HSC 2012-2015 Chemistry Marathon (archive) (9 Viewers)

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Menomaths

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re: HSC Chemistry Marathon Archive

2)Describe how to quantitatively measure the amounts of nitrates and phosphates

Is it by measuring dissolved oxygen and biochemical oxygen demand? Or is that for eutrophication? Or am I completely off?
Are you trying to answer my question....?






(If you are, you're waaaaaaay off lol)
 

rednellav

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re: HSC Chemistry Marathon Archive

Are you trying to answer my question....?


(If you are, you're waaaaaaay off lol)
Just started re-studying chem tonight after business. Ease me in with a few moderate questions (not too hard)? <3
 

rednellav

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re: HSC Chemistry Marathon Archive

I'll give one that I'm looking over now.

Describe 3 processes used to purify and sanitize mass water-supplies.
 

bedpotato

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re: HSC Chemistry Marathon Archive

Just started re-studying chem tonight after business. Ease me in with a few moderate questions (not too hard)? <3
Explain why models are useful in chemistry. [2]

Are you trying to answer my question....?






(If you are, you're waaaaaaay off lol)
lol guess I really do know nothing from module 3.
 

Menomaths

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re: HSC Chemistry Marathon Archive

A wild-question appears

Wild-question used content that im not rote learning

its super effective!

rote learning student fainted
Hahahaha
Explain why models are useful in chemistry. [2]



lol guess I really do know nothing from module 3.
Yeah, I only learnt this today after HeroicPanda Skyped me the question haha.
 

hamstar

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Explain why models are useful in chemistry. [2]
Isn't that from last year's exam paper. It is highly unlikely they will ask that question this year.
But you never know, there is no harm in practicing.
 

mahmoudali

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re: HSC Chemistry Marathon Archive

Magnetite- provides a favourable surface for the reaction in the Haber Process
Sulfuric Acid- Good dehydrating agent so used in Esterification
since when was sulfuric acid (dehydrating agent) considered a catalyst?
 

superSAIyan2

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^its considered a catalyst since it lowers the activation energy in esterification and hence increases rate of reaction.

However it is also a dehydrating agent and removes water from the system to drive the equilibrium to favour ester yield. But this is not the reason why its considered a catalyst
 

bibi34

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re: HSC Chemistry Marathon Archive

outline the role of a chemist employed in a named industry or enterprise, identifying the branch of chemistry undertaken by the chemist and explaining a chemical principle that the chemist uses
 

someth1ng

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Ethane and ethene have similar physical proeprties as they are both non-polar hydrocarbons with similar molecular mass. They have similar MP/BP, both are water insoluble and cannot conduct electricity
However their chemical properties differ greatly due to their functional groups. Ethane is saturated and relatively unreactive whereas unsaturated ethene is highly reactive due to the presence of the C=C double bond, which is a site of high electron density. This allows ethene to participate in addition reactions by opening up the double bond.

Question: Assess current developments in the use of biopolymers. 5M or Explain how O2 and O3 have different physical and chemical properties despite both being allotropes of oxygen. 4m
Clearly state that ethane does not have a double bond.
 

AnimeX

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Q: Compare the chemical and physical properties of ethane and ethene 3 marks
ethane (C2H6) is a gas with a single bond between the carbons, it is considered saturated and cannot undergo addition reactions due to this property. ethane has a lower BP than ethene due to smaller amounts of dispersion forces (is this right??)
ethene (C2H4) is also a gas, but with a double bond in between the carbons, this double bond is highly reactive and is a reactant for many commerical polymers such as polyethylene, polystyrene and PVC.

Here's some questions for the rote learners:

1)Describe how to qualitatively check for the presence of nitrates and phosphates

2)Describe how to quantitatively measure the amounts of nitrates and phosphates
1) lol i've got no idea for this one but I'll try:
add Fe3+, filtrate (assuming no ppt), add Fe2+, filtrate (if there is a green ppt present, PO4 (3-) is present, add Ba2+, filtrate (assuming no ppt), add Pb2+,filtrate (assuming no ppt), if nothing else ppts except the green ppt from Fe2+ the nitrate could be in the solution.

2)phosphates: precipitate with Fe2+, filter, weigh the mass of ppt, multiple molecular mass of phosphate by mass of the ppt, divide by molar mass of precipitate, multiply by 100
nitrates: no idea..

