Documentation:CHBE Exam Wiki/Module 1 - Process Basics

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CHBE 241
Exam resources wiki
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Chemical and Biological Engineering
Welcome to the CHBE Exam Resources Wiki!

This wiki is intended to host past exams

with fully worked-out hints and solutions
Past Exams
Final Exam 2016W
Midterm Exam 1 2016W
Midterm Exam 2 2016W
Problem Sets
Module 1 - Process Basics
Module 2 - Reactors
Module 3 - Separations 1
Module 4 - Separations 2
Module 5 - Non-reactive Energy Balances
Module 6 - Reactive Energy Balances


Question 1

Given a solution that is 20 wt% HCl with a specific gravity of 1.2, find the molarity of the solution.
The molecular weight of HCl is 36.5 g/mol.

Solution




Question 2

The molar composition of a gas mixture composed of species A, B and C are 30 mole%, 50 mol% and 20 mol% respectively. The molecular weights of species A, B and C are MA = 12 g/mol, MB = 32 g/mol and MC = 50 g/mol respectively.

Question 2a

Calculate the average molecular weight of the gas mixture

Solution





Question 2b

What are the weight fractions of species A, B and C? Using 100 moles as the basis

Solution
Number of moles (mol) Molecular Weight (g/mol) Mass (g) X
30 12 360 0.1216
50 32 1600 0.5405
20 50 1000 0.3378
Total - 2960 1


Question 3

A stream is 70% H2 and 30% N2 by mass. Will the mole fraction of H2 be greater than, equal to or less than 70%? Explain.

Solution

Since H2 has a smaller molecular weight, the number of moles and mole fraction of H2 will be larger. Hence, the mole fraction will be larger than 70%.



Question 4

Blueberries contain about 85 wt% water and 15 wt% sugar (solids). To make blueberry jam, blueberries and pure sugar (solids) are mixed at a ratio of 60:40 by mass. Upon mixing, the mixture is then heated until the final water content of the mixture is one-third water by mass.

Question 4a

Draw and label a flowchart of this process.

Solution

Block flow diagram for CHBE 241 MOD1Q4


Question 4b

Perform the degree of freedom analysis

Solution
Parameter Values
Unknowns 3 (m1, m2, m3)
Species balances 2
Feed ratio 1
DOF 0

Question 4c

Calculate how many kilograms of blueberries are needed to make a kilogram of jam.

Solution

Based on the feed ratio given,

The sugar balance is

By solving both the equations simultaneously,


Question 4d

The cost of sugar and blueberries are $0.15/lb and $2/lb respectively while the cost of operating the evaporator is $85 per day. If the blueberries are fed at 50 kg/hr, what is the cost to produce jam per day? Assume that the production period per day is 10 hours.

Solution

Cost of blueberries:


Cost of sugar:


Total cost: