A compound which contains one atom of X and two atoms of Y for each three atoms of Z is made by mixing 5.00 g of X, `1.15 xx 10^(23)` atoms of Y and 0.03 mole of Z atoms. Given that only 4.40 g of the compound is formed. Calculate the atomic weight of Y if the atomic weights of X and Z are 60 and 80 amu respectively.

Explanation

Moles of X =`(5)/(60)= 0.08` mole
Moles of Y = `(1.15xx10^(23))/(6.022xx10^(23))=0.19` mole
Moles of Z = 0.03 mole .
Since the formula of the compound is `XY_(2)Z_(3)`
moles of X : moles of Y : moles of Z =1 : 2:3 = 0.01 : 0.02: 0.03 . Comparing these values with the moles of X, Y and Z calculated above, we find that moles of X and Y are in excess and therefore, moles of X and Y associated with 0.03 mole of Z are 0.01 and 0.02 mole respectively. Now,
wt of Z + wt . of Y + wt. of Z = wt. of `XY_(2)Z_(3)`
or `0.01xx60 +0.02 xx ` at. wt. of Y + `0.03xx80 = 4.4 `
`:. ` at .wt. of Y = 70 amu .