No because the mass of the empty beaker , mass of beaker is not balanced the amount of alcohol in the beaker.
Answer: Thus 0.724 mol of
are needed to obtain 18.6 g of 
Explanation:
To calculate the moles :

According to stoichiometry :
2 moles of
are produced by = 1 mole of 
Thus 1.09 moles of
will be produced by =
of 
But as yield of reaction is 75.6 %, the amount of
needed is =
Thus 0.724 mol of
are needed to obtain 18.6 g of 
SI unit of frequency is Hertz(Hz)