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I recently gave an exam that had a particular short answer question where I asked the students, "What type of reaction is this?". I was looking for neutralization reaction, as aqueous NaOH was reacting with aqueous HCl. However, one student identified it as a double displacement reaction, which is also correct. I only gave partial credit for this answer and I am getting pushback from the student. Should I concede the technicality and give full credit?

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    Please don’t write answers in comments. It bypasses our quality measures by not having voting (both up and down) available on comments, as well as having other problems detailed on meta. Comments are for clarifying and improving the question; please don’t use them for other purposes.
    – cag51
    Oct 5, 2022 at 23:30
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    Note to OP: at the next exam, please ask "What type of double displacement reaction is this?" By asking what type of reaction, instead of what reaction, a student may have felt the pressure of recognizing the overarching family of reaction (i.e. double displacement) instead of the specific one.
    – EarlGrey
    Oct 6, 2022 at 12:19
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    Is there any way that your students could have known that the expected answer was "a neutralization reaction" and not "a double displacement reaction"? Oct 6, 2022 at 15:13
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    It is unclear that you are only expecting people who have a strong understanding of the relationship between the expected answer and the student's answer to be advising you. You should explain how the two answers are related and the rationale for considering the student's answer to only being partially correct.
    – jxh
    Oct 6, 2022 at 16:15
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    Seeing some comments to the answers given (arguing that "a chemical reaction" should also get credit), it would be great to clearly state in the question what the overall topic of the exam was.
    – Sabine
    Oct 6, 2022 at 20:26

7 Answers 7

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If the answer is correct it should get full marks, even if it wasn't the answer you expected. The student can't know what you expected, of course. Yes, concede, though I don't see it as a technicality.

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    (+1) I completely agree. In fact, I'm surprised that this is even an issue. For me things like this were learning experiences for writing questions in the future, although over a 20+ period of time it very, very rarely occurred, because I knew many potential pit falls from my personal student experience when I jumped all over these things and because after one or two of them I got pretty careful with writing test questions -- one example of many that I could give. Oct 4, 2022 at 15:02
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    I use these situations as 'learning' moment in the lectures after the exams, particularly if there was some point that was interesting about the alternate choice. I describe the answer I was expecting for particular question was XYZ and explain why, then note that that some students answered YZA and discuss subtleties that distinguished the two approaches.
    – Carol
    Oct 5, 2022 at 16:04
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    Would you also have accepted "a chemical reaction" as a 100% correct answer? Oct 6, 2022 at 8:15
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    What about "an exothermic reaction"?
    – minseong
    Oct 6, 2022 at 12:31
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    @FedericoPoloni Quibbling over a precise line for an imprecise question is an exercise in futility. The right thing to do here is accept that the question is bad and do better next time. Oct 6, 2022 at 17:44
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which is also correct

I think you've answered your own question. If it's correct, then it's correct and should be marked as correct. Why would you mark an answer you've identified as correct as anything besides correct? If it deserved partial marks, you would've said "which is kind of correct".

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    Would you also have accepted "a chemical reaction" as a 100% correct answer? Oct 6, 2022 at 8:15
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    @Frederico Poloni Of course not - that's just a non-answer offered by someone not studying their lecture notes. It is true but is simply a restatement of the question, a question that might have been more precisely stated as: What type of chemical reaction is this ?
    – Trunk
    Oct 6, 2022 at 13:04
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    Neutralization reactions are a special type of double displacement reactions, which are a special type of chemical reactions, which are a special type of reactions. Your arguments do not seem that clear-cut to me in identifying where the dividing point is. You say "a chemical reaction" is technically true, but then by your argument it should be marked as correct, right? Where do the restatements stop and where does the actual content start? I'm sure the lecture notes also say what neutralization reactions are, so why is a student not expected to know that? Oct 6, 2022 at 13:17
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    @FedericoPoloni I think the test that I would use is: is it likely that a student who knows the material well would reasonably think that this is the expected answer? The answer "a chemical reaction" would fail that test, so I wouldn't accept it. I don't know enough about chemistry to know whether the answer "a double displacement reaction" would pass that test or not. Oct 6, 2022 at 15:11
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    @TannerSwett What I find interesting (as someone with little chemistry background as well) is that in my mind, calling this out as a "double displacement" reaction takes more knowledge than calling it a neutralization reaction. I havent been in a chemistry class in over a decade, but I still remember that HCL is an acid and NaOH is a base. I also remember that a reaction between the two will neutralize them. Googling double displacement reaction only reinforces my opinion, that sounds way more technical than a neutralization, or at least requires more chemistry knowledge to recognize it.
    – JMac
    Oct 6, 2022 at 16:20
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Unless you're also teaching your students how to read your mind, in which case only the answer you were thinking of deserves full credit, then yes, the student deserves full credit.

