1. ## chemistry question

An element containing only 2 isotopes , 50P and 53P (50 and 53 are the nucleon numbers) have been analysed in a mass spectrometer . If the relative atomic mass of P is 51.9 , what is the relative abundance of 50P ?

THanks ..

2. Originally Posted by thereddevils
An element containing only 2 isotopes , 50P and 53P (50 and 53 are the nucleon numbers) have been analysed in a mass spectrometer . If the relative atomic mass of P is 51.9 , what is the relative abundance of 50P ?

THanks ..
If an element X has isotopes of $\displaystyle X_a \: , \: X_{b} \: , \: X_c \: ... \: X_n$ and relative abundance $\displaystyle n_a \: , \: n_{b} \: , \: n_c \: ... \: n_n$ respectively (note that the sum of relative abundances is always 1) then the relative atomic mass ($\displaystyle M_r$) is given by:

$\displaystyle M_r = {X_an_a + X_bn_b + X_cn_c + ... + X_nn_n}$

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As a rough check you can check the location of 50, 51.9 and 53 on a number line from 50 to 53. Note that 51.9 lies about 2/3 of the way along it thus it would follow that it will be roughly 1/3 of 50 and 2/3 of 53.

• $\displaystyle M_r = 51.9$
• $\displaystyle X_a = 50$
• $\displaystyle n_a = n_a$
• $\displaystyle X_b = 53$
• $\displaystyle n_b = (1-n_a)$

$\displaystyle 51.9 = 50n_a + 53 - 53n_a$

Solve for $\displaystyle n_a$. Express in whichever method your teacher wants.

3. Originally Posted by thereddevils
An element containing only 2 isotopes , 50P and 53P (50 and 53 are the nucleon numbers) have been analysed in a mass spectrometer . If the relative atomic mass of P is 51.9 , what is the relative abundance of 50P ?

THanks ..
you are missing information. i believe when you typed "P", you meant to type either "50P" or "53P". please make the necessary changes and make sure there are no other errors

4. Originally Posted by Jhevon
you are missing information. i believe when you typed "P", you meant to type either "50P" or "53P". please make the necessary changes and make sure there are no other errors
that 50 should be higher(its the nucleon number) . I cant find a way to post it here .

5. Originally Posted by thereddevils
An element containing only 2 isotopes , 50P and 53P (50 and 53 are the nucleon numbers) have been analysed in a mass spectrometer . If the relative atomic mass of P is 51.9 , what is the relative abundance of 50P ?

THanks ..
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