A binary compound created by reaction of nitrogen and an unknown element E contains 30.46% N and 69.54% E by mass. If the formula of the compound is N2E4, calculate the atomic mass of E.

15.95

Explanation:

This question is a modification of the calculation of the empirical formula of a compound given its percent composition and atomic weights of the elements in the compound.

Here we are given the formula and the percent composition, so we know that there are 4 atoms of E per 2 atoms of N so lets solve using the information given.

In 100 grams of the binary compound we have

30.46 g N

69.54 g E

The number of moles is the mass divided by atomic weight:

mol N = 30.46 g / A. W N = 30.46 g / 14.00 g/mol = 2.18 mol N

mol E = 65.54 g / A. W E

Thus,

4 mol E / 2 mol N = (69.54 g / A. W E) / 2.18

2 A. E = 65.54 g / 2.18 ⇒ A. W E = 69.54 g / (2 x 2.18) = 15.94 g

So the A. W is 15.94 g/mol which is close the atomic weight of O.