Chemistry & Biochemistry
Twenty-three chemistry calculators covering stoichiometry, acid-base equilibria, gas laws, thermodynamics, kinetics, and spectroscopy. IUPAC 2021 atomic weights and NIST CODATA constants throughout.
Chemistry calculations divide cleanly into two camps. One is bookkeeping: balanced equations, mole conversions, molar mass arithmetic, dilution from a stock. The math is exact and the bottleneck is care with units and sign conventions. The other is equilibrium: pH, buffer composition, Ksp, K vs Q, ΔG at non-standard conditions. The math involves logarithms and approximations that work over specific ranges and fail outside them.
A textbook can give you the formulas but not the warning when an approximation breaks. A calculator can run the arithmetic but won't tell you whether the inputs make physical sense. The chemistry suite on this site sits between those two failure modes. Twenty-three tools cover the standard general-chemistry and physical-chemistry workflows. All values use IUPAC 2021 atomic weights and NIST CODATA 2022 fundamental constants. Every tool that runs an approximation (the 5% rule on weak acids, the van't Hoff factor for electrolytes, the ideal-gas assumption for room-temperature mixtures) shows its work and flags where the approximation breaks. The output is meant to be defensible to a working chemist, not just visually plausible to an undergraduate.
Pick a tool by what you're trying to do
- "I need to calculate the pH of a solution."
- For single-component acids or bases (strong or weak, with Ka or Kb), use the pH Calculator. For mixing two strong electrolytes (HCl + NaOH and so on), the pH of Mixtures Calculator handles stoichiometric neutralization without Ka math. For buffer pH from a known acid-base ratio, the Buffer Maker applies Henderson-Hasselbalch directly.
- "I need to balance a chemical equation."
- The Chemical Equation Balancer handles combustion, single and double replacement, and net ionic equations using the matrix method. For redox specifically (acidic or basic media, electron tracking, oxidation-state changes), the Redox Reaction Balancer applies the half-reaction method.
- "I need to prepare a solution."
- From a stock concentrate, the Dilution Calculator solves C₁V₁ = C₂V₂ for any unknown with serial-dilution chaining for large concentration drops. From scratch to a target pH, the Buffer Maker picks the right weak acid (acetate at pH ~5, phosphate at pH ~7, Tris at pH ~8) and computes the recipe. From reactant amounts, the Stoichiometry Calculator returns theoretical yield and limiting reagent.
- "I need a molar mass or percent composition."
- The Molar Mass Calculator handles any formula including hydrates (CuSO₄·5H₂O), isotopes (²H, ¹³C), and nested parentheses. The Percent Composition Calculator returns mass fraction by element. The Empirical & Molecular Formula Calculator runs the reverse direction: from combustion analysis percentages and a measured molar mass, back-solve the molecular formula.
- "I need to solve a gas-law problem."
- For single-component gases or a fixed mole count, the Ideal Gas Law Calculator solves PV = nRT for any unknown plus the combined gas law. For mixtures, the Gas Mixture Partial Pressure Calculator applies Dalton's law with mole-fraction weighting. Both work in atm, kPa, mmHg, or bar.
- "I need to compute equilibrium or thermodynamics."
- The K vs Q Checker compares current state to equilibrium and predicts the direction of shift. The Gibbs Free Energy Calculator converts between ΔG°, K, and Q at any temperature using ΔG = ΔG° + RT ln Q. For acid-base equilibria specifically, the pH and Buffer tools cover the Ka/Kb cases.
- "I need to handle precipitation or solubility."
- The Ksp & Precipitation Checker compares Qsp to Ksp, returns molar solubility, and handles the common-ion effect when an ambient concentration is set. For pH-dependent shifts (metal hydroxides, carbonates), pair with the pH Calculator since those Ksp values are pH-sensitive. The Solubility Rules reference page tabulates the standard qualitative rules.
- "I need spectrophotometry."
- For wavelength-to-energy conversion (eV, kJ/mol, frequency, wavenumber, spectral region), use the UV-Vis Wavelength & Energy Converter. For absorbance-to-concentration via Beer-Lambert (A = εlc), cross to the Beer-Lambert Law Calculator.
