HSC 2012-2015 Chemistry Marathon (archive) (4 Viewers)

[Ekman]

re: HSC Chemistry Marathon Archive

well you said you can add anything.

I didn't say that you should add anything. I just said you can generalise the process of precipitating out the lead by saying "through the addition of iodide ions". Also you should be sensible with your answers as BOSTES doesn't have a sense of humour.

 

[rand_althor]

re: HSC Chemistry Marathon Archive

Poisoning refers to heating im pretty sure youre talking about contamination

After visiting various websites, I think it refers to what I said.

http://www.essentialchemicalindustry.org/processes/catalysis-in-industry.html

"Many catalysts are prone to poisoning which occurs when an impurity attaches itself to the surface of the catalyst and prevents adsorption of the reactants."

https://en.wikipedia.org/wiki/Catalyst_poisoning#Poisoning_Process

"Poisoning involves compounds which bonds chemically to the active surface sites of a catalyst. This may have two effects: the total number of catalytic sites or the fraction of the total surface area that has the capability of promoting reaction always decreases..."

https://goo.gl/jMhGIC

"In most of the cases, the poisoning of catalyst is due to preferential adsorption of the poisoning material (as impurity) on the active centres of the catalyst surface, thus preventing the reactant species from approaching the catalyst surface"

 

[porcupinetree]

re: HSC Chemistry Marathon Archive

Next Q - 2007 HSC Q19

There are many benefits and problems associated with the use of radioisotopes in industry and medicine.
Evaluate the impact on society of the use of radioisotopes in both industry and medicine. In your answer, give specific examples of radioisotopes making reference to their chemical properties. 7 marks

 

[leehuan]

re: HSC Chemistry Marathon Archive

Cobalt-60 is a radioisotope used in industry, typically to detect faults and cracks in metals. It is chosen due to its relatively long half-life of 5.3 years as well as typically emitting low energy radiation. Cobalt-60 decays into Nickel-60 and emits beta particles and gamma radiation (normally I would put an equation here). Photographic film is used to reveal the gamma radiation, and it is possible to deduce regions where there are cracks by the darker appearance of regions the film. Generally, this radioisotope is highly advantageous as the mentioned properties show that it does not have to be frequently replaced or maintained, and it is also safe to use without the person being harmed severely. It is important to note that nonetheless, gamma rays are emitted, and due to their strong penetrating power, there is still some damage to the user's health.
Technetium-99m, produced easily from bombarding neutrons with a molybdenum-99 molecule, is a radioisotope used in industry, generally to reveal cancers and tumours etc. which prose a problem to health. Technetium-99m emits a gamma ray to decay into the stable technetium-99, which is not absorbed by the body. Properties of this radioisotope are its short half-life of 6 hours, the fact that it also emits low energy radiation and that it readily sticks to specifiable bodily compounds. This allows the radioisotope to travel directly to where health problems are, and it is unable to pose significant tissue damage to the patient. Photographic film can once again be used, and depending on how many gamma rays are detected, it is possible to identify and thus tag the region that the patient may need to undergo surgery for.
In both cases, the primary problem is essentially that the person will always be affected by radiation to varying extents. However, the gain resulted from the useful properties of these radioisotopes evidently outweigh this single problem, and these radioisotopes have been well used in society today.


Edit: Oh dear that was too long.

 

[leehuan]

re: HSC Chemistry Marathon Archive

(a) Explain why refluxing is a suitable means of preparing an ester. (3)
(b) Name the catalyst used. (1)
(c) Give a method to how this experiment should be performed. (5)
(d) Sometimes, it helps to wash the ester with Na2CO3 or NaHCO3. Why is this the case? (2)

 

