Molecule number evaluator to grade chemistry answers

Updated 30 Aug 2024

Use the Number of Molecules answer evaluator (expressionOchemEvalNumMols) to compare the number of molecules (contiguous atoms connected by bonds) in the student’s answer to the integer set in the evaluator answer. Both skeletal and mechanism questions support the Number of Molecules evaluator.

Select Grade as Correct or Grade as Incorrect, then enter the conditions you want to be checked in student answers.
Select either:
- total number of compounds
  All the compounds in the student’s response are compared to the author coded value
- number of distinct compounds
  The number of different molecules is compared to the number in the evaluator. For example, if the student’s answer has three Benzene molecules, that would count as one distinct compound.
Select an “is” option.
“Is” options
exactly
Student answer number = the number in this box
more than
Student answer number > the number in this box
fewer than
Student answer number < the number in this box
not exactly
Student answer number <> the number in this box
fewer than or equal to
Student answer number ≤ the number in this box
more than or equal to
Student answer number ≥ the number in this box
Select the number of molecules.
Select any chemical transformation check boxes you want to apply:
- Check both enantiomers
- Check for both resonance structures as well
- Check for identity of sigma-bond networks only
- Eschew normalization (aromatization and ylide standardization)
For example, when “check for both enantiomers” is selected, the evaluator compares the student’s answer to the correct answer and compares the enantiomer of the student’s answer to the correct answer. If either of those comparisons creates a match, the answer is graded as correct.
More about these transformation options
- If you draw a chiral compound without specifying stereochemistry, the system assumes that both enantiomers are included in the evaluation.
  For example
  Say you want to set an answer as being wrong when no stereochemistry is specified. In this case, it’s better to use a Boolean answer evaluator stating that if the specific R enantiomer and the specific S enantiomer are not present, then the answer is wrong.
- The sigma-bond networks refer to the connectivity of the sigma bonds (rather than the pi bonds) of a molecule. For example, choose this option to grade an E and Z isomer as the same.
- Mastering normalizes student responses before evaluating them. Since ylides and aromatics can be drawn in more than resonance form, Mastering normalizes ylides and aromatics to a single conventional resonance form before comparing them. For example, the structures Me2S+-O- and Me2S="O" are viewed as identical compounds, as are the two aromatic resonance forms of 1,2-dichlorobenzene. The normalization process happens by default.
- When you do not want student answers normalized, use "eschew normalization".
  For example
  Choose eschew normalization for "draw a resonance structure" questions. This lets Mastering distinguish different resonance structures of ylides and aromatics. If different resonance structures should NOT be distinguished, do NOT select this option.