Chemistry Calculator
Balance equations, turn grams into moles, and work out concentration, pH and significant figures.
Learn this properly
Lessons from GCSE Combined and Separate Science on this topic: worked steps, then exam-style questions with new numbers every time.
- Moles, the Avogadro constant and reacting massesQuantitative chemistry and the molePlus
- Percentage yield and atom economyQuantitative chemistry and the molePlus
- Concentration in mol/dm³, titrations and gas volumesQuantitative chemistry and the molePlus
See the whole courseThe full course, topic tests and mock papers come with Plus. See Plus
Formulas
| Moles | n = m / M |
|---|---|
| Concentration | c = n / V, with V in dm³ |
| Dilution | c₁V₁ = c₂V₂ |
| pH | pH = −log₁₀[H⁺], and pH + pOH = 14 at 25 °C |
Worked example
Balance Fe + O₂ → Fe₂O₃.
- Oxygen: 2 atoms on the left and 3 on the right. The lowest common multiple is 6, so write 3 O₂ and 2 Fe₂O₃.
- That makes 4 Fe on the right, so write 4 Fe on the left.
- Check: 4 Fe and 6 O on each side.
Answer: 4Fe + 3O₂ → 2Fe₂O₃
Common mistakes
- Changing the small numbers inside a formula to balance it: only the numbers in front can change.
- Putting cm³ straight into c = n / V: divide by 1000 to get dm³ first.
- Forgetting that pH is a log scale: ten times more H⁺ lowers the pH by 1.
- Miscounting significant figures: 0.00450 has three, the 4, the 5 and the final 0.
About this tool
This chemistry calculator does the sums that come up in every GCSE and A-level chemistry course. It balances equations, including ionic half-equations with charges, and shows the atom count on each side so you can see why. It converts between mass, moles and particles from a formula, works out concentration and dilution, finds pH, pOH, [H⁺] and [OH⁻] from any one of them, and counts significant figures.
Tips
- Convert cm³ to dm³ by dividing by 1000 before using c = n ÷ V; the calculator shows this step.
- pH is a log scale: each step of 1 is ten times more or less H⁺.
FAQ
- How does the equation balancer work?
- It counts every element (and the charge) on each side and finds the smallest whole numbers that make both sides equal, by exact algebra rather than trial and error. If no whole numbers work, or more than one set does, it says so.
- Which atomic masses does it use?
- The standard atomic weights from IUPAC, the values most school data books print, so answers match your textbook to the usual 1 or 2 decimal places.
- Does the pH calculator work for weak acids?
- It converts between pH, pOH, [H⁺] and [OH⁻] at 25 °C. For a weak acid you first need [H⁺] from Ka, which this version does not do.