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HSC 2012-2015 Chemistry Marathon (archive) (7 Viewers)

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porcupinetree

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re: HSC Chemistry Marathon Archive

Explain why monitoring the reaction vessel used in the Haber process is crucial and describe the monitoring required (6 marks)
 

Drsoccerball

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Explain why monitoring the reaction vessel used in the Haber process is crucial and describe the monitoring required (6 marks)
Covers up the bad joke with a question :L...
The optimal conditions for the production of Ammonia is that of around 300 degrees and around 200 atmospheric pressure.
Le Chatlier's principle states that a change in pressure, concentration or temperature would cause the equilibrium to shift in the direction that minimises the disturbance. An increase in pressure would cause the equilibrium to shift to the side with the least number of moles. Thus as pressure is high the equilibrium shifts to the right increasing the yield of ammonia. However, there is a specific amount of strain the pipes can hold thus the pressure is not increased to high. A decrease in temperature, due to the systems exothermic nature, would cause the equilibrium to shift to the right. However, due to the Kinetic theory this will slow down the rate of reaction and rate of production of Ammonia. Thus in order to get a compromise higher temperature is used. Thus showing that the suitable conditions are around 300 degrees and 200 times AP
Similar question asked before but since this is 6 marks as many people mentioned id mention the Catalyst which needs to be monitored to make sure its providing the surface area needed for the reaction. Also dispensers using perfect mole ratios of hydrogen and nitrogen.
Talk about safety, economic factors and reaction rate and youre done
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Guys i dont get the displacement BS. Elements higher in the activity series displace ones that are lower ? dont understand plz explain :)
 

porcupinetree

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Similar question asked before but since this is 6 marks as many people mentioned id mention the Catalyst which needs to be monitored to make sure its providing the surface area needed for the reaction. Also dispensers using perfect mole ratios of hydrogen and nitrogen.
Talk about safety, economic factors and reaction rate and youre done
----------------------------------------------------------------
Guys i dont get the displacement BS. Elements higher in the activity series displace ones that are lower ? dont understand plz explain :)
Elements higher in the activity series are more reactive; physically, what this means is that the element is more likely to want to give up its valence electrons. In a salt solution, e.g. AgCl, what is actually present in the solution is Ag+ and Cl- ions: the silver has given its one valence electron to chlorine. The element silver has a measurable tendency, or 'desire' to want to do this: this is its reactivity (silver actually has quite a low reactivity: it doesn't mind keeping its valence electron, whereas a element with high reactivity wants to get rid of its valence electron). If we introduce another metal, a more reactive one such as sodium, what we now have in the system is Ag+ and Na (forget the Cl- for the moment). As the sodium is more reactive, it has a greater desire to get rid of its valence electron than silver. There are two possibilities that could happen:
1. Nothing happens: the silver keeps its 1+ charge and sodium keeps its one valence electron which it desperately wants to get rid of, or
2. The sodium gives its valence electron to the silver, which doesn't mind having a valence electron (due to its low reactivity).

Which possibility do you think will happen? In possibility 1, silver is fairly stable; it doesn't really mind whether it has a 1+ charge (or a 0 charge), whereas sodium is very unstable and desperately wants to rid itself of its valence electron. Whereas in possibility 2, both elements are stable: the sodium has given up its valence electron and is thus stable, and silver is stable; it doesn't really mind what charge it has. Hence possibility two will happen, and sodium will 'displace' silver from the solution.

Hopefully that explanation helps. Excuse my extensive personification of elements; obviously silver and sodium aren't sentient beings, but it helps to pretend that they are.
 

Drsoccerball

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re: HSC Chemistry Marathon Archive

Elements higher in the activity series are more reactive; physically, what this means is that the element is more likely to want to give up its valence electrons. In a salt solution, e.g. AgCl, what is actually present in the solution is Ag+ and Cl- ions: the silver has given its one valence electron to chlorine. The element silver has a measurable tendency, or 'desire' to want to do this: this is its reactivity (silver actually has quite a low reactivity: it doesn't mind keeping its valence electron, whereas a element with high reactivity wants to get rid of its valence electron). If we introduce another metal, a more reactive one such as sodium, what we now have in the system is Ag+ and Na (forget the Cl- for the moment). As the sodium is more reactive, it has a greater desire to get rid of its valence electron than silver. There are two possibilities that could happen:
1. Nothing happens: the silver keeps its 1+ charge and sodium keeps its one valence electron which it desperately wants to get rid of, or
2. The sodium gives its valence electron to the silver, which doesn't mind having a valence electron (due to its low reactivity).

