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Improving Performance on the AP Chemistry Examination
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by Lisa Zuraw
The Citadel
Charleston, South Carolina
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Eight Suggestions for More Effective FRQ Responses
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.
Each year, the Chief Reader prepares a report called the Student Performance Q&A: Chemistry Free-Response Questions.1,2,3,4 The report contains an analysis of each question, including common mistakes and suggestions to improve student performance. Comments were made on several questions in the 2001 through 2004 Student Performance Q&A reports concerning the students' inability to write effectively to answer the essay questions. These questions are provided in the following table.
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Questions with Comments Made |
| Year |
Concerning Students' Writing Skill in the Q&A |
| 2001 |
5, 7 |
| 2002 |
2, 5, 6, 7 |
| 2003 |
5, 6, 7 |
| 2004 |
1, 2, 5, 6, 7 |
As a Reader, I scored answers that students probably thought were correct, but due to their poor writing skills they received little or no credit. The Student Performance Q&A suggests teaching students the following:
- Be specific in their answers
- Answer the question asked
- Understand the difference between a justification and a definition
- Realize trends are not justifications
- Use and understand chemical vocabulary
- Write in sentences
- Know the proper use of it and other words
- Review their writing
I discuss each of these suggestions in the remainder of this article.
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.
If a question asks for a justification, one should be provided. For example, question 8, part (e) from the 2004 examination provided students with samples of carbon dioxide and carbon monoxide gas at defined conditions and asked them to relate the (i) average kinetic energies, (ii) root mean square speed, and (iii) number of molecules of the samples and to justify their answers.5 Each part of the question had a point value of one. Therefore, a student who had the correct relationship but did not justify the answer did not receive the point for that part.
Answers need to be specific and refer to the chemical species in the question.
Question 6(a) of the 2003 exam asked:
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.6
A common answer was that an acid-base neutralization reaction occurred. No further explanation or chemical equation was given.2 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.6
Another example is question 7(a) of the 2004 examination. It provides the observation that at 25°C and 1 atm, F2 is a gas, whereas I2 is a solid. The student is asked to account for this observation using appropriate chemical principles and to include specific information about both substances.5 An answer that attributed the difference in the phases as being due to the difference in boiling points received no points since the question asked was not answered. Chemical principles were not used in this answer. The students needed to address the difference in intermolecular forces that account for the difference in boiling points. Also, the students needed to mention both the fluorine and the iodine in the answer to receive both points.7
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."8 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.
For example, question 7 in the 2002 free-response section provided a proposed mechanism for the depletion of ozone in the stratosphere. Part (b) asked the student to clearly identify the catalyst in the mechanism and to justify the answer. Many students were able to identify the catalyst, but few were able to provide a correct justification. A correct justification would be "Cl is a reactant in Step I and reappears as a product in Step II."9 A common answer was the definition of a catalyst as something that speeds up a reaction or something that is added to the reaction that doesn't affect the end products. Neither of these are correct justifications for the example in the question. Part (c) of the question asked the student to clearly identify the intermediate in the mechanism and to justify the answer.9 As in part (b), students were able to identify the intermediate but were unable to justify it. The correct justification would be "ClO appears as a product in Step I and is consumed as a reactant in Step II."9 A common answer was that the intermediate is in the middle step. Student answers to both of these questions usually lacked specificity in relating the justification to the species and mechanism given in the question. They did not explain correct reasoning as to why the Cl is the catalyst and ClO is the intermediate.
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."8 It is an observation, not a justification. An example is found on question 6 from the 2002 examination. 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.9
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. Students confused these terms on the carbon monoxide/carbon dioxide question (number 8) of the 2004 examination.1 They also need to understand the difference between intermolecular and intramolecular. Students confused these terms on question 8(b) of the 2003 examination,2 which asked students to explain the differences for the heats of vaporizations for organic molecules containing three carbon atoms. Additionally, students should not use shorthand notations unless they are universal. Some students use notations from class that have no meaning to the Reader. Therefore, they receive no credit.
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.
Conclusion
I encourage you to take the time to evaluate your students in these areas. These problems have been observed by AP Exam Readers and documented in the Student Performance Q&A by the Chief Reader over several years. Ensure that your students can communicate the chemistry they know, so they do not lose points on the AP Chemistry Examination due to problems with their writing. I also encourage you to integrate writing into your chemistry curriculum. Writing helps students learn by helping them process their knowledge as well as communicate their thoughts.
Notes
1Student Performance Q&A: 2004
2Student Performance Q&A: 2003
3Student Performance Q&A: 2002
4Student Performance Q&A: 2001
52004 Free-Response Questions
62003 Scoring Guidelines
72004 Scoring Guidelines
8Webster's New Collegiate Dictionary, 1975, s.v. "definition," "justify," and "trend."
92002 Scoring Guidelines
Lisa Zuraw is an associate professor of chemistry at The Citadel, where she recently received the Medbery Award for Excellence in Teaching. She was a member of the AP Chemistry Development Committee, and the chair from 2001 to 2004.
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