A Nitrogen and Oxygen compound contains 4.2 g of Nitrogen and 12 g of Oxygen. Find the empirical formula. If the molar mass is 756 g per mol, what is the molecular formula?

Expert Answers
justaguide eNotes educator| Certified Educator

A compound of nitrogen and oxygen has 4.2 g of nitrogen and 12 g of oxygen.

As the molar mass of nitrogen is 14 and that of oxygen is 16, the ratio of the number of moles of nitrogen and oxygen in the compound is 1 : 2.5. Multiplying the two by two to yield whole numbers for both gives an empirical formula of 2: 5.

The empirical formula of the compound is N2O5. The molecular mass pf the compound is 756 g/mole. The mass of the empirical formula is 108. This gives a molecular formula of N14O35

The molecular formula of the compound is N14O35.

llltkl | Student

The compound contains 4.2 g of Nitrogen per 12 g of Oxygen.

now consider  atoms   mass ratio   atom ratio(=mass ratio/at.mass)

                     N :O     4.2:12.0        4.2/14:12.0/16

                                              =0.3:0.75 = 1:2.5 =2:5

Hence empirical formula of the compound is N2O5

Now suppose the molecular formula be (N2O5)f, where f is a numerical factor. 

molar mass = (2x14 + 5x16)f = 108f

by condition 108f = 756

or f= 7 Hence the molecular formula of the compound is (N2O5)7 or, N14O35.


Jyotsana | Student

Nitrogen 4.2/14= 0.3      0.3/0.3=1       1*2=2 

Oxygen   12/16=0.75        0.75/0.3=2.5     2.5*2=5

Empirical Formula: N2O5

Molar mass= (2*14)+(5*16)=108g/mole

MFM/EFM= Molecular formula

756g/108g= 7

Molecular Formula= (N205)7  OR  N14O35