A 7.36 g sample of copper is contaminated with a additional 0.51 g sample of zinc. suppose an atomic mass measurement was performed on this sample. What would be the measured atomic mass? Answer choices are 64.46 63.67 3.94 65.38

Question

A 7.36 g sample of copper is contaminated with a additional 0.51 g sample of zinc. suppose an atomic mass measurement was performed on this sample. What would be the measured atomic mass? Answer choices are 64.46    63.67     3.94     65.38

australopithecus · Answer

I would guess that the atomic mass would be

atomic mass of metal 
= (7.36/(7.36 + 0.51))*63.546g/mol + (0.51/(7.36 + 0.51))*65.409g/mol
which is essentially:   
(ratio of copper in sample)*Grams of Copper in sample + (ratio of zink in sample)*Grams of zink in sample = molecular mass 

This is just my assumption though.

Alternatively you can do this with each answer or the one calculated using my assumption to see if it is correct:

you can check this by calculating the moles of zink and moles of copper individually
Then taking the full mass of the sample 7.87g and finding the moles with the adjusted molecular mass. If they equal you have the right molecular mass for the sample