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Desolation

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organic compound identification question
« on: April 10, 2005, 08:23:21 AM »
This question is from one of my hmk assignments, i attempted it, but got confused by the different parts... :-\

1.475g of an organic compound containing only carbon, hydrogen, oxygen and nitrogen was completely burnt in oxygen gas. The products included 2.200g of carbon dioxide and 1.125g of water. 2.360g of the compund reacted with excess alkali to produce sufficient ammonia to neutralise 18.2mL of 1.110 mol L-1 sulphuric acid. 0.177g of the vaporised compound occupied a volume of 135.8mL at 300`C and 101.8kPa.
a) Determine the empirical formula of the compound.
b) Determine the approximate molecular weight and molecular formula of the compound.
c)The compound contains a carbonyl (c=o) group. Draw a possible structural formula and give the I.U.P.A.C. name of the compound u have drawn.


i'm confused as to what happens to the N in the first part, and what the second equations (neutralization and the vaporized compound) can do to help me get the formulas. help much appreciated.

Garneck

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Re:organic compound identification question
« Reply #1 on: April 10, 2005, 11:59:26 AM »
2.360g of the compund reacted with excess alkali to produce sufficient ammonia to neutralise 18.2mL of 1.110 mol L-1 sulphuric acid.

Does that ring a bell where the nitrogen went?

Offline Borek

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Re:organic compound identification question
« Reply #2 on: April 10, 2005, 12:22:05 PM »
Vapourization gives molar mass.

N gives ammonia - if you can calculate amount of ammonia, you know what the amount of N in the sample was.

Hint to make your calculations easier: if 2.360 g sample gives enough ammonia to neutralise 18.2mL of sulphuric acid, 1.475g sample will give enough ammonia to neutralize 1.475/2.360*18.2 mL of the same solution. This way you will be able to do all calcuations for one sample and it will be easier to compare number of moles in the sample.

Oxygen fills the gap between CNH and and the total sample mass.

I know what the formula is :) but you should know enough to do it now by yourself.
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Offline AWK

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Re:organic compound identification question
« Reply #3 on: April 11, 2005, 02:17:52 AM »
Burning of organic compounds produces nitrogen, alkaline hydrolysis of amides - ammonia.
Vaporization gives only approximated molecular mass, because we use the ideal gas law.

Assume H2SO4 react with 2 molecules of ammonia
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Re:organic compound identification question
« Reply #4 on: April 11, 2005, 04:42:45 AM »
Vaporization gives only approximated molecular mass, because we use the ideal gas law.

Exactly - in this particular case error is a little bit higher than 3%.
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