Free chemistry calculators for the lab
15 everyday chemistry calculations: moles, solutions, dilutions, pH, buffers, titrations, hardness and gases. Formula shown, with practice problems.
Moles and solutions
Mass to moles
M = sum of the atomic masses in the formula. E.g. NaCl 58.44; NaOH 40.00; CaCO₃ 100.09; H₂SO₄ 98.08 g/mol.
Molarity and normality
z = H⁺ or OH⁻ exchanged per molecule: HCl, NaOH = 1; H₂SO₄, Ca(OH)₂ = 2; H₃PO₄ = up to 3. V = final volume in the volumetric flask.
Making a solution: mass to weigh
For a hydrate, use the hydrate's molar mass (e.g. CuSO₄·5H₂O = 249.69 g/mol). Dissolve, then make up to the mark.
Dilution (C₁V₁ = C₂V₂)
Same units for C₁ and C₂ (mol/L, mg/L, %…). The water volume is approximate: better to make up to the mark of a volumetric flask.
% w/w and density → mol/L
E.g. HCl 37 % ≈ 12 mol/L; H₂SO₄ 96 % ≈ 18 mol/L; NaOH 50 % ≈ 19 mol/L. Take the density from the data sheet at the actual temperature.
mol/L and density → % w/w
Reverse of the previous calculation. For a dilute solution (ρ ≈ 1), % ≈ g/L ÷ 10.
mg/L, ppm, mmol/L and meq/L
In dilute water (ρ ≈ 1 kg/L), mg/L = ppm. E.g. Ca²⁺ 40.08 g/mol, z = 2; Mg²⁺ 24.31, z = 2; Na⁺ 22.99, z = 1; Cl⁻ 35.45, z = 1.
Average molar mass of a mixture
Defaults: dry air (N₂, O₂, Ar) → 28.96 g/mol. Enter 0 for a missing component. Fractions are normalised if they do not add up to 100.
pH, acids, bases and titrations
pH of a strong acid or base
Complete dissociation, activities ignored, 25 °C (Kw = 10⁻¹⁴). Valid from 10⁻⁶ to about 0.1 mol/L. H₂SO₄ with z = 2 is an approximation.
Buffer pH (Henderson-Hasselbalch)
pKa at 25 °C, activities ignored. A buffer works at pKa ± 1; beyond a 10:1 ratio it hardly buffers any more.
Titration: unknown concentration
r comes from the balanced equation: HCl + NaOH → r = 1; H₂SO₄ titrated with NaOH → r = 0.5; Na₂CO₃ titrated with HCl to pH 4.5 → r = 0.5.
Water hardness as CaCO₃
Soft: under 60; moderate: 60 to 120; hard: 120 to 180; very hard: over 180 mg/L CaCO₃. 1 °f = 10 mg/L; 1 °dH = 17.8 mg/L CaCO₃.
Gases and reactions
Ideal gas: PV = nRT
kPa × L = J, hence R = 8.314. At 0 °C and 101.325 kPa, 1 mol occupies 22.41 L; at 25 °C, 24.47 L. Absolute pressure, not gauge.
Combined gas law
Same amount of gas, absolute pressures. Temperatures are converted to kelvin (T + 273.15).
Percent yield of a reaction
Start from the limiting reactant (the one giving the least product). Defaults: ethanol → ethyl acetate (ν = 1). Over 100 %: wet or impure product.
Learning and checking tools. The ranges shown are general guidance: always follow your plant's procedures, permits and set points. Nothing is sent anywhere: the calculations run in your browser.