Chapter 13, Problem 114A

Interpretation Introduction

Interpretation:

The molecular formula is to be calculated using percentage composition.

Concept introduction:

The molecular formula is the formula which gives the whole number ratio of the atoms present in nature.

Answer to Problem 114A

The molecular formula is $C_8{H}_4{O}_6$.

Explanation of Solution

To calculate empirical formula of a compound, percentage to the atomic mass ratio is calculated and converted into simple whole number ratio.

Element	Percentage	Atomic mass	%/mass	Simple ratio	Whole no. ratio
C	57.8	12	4.82	2	4
O	38.5	16	2.40	1	2
H	3.64	1	3.64	1.5	3

The simplest whole number ratio is:

$C:O:H=4:2:3$

Therefore empirical formula is $C_4{H}_2{O}_3$

Empirical formula mass = $4\times 12+2\times 16+3\times 1$

= 83

Now applying the formula:

$\begin{array}{c}n=\frac{molecularmass}{empiricalmass}\\ =\frac{166}{83}\\ =2\end{array}$

Molecular formula is calculated by multiplying this n with simplest whole number ratio.

Therefore molecular formula is: $C_8{H}_4{O}_6$

Conclusion

The calculations show that the molecular formula is $C_8{H}_4{O}_6$.