December 05, 2022, 06:19:58 AM
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21
Analytical Chemistry Forum / Sodium Acetate Buffer
« Last post by znaes97 on December 01, 2022, 11:19:07 AM »
Hey everybody,
I have a procedure to check for the presence of chlorine in waste water. The procedure says to use a sodium acetate buffer. Does it have to be sodium acetate or can we use something else like an ammonium acetate buffer? Any help is greatly appreciated.
22
During GCMS same compound show peak at different retention times. Any justification why this happen. How to interpret the data?
23
Organic Chemistry Forum / Re: Can oxidize methanol to formic acid using NaClO?
« Last post by Kasteli on December 01, 2022, 06:07:59 AM »
Can you give example of such catalist I have found about copper metal i high temperatures react with air to produce CuO then oxidize methanol to formaline regenerating metalic copper and so on but conditions makes this method inpractical for amatour chemist like me.
24
High School Chemistry Forum / Re: Some questions regarding pH, bases and acids
« Last post by Borek on December 01, 2022, 03:58:56 AM »
I have an exam coming up on this topic and have a few questions.I have an exam coming up on this topic and have a few questions.
(...)
That's all I need to know thanks

These questions are almost impossible to answer, they are way too ambiguous and make no sense without context - which suggests these are not "the only things" you don't know. It is rather that you don't grasp underlying concepts and these things are just a tip of an iceberg :(

Quote
Okay so first of all when do I use -log10 vs just -log because there are some questions that involve -log10 and they don't even use the Molarity they just come up with the number of moles and then do it -log only. What is -log10 basically

If it is all about pH can be it is just a lousy used notation and it is log base 10 all the time. Hard to say without seeing problems in which these logarithms were used. log10 means logarithm base 10, log can mean natural logarithm or logarithm base 10, there is no single convention.

Quote
How do I calculate mass vs calculating concentrations ?

No way to answer that, you could as well ask "how do I calculate length and how do I calculate weight" and it would make about as much sense.

Quote
When is it necessary to convert grams to litres regarding these questions?

When you need volume and you have mass, you try to convert mass to volume. Again, this question doesn't make much sense without context.

Quote
In Va x Ma/Na = Vb x Mb/Nb how do I know when Na and Nb are 1 and 1 or 1 and 2

Sigh, how do we know what these symbols mean? They are not established, just because your lecturer used them doesn't mean everyone knows what they mean. If I were to guess I would assume Na and Nb are stoichiometric coefficients or numbers of dissociable protons in reacting substances.
25
Organic Chemistry Forum / Caffeine: reducing the keto-groups to alkanes
« Last post by naalya on December 01, 2022, 02:06:44 AM »
Hi,
i'm wondering if you could reduce both keto-groups in caffeine to their alkanes.
the reduction method i'm thinking of is mainly used to reduce secondary alcohols to alkanes, but i found some rather 'not properly reliant' information on the internet, that it will also reduce ketones to alkanes (using hydroiodic acid, generated in situ using two elements in the presence of water. i'm not sure if it's allowed to specify this procedure, since it's often used by hobby 'chemists' to get an illegal product).

if it works and both keto-groups would be reduced, the product should be 1,3,7-trimethyl-3,7-dihydro-1H-purine (see attachment). it should be less water soluble than caffeine. i found information about 6-methylpurine, but nothing on (hydrated) (tri)methylpurines.

my questions are:
1. has anyone ever tried reducing the keto-groups of caffeine?
2. has anyone ever come upon the proposed product?
3. can anyone with access to SciFinder try a quick search, if it has been mentioned in literature anywhere?
(4. are i am allowed to post the procedure i would use (i think some people here will know which one i mean)?)
26
Inorganic Chemistry Forum / Crystallisation via vapor diffusion
« Last post by naalya on November 30, 2022, 05:43:01 PM »
Hi,
i remember performing a crystallisation method during my (failed, due to several reasons) time as a PhD student:

the substances we synthesized were pyrophoric complexes of late transition metals with a organic ligand (working under argon atmosphere, Schlenk technique, gloveboxes etc.). to do XRD we obviously needed single crystals.

