Question

Anne completely fills the fuel tank of her car with a mixture of gasoline and ethanol, C2H5OH. When filled, the fuel tank contains 2350 g of C2H5OH. How many moles of C2H5OH are in the fuel tank?

Answer 1

There are 51.09 moles of C₂H₅OH in the fuel tank

Further explanation  

A mole is a number of particles(atoms, molecules, ions)  in a substance

This refers to the atomic total of the 12 gr C-12  which is equal to 6.02.10²³, so 1 mole = 6.02.10²³ particles  

Can be formulated :

N = n x No

N = number of particles

n = mol

No = 6.02.10²³ = Avogadro's number

moles can also be obtained by dividing the mass (in grams) with the molar mass

m = mass  

M = relative molecular mass / molar mass  

$\tt n=\dfrac{mass}{MW}$

The fuel tank contains 2350 g of C₂H₅OH, so mol  C₂H₅OH(MW= 46 g/mol) :

$\tt moles~C_2H_5OH=\dfrac{2350}{46}\\\\moles~C_H_5OH=51.09$