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Why do a redesign?

Over the last decade, the College Board has made significant changes to the way students are assessed on the AP Chemistry exam. Although the test format is generally the same, with a multiple-choice section followed by a free-response section, the questions are less about knowledge recall and significantly more about application. The questions tend to rely on passages, examples, diagrams, data, and graphs.

I teach the AP chemistry course at my school along with a section of Honors Chemistry, and so I incorporate similar types of questions for my first-year students to solve. I do this to help prepare them for what is to come in AP Chemistry, as well as to challenge them with more thought-provoking, application-based questions. This year in my Honors Chemistry class, I decided to use this type of questioning in our semester exam. Rather than give a traditional multiple-choice semester exam, I gave students open-ended questions, which required them to apply their knowledge and make corrections to inaccurate chemistry answers. This experience was unique for my students, and created an authentic assessment opportunity.

What is authentic assessment?

According to Wiggins1, authentic assessment:

  1. Is realistic.
  2. Requires judgement and innovation.
  3. Asks the student to “do” the subject.
  4. Replicates or simulates the contexts in which adults are “tested” in the workplace, in civic life, and in personal life.
  5. Assesses the student’s ability to efficiently and effectively use a repertoire of knowledge and skills to negotiate a complex task.
  6. Allows appropriate opportunities to rehearse, practice, consult resources, and get feedback on and refine performances and products.

In sum, authentic assessment gives students the opportunity to apply their knowledge to novel and complex situations. This allows teachers to gather relevant information about what students do and do not understand. There is no room for guessing answers, as a multiple-choice test allows. Although our exam did not meet all of the requirements laid out by Wiggins, it did fit the majority.

How to redesign?

During the 2020 spring semester of e-learning due to the Covid-19 pandemic, it became apparent how easy it was for students to “google” answers to questions compared to truly understanding and applying their knowledge. Not knowing whether exams would be in-person or online this fall, I thought that one way to redesign an exam would be to make the questions “ungoogleable” by creating scenarios for students to read, apply, and explain. I started by compiling a list of topics that were covered during the fall semester, and then narrowed it down to overarching themes such as atomic structure, electron configurations, periodic trends, nomenclature, reactions, lab experiments, and stoichiometry. These are the topics I felt would allow students to display a good understanding of basic chemistry concepts.

Designing the questions

Once I decided on the topics, I started writing questions that I would generally ask students to answer using justifications, such as, Which element — calcium or zinc — would have the larger atomic radius? I compiled 12 such questions, and started answering them with common student misconceptions. For this question in particular, students often use the periodic trend as justification for their answer, stating something like “calcium has the larger atomic radius because it is farther to the left on the periodic table.” While this trend is an observation, it does not explain anything about the radius of an atom or an understanding of Coulomb’s law. So rather than ask the student the question, I gave them an incorrect answer — and had them explain why the answer was incorrect, and then give the correct answer. There were no additional question types on the exam, which took students approximately two hours to complete.

Sample exam items

Sample 1

Using the periodic table, a student states that the atomic radius of zinc is larger than the atomic radius of calcium because it is farther to the right on the periodic table and has more electrons. The additional electrons result in greater electron-electron repulsions, expanding the electron cloud radius.
Explain what is wrong with this conclusion, and correct the misinformation.

Sample 2

A student is given various solutions and metals to conduct single displacement reactions.
METALS: Calcium, zinc, and copper
SOLUTIONS: (1.0 M): silver nitrate, hydrochloric acid, aluminum chloride, and lead(II) nitrate

The student labels the bottles A-silver nitrate, B-hydrochloric acid, C-aluminum chloride, and D-lead(II) nitrate. After recording the results, the student realizes that they made a mistake in labeling the solutions. Use the student observations along with your knowledge of single displacement reactions to determine the correct solution in the bottles labeled A-D, and justify your answers. (Note: students did have access to an activity series and solubility rules for the exam).

Data Table: Single Displacement Results

Metals Solution A Solution B Solution C Solution D
Ca Bubbles vigorously Bubbles vigorously Bubbles vigorously Bubbles vigorously
Zn Bubbles slowly No reaction Gray, fuzzy-looking metal forms around the zinc Shiny, silvery metal forms around the zinc
Cu No reaction No reaction No reaction Shiny, silvery metal forms around the copper

Sample 3

The following table shows successive ionization energies for several elements in row 3 of the periodic table.

