Suppose there are two known compounds containing the generic elements X and Y. You have a 1.00-g sample of each compound. One sample contains 0.30 g of X and the other contains 0.39 g of X. Identify plausible sets of formulas for these two

compounds.

XY and X3Y

X3Y and X4Y

XY3 and XY4

X2Y and X3Y

X4Y2 and X3Y

X2Y5 and X3Y5

XY and X2Y

To solve this, we must remember that the number of moles in each formula must a whole number.

So we are given two X’s:

X = 0.3

X = 0.39

We divide the two by the smallest X, so divide by 0.3:

X = 0.3 / 0.3 = 1

X = 0.39 / 0.3 = 1.3

However the second X is not a whole number yet, therefore multiply the two X’s by 3 to make them whole numbers:

X = 1 * 3 = 3

X = 1.3 * 3 = 4

So the X’s must be: X3 and X4 and based from the choices, the answer is:

X3Y and X4Y