Free Online Chemistry Calculators

About ChemCalc

ChemCalc provides free, accurate chemistry calculators for students, educators, and professionals. From basic molar mass calculations to stoichiometry and solution chemistry, every tool gives instant results with no registration required. All calculations use IUPAC atomic masses from the latest periodic table data.

Molar Mass and the Mole Concept

The mole is the central unit of chemistry — it links the macroscopic world of grams and litres to the microscopic world of atoms and molecules. One mole is defined as exactly 6.02214076 × 10²³ entities (Avogadro's number). The molar mass of a compound (in g/mol) is numerically equal to its molecular weight expressed in atomic mass units (amu). To calculate molar mass, sum the atomic masses of all atoms in the molecular formula: water (H₂O) = 2(1.008) + 15.999 = 18.015 g/mol. Our molar mass calculator handles any chemical formula, including hydrates and parenthetical groups.

Solution Chemistry: Molarity, Dilution, and pH

Molarity (M) is the number of moles of solute per litre of solution: M = mol ÷ L. Dilution follows the conservation of moles: C₁V₁ = C₂V₂, where C is concentration and V is volume. This means that to prepare 500 mL of a 0.1 M solution from a 2 M stock: V₁ = (0.1 × 0.5) ÷ 2 = 0.025 L = 25 mL of stock, diluted to 500 mL total. pH is the negative base-10 logarithm of the hydrogen ion concentration: pH = −log[H⁺]. Pure water at 25°C has [H⁺] = 10⁻⁷ M, giving pH = 7. Acidic solutions have pH below 7; basic solutions above 7.

Stoichiometry and Reaction Calculations

Stoichiometry uses the balanced chemical equation as a conversion factor between reactants and products. The molar ratios from the balanced equation (stoichiometric coefficients) determine how many moles of each product form from a given amount of reactant. The limiting reagent is the reactant that runs out first and determines the maximum theoretical yield. Percent yield = (actual yield ÷ theoretical yield) × 100. Industrial chemical processes aim for the highest possible percent yield, while academic laboratory reactions typically achieve 70–90%. Identifying and minimising yield losses (side reactions, incomplete reactions, product loss during transfer) is a core skill in synthetic chemistry.

Frequently Asked Questions

How do I calculate the molar mass of a compound?

To calculate molar mass, add up the atomic masses of every atom in the molecular formula. For water (H2O): 2 hydrogen atoms (2 x 1.008 g/mol) + 1 oxygen atom (15.999 g/mol) = 18.015 g/mol. For glucose (C6H12O6): 6(12.011) + 12(1.008) + 6(15.999) = 180.156 g/mol. Our molar mass calculator handles any formula including parenthetical groups and hydrates automatically using IUPAC atomic masses.

What is the difference between molarity and molality?

Molarity (M) is moles of solute per litre of solution. Molality (m) is moles of solute per kilogram of solvent. The key difference: molarity changes with temperature because liquid volume expands and contracts, while molality does not because mass is temperature-independent. For dilute aqueous solutions near room temperature, the two values are approximately equal because 1 litre of water weighs about 1 kg.

How do I use the dilution formula C1V1 = C2V2?

The dilution equation C1V1 = C2V2 expresses conservation of moles: the moles of solute before dilution equal the moles after. C1 is the initial concentration, V1 is the volume you take from the stock, C2 is the desired final concentration, and V2 is the desired final volume. To make 500 mL of 0.1 M NaCl from a 2 M stock: V1 = (0.1 x 500) / 2 = 25 mL. Take 25 mL of stock and add water to reach 500 mL total volume.

What is the limiting reagent in a chemical reaction?

The limiting reagent is the reactant that is completely consumed first in a chemical reaction, determining the maximum amount of product that can form. To find it: convert all reactant masses to moles, divide each by its stoichiometric coefficient, and the reactant with the smallest result is limiting. The other reactant(s) are in excess. Our limiting reagent calculator performs this analysis step-by-step.

How do I calculate pH from hydrogen ion concentration?

pH is the negative base-10 logarithm of the hydrogen ion concentration: pH = -log[H+]. For example, if [H+] = 0.001 M (or 10^-3 M), then pH = -log(10^-3) = 3. Pure water at 25 degrees C has [H+] = 10^-7 M, giving pH = 7 (neutral). Solutions with pH below 7 are acidic; above 7 are basic. Our pH calculator converts between pH, [H+], and [OH-] instantly.