Question

Elements x and y form 2 binary compounds. In the first 14.0 g of x combines with 3.0 g of y. In the second, 7.00 g of x combine with 4.50 g of y. The second compound has formula xy, what is the formula of the first one?

Answer 1

second compound

Let molar mass of x is = X

Let molar mass of y is = Y

Moles of x in second compound = Mass / molar mass = 7 / X

Moles of y in second compound = Mass / molar mass = 4.5 / Y

For second compound  

7 / X : 4.5/ Y = 1:1

Therefore

X / Y = 7/4.5

Y / X = 4.5/ 7

The mass of x in first compound = 14g

moles of x in first compound = 14/X

Mass of y in first compound = 3

moles of y in first compound = 3 / Y

14 / X : 3/ Y = 14Y / 3X = 14 X 4.5 / 3 X 7 = 3 :1

Thus molar ratio in first compound = moles of x / Moles of y = 3:2

Formula = x3y