Chemistry, please help me?

Question

A Newly discovered element has two isotopes. One has an atomic weight of 120.9038 amu with 57.25% abundance. The other has an atomic weight of 122.8831 amu. What is the atomic weight of the element?

Please tell me how to do this problem, by showing the steps. I looked for examples in my chem book, but I couldn't find one.

Answer 1

The way to operate should be this:

120,9038 amu x 0,5725 + 122,8831 amu x 0,4275 = 69,2174 amu + 52,5325 amu = 121,7499 amu --> atomic weight of the element

Answer 2

This isn't that hard of a problem once you know how to solve it. (The same goes with most chemistry).

You know that the total of the 2 isotopes has to add up to 100%, and that the atomic weight is a weighted average of the atomic weight of each isotope.

To find the atomic weight of your element, take 57.25% * 120.9038 and add it to 42.75% * 122.8831.  

0.5725*120.9038 + 0.4275 * 122.8831 = 121.74995 amu

It's always a good idea to check your work when you are done to see if the answer makes sense, this will help you correct math or conceptual errors before you get the answer wrong on a test.  The answer we got is logical, because it is between the two weights of the isotopes, which is what we would expect from an average.

If any of this doesn't make sense, repost or email me and I can try and explain it better.  Good luck!

Answer 3

You need to multiply the atomic weight with the abundance to calculate the ratio of total weight.

120.9038 x (57.25/100) + 122.8831 x ((100-57.25)/100) = 121.7500