Chemistry tools for coursework, lab prep and the kind of checking you want before mixing anything. Balancing equations, working out molar masses, diluting a stock solution, reading electron configurations and computing decay.

Formulas come from standard references and the working is shown on the page, which is deliberate — for schoolwork you usually need the method rather than the answer, and for lab work you should be verifying rather than trusting.

Which tool do I want?

If you…	Use
You need coefficients for a reaction	Gleichungsausgleicher
You are looking up an element or a periodic trend	Periodensystem
You need molar mass for a compound	Molekülbauer
You are diluting a stock solution	Verdünnungsrechner
You need pH, pOH or hydrogen ion concentration	pH-Rechner
You are working with a radioactive sample	Halbwertzeit-Simulator
You need the electron configuration of an element	Elektronenkonfiguration

C1V1 = C2V2 tells you the volume of stock, not the volume of solvent

The commonest dilution mistake is arithmetic that is right and a procedure that is wrong. Solve for V1 and you get the volume of concentrate to take. The solvent you add is V2 minus V1 — the difference, not V2.

In practice you rarely measure the solvent at all. You take V1 of stock, put it in a volumetric flask, and top up to the V2 graduation. Dissolving changes the total volume slightly, so measuring the two separately and adding them does not reliably land on V2.

One safety point that is not arithmetic: when diluting concentrated acid, the acid goes into the water, never the reverse. The mixing is strongly exothermic, and adding water to concentrated acid can boil it and throw acid out of the vessel.