Chemistry Calculators

Five tools, each doing one thing properly. They run entirely in the browser, so nothing typed into them is sent anywhere, there is no account and no usage limit, and they work offline once the page has loaded.

The rule they are all built to is that an answer on its own is close to useless. Every one of them shows the intermediate quantities that produced the result — the per-element contributions, the elimination steps, the subshell sequence — because the reason to use a chemistry calculator is usually to find out where a hand calculation went wrong, and a bare number cannot tell you that.

Pick by what you already have

The five split cleanly by input.

• You have a formula. Molar mass, percent composition and mole conversion all start from something like Fe2O3 or Ca(OH)2. Which one you want depends on the question: a mass per mole, a breakdown by mass share, or a conversion between moles, grams and particle counts.
• You have an element. The electron configuration tool takes a name, symbol or atomic number and returns the full configuration, the shell-by-shell occupancy and the noble-gas shorthand, with the known anomalies flagged rather than silently smoothed over.
• You have an equation. The balancer takes an unbalanced reaction and returns the smallest whole- number coefficients, along with the working that found them.

The formula rules they all share

Three of the five parse chemical formulas, and they parse them the same way. Getting the input right is most of getting the answer right.

Case is significant, and it is the single commonest source of a wrong result. Co is one atom of cobalt; CO is carbon monoxide, one carbon and one oxygen; co is not a formula at all. The same trap catches Ni and NI, Cs and CS, Pb and PB. A formula that returns an unexpected molar mass is nearly always a capitalisation slip rather than an error in the tool.

Groups nest. Parentheses and square brackets both work and can be nested, so Ca(OH)2 and K4[Fe(CN)6] are both read correctly, with the subscript applying to everything inside the bracket.

Hydrates use the dot. CuSO4·5H2O is understood as the anhydrous salt plus five waters, and the molar mass includes them. Leaving the water out is the second commonest input error, and it changes the answer by a great deal.

Why your textbook may give a slightly different number

Standard atomic weights are not constants of nature; they are recommended values that IUPAC's commission revises as measurements improve, and they have moved for a good many elements over the past few decades. A book printed in 2005 will disagree with a book printed last year in the third or fourth significant figure for several elements, and neither is wrong.

A small set of elements has no single agreed figure at all, only a published range — and any tool or textbook that prints one number for them has made a choice within it. The molar mass tool names the value it used whenever that applies, so the source of a disagreement is visible rather than hidden.

There is also an arithmetic difference. Many worked examples round each atomic weight to one or two decimal places before multiplying, which compounds through a large formula; these tools carry the full precision and round once at the end. The gap between the two approaches is usually in the second decimal place of the final answer, and it is worth knowing about before assuming a mistake.

Every value used here comes from the same dataset as the element pages, so a molar mass computed by a tool and the atomic weights shown on the individual element pages will always be consistent with each other.

Learn the method first

Each tool has a matching concept guide under Learn that works the same calculation through by hand. The sensible order is to read the guide, do a few by hand, and then use the tool to check rather than to substitute.