Mothballs contains 93.71% carbon and 6.29% of hydrogen. If its molecular mass is 128 g/mol. Calculate its molecular formula.

Asked by shahishrishti | 27th Jul, 2014, 08:11: PM

Expert Answer:

 

                                                            Carbon                                   Hydrogen 

Mass of element                                    93.71                                       6.29

We can calculate number of moles from the mass of the element in the compound,

Number of moles                             93.71/12 = 7.8                            6.29/ 1 = 6.29

 

Ratios between the number of moles of each element,

Divide the number of moles by the smallest value:

Most simple ratio                           7.8/ 6.29 =  1.25                            6.29/6.29 = 1

 

Since it is not a whole number we multiply the ratio by 5 to get a whole number ratio. 

Lowest whole number ratio                     5                                                  4

 

Empirical formula:                                                     C5H4

 

Ratio molecular formula /empirical formula:  128g/ 64g = 2 

Molecular formula = 2 x C5H4  =                                C10H8

Answered by Hanisha Vyas | 28th Jul, 2014, 10:24: AM