If "neutralization" is more specific, and conveys more information than "double displacement", you could do the following:

This is now officially a tricky question. If that was unintended, change it, and be careful in the future to not lay similar traps.

If that was intended, then you need to be clear with your students that on your exam "multiple answers may be true, but you need to pick the best, most specific, one". I'd make sure that a couple of times during lectures I would say "X is a double displacement rxn, which is a very general class, but more specifically it is a neutralization rxn..."

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    Would you also have accepted "a chemical reaction" as a 100% correct answer? Oct 6, 2022 at 8:15
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    @FedericoPoloni It depends on the context of the test. If the test or instructions (written or verbal) for the test include the assumption that all discussed reactions are chemical (i.e. a chemistry test in chemistry class) then no, as it is a simple restatement of the question being all discussed reactions are chemical. If the class also discusses other types of reactions, say nuclear, and the test or instructions didn't specify chemistry in any way, then yes, that would be an acceptable answer. However, with context provided in the question, it is unclear how to answer your hypothetical.
    – David S
    Oct 6, 2022 at 14:32
  • @FedericoPoloni - I probably wouldn't, but as to the distinction between "double displacement" and "neutralization", I'm very unqualified to make a judgement, which is why I left so much up to the OP....
    – JonathanZ
    Oct 6, 2022 at 14:36
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    All we had to go on was the OP's statement that it "was also a correct answer". If, as it seems like, there are more facts in play, like one is less specific than the other, OP should have told us. In fact, if two instances make a pattern, this is now a pattern of OP not giving enough information for people to answer their questions well - once for their students in class and on the exam, and once for us here. Which is excellent, because having identified it, the OP now knows "I need to work on communicating more explicitly, with more details."
    – JonathanZ
    Oct 6, 2022 at 14:42
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    +1 for pointing out that it's a chemistry exam, not a mind-reading exam! (I hate exams which turn out to be about second-guessing the examiners as much as answering questions… I've faced questions where several answers were correct, where none were correct, and where one was correct but only for reasons that we hadn't been taught yet. In each case you have to try to work out what the examiners expect you to know and how they want you to think, which is often much harder — and even then it's still really painful having to put an answer that you know is technically wrong…)
    – gidds
    Oct 6, 2022 at 21:23
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Like Federico Poloni, I can’t fully agree with the top answers. Correctness isn’t the only criterion answers are typically judged by: there’s also usually an expected level of completeness or specificity. As Federico says in comments, “a chemical reaction” would be completely correct, but very few teachers would give it full credit.

However, the expected level of detail must be clearly communicated to students. Usually it’s best to do this in the question itself: don’t just ask “simplify this fraction”, ask “simplify this fraction as far as possible”, or “…to reduced form”, or similar. But sometimes the expectation comes from the teaching: if a calculus class has clearly emphasised the classification of stationary points into local maxima, local minima, and inflection points, then it’s fair to ask “What type of stationary point is this?” and expect one of those three answers, and not give full credit for answers like “It is a stationary point above the x-axis.” In such a case, understanding the expected level of detail is part of the course content.

So in the OP’s case: If the class teaching has unambiguously established an expected level of precision — e.g. putting clear emphasis on a specific classification of reaction types — then it may be reasonable to give only partial credit. But the question in itself is very non-specific about the level of precision expected, so if the context hasn’t clearly established that more precision was expected, you should give full credit.

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    A part from the class teaching setting the bar, I would like to point out that correctness is also proportionated to the question, If the question was What is this? I would have give full points to the answer "a chemical reaction". Here. the question was what type of reaction?. A student may have felt the pressure of recognizing the most general possible overarching family of reaction (the type of reaction where type can be read as family) instead of the most speific (type as specific kind).
    – EarlGrey
    Oct 6, 2022 at 12:23
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    +1 for needing to clearly communicate expectations to students.
    – JonathanZ
    Oct 6, 2022 at 14:57
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I'll go against the other answers and argue here that there are valid reasons to assign only partial credit.

