I need help on an A level Chemistry question please

https://cdn.discordapp.com/attachments/775489286979977216/1096501513087623199/IMG_1139.jpg

I don’t know if this link will work but there’s the question. The answers supposed to be 187.1 but I don’t know how to find the answer.

Reply 1

anonymousssss15

So when you use the standard example of chlorine,
You are given 35 with an abundance of 75% and 37 with an abundance of 25%
So to find the relative atomic mass you do:
(35 x 75)/100 + (37 x 25)/100
Therefore you are multiplying the percentage abundance by each relative isotopic mass.

Another way this example could be asked is
35 with an abundance of 15 and 37 with an abundance of 5.
So to find the relative atomic mass you do:
(35 x 15)/20 + (37 x 5)/20

So you can see how to find the relative atomic mass we multiply the relative isotopic masses by their corresponding abundance and divide by the total abundance and add these together.

Therefore the first step of your problem should be substituting your to be calculated isotopic mass with the unknown variable x. Try to solve for x