Is this a valid method to find percentage of pure ethanol in an impure sample?
What if this unknown material produce part of the energy stated in the problem?


It would be stated in the problem that the amount of heat that the unknown material produced.


  The standard molar enthalpy is measured under standard conditions (1 atm, 25°C). However, the condition inside the bomb calorimeter is unknown.


We are given some information, the final temperature of the system. But you are right in that we do not know the pressure, and the specific heat of the remaining items is difficult to calculate.