Unit 3 Questions MEGATHREAD :)

[scocliffe09]

Could someone please help me with part b) of this question? I'm fairly certain that the solutions are wrong :\

Argh that's from Engage right? I wasn't sure of the answer for part b) either. How would you even work it out? :S

Yeah it is, I was like 'WTF' at the question. The solutions don't even make sense, they state that C is the limiting reagent when it had the greatest amount of mol ==

For the question: Name the type of bonding that is present between a deoxyribose molecule and phosphate molecule,
I wrote phosphodiester bonding - the answers stated hydrogen bonding. Am I right or is it actually H-bonding?

Thanks!

Nope you're definitely right - It is (if we're being picky), technically a phosphate ester bond (it's only in a nucleic acid that phosphodiester bonds are formed). But it's not H bonds.
Nacho - concentrations (2M) are definitely counted in sig figs. Some papers are just slack (e.g. tsfx).
Luken - all of those reactions are fine. But remember, you want the examiner to give you the marks you deserve, so make whatever the question is asking for REALLY obvious - treat the examiner like both a complete douche and a chem nut
JayCanteloupe - DEFINITELY know the solubility table. REALLY important.
pi - the OH at the end (I assume you mean the 3' end) is connected to a carbon, so it's much less polar than the phosphate group, so much less likely to be acidic - so it's almost always going to be an OH group.
Hope that helps everyone

Moderator action: removed real name, sorry for the inconvenience

[Andiio]

Could someone please help me with part b) of this question? I'm fairly certain that the solutions are wrong :\

Argh that's from Engage right? I wasn't sure of the answer for part b) either. How would you even work it out? :S

Yeah it is, I was like 'WTF' at the question. The solutions don't even make sense, they state that C is the limiting reagent when it had the greatest amount of mol ==

For the question: Name the type of bonding that is present between a deoxyribose molecule and phosphate molecule,
I wrote phosphodiester bonding - the answers stated hydrogen bonding. Am I right or is it actually H-bonding?

Thanks!

Nope you're definitely right - It is (if we're being picky), technically a phosphate ester bond (it's only in a nucleic acid that phosphodiester bonds are formed). But it's not H bonds.
Nacho - concentrations (2M) are definitely counted in sig figs. Some papers are just slack (e.g. tsfx).
Luken - all of those reactions are fine. But remember, you want the examiner to give you the marks you deserve, so make whatever the question is asking for REALLY obvious - treat the examiner like both a complete douche and a chem nut
JayCanteloupe - DEFINITELY know the solubility table. REALLY important.
pi - the OH at the end (I assume you mean the 3' end) is connected to a carbon, so it's much less polar than the phosphate group, so much less likely to be acidic - so it's almost always going to be an OH group.
Hope that helps everyone

Awesome thanks. So many errors in that paper D:
Do you think it'd be best to simply write covalent bonding in the exam if a question came up asking about the type of bonding between a deoxyribose sugar and a phosphate group?

Moderator action: removed real name, sorry for the inconvenience

[nacho]

Could someone please help me with part b) of this question? I'm fairly certain that the solutions are wrong :\

is the answer .1 mol?

can someone link me to the solutions please?

[luken93]

Well that is technically the "type of bonding", phosphodiester is more the name of the specific bond...

So scocliffe, even though my 3rd reaction is as cltf said, "a hybrid", it can still be used? I didn't think it would be either, but if you had a fatty acid I'm not going to write out a 20 carbon chain with 3 double bonds all in semi-structural while still showing the carboxyl aspect of it...

[luken93]

Next question, when you're talking about which molecule is the reductant and which is the oxidant, should you always state ie "SO4 is the oxidant, as the oxidation number of S has gone from 8+ -> 6+" as it is the entire molecule that is the oxidant, not the individual atom yes?

[mickeymouse]

yes not individual atoms the whole compound would be the oxidant

[nacho]

out of all the spectroscopic techniques, which ones do we need to know in detail?
i.e the instruments used/purposes and their names
also,
whats the answer to andiio's question?
is it 0.1 mol for part b) ?

