Water's Noobie Chem Thread.

[luken93]

In UV however, you actually have to change the substance. In the others, another substance is added to allow it to become equi-molar, or to precipitate, but in UV you can't actually use AgNO3 if you get what I mean?

Yes, there are many dye bases to which we can react with the analyte selectively to find their concentration with photospectrometry. In the typical case, we are probably looking at a dye that will react with NO3- only (We add the dye base in excess, and all the nitrate will form a coloured dye). It is correct that we cannot measure some things directly.

So then what actually is the right answer? Or are we going a lot deeper than the book requires?

[Water]

In UV however, you actually have to change the substance. In the others, another substance is added to allow it to become equi-molar, or to precipitate, but in UV you can't actually use AgNO3 if you get what I mean?

Yes, there are many dye bases to which we can react with the analyte selectively to find their concentration with photospectrometry. In the typical case, we are probably looking at a dye that will react with NO3- only (We add the dye base in excess, and all the nitrate will form a coloured dye). It is correct that we cannot measure some things directly.

So then what actually is the right answer? Or are we going a lot deeper than the book requires?

I suspect that, what hes saying is, AgNO3, you make all of the NO3 in AgNO3 react with the dye. And through there, we can find the concentration/mol of AgNO3, similar to gravimetric analysis with excess precipitating agent. Though we can have the chem man himself say it/ or correct me as  "always"

[luken93]

Well I think overall, we are kinda both right? It can indeed be done, but it requires a few procedures to do so. but ultimately I don't think the book aimed for us to go this in depth? A good learning excercise nonetheless

[Mao]

In UV however, you actually have to change the substance. In the others, another substance is added to allow it to become equi-molar, or to precipitate, but in UV you can't actually use AgNO3 if you get what I mean?

Yes, there are many dye bases to which we can react with the analyte selectively to find their concentration with photospectrometry. In the typical case, we are probably looking at a dye that will react with NO3- only (We add the dye base in excess, and all the nitrate will form a coloured dye). It is correct that we cannot measure some things directly.

So then what actually is the right answer? Or are we going a lot deeper than the book requires?

I suspect that, what hes saying is, AgNO3, you make all of the NO3 in AgNO3 react with the dye. And through there, we can find the concentration/mol of AgNO3, similar to gravimetric analysis with excess precipitating agent. Though we can have the chem man himself say it/ or correct me as  "always"

You are correct.

What I'm trying to say is if you just put a 'neat' solution of AgNO3 into the UV-vis spectrometer, most probably nothing will happen. However, you can react your sample to form other stuff which will have absorption in the UV-vis spectrum.

The book is trying to target the knowledge that UV-vis is generally suitable for coloured compounds, AAS is generally suitable for metal ion solutions.

[Water]

Hey guys, when your looking for isomers of pentene


Does 2- methyl But-4-ene exist?  And if no, why not? Because  Heineman only gave me 4  solutions, but it doesn't nclude this one?

[Greatness]

But-4-eme = but1ene = butene?

[Water]

Elaborate more please ?

[jasoN-]

No such thing as But-4-ene, cos it would be named Butene (carbon 1 is the double bond carbon)

This is 2-methylbutene
       CH3
\    |  |    /
-C-C-C=C         
/    |       \



i don't see why it won't exist if that's what you're asking

what are the four solutions you're given?

[Water]

1-pentene, 2-pentene, 2-methyl-1-butene, 2-methyl-2-butene



The problem is, you could draw it out


CH3 CH(CH3)CHCH2


Your counting from your nearing side groups first before you count double bonds I"m assuming. So from this...

I'd get 2 MethylBent-4-ene.

[jasoN-]

Can u post up the question? this doesnt make sense to me.
But you count from double bonds before side groups

[Water]

Lol...ohh, damnit, Jason, yes, I got it mixed up with Alkane numbering., Thanks

you count from double bonds before side groups

But it was asking for isomers of Pentene


CH3 CH(CH3)CHCH2

So It'd be 3-methylbent-1ene 

[Water]

When you have something like

                          MnO4- or Cr2O7
CH3CH2OH (aq) ---------------------> CH3COOH

                                 H+



What is the H+ meant to be symbolic of? What is its purpose?

[andy456]

It means the solution must be acidic but I can't remember why....
This is probably wrong but: I think it has something to do with the electrochemical series. As in the MnO4 won't react unless in acidic solution.

[luken93]

It means the solution must be acidic but I can't remember why....
This is probably wrong but: I think it has something to do with the electrochemical series. As in the MnO4 won't react unless in acidic solution.

Yeah that's pretty much correct, you pronounce it as "Acidified Permangante/Dichromate"

[Mao]

Balance the equation of MnO4- --> Mn2+ or Cr2O7 2- --> Cr3+, they both require H+ to react