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Is it the same to say "Hydrocarbons are compounds of hydrogen and carbon." as saying "Hydrocarbons are compounds of carbon and hydrogen." I got a B in my chemistry test just because of writing "hydrogen and carbon" instead of "carbon and hydrogen".

So i need to know if its the same and my teacher made the mistake or if it's me that made a mistake.

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    $\begingroup$ I’m voting to close this question because that not even chemistry, but how language works. $\endgroup$
    – Mithoron
    Commented Dec 27, 2022 at 17:50
  • $\begingroup$ More precisely, it would be so called pragmatics here, it seems. $\endgroup$
    – Mithoron
    Commented Dec 27, 2022 at 17:56
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    $\begingroup$ @Mithoron My original comment was it is not about chemistry, but English, logic and semantics ( or rather pragmatics, I have not known this meaning). But then I got a Xmas urge to be nice. $\endgroup$
    – Poutnik
    Commented Dec 27, 2022 at 18:01
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    $\begingroup$ I think your teacher wishes to emphasize carbon, so carbon comes first. Organic chemistry is the study of carbon (in the limelight) $\endgroup$
    – ACR
    Commented Dec 27, 2022 at 18:42
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    $\begingroup$ I'd vote to improve the heading to point out it is about the order of words. As of now it sounds too trivial to avoid downvotes. $\endgroup$
    – datenheim
    Commented Dec 28, 2022 at 10:54

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Rather, in a way, you have been both right.

While there are subtle differences in context of pragmatics as below, it should not be the bases of rejecting the answer. It rathers looks like the teacher deliberately marked it as wrong, as it did not literally matched the given answer.

IMHO, instead of asking, you should rather stand up for yourself and confront your teacher. The fact you had to ask about it is evidence of your failure to be confident in your knowledge.

The right order A and B has two points of view(POV):

POV of logic: The order A and B is equivalent to B and A.

POV of pragmatics: A and B is usually used as "A is the main descriptor" while "B is the modifier". In similar sense as if A was a noun and B was a descriptive adjective.

  • Organic compounds are primarily compounds of carbon.
  • Not all carbon compounds are organic ones, but all organic compounds contain carbon.
  • Most of organic compounds contain hydrogen, but not always.
  • Typical exceptions are per-halogenated hydrocarbons, or mellitic anhydride $\ce{C12O9}$, containing just carbon and oxygen.
  • It is therefore natural to start with carbon, when specifying a subclass of organic compounds.

So, primarily, in context of organic compounds, "Hydrocarbons are compounds of carbon and ....."

Now, hydrogen comes as the modifier, specifying which carbon compounds are hydrocarbons.

Therefore, "Hydrocarbons are compounds of hydrogen and carbon." is logically right, pragmatically not exactly wrong, but suboptimal and less usual.

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    $\begingroup$ Frankly, I have to disagree, there really isn't any good reason for marking "hydrogen and carbon" as wrong. If the teacher says it's wrong because it emphasises hydrogen over carbon, that's their own subjective interpretation of it, which shouldn't come into play when assigning marks for a question which has an objectively correct answer. $\endgroup$
    – orthocresol
    Commented Dec 27, 2022 at 20:09
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    $\begingroup$ @orthocresol While there are subtle differences in context of pragmatics, I do agree with you, and omitted to say so explicitly, that it should not be the bases of rejecting the answer. $\endgroup$
    – Poutnik
    Commented Dec 27, 2022 at 20:14
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    $\begingroup$ That's fair, I don't know whether I was really disagreeing with you or with the teacher :) $\endgroup$
    – orthocresol
    Commented Dec 27, 2022 at 20:17
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    $\begingroup$ I feel sorry the OP got stuck with that teacher. No good was served by deducting marks for such a pettifogging reason. $\endgroup$
    – Ed V
    Commented Dec 27, 2022 at 20:33
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    $\begingroup$ @EdV Some teachers hardly know the topic better than students and follow exact wording of given answers. If the answer deviates, they mark it as wrong, even if it may be and often is correct. The extra bad case are expectations of the particular numeric value with given valid digits to be filled in an input form of some webpage. $\endgroup$
    – Poutnik
    Commented Dec 27, 2022 at 20:42

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