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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Simo on November 25, 2021, 01:30:06 AM

Title: Cl Mass Spec exercise
Post by: Simo on November 25, 2021, 01:30:06 AM

Good morning guys! Is there any good soul who can please help me understand this exercise so I can start sleep again at night?  ;)

Exercise 5 : A sample of chlorine atoms was placed in a mass spectrometer. In this sample of chlorine,
75% of the atoms were 35Cl atoms and 25% were 37Cl atoms.
The mass spectrometer detected only Cl+ ions and Cl+2 ions. The spectrum
obtained contained four peaks. Draw the mass spectrum obtained.

To my understanding, there either should be 2 columns for the chlorine isotopes ions 35 and 37, or 5 columns if they also detected the molecular ions m/c 70, 71, 72, but they don't say so.
Unless they expect me to draw a different column for the ions +2, due to their difference in mass for the loss of an extra electron, which it sounds very improbable to me.
Long story short, it doesn't make sense to me.

Please heeeeelp!

Thanks everyone and have a lekker day!!

Title: Re: Cl Mass Spec exercise
Post by: Orcio_87 on November 25, 2021, 02:30:52 AM

Did you read about MS spectrum ? It is a graph of relative abundance vs m/z (mass to charge ratio).

Thus mixture of Cl³⁵ and Cl³⁷ (Cl⁺ and Cl²⁺) will give four peaks in total.

Title: Re: Cl Mass Spec exercise
Post by: scanjo on November 28, 2021, 04:44:45 PM

Try here it may help you work it out

https://www.science-revision.co.uk/A-level_mass_spectra.html

Title: Re: Cl Mass Spec exercise
Post by: Orcio_87 on November 28, 2021, 05:26:02 PM

But he placed a mixture of Cl³⁵ and Cl³⁷ atoms, not a Cl₂ gas.

Even if they recombined the spectrometer detected only Cl⁺ and Cl²⁺.

Title: Re: Cl Mass Spec exercise
Post by: Babcock_Hall on December 01, 2021, 03:56:59 PM

@OP, What is the x-axis in a mass spectrometry experiment?