Question

A sample containing only carbon, hydrogen, and silicon is subjected to elemental analysis. After complete combustion, a 0.7020 g sample of the compound yields 1.4 g of CO₂, 0.86 g of H₂O, and 0.478 g of SiO_2. What is the empirical formula of the compound?

Answer 1

Given:-

  

First we have to calculate moles of CO₂ , H₂O and SiO₂ formed.

Then we have to calculate the moles of C, H and Si from the moles of CO₂, H₂O and SiO₂ respectively.

lastly by compairing the moles of C,H and Si, we can deteremine the empirical formula of the compound.

The molar masses of C, H, O and Si are 12 g/mol, 1 g/mol, 16 g/mol and 28 g/mol respectively

Formula:-

​​​​​​​ i)

​​​​​​​

Now ,

Hence, Number of Moles of Carbon = 0.032 mol

ii)

Now,

Hence, Number of Moles of Hydrogen = 0.096 mol

iii)

Now,

Hence, Number of Moles of Silicon = 0.008 mol

​​​​​​Therefore, the ratio of number of moles of C to H to Si is

Here, the smallest number is 0.008

Hence, by dividing 0.008 to all the numbers we get the simplest ratio

Thus,

The simplest ratio represent empirical formula.

Hence, the empirical formula of compound is C₄H₁₂Si.