394 ❯ Avoiding “Stupid” Mistakes on the Free-Response Sectioncorrect NH 4 + + NO 3 – → NH 4 NO 3. Remember, ionic equations, of any type, have ions
(with charges) on one or both sides of the reaction arrow.
• Don’t do a calculator dump (write down every number displayed by your calculator).
For example, your final answer will not be 3.27584827 g.
• Keep in mind the meaning of “observe.” If the problem asks about observation, tell
what you would actually observe (see, hear, or smell). You will not see a compound
separating into ions; usually you will not see the excess reagent, and you will not see the
atoms forming bonds. In contrast, you might observe a compound dissolving.
• Remember a solvent is usually not a reactant. Therefore, changing the grams of
solvent to moles is probably wrong. (However, you will need to know the moles of
solvent if you are looking for a mole fraction.)
• Think before creating mole ratios. Since the solvent is not a reactant, a mole ratio
relating the solvent to anything else in the problem is most likely wrong. We have seen
many students change the grams of water to moles and then use these moles in a mole
ratio to relate to some other substance in the problem.
• Don’t go off on a tangent. Stay focused on answering the original question.
• Double-check the numbers you use. We have seen many cases where the problem gave
a number like 2.75 × 10 –18, and the student worked the problem with 2.75 × 10 –8. If
you show your work, it will be obvious to the grader that you miscopied the value and
you might pick up some points; otherwise, you just have a wrong answer.
• Remember that sometimes not all of the information given is needed to solve the
problem. For example, in the equilibrium problem, many times the temperature is given
but it is not actually part of the calculations.
• Only round your final answer. Don’t round off the results of intermediate calculations;
only use rounding after you’ve gotten your final answer.
• Be careful in reading graphs. Especially take care in reading the scales. We have seen
students write down that 0.5 is between 1.0 and 2.0.
• Don’t confuse intermolecular and intramolecular forces. These are two different
concepts and are not interchangeable.
In addition to avoiding the careless mistakes mentioned above, here are some easy ways to
help improve your score on the free-response questions:
• Show your work. In most cases, no work, no credit.
• Use the space provided for answers. It helps you and the grader if you answer the ques-
tion in the space provided instead of crowding the answers between the questions. You
will have more than enough room on the following page(s). It also helps to label the parts
(a, b, etc.) and to answer the parts in order.
• Make sure your answer can be easily read. It will really help the grader—and your
score—if you write legibly, in a normal size (not too small, please), and use a pencil or
pen that writes dark enough to be easily read.
• Don’t use periodic trends and general rules as explanations. General rules such as “like
dissolves like” are never explanations. They may help you in answering the multiple-choice
part of the exam, but will be of little benefit by themselves in the free-response section.
• Don’t confuse “define” and “describe.” They are two different processes. If you are
asked to describe or explain, simply giving a definition will earn you very few points.
• Use only standard abbreviations. Your instructor may understand your abbreviations,
but the grader may not. If you want to use abbreviations in a response, be sure to define
them.
• Don’t ramble. Normally an explanation or justification can be done in five sentences or
less. Your answers should be clear, concise, and to the point.22-Moore_APP_p371-412.indd 394 31/05/18 1:59 pm