HSC 2012-2015 Chemistry Marathon (archive) (6 Viewers)

[someth1ng]

re: HSC Chemistry Marathon Archive

Please remain on topic.

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

sorry. Back on topic.
Describe the structure of cellulose and identify it as an example of a condensation polymer found
as a major component of biomass.

-Alternating flipped beta-glucose molecules linked by glycosidic bonding (C-O-C)
-Presence of hydroxy groups existing along the cellulose chains allow the formation of hydrogen bonds with adjacent chains->can align more closely->high strength
-Biomass is material produced by biomass, cellulose is the most abundant polymer on earth and is the main component of biomass as it comprises plant cell walls

ok tbh, i have trouble applying knowledge on questions lol

 

[deswa1]

re: HSC Chemistry Marathon Archive

^I don't like that tbh. The easiest way to answer that question would be to actually DRAW cellulose, and then comment on its structure. Deal systematically with it-> like comment on what it's made up of (carbon-carbon chains etc), then go into its bonding or whatever. Although what you've said is correct, it is hard to follow.

 

[madharris]

re: HSC Chemistry Marathon Archive

-Alternating flipped beta-glucose molecules linked by glycosidic bonding (C-O-C)
-Presence of hydroxy groups existing along the cellulose chains allow the formation of hydrogen bonds with adjacent chains->can align more closely->high strength



-Biomass is material produced by biomass, cellulose is the most abundant polymer on earth and is the main component of biomass as it comprises plant cell walls

ok tbh, i have trouble applying knowledge on questions lol

You haven't mentioned at all anything about how it's an example of a condensation polymer or even what a condensation polymer is

You obviously know your stuff but if you're having trouble answering questions.I suggest you read and highlight import points to break down the question so you know what it's asking you to do. It wouldn't hurt to plan questions as well, especially 4+ markers.
You also need to learn the hsc verbs e.g. Describe, identify, explain

 

[epz]

re: HSC Chemistry Marathon Archive

Name two radioactive isotopes, one that is commonly used in the industry and one that is used in medicine. Discuss their impact to the environment. Include chemical formulas when naming.

 

[HeroicPandas]

re: HSC Chemistry Marathon Archive

^I don't like that tbh. The easiest way to answer that question would be to actually DRAW cellulose, and then comment on its structure. Deal systematically with it-> like comment on what it's made up of (carbon-carbon chains etc), then go into its bonding or whatever. Although what you've said is correct, it is hard to follow.

You haven't mentioned at all anything about how it's an example of a condensation polymer or even what a condensation polymer is

You obviously know your stuff but if you're having trouble answering questions.I suggest you read and highlight import points to break down the question so you know what it's asking you to do. It wouldn't hurt to plan questions as well, especially 4+ markers.
You also need to learn the hsc verbs e.g. Describe, identify, explain

ok thanks for the tips

 

[Eg155]

re: HSC Chemistry Marathon Archive

I found this one today. Thought it was pretty good as it draws on prelim content as well as HSC.

Explain the trends in boiling points shown in the graph (4 marks)


This is my rough answer from what I can think of now, but I would draw an example of each molecule to show & explain diagrammatically.
Something like: Alkanols have one lone pair of electrons on 1 O atom (strong intermolecular forces: Hydrogen bonding accounting for the high BP).
Alkanoic acids--> 1 lone pair of electrons on each of O atom (2 O atoms)= stronger hydrogen bonding than Alkanols- stronger hydrogen bonds accounting for this molecular group to the the highest BP.
Low BP of alkanes because of weak London dispersion forces ...
Increasing molecular mass= increasing carbon chain lengths ->strengthened dispersion forces of molecules in each group accounts for the ^ BP trend for each alkanoic acids, alkanols and alkanes.

Sorry, not concise. Someone explain better

 

[darkfenrir]

re: HSC Chemistry Marathon Archive

Name two radioactive isotopes, one that is commonly used in the industry and one that is used in medicine. Discuss their impact to the environment. Include chemical formulas when naming.

Sodium 24 used in evironmental management and assessing oil leakages and blocks in pipes
Technetium 99 used in medicine to detect blood clots and constriction etc

I forgot benefits/drawbacks of sodium 24, technetium has short half life of 6hrs and low gamma energy emitting it is, meaning little harm to patient. But it can also make patient radioactive for a period of time.

BLEH

 

[nightweaver066]

re: HSC Chemistry Marathon Archive

I found this one today. Thought it was pretty good as it draws on prelim content as well as HSC.

Explain the trends in boiling points shown in the graph (4 marks)
View attachment 27307

This is my rough answer from what I can think of now, but I would draw an example of each molecule to show & explain diagrammatically.
Something like: Alkanols have one lone pair of electrons on 1 O atom (strong intermolecular forces: Hydrogen bonding accounting for the high BP).
Alkanoic acids--> 1 lone pair of electrons on each of O atom (2 O atoms)= stronger hydrogen bonding than Alkanols- stronger hydrogen bonds accounting for this molecular group to the the highest BP.
Low BP of alkanes because of weak London dispersion forces ...
Increasing molecular mass= increasing carbon chain lengths ->strengthened dispersion forces of molecules in each group accounts for the ^ BP trend for each alkanoic acids, alkanols and alkanes.

