[Prim3]

Hello,

I have 2 questions that I would like help on.

1)

Phosgene, a highly toxic, gasesous, industrial chemical (used somewhat unsuccessfully as a chemical warfare agent in WWI) has the molecular formula COCl2.
A portion of the mass spectrum of phosgene is represented below.
Parent Ion MS for COCl2 Given the following natural isotopic abundances (and atomic masses):

    * 12C 98.9% (12.000000 amu)
    * 13C 1.1% (13.003355 amu)
    * 16O 99.76% (15.994915 amu)

IMAGE:

What is the atomic mass of the most massive isotope of chlorine present in the sample (in amu,to at least 4 decimal places):

Also, what are the masses (amu) to the following molecular ions?

[13C16O35Cl2]+
[12C16O35Cl2]+
[13C16O37Cl2]+

What is the approximate % isotopic abundance of the most abundant isotope of chlorine present in the sample (try to get it within ±1%):

To be completely honest, I have no idea how to even start this question. The image scared me.

However, I gave #2 a full try.

Here it is:

2) A white powder, consisting of a simple mixture of tartaric acid (C4H6O6) and citric acid (C6H8O7) was analysed to determine the elemental composition. Combustion of a 407.1-mg sample produced 506.5 mg of CO2 and 148.8 mg of H2O.

Use atomic masses: C 12.011; H 1.00794; O 15.9994.

I've seen this question before and I tried to attempt it as well but I failed.

I realized that first I have to find the Molar Mass which is 44.01 g/mol. I then however found the moles to be: 0.1463764889 (I am not 100% sure on this, could someone confirm it please?).

After that I am completely lost.

Thank-you for your help.

[Prim3]

I found:

Carbon = 33.96%
Hydrogen = 4.090%
Oxygen = 61.95%

I can't seem to find the % tartaric acid by mass in the sample.

[Borek]

mass of tartaric acid + mass of citric acid = mass of the sample

mass of CO₂ poduced from tartaric acid + mass of CO₂ poduced from citric acid = total mass of CO₂

Just remember, that mass of CO₂ poduced from acid can be calculated from stoichiometry of the combustion if you know acid formula - that means you can prepare two equations in two unknowns.

[Prim3]

^ I'll give it a try. Thanks.

Can anyone help me with the first question? Thank-you.

[marquis]

Try looking up "A+2" elements as a starting point.  A good reference is Interpretation of Mass Spectra by Fred McLafferty and Frantisek Turecek.

It is a good starting point for interpretation.

[Prim3]

I tried figuring out #2 using this method by AWK here: http://www.chemicalforums.com/index.php?topic=1923.0

I can't seem to get it though. Two equations.

My work:

p1 + p2 = 100 (we dont know p1 or p2)
p1 = 100 - p2

(p1) * (pC1) + (p2) * (pC2) = (100) * (pC_total)

For tartaric acid I have:

Carbon = 32.01%
Hydrogen = 4.03%
Oxygen = 63.96%

Citric acid I have:

Carbon = 37.51%
Hydrogen = 4.2%
Oxygen = 58.29%

Now I substitute:

(32.01)*(p1) + (37.51)*(100-p1) = (100)*(37.51 + 32.01)

32.01*p1 + 3751 - 37.51*p1 = 6952

3751 - 5.5*p1 = 6952
p1 = (6952-3752)/(-5.5)
p1 = 682?

I have on idea but I'm sure I'm doing something wrong.

Can someone help me? Thanks!