in to show the product forming... He did the same thing for the previous part with barium sulphate.

I am pretty sure no hsc marker will identify iodide ions as lead iodide...
By saying iodide ions you're asserting that i can use any other ion with it in the reaction
 

Ekman

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By saying iodide ions you're asserting that i can use any other ion with it in the reaction
Yes you can. You can use potassium iodide, ammonium iodide, sodium iodide.
 

Ekman

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Can i add silver iodide ?
Lol why would you add a precipitate to cause another precipitate. If you are going to cause a precipitation, you wouldn't add another precipitate as nothing will occur, that's a no-brainer...

By saying adding iodide ions to cause a precipitate, you are automatically removing other precipitate combinations such as silver iodide or mercury iodide.
 

Drsoccerball

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Lol why would you add a precipitate to cause another precipitate. If you are going to cause a precipitation, you wouldn't add another precipitate, that's a no-brainer...
well you said you can add anything.
 
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