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Analytical Chemistry Forum / Chromatography
« Last post by John55 on Today at 08:05:53 AM »
hi ,
i'm desperate,could anyone help me please?

We use an analytical column to optimize the separation and then carry out a preparative separation of two substances. We have a 10 cm long preparative HPLC column with 40 separation steps per cm and an analytical column (also 10 cm) with 400 separation steps per cm. Both columns are packed with the same separating material and therefore have the same retention factors for the two components of our two-component mixture. For the preparative separation, the resolution must be at least 2. To what value do we have to optimize the resolution with the analytical column so that we can then transfer the separation to the preparative column?

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Analytical Chemistry Forum / theory of Gravimetric analysis
« Last post by filip jovic on Today at 07:32:53 AM »
can someone explain fully the theory of Gravimetric analysis.
The sign refers to the wavefunction amplitude, which may be positive or negative. Positive and negative regions are separated by a node, where the electron density is zero. The wavefunction alone does define the electron density, rather the probability distribution function does, which is typically related to the square of the wave function. The probability distribution function is therefore always positive.

That said, the amplitude of the wave function is important because mixing of atomic orbitals (wavefunctions) to form molecular orbitals (wavefunction) is accomplished by taking linear combinations of the atomic wavefunctions - in the LCAO-MO approximation. So for example if you have two P orbitals being brought together to form a pi orbital, they can be oriented in the same direction (the positive and negative regions being oriented in parallel) or in the opposite direction (antiparallel). In the former case the wavefunction constructively add, forming a strong molecular bonding orbital. In the latter case the positive and negative amplitude regions cancel out, basically, leading to an antibonding pi orbital with no electron density (the square of the molecular orbital wavefunction) between the two atomic centers. In physical organic chemistry, these same considerations come into play when determining rotation of certain groups during bond formation. In order for a bond to form the "+" regions have to overlap, otherwise the wavefunctions cancel each other out.

Good Explanation.
Analytical Chemistry Forum / Re: Theory precipitation iron
« Last post by mjc123 on Today at 07:02:15 AM »
What's your monster? King Kong? Godzilla? We need to know in order to explain the theory.

Seriously though, if you're writing a thesis, a elementary part of the work for your thesis is to learn the theory behind what you're doing. We're not here to do your work for you. Anyway, how much theory is there behind a precipitation? You make something insoluble, it precipitates.
They tell you it's Kp. Admittedly textbooks sometimes have misprints, but why do you think it might not be Kp?

(Also, you can tell it's Kp because K = e-ΔG°/RT. Why would this not be the case for Kc?)
Analytical Chemistry Forum / Theory precipitation iron
« Last post by filip jovic on Today at 06:39:48 AM »
I have to determine the iron3+ in a monster. The procedure is: i have to take 0,800 gram of my monster, add 50 ml water and 2 ml HCl then i have to heat it till boiling point then add 1 ml HNO3. And lengthen it to 200 ml. Then i have to add 20 ml NH3 very slowly. Etc..

My question is what is the theory behind this particular precipitation. Can someone explain this to me. It is for my thesis
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Analytical Chemistry Forum / Re: gravimetric determinetion of iron(III)
« Last post by AWK on Today at 05:08:56 AM »
Search textbooks, handbooks, and original literature. Maybe even the internet will help.
thank you for the instructions. but can you explain the theory behind it, i have to give the theory aswell but i dont re&ally understand it that well
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