[Crisium]

re: HSC Chemistry Marathon Archive

Cobalt-60 is a radioisotope used in industry, typically to detect faults and cracks in metals. It is chosen due to its relatively long half-life of 5.3 years as well as typically emitting low energy radiation. Cobalt-60 decays into Nickel-60 and emits beta particles and gamma radiation (normally I would put an equation here). Photographic film is used to reveal the gamma radiation, and it is possible to deduce regions where there are cracks by the darker appearance of regions the film. Generally, this radioisotope is highly advantageous as the mentioned properties show that it does not have to be frequently replaced or maintained, and it is also safe to use without the person being harmed severely. It is important to note that nonetheless, gamma rays are emitted, and due to their strong penetrating power, there is still some damage to the user's health.
Technetium-99m, produced easily from bombarding neutrons with a molybdenum-99 molecule, is a radioisotope used in industry, generally to reveal cancers and tumours etc. which prose a problem to health. Technetium-99m emits a gamma ray to decay into the stable technetium-99, which is not absorbed by the body. Properties of this radioisotope are its short half-life of 6 hours, the fact that it also emits low energy radiation and that it readily sticks to specifiable bodily compounds. This allows the radioisotope to travel directly to where health problems are, and it is unable to pose significant tissue damage to the patient. Photographic film can once again be used, and depending on how many gamma rays are detected, it is possible to identify and thus tag the region that the patient may need to undergo surgery for.
In both cases, the primary problem is essentially that the person will always be affected by radiation to varying extents. However, the gain resulted from the useful properties of these radioisotopes evidently outweigh this single problem, and these radioisotopes have been well used in society today.


Edit: Oh dear that was too long.

It's not that long for a 7 marks

Your response had a good structure

A lot of people tend to leave out a final/overall evaluation statement, but you included it

However, I do believe you are lacking in information for the first paragraph

I find with chemistry that you get deducted marks for lack of specificity and I noticed that you were being really general in regards to the effects that Cobalt-60 has on society (Try stating specific implications of it being used to detect defaults (I assume you mean in thickness gauges when measuring the thickness of certain materials?), and how this impacts society in both a detrimental and beneficial manner)

Sorry if this sounds harsh in any way, shape or form :/

 

[rand_althor]

re: HSC Chemistry Marathon Archive

... typically emitting low energy radiation. Cobalt-60 decays into Nickel-60 and emits beta particles and gamma radiation

Contradictory as gamma radiation has a high energy.

Photographic film is used to reveal the gamma radiation

I think it's a gamma camera. Photographic film seems impractical, especially if it's a long pipe or something.

Generally, this radioisotope is highly advantageous as the mentioned properties show that it does not have to be frequently replaced or maintained

You should go on to say that it reduces labour costs or something similar (impact on society).

... and it is also safe to use without the person being harmed severely. It is important to note that nonetheless, gamma rays are emitted, and due to their strong penetrating power, there is still some damage to the user's health.

Perhaps stick to one side - detrimental to health or not that harmful. If you choose to go with having a negative health impact, expand on this and relate it to an impact on society. E.g. excessive exposure to radiation results in increased cases of cancer, resulting in a greater strain on the healthcare system.

Technetium-99m, produced easily from bombarding neutrons with a molybdenum-99 molecule, is a radioisotope used in industry

Should be medicine.

generally to reveal cancers and tumours etc. which prose a problem to health

Mention how it allows for earlier detection of health issues, allowing for earlier diagnosis and treatment of problems. This results in a lower strain on the healthcare system.

Properties of this radioisotope are ... that it readily sticks to specifiable bodily compounds.

What do you mean by this?

Photographic film can once again be used

I think you actually use a gamma camera for this.

Also, as it is 7 marks, you should probably include one more radioisotope.

 

[Librah]

re: HSC Chemistry Marathon Archive

No1 wants to hear yer life stories, just make a short table with the isotope, type of decay/problems/benefits/impacts on society. You can include evaluation in your table or just sum it up somewhere.

 

[trumanblack]

re: HSC Chemistry Marathon Archive

I was doing a trial paper and then when I reached the end I realised that I didn't have any solutions......
Due to this, can someone please do the following question(s)? Not too confident with my answers and reasoning. Thanks!

