Unit 3 Questions MEGATHREAD :)

[thatricksta]

NEAP 2008 has a question which specifies that C4H604 will have an IR band at 1700 which indicates a C=O bond, it then also states that 0.134g dissolved in water is titrated with a standardised 0.106 M NaOH solution. A titre of 21.43 was required to reach the end point.

B) "Does the information provided about experiment 2 allow you to state the functional group present in the compound?

"In experiment 2, the infrared spectrum of the compound was obtained. The spectrum included a band at a
wavenumber of approximately 1700 cm -1 ."

Experiment 2 is only the IR, you're jumping ahead of yourself.

Also, the final question on this exam states

"How would an appropriate wavelength be determined for this analysis?"
This is in respect to an experiment using "spectroscopy" (not specified) and indicates that the compound being tested is "bore water", containing iron (we are determining the concentration of Fe in the bore water), which is first added to ferrozine to form a PURPLE complex. It goes on to suggest "their absorbances were determined in a spectrometer using an appropriate wavelength of light" (which I would assume corresponds to UV-Visible spec??)

NEAP writes its answer as:
A graph of the absorbance versus wavelength for a solution of iron/ferrozine complex would be obtained (1 mark)
The absorbance of maximum wavelength would be chosen (provided that no other component of bore water sample absorbed this wavelength) (1 mark)

ME:
I straight away recognised the complimentary colour yellow and wrote that
Yellow would be used as it is complimentary to purple.

Is my answer OK? Or is it straight up WRONG?
Thank you

Nah, I wouldn't say you'd get the mark either. The important aspect of choosing a wavelength is that it is a) Strong absorbance, and b) No other compounds absorb strongly at this wavelength. As for complimentary colours, although it may absorb strongly, it's not necessarily true that it would be the best.

I thought experiment two was the entire experiment =/

Miss reading the question = fail

Thanks for the help

[jane1234]

Yeah bitch! One of the Companies discretely added the complementary colour and I was LIKE ASJFGASKJGASJKFAJSGAHGSJKG, your screwing with me right? I have to know complementary colours. Lolol. When I did two VCAA Exams, I realized, I didn't need to .

It's assumed knowledge.

From Year 7 art

And yeah, best absorbance is not necessarily the complementary colour, as you have to consider the other components of the solution that may also absorb it. This has tripped me up a fair few times

[nacho]

sorry, but no one answered before:
are we required to know that a nickel catalyst is present in hydrogenation from ethene to ethane?
and do we need to know states of catalysts involved in reaction pathways?

Also, if our reaction pathway is efficient, but a bit longer than the suggested one
eg: ethene to ethane to chloroethane to ethanol
as opposed to ethene to ethanol

would we be marked down?

[luken93]

Yeah, you need to know catalysts for them.

As for the pathway, I assume you can jump straight there, but the majority I've seen have highlighted the pathway, and you have to fill in the spaces..

[scocliffe09]

Yeah, you need to know catalysts for them.

As for the pathway, I assume you can jump straight there, but the majority I've seen have highlighted the pathway, and you have to fill in the spaces..

Yes I agree - it's best to know both pathways, because you might have to use either.
And yes, you should know states, even of catalysts - the most important one that comes to mind is H2SO4 (l).

[nacho]

are there any catalysts present in the substitution reaction when forming an alcohol from a chloroalkane?
Books do not have any listed
thanks

[thatricksta]

Yeah, you need to know catalysts for them.

As for the pathway, I assume you can jump straight there, but the majority I've seen have highlighted the pathway, and you have to fill in the spaces..

Yes I agree - it's best to know both pathways, because you might have to use either.
And yes, you should know states, even of catalysts - the most important one that comes to mind is H2SO4 (l).

Why is H2SO4 not (aq)? It is only 98% pure at the most I believe

[luken93]

are there any catalysts present in the substitution reaction when forming an alcohol from a chloroalkane?
Books do not have any listed
thanks

PCl5

[jane1234]

are there any catalysts present in the substitution reaction when forming an alcohol from a chloroalkane?
Books do not have any listed
thanks

PCl5

Nah just NaOH or KOH as reactants I'm fairly sure.

luken93, I think PCl5 is only used for synthesising chloroalkanes from alcohols, could be wrong though...

[RobM8]

Yeah, you need to know catalysts for them.

As for the pathway, I assume you can jump straight there, but the majority I've seen have highlighted the pathway, and you have to fill in the spaces..

Yes I agree - it's best to know both pathways, because you might have to use either.
And yes, you should know states, even of catalysts - the most important one that comes to mind is H2SO4 (l).

Why is H2SO4 not (aq)? It is only 98% pure at the most I believe

It would work the reaction backward if it was aqueous.

[luken93]

are there any catalysts present in the substitution reaction when forming an alcohol from a chloroalkane?
Books do not have any listed
thanks

PCl5

Nah just NaOH or KOH as reactants I'm fairly sure.

luken93, I think PCl5 is only used for synthesising chloroalkanes from alcohols, could be wrong though...

Woops, read it te other way around :S
Yeah, NaOH in that case

[RobM8]

Luken is alkanol ---> chloroalkane for VCE or Uni Chem?

[luken93]

Luken is alkanol ---> chloroalkane for VCE or Uni Chem?

Either/Both AFAIK, I don't see any reason why you can't?

[thatricksta]

Yeah, you need to know catalysts for them.

As for the pathway, I assume you can jump straight there, but the majority I've seen have highlighted the pathway, and you have to fill in the spaces..

Yes I agree - it's best to know both pathways, because you might have to use either.
And yes, you should know states, even of catalysts - the most important one that comes to mind is H2SO4 (l).

Why is H2SO4 not (aq)? It is only 98% pure at the most I believe

It would work the reaction backward if it was aqueous.

Thanks, its just used as a dehydrating agent, so we would have to use pure H2SO4 yes? (does this even exist??)
Or do impurities caused by metals not affect the reaction? (sorry if this doesn't make sense, I'm finding it very difficult to explain)

- I am going to bed and will check answer tomorrow morning, thanks for the help

[Shark 774]

Why can't non-metals be analysed by AAS?