The Student Room Group
Uni students - Complete our survey >>
Uni students - Complete our survey >>
Uni students - Complete our survey >>

Mass Spec CHEM1 Question help

The question is from AQA CHEM1 Jan11:

2) A mass spectrum of a sample of indium showed two peaks at m/z =113 and m/z = 115. The relative atomic mass of this sample of indium is 114.5

(ii) Use the data to calculate the ratio of the relative abundance of the two isotopes

The answer is 1:3 however I can't seem to figure out how to get there,

Any help would be much appreciated :smile:
Original post by Patchoulli
The question is from AQA CHEM1 Jan11:

2) A mass spectrum of a sample of indium showed two peaks at m/z =113 and m/z = 115. The relative atomic mass of this sample of indium is 114.5

(ii) Use the data to calculate the ratio of the relative abundance of the two isotopes

The answer is 1:3 however I can't seem to figure out how to get there,

Any help would be much appreciated :smile:


Remember that if one of the isotopes has a relative abundance (percentage) of 'x' then the other isotope must have a relative abundance of (100-x)

And that the abundances multiplied by the mass numbers added together and divided by 100 gives the weighted average mass of 1 atom ... which is equal to the relative mass.
Reply 2
Avatar for goose183
goose183
1
Original post by Patchoulli
The question is from AQA CHEM1 Jan11:

2) A mass spectrum of a sample of indium showed two peaks at m/z =113 and m/z = 115. The relative atomic mass of this sample of indium is 114.5

(ii) Use the data to calculate the ratio of the relative abundance of the two isotopes

The answer is 1:3 however I can't seem to figure out how to get there,

Any help would be much appreciated :smile:


All you have to do is look at the difference of the 2 m/z values compared to the relative atomic mass.

114.5-113= 1.5
115-114.5= 0.5

Now it's just a case of dividing 0.5/1.5= 0.333
Reply 3
Avatar for Patchoulli
Patchoulli
OP
Original post by charco
Remember that if one of the isotopes has a relative abundance (percentage) of 'x' then the other isotope must have a relative abundance of (100-x)

And that the abundances multiplied by the mass numbers added together and divided by 100 gives the weighted average mass of 1 atom ... which is equal to the relative mass.


Ah! Thank you very much :biggrin:

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you