this always was a tough thing; we used a method we called 'vapor diffusion' (or in german 'gasphasendiffusion'):
putting a very small vial with a concentrated solution of our compound into a larger vial, containing a solvent which would not solve the compound. the outter vial was sealed. over time, the solvent in the larger vial would diffuse into the concentrated solution in the inner vial and crystallisation was observed.

i'm looking for literature and experiences on this method. i'm not sure if i'm using the correct keywords in my search on the internet; i'm mostly finding information about the 'sitting drop' method (used for protein crystallisation).

maybe someone here has any hints for me?
27
High School Chemistry Forum / Some questions regarding pH, bases and acids
« Last post by Shaderxd on November 30, 2022, 05:22:11 PM »
I have an exam coming up on this topic and have a few questions.
Okay so first of all when do I use -log10 vs just -log because there are some questions that involve -log10 and they don't even use the Molarity they just come up with the number of moles and then do it -log only. What is -log10 basically

How do I calculate mass vs calculating concentrations ?

When is it necessary to convert grams to litres regarding these questions?

In Va x Ma/Na = Vb x Mb/Nb how do I know when Na and Nb are 1 and 1 or 1 and 2
That's all I need to know thanks
28
Other Sciences Question Forum / Re: Ingredients in gel polish
« Last post by wildfyr on November 30, 2022, 10:34:35 AM »
The gel nail polish formulas you posted are very industry standard. I personally handle all these sorts of materials every day in their pure form (albeit wearing gloves and a lab coat).

Are they perfectly studied and definitely have no ill effects? No.

Are they generally considered pretty safe by most people who use and regulate them? Yes.
29
Other Sciences Question Forum / Generators for Ukraine
« Last post by Enthalpy on November 30, 2022, 08:56:20 AM »
Hello everybody, those in the cold and those in comfort!

As Ukraine's power grid is destroyed by the war, Germany plants to ship parts of Diesel locomotives to provide electricity.

My interpretation: the transformers stations are destroyed, more than power plants, but a generator can replace a transformer to make power locally, and this was available more quickly. Probably from Diesel locomotives with electric transmission. This was the preferred design in French railways, while Germany had more Diesel with hydraulic transmission. In other words, other countries could imitate Germany.

Some thoughts from me, and you're kindly invited to contribute.

Older Diesel can run with vegetable oil if needed. I did it with my Citroen Cx car. It needs
  • An Diesel with a pre-chamber, vital. Should be the case of all old railway engines.
  • The oil must not freeze. Canola oil is better.
  • Some injector pumps (Reiheneinspitzpumpe) cope with 100% vegetable oil, even in Bavarian winter, others (Verteilereinspritzpumpe) with 30% vegetable oil and 70% Diesel oil.
  • The old Diesel engines can run on kerosene too. I suppose this allows a higher proportion of vegetable oil in winter.

APU from discarded airliners make electricity too
  wikipedia
around 1MW each. Usually at 115/200V and 400Hz, but for instance present speed controllers for AC motors convert it to 50Hz and whatever desired voltage.

Engines have 1/3 efficiency, the rest is exhaust heat, which should be used in Ukraine's winter. It only needs to tinker an exhaust-to-air or exhaust-to-water heat exchanger and send the heat to houses and shelters. Recycle engine coolers from destroyed battletanks? Or just use the existing railway engine's cooler, possibly with a limited air throughput?
30
Organic Chemistry Forum / Re: Can oxidize methanol to formic acid using NaClO?
« Last post by Enthalpy on November 30, 2022, 08:29:34 AM »
From what Google told me
formaldehyde oxidation "formic acid"
it doesn't even need an artificial oxidizer. Just air and water vapour suffice, over a catalyst.

Oxidation from alcohol to aldehyde too happens with air and a catalyst. Google
methanol oxidation formaldehyde

Done in trains amount.
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