Changelog

We had it re-checked, and fixed what the check found

After the last release we asked for an independent re-test of everything we had fixed, with instructions to break it. The answer keys held. Other things did not, and they are fixed here.

Typed answers are read more fairly: iron., 0.667 mols and 2/3 now count, and an answer the app cannot read asks you to try again without marking you wrong. Studying in two tabs no longer loses progress. Reviewing a card early no longer pushes it too far into the future, and a slow but correct answer never shortens its interval. On phones the tap-the-table cards use a two-step picker with tiles you can actually hit. A stray line of developer text that appeared at the top of the page is gone.

The element pop-up is a proper dialog for keyboard and screen-reader users, there is a skip link to the table, and Professional mode shows one panel at a time on anything narrower than 720 px. The oxidation tool refuses symbols that are not elements, the small molar-mass tools stop misreading 1,5, and answer choices in Levels 2, 3 and 5 no longer stand out by their length.

Study Mode you can trust, and calculators that reach your phone

Every one of the 439 study questions was checked. Nine answer keys were wrong or unanswerable and are fixed. Wrong answers no longer describe their own mistake, and correct answers no longer carry the working, so you can't pick the right one by its shape. Level 1 stories are complete again, and its wrong answers are now real look-alikes instead of the same three elements. A test now runs before every release so none of this can come back.

Study Mode asks you to type the answer first on symbol and name cards, with the choices one tap away. A card you miss comes back once before the summary. Speed is judged against your own pace, not a fixed clock. The summary lists what you missed with the right answer, and the level screen keeps a daily streak, a Missed this week list you can retry, a topic heat strip, and a new Weak topics session. Levels 3 and 4 gain a stoichiometry practice unit that makes fresh problems every time. Your existing progress moves to a new store automatically; nothing is deleted.

The calculator panel opens with a search box (“What do you need?”) and, on phones, a tool picker: all twelve tools are reachable again. Formulas with real subscripts (H₂O) are read correctly; unknown characters and unclosed brackets are refused instead of silently dropped. Every result shows how it read your input, molar mass and the balancer show their working, results and links can be copied, and Stoichiometry gains a limiting reagent and percent yield mode. One set of constants and pKa values feeds every tool.

Correctness and keyboard pass

An audit of the live site found nine things worth fixing. Eight are fixed in this release; the ninth (phone panels) is fixed for phones and finished in the next entry.

The Oxidation State Finder now reads ion charges the way you'd write them: Fe3+, Fe³⁺, and Fe 3+ all mean iron(III). It shows you how it read your formula before it answers, and asks for a space or a superscript when the charge is genuinely ambiguous (SO42-). The Molar Mass calculator and the Equation Balancer now reject an explicit zero count (H0O) instead of quietly treating it as one.

The periodic table works from the keyboard: Tab to it, move with the arrow keys, open an element with Enter. The calculator panel keeps focus inside itself, closes with Escape, and hands focus back where you were. On phones, Professional mode's filter and detail panels no longer push each other off the screen.

Live element data comes from PubChem again (the old request had stopped working), and the copy now says PubChem where it used to say NIST. Offline updates can no longer delete your working copy if a download fails part-way. The For Schools page carries a real accessibility statement with its known limitations.

Study Mode, rebuilt

The rating buttons are gone. Answer a question and the spaced-repetition engine grades it from whether you were right and how quickly — then schedules your next review on its own. Sessions now come in three shapes: Quick 5 for a spare minute, Standard for a full sit-down, and Due only when you just want to clear your reviews.

The question banks nearly tripled: 146 → 423 questions across all five levels, every one independently checked before shipping. AP/IB exam prep grew from 15 questions to 111. College General Chemistry gained a new Intermolecular Forces unit with a full lesson companion.

And Study Mode finally uses the periodic table itself: some cards now ask you to tap where an element lives instead of picking from a list. Cards no longer hint at their own answers, and each session spreads across ~15 different elements instead of drilling one at a time.