[can someone explain where i went wrong/right here]?
edit: nitrates identification isn't in the syllabus is it?
 
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Menomaths

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Here's some questions for the rote learners:

1)Describe how to qualitatively check for the presence of nitrates and phosphates

2)Describe how to quantitatively measure the amounts of nitrates and phosphates
Since not many people know the second part (a few don't know the first part) I'll post my solutions. By no means is it the perfect answer, it's just my answer (which is usually incorrect)

1)Qualitative test for phosphate: The presence of phosphate is indicated by a yellow ppt with ammonium molybdate
Qualitative test of nitrate: The presence of nitrate is indicated by the Brown Ring Test where FeSO4 is added to a water sample then concentrated sulfuric acid. If a brown ring forms at the junction, nitrate is present.

2)Quantitative test for phosphate: A sample of the water is mixed with ammonium molybdate and Vitaman C (ascorbic acid) which produces an intense blue colour. This colour can be compared against known standard solutions to come up with an approximation.
Quantitative test of nitrate: Nitrate ions are reacted with a reductant to form nitrite ions. These nitrite ions react with colour reagents to produce pink/purple dye which is compared against known standards.
 

Menomaths

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ethane (C2H6) is a gas with a single bond between the carbons, it is considered saturated and cannot undergo addition reactions due to this property. ethane has a lower BP than ethene due to smaller amounts of dispersion forces (is this right??)
ethene (C2H4) is also a gas, but with a double bond in between the carbons, this double bond is highly reactive and is a reactant for many commerical polymers such as polyethylene, polystyrene and PVC.



1) lol i've got no idea for this one but I'll try:
add Fe3+, filtrate (assuming no ppt), add Fe2+, filtrate (if there is a green ppt present, PO4 (3-) is present, add Ba2+, filtrate (assuming no ppt), add Pb2+,filtrate (assuming no ppt), if nothing else ppts except the green ppt from Fe2+ the nitrate could be in the solution.

2)phosphates: precipitate with Fe2+, filter, weigh the mass of ppt, multiple molecular mass of phosphate by mass of the ppt, divide by molar mass of precipitate, multiply by 100
nitrates: no idea..

[can someone explain where i went wrong/right here]?
edit: nitrates identification isn't in the syllabus is it?
It should be in the syllabus.
The bolded is wrong, alkanes have a HIGHER bp/mp then corresponding alkenes as they higher electron density
The underlined bit can be incorrect, you must state at room temperature
 

bangladesh

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Since not many people know the second part (a few don't know the first part) I'll post my solutions. By no means is it the perfect answer, it's just my answer (which is usually incorrect)

1)Qualitative test for phosphate: The presence of phosphate is indicated by a yellow ppt with ammonium molybdate
Qualitative test of nitrate: The presence of nitrate is indicated by the Brown Ring Test where FeSO4 is added to a water sample then concentrated sulfuric acid. If a brown ring forms at the junction, nitrate is present.

2)Quantitative test for phosphate: A sample of the water is mixed with ammonium molybdate and Vitaman C (ascorbic acid) which produces an intense blue colour. This colour can be compared against known standard solutions to come up with an approximation.
Quantitative test of nitrate: Nitrate ions are reacted with a reductant to form nitrite ions. These nitrite ions react with colour reagents to produce pink/purple dye which is compared against known standards.

I hardly doubt that the quantitate test of nitrates is in the syllabus. Which dot point is it?
 

Menomaths

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I hardly doubt that the quantitate test of nitrates is in the syllabus. Which dot point is it?
gather, process and present information on the range and chemistry of the tests used to:

identify heavy metal pollution of water
monitor possible eutrophication of waterways

Hmm it looks like you can choose which tests you want, I thought it'd be in the syllabus because it was in my book (well at least you guys learnt a new test :))
 

bedpotato

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gather, process and present information on the range and chemistry of the tests used to:

identify heavy metal pollution of water
monitor possible eutrophication of waterways

Hmm it looks like you can choose which tests you want, I thought it'd be in the syllabus because it was in my book (well at least you guys learnt a new test :))
I used the tests for BOD and DO for this. Is that wrong...?
 

Menomaths

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I used the tests for BOD and DO for this. Is that wrong...?
No idea tbh

edit: For heavy metals I did the sulfide test(qualitative) and for eutrophication I did the two tests mentioned above
 
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