Element IE-1 IE-2 IE-3 IE-4 IE-5 IE-6 IE-7
A 738 1451 7733 10543 13630 18020 21711
B 578 1817 2745 11577 14842 18379 23326
C 787 1577 3232 4356 16091 19805 23780
D 1012 1907

2914

4964 6274 21267 25432
A student states that elements must be halogens, because they all have seven valence electrons. Explain to the student which elements are represented by A, B, C, and D and how to determine that information from the periodic table, along with the given ionization energies.

Scoring guidelines

Much like the AP Chemistry exam, for which I am a current reader, I created scoring guidelines before the students took the exam so that the other teacher and I could grade consistently. I intentionally made the scoring simple, in order to cut down on the amount of time required to read through the exams — although it was still significantly longer than a multiple-choice test. The method I use is to grade the same question for all students before moving to a different question. For the questions above, the following scoring was utilized.

Sample 1 Scoring Rubric: 3 possible points
Answer 1 point for correct response
(0 points for incorrect response)
The atomic radius of Zn is actually smaller than that of Ca (or the opposite relationship accepted). 1 point for noting that either zinc has a smaller radius, or calcium has a larger radius.
Zn and Ca both have 4 occupied energy levels. 1 point for explaining that Zn and Ca have the same number of energy levels.
Zn has more protons (30) than Ca (20) and therefore has a greater effective nuclear charge which increases the force of attraction for the electrons and decreases the radius. 1 point for the correct explanation of why Zn is smaller (or Ca is larger) using Coulomb’s law or effective nuclear charge.
Sample 2 Scoring Rubric: 4 possible points
Answer 1 point for correct response
(0 points for incorrect response)
Solution A – HCl because hydrogen in an acid can be replaced by Ca and Zn but not Cu. 1 point for correct solution with justification.
Solution B – AlCl3 because Al can be replaced by Ca and not Zn and Cu. 1 point for correct solution with justification.
Solution C – Pb(NO3)2 because Pb can be replaced by Ca and Zn but not Cu. 1 point for correct solution with justification.
Solution D – AgNO3 because Ag can be replaced by all of these metals. 1 point for correct solution with justification.
Sample 3 Scoring Rubric: 5 possible points
Answer 1 point for correct response
(0 points for incorrect response)
This is not correct because ionization energy (IE) does not just refer to valence electrons. It is the energy to remove one mole of the most loosely-held electron from a gaseous ion. 1 point for a reasonable explanation about why the student is wrong.

IE increases with each successive electron removed due to the increased nuclear attraction for the remaining electrons. Once the valence electrons are removed there is a quantum leap in energy between the valence energy level and a core energy level, which is closer to the nucleus and experiences a greater Coulombic force of attraction.

Looking at the successive IE in the table, there is a quantum leap in energy between the IE2 and IE 3 for the first element indicating that the element has 2 valence electrons.

This trend continues with the jump occurring between IE3 & IE4 for Al, IE4 & IE5 for Si and IE5 & IE6 for P.

1 point for each correct element with justification.
The elements are Mg, Al, Si, and P (4 points possible).

Outcomes

The student answers to the exam were an excellent indicator of the depth of their chemistry knowledge and understanding. The majority of students tended to be strong in some concepts while weak in others, which I find typical. The overall student scores were generally similar or in some cases slightly lower than their unit tests. The students answered an anonymous survey three weeks following the exam to provide feedback. The number of students who answered the survey was 33 out of 41 (80%). The biggest takeaways from the feedback were that students felt the exam allowed them to show their understanding of chemistry concepts (84%), and thought the exam difficulty was about the same as our unit tests (63%) or harder (27%).

Although my typical assessments are multiple-choice and short answer/discussion, they have not included correcting wrong answers. In the future, I intend to use these types of questions as part of every unit assessment so that students have more experience answering them. I would also like to include more particle diagrams and questions requiring claim/evidence/reasoning answers. I do not allow students to take retests on material, but instead allow them to earn back partial credit (25%) for corrections. I am overall pleased that I created this type of assessment, and look forward to improving on the types of questions.

References

  1. Wiggins, G. Educative Assessment: Designing Assessments to Inform and Improve Student Performance; Joey-Bass Publishers: San Francisco, 1998.

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