Question

an oxide of nitrogen contains 30.43% of nitrogen . if its molar mass is 98g / mol , find its molecular formula

Answer 1

Dear student!

 

Constituents

 Symbol

%age

Atomic mass

moles of the element = %age/at. mass (relative no. of moles)

Simplest molar ratio

Simplest whole no. ratio

Nitrogen

N

30.43

14

30.43/14=2.17

2.17/2.17=1

1

Oxygen

O

69.57

16

69.57/16=4.34

4.34/2.17=2

2

Thus, empirical formula (NO2)

As, n =  molecular formula mass /empirical formula mass =  98/46= 2.1

Now, molecular formula = n x empirical formula = 2[NO2] = N2O4 

[Practically the molar mass should be 92 instead of 98]

Answer 2

Dear student!

 

Constituents

 Symbol

%age

Atomic mass

moles of the element = %age/at. mass (relative no. of moles)

Simplest molar ratio

Simplest whole no. ratio

Nitrogen

N

30.43

14

30.43/14=2.17

2.17/2.17=1

1

Oxygen

O

69.57

16

69.57/16=4.34

4.34/2.17=2

2

Thus, empirical formula (NO2)

As, n =  molecular formula mass /empirical formula mass =  98/46= 2.1

Now, molecular formula = n x empirical formula = 2[NO2] = N2O4 

[Practically the molar mass should be 92 instead of 98]