Question

An organic compound containing oxygen,carbon,hydrogen and nitrogen contains 20%carbon,6.7%hydrogen and 46.67% nitrogen. Its molecular mass was found to be 60. Find the molecular formula of the compound.

Answer 1

Answer:  $C_1H_4N_2O$

Explanation:

If percentage are given then we are taking total mass is 100 grams.

So, the mass of each element is equal to the percentage given.

Mass of C = 20 g

Mass of H = 6.7 g

Mass of N = 46.67 g

Mass of O = 100 -(20+6.7+46.67) = 26.63

Step 1 : convert given masses into moles.

Moles of C = $\frac{\text{ given mass of C}}{\text{ molar mass of C}}= \frac{20g}{12g/mole}=1.67moles$

Moles of H =$\frac{\text{ given mass of H}}{\text{ molar mass of H}}= \frac{6.7g}{1g/mole}=6.7moles$

Moles of N =$\frac{\text{ given mass of O}}{\text{ molar mass of N}}= \frac{46.67g}{14g/mole}=3.33moles$

Moles of O =$\frac{\text{ given mass of O}}{\text{ molar mass of N}}= \frac{26.63g}{16g/mole}=1.6moles$

Step 2 : For the mole ratio, divide each value of moles by the smallest number of moles calculated.

For C =$\frac{1.67}{1.67}=1$

For H =$\frac{6.7}{1.67}=4$

For N =$\frac{3.33}{1.67}=2$

For O =$\frac{1.6}{1.67}=1$

The ratio of C:H:N :O= 1 :4: 2:1

Hence the empirical formula is $C_1H_4N_2O_1$.

equivalent weight = 12(1)+1(4)+14(2)+16(1)= 60g/mol

The molecular weight = 60 g/mole

Now we have to calculate the molecular formula.

$n=\frac{\text{Molecular weight of metal}}{\text{Equivalent of metal}}=\frac{60}{60}=1$

The molecular formula will be=$1\times C_1H_4N_2O=C_1H_4N_2O$

Thus the molecular formula will be $C_1H_4N_2O$

Answer 2

Explanation:

C H N O

20 6.7 46.67 26.63

12

20

6.7

14

46.67

16

26.63

1.6 6.7 3.3 1.6

1 4 2 1

CH

4

N

2

O formal mass=60

molecular mass=60

n=

60

60

=1

Molecular formula CH

4

N

2

O