The steady-state material balance is addressed in Questions
9 and 21 (see Boxes 3 and 4). Both questions are very
similar in the concepts and misconceptions that they are testing
but they differ in the way in which they are phrased.
In Question 9 the simple material balance problem posed is
disguised by the addition of extraneous and irrelevant information.
Information regarding the length of the pipe run and
temperature of the flow streams is irrelevant to the simple
point that the mass flow rate of the product stream must be
36 kg/min. The last two distracters present the test-taker with
two different reasons why it might be impossible to answer
the question as posed. Much of the extraneous data of Question
9 is absent from Question 21. Again the test-taker is given
two different reasons why it might be impossible to know the
correct flow rate.