Improving Performance on the AP Chemistry Examination
Writing is an important communication skill, one that affects a student's score on the AP
Chemistry Examination. On the free-response section of the exam, students must communicate
their knowledge of chemistry to the Reader through writing.
Be Specific, Answer the Question
Students need to make sure they answer the question asked. The whole question should be read
before and then again after answering. Students should then make sure they relate their answer to
the specific question asked and include chemical species in the answer.
Answers need to be specific and refer to the chemical species in the question.
Example:
For each of the following use appropriate chemical principles to explain the observation.
Include equations as appropriate.
a. In areas affected by acid rain, statues and structures made of limestone (calcium carbonate)
often show signs of considerable deterioration.
A common answer was that an acid-base neutralization reaction occurred. No further explanation
or chemical equation was given. This general answer does not address the question, does not
include references to the specific chemical species (the limestone and acid rain), and does not
include a chemical equation in the answer as requested. A more detailed explanation is required
to receive the full two points. One point was given for indicating acid rain has a relatively high
[H+], and the second point was given for indicating that calcium carbonate solid reacts with the
acid rain to form gaseous carbon dioxide.
Justification vs. Definitions and Trends
Many questions in the free-response section of the examination require a justification of the
student's answer or an observation. According to Webster's New Collegiate Dictionary, justify is
defined as "to prove or show to be just, right, or reasonable," while a definition is "a statement or
meaning of a word or word group." While a definition could be part of a justification answer,
providing a generic definition alone is not sufficient. The justification should include reference to
the species in the question.
Often students use a periodic trend to justify an answer requesting the student to use chemical
principles. A trend is defined in Webster's as "a line of general direction or movement." It is an
observation, not a justification.
Example:
This question provided four statements and asked the student to use principles of atomic
structure and bonding to explain each one, making sure to include references to both substances.
The first statement is that the atomic radius of lithium is larger than that of beryllium.
An answer containing only the trend that the atomic radius decreases as you go across the
periodic table received no credit. A correct explanation addressed the larger number of protons in
beryllium than lithium and stated that while the electrons of both beryllium and lithium are in the
same shell, the electrons in beryllium have has a stronger attraction to the nucleus since it has
more protons.
Vocabulary
Students need to know and to use chemical vocabulary. Students often use chemical terms
inappropriately. They also will use words like "happy" to describe atoms. Atoms are inanimate
objects that can't have feelings. Students who write about "happy" atoms receive no credit
without further explanation as to what they mean by "happy" chemically.
Students also need to distinguish common words that they use. For example, the difference
between bigger and smaller versus heavier and lighter in reference to mass comparisons can
cause problems.
Write in Sentences
A one-word justification is not sufficient. Students should write in complete thoughts and
therefore sentences. The Reader is not a mind reader, and fragmented answers may not always be
interpreted by the Reader as the student intended. To prevent this from occurring, students
should write their thoughts in complete sentences, including a subject and verb. The subject
should be stated, preferably without the use of pronouns. Students should refrain from using the
word it. They often use the word it without providing the Reader with a clear reference.
Therefore, they receive no points.
Review Answers
Proofreading and editing should be encouraged. Students should make sure they have answered
the question asked. They should check to make sure their thoughts are clear and complete.
Example with 3 Student Responses and Scores
6. Use the principles of atomic structure and/or chemical bonding to explain each of the following. In
each part, your answer must include references to both substances.
(a) The atomic radius of Li is larger than that of Be.
(b) The second ionization energy of K is greater than the second ionization energy of Ca .
a) 2/2 points
b) 2/2 points
a) ½ points because it does not address whether or not the electrons are in same shell.
b) 2/2 points
a) 2/2 points b) ½ points because it does not address why it is harder to remove an
electron from a filled shell.