Sorry, not concise. Someone explain better

Your explanations for the intermolecular forces with alkanoic acids, alkanols and alkanes isn't clear.

The last part about increasing molecular mass etc. is fine though. (just add that boiling point depends on the strength of IMF and put it all in to sentences)

 

[Eg155]

re: HSC Chemistry Marathon Archive

Your explanations for the intermolecular forces with alkanoic acids, alkanols and alkanes isn't clear.

The last part about increasing molecular mass etc. is fine though. (just add that boiling point depends on the strength of IMF and put it all in to sentences)

Thanks I wrote it out properly on paper, I'll type it properly soon for critique.

 

[deswa1]

re: HSC Chemistry Marathon Archive

Next question: Describe how you would coat an iron spoon with gold.

 

[nightweaver066]

re: HSC Chemistry Marathon Archive

Next question: Describe how you would coat an iron spoon with gold.

Haha nice question :L

 

[darkfenrir]

re: HSC Chemistry Marathon Archive

Haha nice question :L

dont u use electroplating or something like that?

 

[nightweaver066]

re: HSC Chemistry Marathon Archive

Next question: Describe how you would coat an iron spoon with gold.

Variation: Describe how you would coat a gold spoon with iron.

 

[theind1996]

re: HSC Chemistry Marathon Archive

Next question: Describe how you would coat an iron spoon with gold.

I'm thinking of gold being extremely unreactive as a REASON for the coating. Not sure about the process... hmm..

 

[Eg155]

re: HSC Chemistry Marathon Archive

Next question: Describe how you would coat an iron spoon with gold.

ah that oxidation resistance thing i think. Au coated Fe nanoparticles are used in the biotechnology sect.

Dunno how you would do it.

 

[deswa1]

re: HSC Chemistry Marathon Archive

Ok while you guys are thinking about that, here's another one:

The measured potential difference of a galvanic cell was different to its theoretical potential difference. What could have caused this difference (assume everything is pure- like an impure liquid isn't a valid answer)

 

[Eg155]

re: HSC Chemistry Marathon Archive

I found this one today. Thought it was pretty good as it draws on prelim content as well as HSC.

Explain the trends in boiling points shown in the graph (4 marks)
View attachment 27307

This is my rough answer from what I can think of now, but I would draw an example of each molecule to show & explain diagrammatically.
Something like: Alkanols have one lone pair of electrons on 1 O atom (strong intermolecular forces: Hydrogen bonding accounting for the high BP).
Alkanoic acids--> 1 lone pair of electrons on each of O atom (2 O atoms)= stronger hydrogen bonding than Alkanols- stronger hydrogen bonds accounting for this molecular group to the the highest BP.
Low BP of alkanes because of weak London dispersion forces ...
Increasing molecular mass= increasing carbon chain lengths ->strengthened dispersion forces of molecules in each group accounts for the ^ BP trend for each alkanoic acids, alkanols and alkanes.

Sorry, not concise. Someone explain better

Edit: Adding to the above.
Trend one:
Bp rises with increasing molecular mass. The MM is increasing due to increasing Carbon chain length. In turn, the BP rises because of ^ dispersion forces- temporarily induced polarity within the non-poplar molecules. This increased length --> increasing dispersion forces and thus more energy needed to break the intermolecular forces.

Trend 2:
Alkanoic acids have a higher BP than alkanols, which also have higher BPs than corresponding alkanes; alkanes having only dispersion forces involved is an attributable factor to this.
The other series have dispersion forces and dipole-dipole interactions. The dipole-dipole (2nd strongest intermolecular force) are greater in alkanoic acids than in alkanols, accounting for the greater BPs of this series.
In alkanoic acids and alkanols there Hydrogen bonding, the strongest of the intermolecular forces, holds the covalently bonded moleucles in structure more tightly than due to the strong force- making the intermolualar forces (all 3 involved, esp. H bonding) to be broken; this accounting for the significantly higher BPs of these two series.

The Hydrogen bonding is more marked in alkanoic acids because of the two O atoms and hence the 2 lone pairs of electrons present in the -COOH group in comparison to only the 1 O atom w/ 1 lone pair of electrons in the -OH alkanol group. The Hydrogen bonding is the strongest acting in the Alkanoic acid molecules thus the series has the highest BPs of the 3 shown in the graph.

 

[Eg155]

re: HSC Chemistry Marathon Archive

Ok while you guys are thinking about that, here's another one:

The measured potential difference of a galvanic cell was different to its theoretical potential difference. What could have caused this difference (assume everything is pure- like an impure liquid isn't a valid answer)

- Oxidation/corrosion on the surface of the electrodes--> decreasing the EMF
- Incorrectly calibrated laboratory equipment (voltmeter in this case)--> above/below theoretical values.

 

[Immortalp00n]

re: HSC Chemistry Marathon Archive

Ok while you guys are thinking about that, here's another one:

The measured potential difference of a galvanic cell was different to its theoretical potential difference. What could have caused this difference (assume everything is pure- like an impure liquid isn't a valid answer)

- differences in surfaces area of the two electrodes
- differences in concentration of the solution in the respective half cells.