Question 20
An engineer was trying to develop a new fuel for a motorboat by blending mixtures of different alcohols in order to find out which mixture released the most energy when used in the engine.
The engineer had a number of alcohols in unlabelled bottles. It was decided to identify the alcohols by determining their enthalpies of combustion and comparing these values with those from a data book.
(a) Outline a simple practical experiment that the engineer could use, including the measurements to be taken, in order to determine the enthalpy of combustion for one of the unknown alcohols. You do not need to include details of any calculations.
(5)
(b) Other than heat loss to the surroundings, identify two major sources of error in the experiment. Do not refer to the precision of the equipment.
(2)
(c) The engineer found that the experimental values for the enthalpies of combustion of butan-1-ol and methylpropan-2-ol were very similar and so these values could not be used to distinguish between the two alcohols.
Identify a reagent that the engineer could use to distinguish between these two alcohols.
Give the observation in each case.
(3)
(d) The filter in the air intake for the engine in the motorboat may become partially blocked by dust and debris.
Explain with the aid of an equation why combustion of methylpropan-2-ol under these circumstances would be of economic and environmental concern to the engineer.
(3)
(Total 13 marks)