Evaluation of chemical formula answers
Updated 30 Aug 2024
The guidelines below explain how a student answer is evaluated against a coded correct or incorrect chemical formula or expression answer. You can edit or create this kinds of chemical answers using the Simple Editor.
Brackets
Brackets in a chemical formula are significant. Na2[MoOCl4] is not the same as Na2MoOCl4.
Parentheses
Parentheses are significant. Zn(OH)4 is NOT equivalent to ZnOH4.
Order of reagents and of products
Order of reagents (molecules on the left side of the reaction arrow) and of products (molecules on the right side of the reaction arrow) are NOT significant. 
is equivalent to 
.
Reagents and products
Reagents and products are not interchangeable, even if the reaction is in equilibrium. 
is not equivalent to 
.
Adjacent superscript and subscript
- A superscript and subscript adjacent to each other
is NOT equivalent to the isotope template 
. - A single subscript, superscript, or stacked superscript/subscript to the left or right of a chemical symbol is a significant modifier of the chemical symbol/formula.
Case
Case is significant. Co is not equivalent to CO.
Coefficients on each reagent/product
The coefficients on each reagent/product are significant. Coefficients must appear in front of the corresponding reagent/product. 2O2 is not O22.
Heat
The word "heat" is a special reagent/product that is case-insensitive.
Order of elements in a compound
The order of elements in a compound is significant. N2O is not the same as ON2.
Correct/specific incorrect answers
- A correct/specific incorrect answer may consist of: a single chemical symbol/formula, multiple chemical symbols/formulas connected by "+" signs, or a complete chemical equation.
- Correct and specific incorrect answers are not limited to contain valid chemical symbols. For example, an author may script an answer involving the chemical "X" as a placeholder.
State marker
A state marker in a subscript is equivalent to a state marker that is not subscripted. Thus, the following are equivalent:
and 
and 
Overbar
An overbar applied to a symbol+subscript is equivalent to an overbar applied to a symbol, followed by a subscript.
-
For example, the following are equivalent:
and 
(difference is slight but look at center of overbar to see that in second example it is centered over the nu and subscript while in the first example it is only over the nu).
- The following are considered equivalent (with and without the subscript 'e'):
- The following notation is NOT recognized as acceptable:
Particles and mass/charge prefixed particles
The following particles and mass/charge prefixed particles are NOT considered equivalent:
If you want to allow either 
or 
to be marked correct, you will have to code both expressions as alternate correct answers. You should not code for every possible combination of particle and mass/charge particle notation. Good form dictates that a student should use all one type of notation.
See also: