Question

If from 2g of sucrose (M = 342 Da) 0.8ml of ethanol was obtained (density = 0.8 g / ml; M = 46.07 Da), what is the Yield of the process?

Answer 1

The balanced chemical reaction to obtain ethanol (C2H5OH) from Sucrose (C6H12O6) is :

C₆H₁₂O₆ → 2 C₂H₅OH + 2 CO₂

Note that 1 Da = 1 g/mol   ( by definition)

So, 1 mol of Sucrose provide 2 mol of ethanol

   When 2 g of Sucrose is taken, mol of Sucrose present = { 2 g/ (342 g/mol)} = 0.00585 mol

Hence, 2 x 0.00585 mol = 0 .0117 mol of ethanol should be produced (Theoretically)

Hence, mass of ethanol (Theoretical yield) = 0.0117 mol x 46.07 g/mol = 0.54g

Now, experimental yield =( volume of ethanol in ml ) x (density of ethanol in g/ml )

                                        = 0.8 ml x 0.8 g/mL = 0.64 g

hence, % yield = (experimental yield / theoretical yield)* 100 = ( 0.64/0.54) x100 % = 118.5 %