Question

17. Which of the following is NOT an empirical formula? *

Answer 1

Answer:

17. C_2 H_6 is not an empirical formula.  

18.  option A - The molecular formula can be a simple whole number multiple of the empirical formula.

Explanation:

17. C_2 H_6 is not an empirical formula.  it is molecular formula of ethane.

Empirical formula of C_2 H_6  is CH_3

18.  option A - The molecular formula can be a simple whole number multiple of the empirical formula.

If molecular formula can not be reduced to further than molecular formula to empirical formula.

Molecular formulas tell about number of atoms that each element has in a compound while  empirical formulas tell about smallest proportion of elements in given compound

Answer 2

Answer: 17) d. $C_2H_6$

18. c. The empirical formula of a compound can be twice the molecular formula.

Explanation:

Molecular formula is the chemical formula which depicts the actual number of atoms of each element present in the compound.  

Empirical formula is the simplest chemical formula which depicts the whole number of atoms of each element present in the compound.  

To calculate the molecular formula, we need to find the valency which is multiplied by each element to get the molecular formula.

The equation used to calculate the valency is:

$n=\frac{\text{molecular mass}}{\text{empirical mass}}$

The empirical mass can be calculated from empirical formula and molar mass must be known.

17. Thus the empirical formula of $C_2H_6$ should be $CH_3$

18. The molecular formula will either be same as empirical formula or is a whole number multiple of empirical formula. Thus the empirical formula of a compound can never be twice the molecular formula.