Writing a Chem 112 exam
This document is a summary of advice that previous students have found
beneficial. For exam regulations see the university website and the front page of
your exam booklet.
Points 9) to 13) cover some very important points on determining problem
solving strategies and checking your work. You may find these points
beneficial when working on your assignments and lab reports.
1) First and foremost, make sure you have the correct day, time, and location
of the exam. Note that in University, exams are not necessarily held during
class time or in the same room as your lecture. You’d be surprised how many
students miss exams because they had the wrong day, time, or location –
always triple check that you have the correct information. (See the course
outline for the Chem 112 midterm date. The midterm location is TBA).
2) Plan to arrive at the exam early so you can use the washroom and set up
before the exam starts. Bring the appropriate materials. For a Chem 112 exam
you will need HB pencils, a good eraser, your student ID, and one of the
approved scientific calculators (see the course outline).
3) You will be let into the exam room a few minutes early. Do not start the
exam until an invigilator announces the exam has begun.
4) Before you start the exam write your name, student number, and section
number on all the material that has been given to you. Pencil your NSID onto
the opscan sheet.
5) Count the pages of you exam to make sure that no pages are missing.
6) If you forget to bring a watch, check the front board, the invigilators will be
writing the time there periodically.
7) Start by ripping out the data sheet from the back of the exam so you can
have it handy. Check to see what information has been provided for you.
8) Start reading through the exam. If you are certain you know how to do a
question, do it right away. If you are not certain, leave that question and come
back to it later. You will be working on it in the back of your mind as you go
through the rest of the test.
9) Ideally, when you studied for the exam, you studied the specific topics in
the chapter breakdown of the course outline (See the document ‘How to
Study for Chem 112’). Each exam question should correspond to one or more
of these topics. Use key words in the question to identify the topic(s) the
question is testing you on. Once you’ve identified the topic, you’ll be able to
narrow down which equations and problem solving strategies you can use.
10) If you do not know how to approach a mathematical question try the
methods suggested below. You may need to use some combination of a) – d).
a) Go through the question, circle each of the numerical values and write
the corresponding algebraic symbol next to it. Consider all the
equations you know that have these algebraic symbols. Keeping in
mind what other algebraic values are available (molar masses,
constants from the data sheet) try to think of an equation that only has
one variable missing. Solve for this missing variable. Then see if your
missing variable can be used along with the other unused numbers in
another equation. [e.g. Say the question is asking for m and gives you P,
V, and T. R can be found on the data sheet so try using PV = nRT as it
only has one missing variable. This will solve for n. Then you’d think of
an equation that has n (which you just solved for) and m (your desired
value) in it. Hopefully you’d remember the equation m = MM.n. MM can
be determined from the periodic table, so you can solve for m.]
b) Try working backwards. Think of the algebraic symbol for your
answer. What equations is that symbol in? Which of those equations
can be used based on the information given in the question?
c) When in doubt, calculate the number of moles then try a) or b) again.
Moles are commonly the intermediate units.
d) If you can’t think of an equation to use, try using dimensional analysis.
Cancel out units until you reached the desired unit.
11) For multiple-choice questions, you will not be marked on your work but
you should jot down your work so you can look for errors when you are
checking an answer. A common misconception is that when you get an
answer that matches one of the options on a numerical multiple-choice
question than your answer is definitely correct. However, this is not the case,
the exam you are writing is incredibly well designed. Professors predict the
most likely mistakes students will make and include those as the incorrect
multiple-choice options. (If exams were not designed this way than students
could just take the numbers from the question and multiply/divide them at
random until they found an answer that matched a multiple-choice option.)
Always double-check your answer, even if it matches a multiple-choice
option. The best time to double check your work is immediately after you’ve
completed the first attempt, so your method is fresh in your mind. Do not
simply re-read your work, you may not locate all the errors that way. Instead,
check for the common errors listed in 12) below.
12) When checking your work on numerical multiple-choice questions there
are two possible scenarios.
A) Your answer does not match any of the multiple-choice options. This
means you made an error that the professors did not predict. Before
reconsidering your problem solving strategy,
i)
ii)
Check that you copied all the numbers from the question down
correctly.
Check for a calculator error by plugging your work back into your
calculator. (Make sure you practice with your calculator before the
exam, you’d be surprised how many students do not know how to
operate their calculators properly)
If you still do not have a reasonable answer, you may be using the
wrong problem solving strategy or it could be a combination of the
errors listed in option B) below.
B) Your answer matches one of the multiple-choice options. You may have
the correct answer or you may have done one or two predictable
errors. It is unlikely that you have made a calculator error or a copying
error. You can skip steps i) – ii) above and move onto to step iii).
iii)
iv)
v)
vi)
vii)
Re-read the question. You may have stopped solving the problem
one or two steps prematurely.
Check that you calculated all molar masses correctly. A common
mistake is to confuse similar elements in the period table (e.g. Ti for
Tl). Another common mistake is missing a subscript (e.g. using the
molar mass of CO instead of CO2)
If there is stoichiometry in the question, double check you’ve used
the correct stoichiometric coefficients, as this is an incredibly
common error.
Double check that your units canceled out properly (this will
determine if you’ve forgotten to do a unit conversion or if you set
up a dimensional analysis incorrectly).
If you are using an equation that involves addition or subtraction,
check that you plugged your numbers into the equations correctly.
viii)
Checking unit cancellation would not have caught mistakes in this
area.
Compare your answer to the other multiple-choice options. If the
only difference is in the use of prefix multipliers or in the exponent
of scientific notation, check that you have set up your conversion
factors for prefix multipliers correctly. An incredibly common
mistake is to switch around the numbers that precede units (e.g.
writing 1 g per 1000 kg when it’s actually 1000 g per 1 kg), your
units would still cancel out with this mistake but your answer
would be incorrect.
Checking for these common errors may seem like a lot of work, but
not all of them will apply for every question. If you use these checks
while studying you’ll likely find that you can do them very quickly
on an exam.
13) When checking your work on long answer questions start by using the
procedure i) – viii) listed above. In long answer questions you will also be
marked on the quality of your work so include the following checks to get full
marks.
a)
b)
c)
d)
Make sure you show all your work. This includes unit conversions.
You do not need to show molar mass calculations. If there was a
reaction involved, include a balanced chemical equation. Include
states and any charges in the balanced equation.
Make sure you include your units. A unit should follow every
number you write. If you are using the same unit but referring to
different species make sure you include qualifiers (e.g. 0.21 mol O 2,
0.56 mol N2).
Make sure you used significant figures correctly. Do not round
intermediate values or constants. Only your final answer should be
rounded off to the correct number of significant figures.
Make sure your work is easy for the marker to follow. If you did
steps out of order, number the steps. Underline intermediate values.
Circle your final answer.
14) Before you hand in your exam. Make sure you filled in your op scan sheet
multiple-choice answers correctly. Guess on any multiple-choice questions
that you did not have time to answer. Make sure you have filled out all the
necessary information on your exam booklet and op scan sheet (name, NSID,
section, etc.). When you are ready to submit your exam, bring your student
card, op scan, data sheet, and exam booklet to where the invigilators are
collecting exams. Hand everything over to the invigilator and sign the tally
sheet. Retrieve your student card. If other students are still writing, pack up
your bag quietly and shut the door quietly when you leave.