kiiten
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So if butanone has a main peak at 72 and a small one at 73 was high resolution mass spec used to find this?
Is there a peak at 73 because of the hydroxy group and what carbon it's located on (second)?

Finally, why do some ions have m/z values that form but the signal is too small to be seen? Im not really sure what this means but i just guessed and put that the isotope is unstable and has a low abundance?

Thanks
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Pigster
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The peak @ 73 will be the m+1 peak (http://www.chemguide.co.uk/analysis/masspec/mplus1.html)

Tiny peaks are due to unstable molecules or fragments.
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charco
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(Original post by kiiten)
So if butanone has a main peak at 73 and a small one at 72 was high resolution mass spec used to find this?
Is there a peak at 73 because of the hydroxy group and what carbon it's located on (second)?

Finally, why do some ions have m/z values that form but the signal is too small to be seen? Im not really sure what this means but i just guessed and put that the isotope is unstable and has a low abundance?

Thanks
Butanone has a molecular ion at m/z = 72
This should be a strong peak.
Anything above this must be due to isotopes of carbon or hydrogen, either of which will produce a very small signal.

I'm not happy about the data given in this question.

EDIT:

Maybe proton capture MS was used for the spectrum, in which case the m/z of the strongest signal will be 73
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kiiten
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(Original post by charco)
Butanone has a molecular ion at m/z = 72
This should be a strong peak.
Anything above this must be due to isotopes of carbon or hydrogen, either of which will produce a very small signal.

I'm not happy about the data given in this question.

EDIT:

Maybe proton capture MS was used for the spectrum, in which case the m/z of the strongest signal will be 73
I dont think it would be that as its not covered on the spec. What about infrared spec?

NOTE: So sorry, must have been a typo. Youre right - the question says the main peak is at 72. Does that mean its caused by isotopes of carbon and hydrogen (why not oxygen)?
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kiiten
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(Original post by Pigster)
The peak @ 73 will be the m+1 peak (http://www.chemguide.co.uk/analysis/masspec/mplus1.html)

Tiny peaks are due to unstable molecules or fragments.
Thanks but what confuses me is that it says its left out of the A level spec yet they ask it as a question
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kiiten
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Are these right?

1. Given the m/z(204, 206, 207 and 208) and relative intensity of lead.
Species responsible for peak at m/z 208? i put Pb 208?
Ion which reaches the detector the fastest? - i put Pb 204 (lowest m/z)

2. Mass spec of butanone has a main peak at m/z 72 and small peak at m/z 73
Also tiny peaks at m/z 74, 75 etc. Why do some ions with these m/z values form but their signals may be too small to be seen? - i put the isotope is unstable and has a low abundance.

3. mass spec of CH3Cl has 2 main peaks (50 and 52)
predict the relative intensity of these 2 signals - i guessed 35 and 37 (i dont know what it means by relative intensity). The first part asks why the 2 peaks form so i said that chlorine has 2 isotopes. But i feel like im repeating myself if i put that for this question too.
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charco
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(Original post by kiiten)
Are these right?

1. Given the m/z(204, 206, 207 and 208) and relative intensity of lead.
Species responsible for peak at m/z 208? i put Pb 208?
Ion which reaches the detector the fastest? - i put Pb 204 (lowest m/z)

1. Don't forget that only positive ions are detected: 208Pb+


2. Mass spec of butanone has a main peak at m/z 72 and small peak at m/z 73
Also tiny peaks at m/z 74, 75 etc. Why do some ions with these m/z values form but their signals may be too small to be seen? - i put the isotope is unstable and has a low abundance.
2. The presence of isotopes such as 13C and 2H.

However both are in low abundance (about 1%)


3. mass spec of CH3Cl has 2 main peaks (50 and 52)
predict the relative intensity of these 2 signals - i guessed 35 and 37 (i dont know what it means by relative intensity). The first part asks why the 2 peaks form so i said that chlorine has 2 isotopes. But i feel like im repeating myself if i put that for this question too.
The relative intensity will be equal to the relative abundance of the chlorine atoms, i.e. about 3:1
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kiiten
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(Original post by charco)

The relative intensity will be equal to the relative abundance of the chlorine atoms, i.e. about 3:1

Thank you

How do i find this out? Are you talking about:

35CI - 35CI
37CI - 37CI
35CI - 37CI
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charco
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(Original post by kiiten)
Thank you

How do i find this out? Are you talking about:

35CI - 35CI
37CI - 37CI
35CI - 37CI
No, I am talking about the relative abundance of chlorine atoms in nature, which is about three 35Cl atoms for every 37Cl atom.
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kiiten
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(Original post by charco)
No, I am talking about the relative abundance of chlorine atoms in nature, which is about three 35Cl atoms for every 37Cl atom.
Ah ok

This is a different question but is it right?

250cm3 of water added to 50cm3 of 0.2moldm-3 HNO3

Is the new concentration
0.2 x 0.05 = 0.01 moles
0.01 / 0.3 = 0.033 moldm-3 ?
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charco
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(Original post by kiiten)
Ah ok

This is a different question but is it right?

250cm3 of water added to 50cm3 of 0.2moldm-3 HNO3

Is the new concentration
0.2 x 0.05 = 0.01 moles
0.01 / 0.3 = 0.33 moldm-3 ?
One thing that you should always do is ask yourself "is this answer reasonable?"

Do you think that it is reasonable to add water to an acid solution and make it more concentrated?
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kiiten
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(Original post by charco)
One thing that you should always do is ask yourself "is this answer reasonable?"

Do you think that it is reasonable to add water to an acid solution and make it more concentrated?
Im sorry ive done it again (typo)

My answer is 0.033...moldm-3
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charco
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(Original post by kiiten)
Im sorry ive done it again (typo)

My answer is 0.033...moldm-3
now you're talkin'
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kiiten
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(Original post by charco)
now you're talkin'
I take it that's right?
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charco
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(Original post by kiiten)
I take it that's right?
:borat:
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