This tool walks through a mole calculation one step at a time. You choose a balanced reaction and the quantity you know, and it shows the route to the quantity you want.
Free tool · Chemistry
Mole and stoichiometry steps
You know the formula for moles but lose track of which number goes where.
Everything you enter stays on this device.
Who is this tool for?
It helps a Chemistry student who can recite n = m ÷ M but gets lost when an equation, a ratio and a gas volume appear in one question.
How do I use it?
- Choose a reaction from the list.
- Choose the substance you know, whether you know its mass, amount or gas volume, and type the value.
- Choose the substance you want and how to give the answer.
- Press “Show the steps”.
- Read the three steps and the warnings below the answer.
How does it work?
Step 1 changes what you know into moles, using n = mass ÷ molar mass or n = volume ÷ molar volume. Step 2 multiplies by the ratio of coefficients in the balanced equation.
Step 3 changes the moles into the quantity asked for. Units are written at every line, and the relative atomic masses used are listed under the answer.
What does a worked example look like?
For Zn + 2HCl → ZnCl₂ + H₂, suppose 13 g of zinc reacts. The molar mass of Zn is 65 g/mol, so n = 13 ÷ 65 = 0.2 mol.
The ratio of Zn to ZnCl₂ is 1 to 1, so 0.2 mol of ZnCl₂ forms. The molar mass of ZnCl₂ is 65 + 2 × 35.5 = 136 g/mol. The mass is 0.2 × 136 = 27.2 g.
What can the tool not tell you?
It does not choose a limiting reactant and it gives no laboratory instructions. It covers a fixed list of reviewed reactions only.
It also cannot tell you if a reaction will happen. For that, see the chemistry lessons below.
Where does this connect to the lessons?
Start with why mole calculations become confusing. Then read repairing mole calculations before mixed chemistry questions.
The link between equations and understanding is in balancing an equation versus understanding the reaction. For practical work, see reading apparatus and measurement precision.
For lessons with a teacher, see Chemistry tuition and the one-hour trial class (from RM50).
Common questions
Why must I convert to moles before using the equation?
The coefficients in a balanced equation compare amounts in moles, not masses. 2H₂ and 1O₂ means 2 mol to 1 mol. Changing to moles first makes the ratio valid, and then you can convert back to grams or dm³.
Which molar volume does the tool use for gases?
You choose. The options are 24 dm³/mol for room conditions and 22.4 dm³/mol for standard temperature and pressure. Check which value your question or syllabus material states, because the answer changes with it.
What if I know the amounts of two reactants?
Then the reactant that runs out first, the limiting reactant, decides the answer. This tool assumes the other reactants are in enough amount and does not choose between them, so it warns you about that assumption.
If mole questions still feel tangled after seeing the steps, a teacher can rebuild the method with you on your own questions in a one-to-one lesson.
- Online one-to-one lessons for your child with an experienced teacher.
- Your first class is a one-hour trial, from RM50. The fee is agreed before you book.
- Happy with the teacher? Continue with lessons of about 1.5 hours. If not, ask for another teacher.