Unit 3 Questions MEGATHREAD :)

[n.]

is peak area and peak height the same thing?

[luken93]

is peak area and peak height the same thing?

Kinda, the reason why we normally just use height is because the width of the peaks is usually tiny, hence the height is usually a decent way to measure.

[cltf]

I would say so

[n.]

thanks

[homosapiens]

Probably not in the study design, but when using IR spectroscopy for quantitative analysis, does transmittance and or peak area indicate the amount?

[mickeymouse]

chloroalkanes , fluoroalkanes, etc do they all form hydrogen bonds with one another and only with water? what about the dispersion forces since they're hydrocarbons?   

[Sakigami]

chloroalkanes , fluoroalkanes, etc do they all form hydrogen bonds with one another and only with water? what about the dispersion forces since they're hydrocarbons?   

I didn't think chloroalkanes and fluoroalkanes can form hydrogen bonds with each other as there isn't any H bonded to F,O,N for them to form hydrogen bonds with. I believe that since they are polar, they would form dipole-dipole bonds if anything? If a chloroalkane or fluoroalkane has a long non-polar end, I suppose the net dispersion forces will be the strongest force of attraction between molecules.

But yes they do form hydrogen bonds with water as the H's are bonded to an O, allowing for hydrogen bonding to occur.

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Another question I have is in relation to calibration curves;
1 method of doing these questions is to use "dilation factors" to calculate the concentration in the sample. But I find its more logically to calculate the mass in the diluted sample and work backwards from here. Is this an acceptable method of working for these type of questions?

[Greatness]

chloroalkanes , fluoroalkanes, etc do they all form hydrogen bonds with one another and only with water? what about the dispersion forces since they're hydrocarbons?   

I didn't think chloroalkanes and fluoroalkanes can form hydrogen bonds with each other as there isn't any H bonded to F,O,N for them to form hydrogen bonds with. I believe that since they are polar, they would form dipole-dipole bonds if anything? If a chloroalkane or fluoroalkane has a long non-polar end, I suppose the net dispersion forces will be the strongest force of attraction between molecules.

But yes they do form hydrogen bonds with water as the H's are bonded to an O, allowing for hydrogen bonding to occur.

---------
Another question I have is in relation to calibration curves;
1 method of doing these questions is to use "dilation factors" to calculate the concentration in the sample. But I find its more logically to calculate the mass in the diluted sample and work backwards from here. Is this an acceptable method of working for these type of questions?

I think you mean dilution factor? hahah
Well yeah i just ratios so much easier - im assuming this is what you do? so you have to fractions and you gotta solve for x?..

[Water]

KBT said Monosaccharides can be used in GC, whilst STAV says otherwise and it will decompose in GC.

Which one is speaking the truth? I don't like some of KBT answers though.

[DavidSheena]

Is transmittance the amount of light/radiation absorbed or not absorbed?

[extcar]

would this be a good thing to remember, as in does it make sense? or not..
more titre= lower concentration of unknown
less titre= more concentration of unknown

[homosapiens]

KBT said Monosaccharides can be used in GC, whilst STAV says otherwise and it will decompose in GC.

Which one is speaking the truth? I don't like some of KBT answers though.

Yeah I just did the KBT paper and got stumped by that question too! I'm pretty sure monosaccharides cannot be vapourised so they aren't suited to GC since they decompose when heated, not absolutely sure though.

Is transmittance the amount of light/radiation absorbed or not absorbed?

Transmittance is the amount of light/radiation that transmits (passes through) the sample, therefore it is the amount that is not absorbed. If you get confused you can look at the IR spectrum - if there isn't a peak, transmittance is 100%, therefore it all transmits and is not absorbed by the bond

[homosapiens]

would this be a good thing to remember, as in does it make sense? or not..
more titre= lower concentration of unknown
less titre= more concentration of unknown

That makes sense for one straight titration, but if you look at the questions where two titrations are involved (back titration), it's actually the opposite, since the second titration is to see how much is left after reacting with the unknown sample that you're trying to find. Hope that makes sense :| Refer to LisaChem '09 Q5 if it doesn't

[luken93]

would this be a good thing to remember, as in does it make sense? or not..
more titre= lower concentration of unknown
less titre= more concentration of unknown

Not necessarily, as the unknown can be in the conical flask or the burette.

Is transmittance the amount of light/radiation absorbed or not absorbed?

Transmittance is the opposite of absorbed, if you think about it this way, if the atoms absorb 20%, they will transmit 80% of the light.

KBT said Monosaccharides can be used in GC, whilst STAV says otherwise and it will decompose in GC.

Which one is speaking the truth? I don't like some of KBT answers though.

I would go with HPLC, as they generally decompose. However, I'm highly doubtful that VCAA will ever ask this. It's usually AAS vs UV-Vis vs IR vs GC/HPLC, never HPLC vs GC

[DavidSheena]

Is transmittance the amount of light/radiation absorbed or not absorbed?

Transmittance is the opposite of absorbed, if you think about it this way, if the atoms absorb 20%, they will transmit 80% of the light.

Thank You; Do we also need to know the ranges of colorimetry and so on? For example 400-750nm etc?