Unit 3 Questions MEGATHREAD :)

[Graphite]

for writing the states for reactants and products... do we have to remember the solubility rules?
Obviously there are some straight forward ones but sometimes I struggled with some compounds!

Yes, in fact that is the point of understanding them. To predict the state of the product.

[pi]

for writing the states for reactants and products... do we have to remember the solubility rules?
Obviously there are some straight forward ones but sometimes I struggled with some compounds!

Yep, you should know them (and most common exceptions)

Has anyone good a decent summary of the "common exceptions"?
Would be handy

I copied from here: http://www.ausetute.com.au/solrules.html

Moderator action: removed real name, sorry for the inconvenience

[luken93]

Cheers pi.

Also, which substances/reactions are liquid rather than aqueous?
This may seem really simple to some, but just want to make sure..

Moderator action: removed real name, sorry for the inconvenience

[luken93]

More questions. Well, more just safeguard checking

 - Hydroxy vs Hydroxyl - Does it matter?
 - Is there a difference between Transesterification and Esterification? Is Trans used for Biodiesel especially?

More will come as I think of them.

[scocliffe09]

More questions. Well, more just safeguard checking

 - Hydroxy vs Hydroxyl - Does it matter?
 - Is there a difference between Transesterification and Esterification? Is Trans used for Biodiesel especially?

More will come as I think of them.

Hydroxy = hydroxyl.
Esterification = formation of ester, usually by the joining of an OH group with a COOH group condensing to produce water.
Transesterification: alcohol + ester → different alcohol + different ester

[luken93]

More questions. Well, more just safeguard checking

 - Hydroxy vs Hydroxyl - Does it matter?
 - Is there a difference between Transesterification and Esterification? Is Trans used for Biodiesel especially?

More will come as I think of them.

Hydroxy = hydroxyl.
Esterification = formation of ester, usually by the joining of an OH group with a COOH group condensing to produce water.
Transesterification: alcohol + ester → different alcohol + different ester

Cheers.

[luken93]

Also, may be a silly question but nonetheless.

Can you write C2H5OH as opposed to C2H6O? I understand what semi-structural and molecular are, but not sure if it's allowed.

[scocliffe09]

Also, may be a silly question but nonetheless.

Can you write C2H5OH as opposed to C2H6O? I understand what semi-structural and molecular are, but not sure if it's allowed.

yep they're both correct I think. When it comes to lipids - just be careful, because they can be written differently on the exam to how they are written in the data book...

[luken93]

Also, may be a silly question but nonetheless.

Can you write C2H5OH as opposed to C2H6O? I understand what semi-structural and molecular are, but not sure if it's allowed.

yep they're both correct I think. When it comes to lipids - just be careful, because they can be written differently on the exam to how they are written in the data book...

Yeah, I wasn't really sure as it's kinda semi-strucural, but it would be harder to recognise a Carboxyl with an Ester if you had to write it in full molecular.

And by the lipids you just mean combining the Carboxyl into the Molecular Formula, ie C18H37COOH = C19H38O2?

[luken93]

So more of just a query, but do people learn about which indicators to use for different titrations, or are you taught how to interpret/choose a suitable indicator.

Also, while on indicators, if you had to choose between Phenolphthalein and Methyl Red as an indicator for a strong vs strong reaction, would any of them be better? By this I mean would it be better to look for a colourless -> red or red -> yellow? It probably sounds stupid, but just want to make sure I'm thinking straight

[Andiio]

Could anyone help confirm why the answer is Thymine to this question?

I got it right but... I'm paranoid that my reasoning is dodgy >_>

Thanks!

[luken93]

Thymine would be the most probable DNA base, as it is exactly the same as 5-bromouracil when the Bromine is replaced?

I know what you mean though, it's pretty obvious. Hence I suppose why it's only a mark.

[scocliffe09]

So more of just a query, but do people learn about which indicators to use for different titrations, or are you taught how to interpret/choose a suitable indicator.

Also, while on indicators, if you had to choose between Phenolphthalein and Methyl Red as an indicator for a strong vs strong reaction, would any of them be better? By this I mean would it be better to look for a colourless -> red or red -> yellow? It probably sounds stupid, but just want to make sure I'm thinking straight

I know this won't quite answer your question, but what you need to know for unit 3 is that you need to choose an indicator so that the end point represents the equivalence point, i.e. so that the equivalence point is as close to the centre of the indicator's pH range (data book). Apart from that, I don't think you need to know anything else about indicators other than that they are weak acids and therefore could potentially affect acid/base titrations (but this is unlikely).

[luken93]

Cheers, that basically answers my question.


Also, in the production of biodiesel, can you skip straight from the triglyceride to the 3 methyl esters? Or are you better off to say an intermediate reaction that breaks the triglyceride into 3 carboxcylic acids before reaction with methanol etc.

[scocliffe09]

Cheers, that basically answers my question.


Also, in the production of biodiesel, can you skip straight from the triglyceride to the 3 methyl esters? Or are you better off to say an intermediate reaction that breaks the triglyceride into 3 carboxcylic acids before reaction with methanol etc.

better off breaking it down and being more detailed. you have the knowledge and understanding so it can't hurt.