I know nothing about chemistry, but from Wikipedia I gather that a neutralization reaction is a special type of double displacement reaction, and I assume that there are specific quantitative results taught in your course that apply only to neutralization reactions, so it is important to identify them and it is not just a matter of naming.

A student that has mastered the material of the course should be able to recognize a neutralization reaction, so that they can apply the relevant results and learn more about it. For another example, I wouldn't want my doctor to say "you have some kind of respiratory disease"; I would like them to be able to identify exactly which one, so that it can be treated with the more appropriate medicine.

A grade, or a question score, should be my best estimate of the mastery of the student; identifying objects that are treated in the course is part of it. This student knows some of the material taught in the course, but clearly not all to a perfect level, otherwise they would have recognized that more specific type of reaction. So partial credit describes the situation perfectly.

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    I have some sympathy with this view, although I think comparing the expected behaviour of a doctor with a student is a little unfair. To nudge the student towards the desired answer, the question might have been better as "What specific type of reaction is this?".
    – TripeHound
    Oct 6, 2022 at 10:17
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    Here there is nothing clear about the student's knowledge based on a flawed question and no context about the class or test. Specificity and clarity matter in language. To be more critical on the student than instructor is a complete failure of thought. The student may very well know how to identify the reaction, but the question didn't demand it. Assumptions not on the test did. You shouldn't punish students for poor instruction. And it is certainly in poor form to demand a greater level of precision in the answer than the test or instruction provides.
    – David S
    Oct 6, 2022 at 14:47
  • @DavidS I agree with you that the instructor should have written a better question, but I see this as a separate point. Sometimes poor questions appear on tests, and we still have to evaluate students based on them. Oct 6, 2022 at 15:20
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    @FedericoPoloni it’s not a separate point. What we mean when we say the question is poor is that it doesn’t test for the knowledge the writer of the question intended to test for. Hence it’s possible that a student will write an answer making it seem like they don’t possess that knowledge, even though they do possess it. In such a case you just have to give them the benefit of the doubt, and if their answer is formally correct, you give them the credit even if you can’t be sure they have the knowledge you wanted them to demonstrate.
    – Dan Romik
    Oct 6, 2022 at 23:15
  • @DanRomik I guess it all depends on how likely we find the scenario of a student knowing perfectly well what a neutralization reaction is and still giving that answer. From my (poor) understanding of the subject, it seems very unlikely. A student knows that neutralization reactions have been treated in the course, recognizes this one, and still decides to go for the more generic answer? Dubious and suspicious. In my view, it is much more likely that they weren't sure whether this was a neutralization reaction or not, and went for a cop-out answer instead. Oct 7, 2022 at 13:57
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I taught high school chemistry, and I would say the answer depends very much on what the overall topic of the exam was. If it was clear from context what you were looking for (say, the topic was "Acids and Bases" or something similar), then yes, this student's answer is technically correct, but clearly missed the point. Partial credit might be appropriate here, or even no credit at all (depending on how far you believe they missed the point).

In another context, "a double displacement reaction" might be the most appropriate answer, for example if the topic of the exam involved the differences between single displacement and double displacement reactions.

If it was a general end-of-semester assessment or an exam on a broader range of topics, you should consider whether it was obvious from context what you were looking for, or not (I would say it's not obvious, but I didn't sit through your course, so I have no idea what you stressed and how). It might be worthwhile to think of what wrong answers a student could reasonably give to such a question, in order to determine if it's sufficiently obvious what you're looking for. In such a case it might be appropriate to give full credit for this answer, and then make the question clearer for next time.

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In my junior high:
If teachers declared a rule, in this situation, "You should be precise when deciding the type of a reaction." Then teachers can regard "double displacement reaction" as wrong answer immediately.
If they haven't declared one, they will consider both "double displacement reaction" and "neutralization reaction" to be right because "neutralization reaction" belongs to "double displacement reaction" you know.

You must have noticed that in both situations, "neutralization reaction" is always a right answer. So teachers will tend to declare such rules if such situations exist.

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