Which possibility do you think will happen? In possibility 1, silver is fairly stable; it doesn't really mind whether it has a 1+ charge (or a 0 charge), whereas sodium is very unstable and desperately wants to rid itself of its valence electron. Whereas in possibility 2, both elements are stable: the sodium has given up its valence electron and is thus stable, and silver is stable; it doesn't really mind what charge it has. Hence possibility two will happen, and sodium will 'displace' silver from the solution.

Hopefully that explanation helps. Excuse my extensive personification of elements; obviously silver and sodium aren't sentient beings, but it helps to pretend that they are.


if a metal was dipped inside a solution how would we know if nothing happens or the ions from solution cover the metal?
 

porcupinetree

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if a metal was dipped inside a solution how would we know if nothing happens or the ions from solution cover the metal?
We would begin to see solid silver (in my example) forming; either as a powder in the solution which falls to the bottom, or it may deposit/accumulate on the solid piece of metal that we insert into the solution in the first place (in my example, the silver depositing itself on the solid piece of sodium we put in. Theoretically. In reality, for my example, the sodium would actually react with the water in the solution to form NaOH, but ignore that). The latter usually occurs, from my experience (depositing on the solid piece of metal).
Sometimes a metal will give the solution a particular colour, e.g. copper in copper sulfate solution will make it blue. However if we displace the copper with, say, magnesium (a more reactive metal), the colour will gradually fade as more and more copper atoms gain valence electrons and become solid and more and more magnesium atoms lose their valence electrons.
 

Librah

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We would begin to see solid silver (in my example) forming; either as a powder in the solution which falls to the bottom, or it may deposit/accumulate on the solid piece of metal that we insert into the solution in the first place (in my example, the silver depositing itself on the solid piece of sodium we put in. Theoretically. In reality, for my example, the sodium would actually react with the water in the solution to form NaOH, but ignore that). The latter usually occurs, from my experience (depositing on the solid piece of metal).
Sometimes a metal will give the solution a particular colour, e.g. copper in copper sulfate solution will make it blue. However if we displace the copper with, say, magnesium (a more reactive metal), the colour will gradually fade as more and more copper atoms gain valence electrons and become solid and more and more magnesium atoms lose their valence electrons.
He's asking how your able to predict if a metal ion will displace a metal of another species. If you have Cu2+ in solution and Zn metal, just add the standard reduction potentials of copper reduction and Zn oxidation and see if the reaction will be spontaneous or not.

If your asking why the reduction potentials are why they are, you need to consider a lot of things, e.g. electron density, atomic radius etc.
 

Drsoccerball

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He's asking how your able to predict if a metal ion will displace a metal of another species. If you have Cu2+ in solution and Zn metal, just add the standard reduction potentials of copper reduction and Zn oxidation and see if the reaction will be spontaneous or not.

If your asking why the reduction potentials are why they are, you need to consider a lot of things, e.g. electron density, atomic radius etc.
YES this is my question i cant determine what displaces what D: Can you explain without using words such as displace and all this bs just say shit like:
The one higher on the table when in solution with the lower one on the table causes...
 

Librah

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YES this is my question i cant determine what displaces what D: Can you explain without using words such as displace and all this bs just say shit like:
The one higher on the table when in solution with the lower one on the table causes...
More positive/higher "reduction" potentials means more likely to reduce (gain electrons). If you have Cu ions in solution, it has a higher reduction potential than Zn(s), which intuitively means that Zn(s) is more likely to oxidise and give up it's electrons. (Zn has lower reduction potential or higher oxidation potential).

If you had Zn ions in solution and a piece of copper metal, nothing will happen. Because you get an overall negative reduction potential when you try to sum up the potentials of Zn2+ +2e- -->>Zn(s) and Cu(s)--> Cu2+ +2e-. So you need to put energy in to drive the reaction, which you can do in a process called electrolysis, which you'll learn if your doing Industrial Chem.

Just think of the words, REDUCTION then POTENTIAL. Potential to reduce, higher reduction potential means it has more potential to reduce. I dunno, I just made that up, you can remember it that way.
 

Drsoccerball

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More positive/higher "reduction" potentials means more likely to reduce (gain electrons). If you have Cu ions in solution, it has a higher reduction potential than Zn(s), which intuitively means that Zn(s) is more likely to oxidise and give up it's electrons. (Zn has lower reduction potential or higher oxidation potential).

