You are Here: Home

# chemistry help Mass spectroscopy watch

1. will upload in a min

2. need help in part b

for a number of molecular ions peak, I think there will be 4 (4 combinations)
for m/z value is it 320 (I have no idea)

can someone please explain me that
3. Spoiler:
Show
4. (Original post by Qer)

need help in part b

for a number of molecular ions peak, I think there will be 4 (4 combinations)
for m/z value is it 320 (I have no idea)

can someone please explain me that
It's just statistics.

Four chlorines
Two isotopes

How many possible (unique) combinations

37, 37, 37, 37
37, 37, 37, 35
37, 37, 35, 35
37, 35, 35, 35
35, 35, 35, 35
5. Imagine you have 4 coins, how many different combinations of heads and tails can you get? All heads, 1H 3T, 2H 2T, 3H 1T, all tails. 5 different possibilities. It is the same principle in the TCDD. This compound has 5 possible molecular weights. The most abundant peak would be one with 3 Cl^37 and 1 Cl^35. Add up the Mr and this would give you 322g
6. (Original post by charco)
It's just statistics.

Four chlorines
Two isotopes

How many possible (unique) combinations

37, 37, 37, 37
37, 37, 37, 35
37, 37, 35, 35
37, 35, 35, 35
35, 35, 35, 35

5...............................
7. (Original post by KESbian)
Imagine you have 4 coins, how many different combinations of heads and tails can you get? All heads, 1H 3T, 2H 2T, 3H 1T, all tails. 5 different possibilities. It is the same principle in the TCDD. This compound has 5 possible molecular weights. The most abundant peak would be one with 3 Cl^37 and 1 Cl^35. Add up the Mr and this would give you 322g
The most abundant peak would be one with 3 Cl^37 and 1 Cl^35. Add up the Mr and this would give you 322g

I don't understand why 3 CL^37 and one cl^35?
8. (Original post by Qer)
The most abundant peak would be one with 3 Cl^37 and 1 Cl^35. Add up the Mr and this would give you 322g

I don't understand why 3 CL^37 and one cl^35?
The most abundant peak wold be the one wth the most likelihood.

The odds of a 35 are 75%, or 3/4 and the odds of a 37 Cl are 25% or 1/4

Hence the odds for each of the following are:

37, 37, 37, 37 = 1/256 = 0.39%
37, 37, 37, 35 = 3/256 = 1.17 and four different ways of doing it = 4.69%
37, 37, 35, 35 = 9/256 = 3.52% and six different ways of doing it = 21.09%
37, 35, 35, 35 = 27/256 = 10.55% and four different ways of doing it = 42.19%
35, 35, 35, 35 = 81/256 = 31.64%
--------------------------------------------------- total percentage checksum = 100%

So the most intense peak will be due to 37Cl35Cl35Cl35Cl
With a relative mass of 322
9. (Original post by charco)
The most abundant peak wold be the one wth the most likelihood.

The odds of a 35 are 75%, or 3/4 and the odds of a 37 Cl are 25% or 1/4

Hence the odds for each of the following are:

37, 37, 37, 37 = 1/256 = 0.39%
37, 37, 37, 35 = 3/256 = 1.17 and four different ways of doing it = 4.69%
37, 37, 35, 35 = 9/256 = 3.52% and six different ways of doing it = 21.09%
37, 35, 35, 35 = 27/256 = 10.55% and four different ways of doing it = 42.19%
35, 35, 35, 35 = 81/256 = 31.64%
--------------------------------------------------- total percentage checksum = 100%

So the most intense peak will be due to 37Cl35Cl35Cl35Cl
With a relative mass of 322
thanks
It makes sense
10. (Original post by Qer)
thanks
It makes sense
Chemistry does (usually)

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 15, 2018
Today on TSR

### University open days

1. University of Cambridge
Wed, 26 Sep '18
2. Norwich University of the Arts
Fri, 28 Sep '18
3. Edge Hill University
Faculty of Health and Social Care Undergraduate
Sat, 29 Sep '18
Poll

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE