January 15, 2021, 09:37:12 AM
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I agree that titration is worth doing any time you have a Grignard that requires any precision - that is, where the separation of products isn't trivial, or where the unconverted halide might cause a side reaction. I generally do Kumadas of thiophenes while cooling with an ice bath, too, although I've never tried a PEG coupling. You may also consider starting in THF to begin with. A lot of reactions simply don't work in ether that do work in THF. I have never seen a Ni Kumada that required reflux, so that is probably not helping.
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I've never had any trouble with using the "as-pasted" graphics, but sometimes have had to generate high-resolution schemes separately in Chemdraw or whatever software I was using.
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Organic Chemistry Forum / Re: hydrolysis of sucrose
« Last post by mjc123 on Today at 06:33:22 AM »
You can't make the assumption 3.0 - x ≈ 3.0. That only works for weak acids where x is small. Your calculation would lead to x ≈ 103M - does that look sensible? pKa = -7 means it is a strong acid that is essentially fully ionised in water. So for 3.0 M HCl, you can take [H3O+] as 3.0 M.

What you could also do is call the concentration of undissociated HCl y; then [H3O+] = [Cl-] = 3.0 - y, and
Ka = (3.0 - y)2/y
and simplify by assuming 3.0 - y ≈ 3.0 (Check the validity of this assumption after calculating y.)
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Analytical Chemistry Forum / Re: Column chromatography
« Last post by Jason09 on Today at 05:55:20 AM »
Hi Motoball

Due to having a shortage of info based on the extraction I'm trying to carry out I'm unable to provide you with answers for some of your questions but hope this helps.

The starting material will be: White Ginger (from Southern Asia)
The compound I need to isolate is: DPPH (2,2-diphenyl-1-picrylhydrazyl) due to its ability to boost the immune system.
The sample matrix: Ethyl Acetate in Hexanes
And the scale of this endeavour is low g of matrix

Hope this helps Motoball, please let me know what you thing.


Thanks
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I think you will have the electrolysis of water. At cathode the hydrogen will be developed and at the Anode oxygen. You are right you will also get corosion there and magnesium hydroxide will be formed.
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Organic Chemistry Forum / hydrolysis of sucrose
« Last post by penovili on Today at 03:58:37 AM »
Hi guys,
So i got the K1 value for this reaction wich was done using HCL
Now i have to plot the graph of k1 vs H3O.
The pka of hcl is -7
what would be [H3O]


I know that [H3O]+ = [H]+

attempt :
pka= -logka= -7
logka= 7
ka=10^7
ka= x^2/ (3.0M - x) aprrox = x^2/3.0M
1.0 * 10^7 = x^2/3.0M

x= [H3O]
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Hello Emmas151, I think that you're right. But to be 100% sure - use sensibility test that ordered by USP
Quote
This solution deteriorates upon standing and is unsuitable for use if, upon the addition of 2 mL of dibasic sodium phosphate TS to 5 mL of the solution, an abundant yellow precipitate does not form at once or after slight warming.
You should check this solution every time before use, unless you carry on some risk analys and profe exact storage time for you solution in your lab prepared with your reagents and ex.
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Basically I have to make an ammonium molybdate solution, but I won't be able to filter it for about 72 hours. I'm worried that will be too long based on the nature of the solution. The USP method says "Allow to stand for 48 hours, and filter through a fine porosity, sintered-glass crucible. This solution deteriorates upon standing and is unsuitable for use if, upon the addition of 2 mL of dibasic sodium phosphate TS to 5 mL of the solution, an abundant yellow precipitate does not form at once or after slight warming. If a precipitate forms during storage, use only the clear supernatant" The way I'm reading this, it seems like it deteriorates over a longer period of time, not in a matter of days, and if it does form precipitate within the few days I haven't filtered it, it should be ok.....right???
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Undergraduate General Chemistry Forum / Re: overall dilution factor
« Last post by AWK on Today at 12:47:27 AM »
Quote
17ml aliquot is taken
One number in your post was different.
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Undergraduate General Chemistry Forum / Re: overall dilution factor
« Last post by addy925 on Today at 12:38:13 AM »
For overall dilution factor, I know you're supposed to get the individual dilution factor then multiply them so would it be DF = 30 * 50/16?

Thanks!
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