chemistry
posted by NONO .
A certain compound contains only vanadium and oxygen. A 35.00 g sample of the compound contains 19.61 g of vanadium. Determine the empirical formula of this compound.

19.61 g V.
35.0019.61 g oxygen
Convert to moles. moles = grams/molar mass
Then determine the ratio of the two elements to each other with the smallest number being 1.00. The easy way to do that is to divide the smaller number of moles by itself thereby assuring you of obtaining 1.00 for that element. Then divide the other number by the same small number. Round to whole numbers unless the fractional parts are close to 1/4 or 1/2 in which case the easy way is to try multiplying both values by 2, 3, 4, etc until both are close enough to whole numbers to round to them. Post your work if you get stuck. 
I can not find the molar mass can you help me more..

Is The Molecular formula is :: V2(O2)5 ????

Why do you need the molar mass? No, your empirical formula is not right (but close).
19.61g V
moles V = 19.61/50.9 = 0.385
35.0019.61 = 15.39
moles O = 15.39/16 = 0.962
V = 0.385/0.385 = 1.00
O = 0.962/0.385 = 2.50
These aren't whole numbers but if we multiply both by 2 we obtain
V = 1.00*2 = 2
O = 2.50*2 = 5
empirical formula is V2O5.
The problem didn't ask for it but you can calculate the molar mass now after you know the empirical formula. 
THANKS ALOT