chemical analysis of a gas has showed that it contained 33.0% Si and 67.0% F by mass.

Question

 chemical analysis of a gas has showed that it contained 33.0% Si and 67.0% F by mass. At 35.0 C, 0.210 L of the compound exerted a pressure of 1.70 atm. if the mass of the 0.210 L sample was 2.38 g, calculate the molecular formula of the compound

Answer 1

Si= 33%     F= 67%

For 100 g of the compound, 

moles of Si present = 33/28 = 1.1785 moles

 

moles of F present= 67/19= 3.5263 moles

 

dividing by the smallest number 1.1785 , we have,  Si= 1 mole , F= 3 moles

Hence the empirical formula is SiF_3.