 

[Crisium]

re: HSC Chemistry Marathon Archive

I was doing a trial paper and then when I reached the end I realised that I didn't have any solutions......
Due to this, can someone please do the following question(s)? Not too confident with my answers and reasoning. Thanks!
View attachment 32185

For A you want to find the equation where it is not an oxidising agent or reducing agent

So you immediately draw to the conclusion that it is not involved in the reaction

Drawing the net ionic equation for all three and see where water is eliminated (as it is the spectator)

Alternatively you can refer to oxidation states on either side of the equation and show that it is being neither oxidised nor reduced

For B

An oxidising agent is a substance that brings about oxidisation in another substance, but is itself reduced.

Look and see where water is being reduced

It would help again if you could write a net ionic equation to eliminate the spectator ions

 

[leehuan]

re: HSC Chemistry Marathon Archive

-suggestions-

Most of the points taken immediately. Thanks for providing them. Especially that "industry" mistake, whoops.

I'm not sure how to describe the adhesive nature of the radioisotope. That was never properly clarified for me. And I actually don't know what a gamma camera is, I have literally never heard of that term before.
Energy was a mistake for the Co-60 part. I realise I should've stated relatively low emission of radiation.

And I definitely had no clue that if they give you 12 lines of writing space you could draw a table. But if that's true I'm taking the idea on board.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

(a) Explain why refluxing is a suitable means of preparing an ester. (3)
(b) Name the catalyst used. (1)
(c) Give a method to how this experiment should be performed. (5)
(d) Sometimes, it helps to wash the ester with Na2CO3 or NaHCO3. Why is this the case? (2)

a) Refluxing is a suitable means of preparing an ester since the flask has toxic and hazardous chemicals such as acids. If heated without reflux the toxic chemicals would form a mist in the atmosphere which is very harmful. This also ensure that no mass is lost. Esterification at room temperature is a Very slow process therefore through reflux we are able to heat the mixture to higher temperatures in turn increasing reaction rate safely.
b) Concentrated
c)*Draws reflux apparatus*
1) Set up as above.
2)Let chemicals heat under reflux for 40 minutes
3) Filter out mixture to obtain the ester
Safety:
Using reflux
Since chemicals are corrosive wear safety jacket, safety goggles and gloves.
Be careful after ester is formed to wait till it cools before filtration
d)Sometimes an excess of sulfuric acid is added and is not completely used up. Therefore the ester has traces of sulfuric acid. Therefore it is washed in a weak base such as Na2CO3 or NaHCO3.

 

[Ekman]

re: HSC Chemistry Marathon Archive

a) Refluxing is a suitable means of preparing an ester since the flask has toxic and hazardous chemicals such as acids. If heated without reflux the toxic chemicals would form a mist in the atmosphere which is very harmful. This also ensure that no mass is lost. Esterification at room temperature is a Very slow process therefore through reflux we are able to heat the mixture to higher temperatures in turn increasing reaction rate safely.
b) Concentrated
c)*Draws reflux apparatus*
1) Set up as above.
2)Let chemicals heat under reflux for 40 minutes
3) Filter out mixture to obtain the ester
Safety:
Using reflux
Since chemicals are corrosive wear safety jacket, safety goggles and gloves.
Be careful after ester is formed to wait till it cools before filtration
d)Sometimes an excess of sulfuric acid is added and is not completely used up. Therefore the ester has traces of sulfuric acid. Therefore it is washed in a weak base such as Na2CO3 or NaHCO3.

You are describing the purpose of a cooling jacket here, not the purpose of refluxing.

 

[Crisium]

re: HSC Chemistry Marathon Archive

Contradictory as gamma radiation has a high energy.


I think it's a gamma camera. Photographic film seems impractical, especially if it's a long pipe or something.


You should go on to say that it reduces labour costs or something similar (impact on society).


Perhaps stick to one side - detrimental to health or not that harmful. If you choose to go with having a negative health impact, expand on this and relate it to an impact on society. E.g. excessive exposure to radiation results in increased cases of cancer, resulting in a greater strain on the healthcare system.


Should be medicine.


