Unit 3 Questions

[Rosie]

Regarding the chapter of 'fats:

Write and equation showing the formation of the triglyceride glyceryl trioleate from the reaction of glycerol and oleic acid, CH₃(CH₂)₇CH=CH(CH₂)₇COOH.

I wanted to know if my answer is correct.
CH₄OCH₄OCH₄O + C₁₇H₃₃COOH ---> CH₃(CH₂)₇CH=CH(CH₂)₇COOH + H₂O
If it is correct, I'm not sure how to balance just because of the large numbers.

[Collin Li]

Glycerol is actually , or (not a conventional way of writing it).

Here is a structural formula for glycerol:

Code: [Select]

  H
  |
H-C-OH
  |
H-C-OH
  |
H-C-OH
  |
  H
If you want an easier way to balance it, just write glycerol as its molecular formula:

However, I suspect this question wishes to see a structural formula. The three -OH groups on glycerol are sites for esterification. Simply draw the product of of a tri-esterification between 3 molecules of oleic acid, and 1 molecule of glycerol. The result will be three fatty acids on a glycerol molecule, hence the name: triglyceride. It looks like you've only done one esterification.

The molecular formula of the final product should be

However, it's not very easy to write a semi-structural formula for it, so I believe you've gotta actually do the structural formula.

This is how a generalised esterification occurs:

Code: [Select]

Z-OH  +  O=C-R   ---> R-C=O
           |            |
           OH           O-Z
You should be able to use this to help you draw your triglyceride.

[Mao]

question about states:

would they be (assuming this reaction carries out at body temperature - because this is where it takes place?):

*corrected*

   
are the states correct?

triolein will be a liquid because it cannot pack dense, right?

[Collin Li]

I'm not too sure, and I doubt you need to know. Glycerol will probably be aqueous in solution, and the unsaturated fatty acids are most likely liquids (lipids).

No idea what the triglyceride is.

[Mao]

riight, should've thought about that..

i've looked up for triglyceride, their melting points are all different apparently, as the fatty acids differ, and if they are polyunsaturated, they have several bends and dont fit together nicely, etc.

for triolein, google says its melting point is around 4^oC (some Wiley publication), so most probably a liquid.

though in the body, wouldnt there be emulsifiers (something or rather from the pancreas)?
In that case, would I still treat it as liquid? (or aqueous?)


and btw, OMG WIKIPEDIA ARTICLE ON "CHEMICAL EQUATIONS" SAYS NOTHING ABOUT STATES!!! =S

[Rosie]

Can someone provide me of a clear explanation of why 'the conjugate acid of a base has one more proton than the base' and why 'the conjugate base of an acid has one less proton than the acid.' I can't seem to get my head around this.

I also don't understand how oxidants will always be reduced and reductants will always itself be oxidised.

Also wanted to know if ammonia is NH3 only and ammonium is NH4. Is this how you distinguish them?

[Mao]

when a base accepts a proton, it becomes its own conjugate acid.
and vice versa.

that's just what they are.

e.g. NH3, ammonia, is a base. It accepts a hydrogen, and becomes NH4+.
hence, NH3 and NH4+ are conjugates (a base and its conjugate acid)

same deal for acid-conjugate base


as for oxidant/reductant, thats the way they work.

an oxidant, such as oxygen, wants to gain electrons [strong electronegativity], and hence it reacts to gain negative charges, hence "reduced"

a reductant react with an oxidant [oxygen], and is "oxidised" [raped by oxygen]


and yes, thats the way you tell:

shorter length = less hydrogen.

ammonia -> ammonium
NH3       ->  NH4+

[polky]

Yeah!
ammoNIA = 3 letters = NH3
ammoNIUM = 4 letters = NH4+

Now I have to figure out a way of remembering that the reductant is the one that undergoes oxidation etc. 

[Mao]

well, we do more redox next unit, but:

OILRIG
oxidation is loss, reduction is gain [of electrons]

and unit 4 specific [galvanic cells]
RedCat
reduction at cathode

[cara.mel]

well, we do more redox next unit, but:

OILRIG
oxidation is loss, reduction is gain [of electrons]

and unit 4 specific [galvanic cells]
RedCat
reduction at cathode

The heinemann book at least combined them to 'an oil rig cat' (anode oxidation is loss reduction is gain cathode)

But yeah, in unit 1/2 my friend that wasn't continuing to 3/4 asked me for last minute important stuff to know so I said 'Reduction is gain' to him and that's it

[Collin Li]

Yeah!
ammoNIA = 3 letters = NH3
ammoNIUM = 4 letters = NH4+

Now I have to figure out a way of remembering that the reductant is the one that undergoes oxidation etc. 

