Calculating Atomic Weight: Solving a Chemistry Problem

[milana]

Big Question!

In my chem class the teacher doesn't explain very much so I decided to see if this site may help. Ok, so my question is: The atomic mass of an element X is 46.80. A 35.78 gram sample of X combines with 84.10 grams of another element Y, to form the compound XY. Calculate the atomic weight of Y.
Explanations are greatly appreciated :)

 

[symbolipoint]

atomic weight and atomic mass can be used to mean the same thing for purposes of this problem. let y = unknown formula weight, or 'atomic weight' of Y. The X and Y react in a 1:1 mole ratio. How many moles of X was combined in the reaction to form XY? Remember, you were given 35.78 grams of X to react. Enough now to find your set-up and result?

 

[symbolipoint]

A 35.78 gram sample of X combines with 84.10 grams of another element Y, to form the compound XY. Calculate the atomic weight of Y.

Note you made (35.78+84.10) grams of XY. Number of moles = (35.78g)/(46.80g/mole) of XY because the number of moles of X in the reaction is equivalent to the number of moles of XY formed, according to the quantities used in the reaction.