[taiga]

Nacho I think pretty much all of them can be asked into the same depth. That said, I think it would be necessary to be most familiar with titration the most

[Andiio]

out of all the spectroscopic techniques, which ones do we need to know in detail?
i.e the instruments used/purposes and their names
also,
whats the answer to andiio's question?
is it 0.1 mol for part b) ?

Yeah it is, what was your reasoning for it though?

[scocliffe09]

Well that is technically the "type of bonding", phosphodiester is more the name of the specific bond...

So scocliffe, even though my 3rd reaction is as cltf said, "a hybrid", it can still be used? I didn't think it would be either, but if you had a fatty acid I'm not going to write out a 20 carbon chain with 3 double bonds all in semi-structural while still showing the carboxyl aspect of it...

As long as you are happy that you convince the examiner of what you want to convince them, then go for it! CHO and CHCOOH are both 100% acceptable forms for fatty acids. Also your oxidation question - you're right.
Hope UNichem went well Luken

[nacho]

I did this:
I assumed there was one mol for each reactant as it says 'for every mole'
that means
1 mol of Ca... 1 mol of Si... and 1 mol of C.

Find the limiting reagent.
1 mol of Ca3(PO4)2 requires 3 mol of SiO2 and 5 mol of C
the limiting reagent is therefore Carbon
with 1 mol of carbon, 1/5 mol of Ca3(PO4)2 will react (simple stoich ratios)
and 2/5 mol of SiO2 will react (but all you dont even need to calculate both of them, you can just use the carbon figure)
Carbon : P4
10 : 1
therefore 1 mol of carbon produces .1 mol of P4
check with the others

[Andiio]

I did this:
I assumed there was one mol for each reactant as it says 'for every mole'
that means
1 mol of Ca... 1 mol of Si... and 1 mol of C.

Find the limiting reagent.
1 mol of Ca3(PO4)2 requires 3 mol of SiO2 and 5 mol of C
the limiting reagent is therefore Carbon
with 1 mol of carbon, 1/5 mol of Ca3(PO4)2 will react (simple stoich ratios)
and 2/5 mol of SiO2 will react (but all you dont even need to calculate both of them, you can just use the carbon figure)
Carbon : P4
10 : 1
therefore 1 mol of carbon produces .1 mol of P4
check with the others

Limiting reagent is carbon?

[nacho]

I did this:
I assumed there was one mol for each reactant as it says 'for every mole'
that means
1 mol of Ca... 1 mol of Si... and 1 mol of C.

Find the limiting reagent.
1 mol of Ca3(PO4)2 requires 3 mol of SiO2 and 5 mol of C
the limiting reagent is therefore Carbon
with 1 mol of carbon, 1/5 mol of Ca3(PO4)2 will react (simple stoich ratios)
and 2/5 mol of SiO2 will react (but all you dont even need to calculate both of them, you can just use the carbon figure)
Carbon : P4
10 : 1
therefore 1 mol of carbon produces .1 mol of P4
check with the others

Limiting reagent is carbon?

yea, because if you have 1 mol of each reactant
and Ca3PO4 needs ten times its own amount to react, doesnt that mean that Carbon is limiting Ca3PO4 from being used up?
1 mol of Ca3PO4 needs 10 mol of carbon, yet there is only 1 mol present

[jane1234]

Hmm...

If a question says that aspirin was hydrolysed in alkaline conditions... and asks you to draw salicylic acid wouldn't you draw it as -COO- instead of -COOH... or just leave it as the -COOH even though it would lose a proton in basic conditions?

[luken93]

Well that is technically the "type of bonding", phosphodiester is more the name of the specific bond...

So scocliffe, even though my 3rd reaction is as cltf said, "a hybrid", it can still be used? I didn't think it would be either, but if you had a fatty acid I'm not going to write out a 20 carbon chain with 3 double bonds all in semi-structural while still showing the carboxyl aspect of it...

As long as you are happy that you convince the examiner of what you want to convince them, then go for it! CHO and CHCOOH are both 100% acceptable forms for fatty acids. Also your oxidation question - you're right.
Hope UNichem went well Luken

Cheers. Yeah, it wasn't too bad - but the completely revamped the format of the previous years which wasn't good

Ah well, I'd rather do better in normal chem