The reductant is the thing that reduces the other species. Reduction and oxidation are always bound together (one does not happen without the other), so the reductant (which has reduced the other species) must have oxidised.

[Rosie]

Q. Propan-1-ol (M = 60g mol^-1) undergoes complete fragmentation in a mass spectrometer. What is the m/e value of the base beak in its mass spectrum? I understand that the base peak is the largest peak in the spectrum and has an intensity of 100%.

Q. 1M solutions of several salts are prepared. Which of the following salts produces the solution with the highest pH?
A. Na₂CO₃
B. NaNO₃
C. NH₄Cl
D. Na₂SO₄         
 How do you know?

Q. Which of the following is a major component of biomass? (Firstly, what is biomass)
A. Natural gas
B. Ethanol
C. Cellulose
D. Crude Oil

thankyou everyone

[Collin Li]

Q. 1M solutions of several salts are prepared. Which of the following salts produces the solution with the highest pH?
A. Na2CO3
B. NaNO3
C. NH4Cl
D. Na2SO4         
How do you know?

Eliminate the options which are not bases: NaNO3, NH4Cl, Na2SO4. How do I know these aren't bases? Recognise that these are ionic compounds, and look at each ion individually: the sodium ion is neutral, so is sulfate, chloride and nitrate. The ammonium ion is acidic. The only remaining option is sodium carbonate, a decent base.

Note: You will not be expected to compare the strength of bases. You should know, however, that inorganic acids are stronger than organic acids (in general - don't worry, they won't produce counterexamples unless it's irrelevant or they tell you about it)

[Collin Li]

Q. Propan-1-ol (M = 60g mol^-1) undergoes complete fragmentation in a mass spectrometer. What is the m/e value of the base beak in its mass spectrum? I understand that the base peak is the largest peak in the spectrum and has an intensity of 100%.

This does not seem like a question you would be expected to know how to answer. My intuition tells me that it will be the isopropylium ion fragment, which has a molar mass of 43, but I would not expect you to have any idea why this is the case. The base peak has the greatest abundance because the base peak is the most stabilised fragment. I have used this basic idea to work it out, but it draws upon theory that is beyond the VCE course.

By the way, if you look at a lot of mass spectrums of organic molecules, the base peak is almost always 43. So if you do get an unfair question like this, just answer with that. For those who wish to understand why (out of curiosity), consider the stability of a fragment. A fragment requires a positive charge to be stabilised. It will certainly not include the electronegative oxygen, which depends on an abundance of negative charge. Here's a hint: alkyl groups are slightly electron donating. Not very, but still significant enough. Now, why did I pick isopropyl instead of just the plain propyl group?

I'm not actually sure if the isopropylium ion can form from this, but I'll just hope that it can. I don't know much about reactions with radicals, so I can't confirm whether this can be formed in the process of ionisation.

Q. Which of the following is a major component of biomass? (Firstly, what is biomass)
A. Natural gas
B. Ethanol
C. Cellulose
D. Crude Oil

From Wikipedia: Biomass refers to living and recently dead biological material that can be used as fuel or for industrial production. Most commonly, biomass refers to plant matter grown for use as biofuel, but it also includes plant or animal matter used for production of fibres, chemicals or heat.

I would pick cellulose - plant matter that will not get digested for energy by many living things, but can still be combusted for energy with some oxygen .

[Mao]

Q. Propan-1-ol (M = 60g mol^-1) undergoes complete fragmentation in a mass spectrometer. What is the m/e value of the base beak in its mass spectrum? I understand that the base peak is the largest peak in the spectrum and has an intensity of 100%.

This does not seem like a question you would be expected to know how to answer. My intuition tells me that it will be the isopropylium ion fragment, which has a molar mass of 43, but I would not expect you to have any idea why this is the case. The base peak has the greatest abundance because the base peak is the most stabilised fragment. I have used this basic idea to work it out, but it draws upon theory that is beyond the VCE course.

By the way, if you look at a lot of mass spectrums of organic molecules, the base peak is almost always 43. So if you do get an unfair question like this, just answer with that. For those who wish to understand why (out of curiosity), consider the stability of a fragment. A fragment requires a positive charge to be stabilised. It will certainly not include the electronegative oxygen, which depends on an abundance of negative charge. Here's a hint: alkyl groups are slightly electron donating. Not very, but still significant enough. Now, why did I pick isopropyl instead of just the plain propyl group?

I'm not actually sure if the isopropylium ion can form from this, but I'll just hope that it can. I don't know much about reactions with radicals, so I can't confirm whether this can be formed in the process of ionisation.

the answer, in this case, is actually CH₂OH⁺, 31 m/z

it was in competition [amongst the choices] with CH₃CH₂⁺, which would be less abundant as it will further fragment down into CH₃⁺

why? i have no clue