If you had Zn ions in solution and a piece of copper metal, nothing will happen. Because you get an overall negative reduction potential when you try to sum up the potentials of Zn2+ +2e- -->>Zn(s) and Cu(s)--> Cu2+ +2e-. So you need to put energy in to drive the reaction, which you can do in a process called electrolysis, which you'll learn if your doing Industrial Chem.

Just think of the words, REDUCTION then POTENTIAL. Potential to reduce, higher reduction potential means it has more potential to reduce. I dunno, I just made that up, you can remember it that way.
So in other words in the activity series if a metal all the way at the top is dipped into a solution all the way from the bottom nothing will happen or would the ions build up on the metal thats being dipped in ?
 

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Explain how the Farsh process can be used to obtain Sulfur. 4 Marks
The Frasch process is the extraction of sulfur and consists of three pipes forced down to the underground sulfur deposits. Superheated steam (which is pressurised to 160 degrees) is inserted into the far right pipe, directly into the sulfur, causing it to melt. Pressurised/compressed air is forced down the far right pipe, which then pushes the molten sulfur and water foam through the middle tube back to the surface. The mixture is then cooled and the sulfur readily separates from the water.

How is this answer? Is there anything I should change?
 

Drsoccerball

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The Frasch process is the extraction of sulfur and consists of three pipes forced down to the underground sulfur deposits. Superheated steam (which is pressurised to 160 degrees) is inserted into the far right pipe, directly into the sulfur, causing it to melt. Pressurised/compressed air is forced down the far right pipe, which then pushes the molten sulfur and water foam through the middle tube back to the surface. The mixture is then cooled and the sulfur readily separates from the water.

How is this answer? Is there anything I should change?
I would mention the emulsion that occurs but other than that sounds legit
Now try this: Why does the frash process need to be monitored and managed? 3 marks
 
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BlueGas

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I would mention the emulsion that occurs but other than that sounds legit
Now try this: Why does the frash process need to be monitored and managed? 3 marks
What's emulsion?

The frasch process needs to be monitored as there are environmental issues such as:
- Sulfur oxidises easily to sulfur dioxide which is a serious air pollutant, and care must be taken to avoid this reaction
- The water used to make superheateed steam cannot be discharged into the environment as it contains contaminants, and will cause thermal pollution do it's intense heat
- Extraction of large amounts of sulfur creates large underground caverns which can possibly collapse upon themselves
 

Drsoccerball

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What's emulsion?

The frasch process needs to be monitored as there are environmental issues such as:
- Sulfur oxidises easily to sulfur dioxide which is a serious air pollutant, and care must be taken to avoid this reaction
- The water used to make superheateed steam cannot be discharged into the environment as it contains contaminants, and will cause thermal pollution do it's intense heat
- Extraction of large amounts of sulfur creates large underground caverns which can possibly collapse upon themselves
Its when to immiscible substances such as sulfur and water mix
 

Drsoccerball

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So how would I word my answer to mention emulsion?
....The superheated temperature causes the sulfur to melt and form an emulsion with water which is easily seperated as it cools down at the surface....
I think that this should be in there somewhere
 

BlueGas

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....The superheated temperature causes the sulfur to melt and form an emulsion with water which is easily seperated as it cools down at the surface....
I think that this should be in there somewhere
Okay sweet, nicely worded.
 

Drsoccerball

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So in other words in the activity series if a metal all the way at the top is dipped into a solution all the way from the bottom nothing will happen or would the ions build up on the metal thats being dipped in ?
BUMP
 

Drsoccerball

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or not...
Justify the use of atomic absorption spectroscopy in the mining industry, and in safeguarding the environment. 5 Marks
 

Kaido

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Where is this mining industry located and what are they mining (and to what extent)?
 

strawberrye

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Where is this mining industry located and what are they mining (and to what extent)?
Usually the question wouldn't give you that much detail-so you can just consider possibilities, i.e. many mines involves extraction of sulfide ores-which can produce acidic residues. Although arguably the original question would have been worded better since 'safeguarding' environment is quite ambiguous, and the main purpose of AAS is a tool, rather than a safeguard in the normal understanding of the word-because it is ultimately up to us, as humans-to decide what we do with the data we gain from AAS-if we do anything about the environment at all.
 
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