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Chemistry calculators

Concentrations, pH, dilutions and reaction yields: the maths behind the lab bench.

Molarity from massConcentration of a solution made from a known mass of solute.Solution dilution (C₁V₁ = C₂V₂)Stock volume and diluent needed to hit a target concentration.pH from hydrogen ion concentrationConversion between [H⁺] and pH, with pOH and [OH⁻] at 25 °C.Henderson–Hasselbalch (buffer pH)Buffer pH from the acid dissociation constant and the base/acid ratio.Percent yieldHow much product a reaction actually gave versus the theoretical maximum.Mass percent concentrationSolute mass as a percentage of total solution mass, plus ppm.Radioactive decay & half-lifeAmount of a substance remaining after a given elapsed time.Beer–Lambert law (absorbance)Absorbance and transmittance of a solution from its concentration.Osmotic pressure (van’t Hoff)Pressure needed to stop osmosis across a semipermeable membrane.Molality of a solutionMoles of solute per kilogram of solvent, a concentration measure independent of temperature.Acid-base titration (equivalence point)Unknown acid or base concentration from the titrant volume at the equivalence point.Freezing point depressionHow much a solvent’s freezing point drops when a solute is dissolved in it (a colligative property).Boiling point elevationHow much a solvent’s boiling point rises when a solute is dissolved in it (a colligative property).Buffer capacity (Van Slyke equation)How resistant a buffer solution is to pH change, from its total concentration and pKa.Arrhenius equationReaction rate constant at a given temperature from activation energy and pre-exponential factor.Mole fraction of a mixtureFraction of the total moles in a mixture contributed by each component.Water hardness (as CaCO₃)Total water hardness as calcium carbonate equivalent, from calcium and magnesium ions.Serial dilution seriesFinal concentration after a series of equal-factor dilutions, and the concentration at each step.Raoult’s law (vapor pressure of a solution)Vapor pressure of an ideal solution containing a non-volatile solute.Weak acid/base pH from Ka or KbpH of a weak acid or base solution from its dissociation constant and starting concentration.Activation energy from two rate constantsActivation energy from rate constants at two temperatures (two-point Arrhenius equation).Kp ↔ Kc equilibrium constant conversionConvert between pressure-based and concentration-based equilibrium constants for a reaction.Degree of unsaturation (DBE)Number of rings and pi bonds in a molecule from its molecular formula.Empirical formula from mass percentSimplest whole-number atom ratio of a compound from percent composition and atomic masses.Ionic strength of a solutionIonic strength from the concentration and charge of every ion present in a solution.Graham's law of effusion/diffusionRelative rate at which two gases effuse or diffuse, from their molar masses.Radioactive activity (Bq / Ci)Decay rate of a radioactive sample from its amount and half-life, in becquerels and curies.Rate constant from concentration vs. timeReaction rate constant k from concentration data, for zero, first or second order kinetics.Atom economyShare of reactant mass that ends up in the desired product versus all products formed.Average atomic mass from isotopesWeighted average atomic mass of an element from its isotope masses and natural abundances.Nernst equation (cell potential)Cell potential under non-standard conditions from the standard potential and reaction quotient.Gibbs free energyReaction spontaneity from the change in enthalpy, entropy and temperature.Partial pressure (Dalton's law)Partial pressure of each gas in a mixture from its moles, volume and temperature.Bond order (MO theory)Bond order and bond stability of a molecule from its bonding and antibonding electron counts.Diffusion coefficient (Stokes-Einstein)Diffusion rate of a spherical particle in a fluid, from its size, viscosity and temperature.Young-Laplace pressure (capillary)Pressure difference across a curved liquid interface, from surface tension and curvature.Isoelectric point (pI)pH at which a molecule such as an amino acid carries no net electric charge.Grams to molesConverts a mass in grams to an amount in moles using the substance’s molar mass.Molar mass of a gasFinds a gas’s molar mass from its mass, pressure, volume and temperature (ideal gas law).Normality of a solutionConverts molarity to normality using the number of equivalents per mole.pKa from KaCalculates pKa from the acid dissociation constant Ka using pKa = -log10(Ka).Alligation mixing ratioFinds the ratio and volumes of two concentrations that mix to a target concentration.Crude protein from nitrogenEstimates crude protein percentage from measured nitrogen content and a conversion factor.PPM to molarityConverts a concentration in ppm (mg/L) to molarity using the solute molar mass.Reaction quotient (Q)Calculates the reaction quotient Q for aA + bB ⇌ cC + dD from current concentrations.Combustion analysisFinds the empirical formula of a CHO compound from the CO2 and H2O produced by combustion.Saponification valueDetermines a fat or oil’s saponification value from a KOH back-titration with HCl.Moles to atomsConverts an amount in moles to a number of atoms or particles using Avogadro’s number.Vapor pressure (Clausius–Clapeyron)Finds vapor pressure at a new temperature from a known point and enthalpy of vaporization.Avogadro's number (particles from moles)Number of particles and sample mass from an amount in moles.Atom composition (protons, neutrons, electrons)Subatomic particle counts from atomic number, mass number and charge.Percent ionic characterIonic character of a bond estimated from the electronegativity difference.Lattice energy (Kapustinskii equation)Ionic crystal lattice energy from ion charges, radii and formula-unit count.Cubic unit cell (packing efficiency)Edge length, atoms per cell and packing efficiency for SC, BCC and FCC lattices.Miller indices from axial interceptsMiller indices (hkl) of a crystal plane, plus interplanar spacing for a cubic lattice.Effective nuclear charge (Slater's rules)Net nuclear charge felt by an electron after shielding, using Slater's rules.Combustion reaction balancerBalanced coefficients for complete combustion of a CxHyOz compound in oxygen.Stoichiometric air-fuel ratioTheoretical air-to-fuel mass ratio for complete combustion of a CxHy hydrocarbon.STP conversionCorrects a measured gas volume to STP and finds the equivalent moles.

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