Mention how it allows for earlier detection of health issues, allowing for earlier diagnosis and treatment of problems. This results in a lower strain on the healthcare system.


What do you mean by this?


I think you actually use a gamma camera for this.

Also, as it is 7 marks, you should probably include one more radioisotope.

"What do you mean by this?"

I think he's referring to Technitium-99m being used as a radio-pharmaceutical - It can label certain molecules in the body such as iodine and it then accumulates in the thyroid gland. Through using PET this can be viewed through a gamma camera and abnormal colours will usually indicate a problem such as a lack of thyroxine or goitre, etc. Talk about the benefits of early diagnosis and perhaps make reference to how the harmful radiation may cause further damage to your body

"You should probably include one more isotope"

I think it would suffice to refer to one isotope for the medical applications (3 marks) and one isotope for the industrial applications (3 marks) and the final mark should be awarded for that overall evaluation.

"Stick to one side"

Nah I think it's good to make reference to both the detrimental and beneficial, but you should focus on one of them and provide a mini-evaluation in regards to whether the benefits out-weigh the detriments, vice versa.

"Photographic film"

I believe they do use it frequently in industry so it was fine putting it there, but for medicine I think they use other means

 

[SilentWaters]

re: HSC Chemistry Marathon Archive

View attachment 32185

Work out the oxidation number/state of each element in redox pairs concerning water, for each reaction. Note that oxygen retains an OS of 2- unless it's in a peroxide, whilst hydrogen retains an OS of 1+ unless it's in a metal hydride. Additionally, pure elements have a zero oxidation state.

Oxidising agents undergo reduction, whilst reducing agents undergo oxidation.

Using these rules, we can see that in reaction:
(1) the OS of H changes from 1+ to 0 (reduction), making water the oxidising agent
(2) the OS of O and H do not change in OH-, so water is neither oxidising nor reducing agent
(3) the OS of O changes from 2- to 0 (oxidation), making water the reducing agent

EDIT: That '3' on your bicarbonate should be subscript.

 

[Crisium]

re: HSC Chemistry Marathon Archive

Most of the points taken immediately. Thanks for providing them. Especially that "industry" mistake, whoops.

I'm not sure how to describe the adhesive nature of the radioisotope. That was never properly clarified for me. And I actually don't know what a gamma camera is, I have literally never heard of that term before.
Energy was a mistake for the Co-60 part. I realise I should've stated relatively low emission of radiation.

And I definitely had no clue that if they give you 12 lines of writing space you could draw a table. But if that's true I'm taking the idea on board.

Since it decays to emit gamma radiation this can basically be picked up by a gamma camera and shown on a screen.

 

[Speed6]

re: HSC Chemistry Marathon Archive

New Question:

Referring to oxidation-reduction reactions, explain the structure AND chemistry of either dry-cell OR lead-acid cell.

3

 

[rand_althor]

re: HSC Chemistry Marathon Archive

"You should probably include one more isotope"

I think it would suffice to refer to one isotope for the medical applications (3 marks) and one isotope for the industrial applications (3 marks) and the final mark should be awarded for that overall evaluation.

I only said that because a similar question was in a trial paper from my school and the marking criteria specified that you need 3 radioisotopes. However, I suppose you are correct as long as the answer has sufficient depth.

"Photographic film"

I believe they do use it frequently in industry so it was fine putting it there, but for medicine I think they use other means

Oh okay, thanks for mentioning that. I was unaware they did so.

 

[Drsoccerball]

re: HSC Chemistry Marathon Archive

You are describing the purpose of a cooling jacket here, not the purpose of refluxing.

Its all apart of the apparatus.

 

[Crisium]

re: HSC Chemistry Marathon Archive

I only said that because a similar question was in a trial paper from my school and the marking criteria specified that you need 3 radioisotopes. However, I suppose you are correct as long as the answer has sufficient depth.

Oh okay, thanks for mentioning that. I was unaware they did so.

Yeah if leehuan had more depth and specificity with his answer I could see him getting those 7 marks

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