Question

7.456 g sample of UF6 is added to water. 6.53 g of a solid containing U, F and O and 1.69 g of a gas are formed. The gas is 5% H and 95% F by mass. a. What is the empirical formula of the gas? In this case, the empirical formula is the same as the molecular formula (I got HF4) b. What is the molecular formula of the solid? c. Write a balanced equation for the reaction between UF6 and H2O.

Answer 1

a. What is the empirical formula of the gas? In this case, the empirical formula is the same as the molecular formula

An empirical formula is a formula that gives the proportions of the elements present in a certain compound however it does not give the actual numbers or the arrangement of the atoms. To determine this, we do as follows:

H = (1.69)(.05) = 0.08 g ( 1 mol / 1.01 g ) = 0.0792 / 0.0792 = 1
F =  (1.69)(.95) = 1.61 g ( 1 mol / 19 g ) = 0.0847 / 0.0792 = 1

The empirical formula would be HF.

b. What is the molecular formula of the solid?
I bet there is a lacking information for the solid. We cannot determine the molecular formula with only the values given above. The closest would be the compound UF2O2.

c. Write a balanced equation for the reaction between UF6 and H2O.
2H2O + UF6 -> UF2O2 +4HF