- "I need reaction kinetics."
- The Reaction Rate Law & Half-Life Calculator handles 0th, 1st, and 2nd order integrated rate laws and half-life calculations. For Arrhenius temperature dependence (ln k vs 1/T linear fit), the regression tool in math handles the slope-and-intercept arithmetic.
- "I need titration curves or buffer capacity."
- The Acid-Base Titration Curve Simulator plots pH vs titrant volume with equivalence and half-equivalence marked. For numerical capacity (β = dCa/dpH at a specific composition), the Buffer Capacity & pH Drift Estimator returns the value plus the pH change after a specific spike. The pKa / pH / Buffer Capacity Explorer is the conceptual visualizer of the β-curve as pKa shifts.
- "I need practice problems for exam prep."
- The Henderson-Hasselbalch Practice Tool generates exam-style buffer problems and checks your work. Solve-for-pH, solve-for-ratio, solve-for-pKa, and post-spike variants rotate so the algebra becomes automatic.
- "I need bond polarity or colligative properties."
- The Bond Polarity Checker uses Pauling electronegativity to classify ionic vs polar covalent vs nonpolar covalent bonds. The Colligative Properties Calculator returns boiling-point elevation, freezing-point depression, and osmotic pressure for dilute solutions.
Sub-areas of chemistry covered here
General chemistry breaks into recognizable sub-areas. The site's twenty-three tools sit in seven of them.
Stoichiometry and composition covers six tools: the Chemical Equation Balancer for atom-conservation in any reaction, the Redox Balancer for electron-tracking specifically, the Stoichiometry Calculator for limiting reagent and yield, the Molar Mass Calculator for formula-to-grams conversion, the Percent Composition Calculator for mass fraction by element, and the Empirical & Molecular Formula Calculator for the reverse direction from combustion analysis. The throughline is conservation: mass, atoms, charge.
Acid-base equilibria and buffers is the largest cluster on the site at seven tools, because the underlying chemistry generates so many distinct workflows. The pH Calculator handles single-component Ka/Kb cases. The Buffer Maker computes recipes via Henderson-Hasselbalch. The pH of Mixtures Calculator handles strong-acid + strong-base stoichiometric neutralization. The Acid-Base Titration Curve Simulator plots full titration curves. The Buffer Capacity & pH Drift Estimator gives numerical β at any composition. The Henderson-Hasselbalch Practice Tool generates exam problems. The pKa Explorer visualizes the β-vs-pH curve as the working pKa shifts.
Gas-phase chemistry uses three tools: Ideal Gas Law Calculator for PV = nRT, Gas Mixture Partial Pressure Calculator for Dalton's law, and the Colligative Properties Calculator (which sits here because vapor-pressure lowering is the connecting concept). Equilibrium and thermodynamics has three more: K vs Q Checker for direction-of-shift predictions, Gibbs Free Energy Calculator for ΔG-K conversion at any temperature, and the Ksp & Precipitation Checker for solubility equilibria. ΔG° = −RT ln K is the recurring connector across that group.
Chemical kinetics has one core tool: the Reaction Rate Law & Half-Life Calculator, which covers 0th, 1st, and 2nd order integrated rate laws plus Arrhenius temperature dependence. That covers most of an undergraduate kinetics course. Spectroscopy sits half here, half in biology. The UV-Vis Wavelength & Energy Converter handles the photon-energy ladder (nm to eV to kJ/mol to cm⁻¹). For absorbance-to-concentration via Beer-Lambert, the bio-lab tool handles that side. Bonding has one tool, the Bond Polarity Checker, which classifies ionic vs polar covalent vs nonpolar covalent from Pauling electronegativity. A small sub-area on this site, but the conceptual entry point for understanding the rest.
Chemistry glossary
Seventeen terms that show up across general and physical chemistry, with the page where each gets used.
- Mole
- Avogadro's number (6.022 × 10²³) of particles. The conversion bridge between mass and particle count, used in every stoichiometry workflow.
- Molarity (M)
- Moles of solute per liter of solution. Temperature-dependent because volume shifts with T. Input for the Dilution Calculator and the pH Calculator.
- Molality (m)
- Moles of solute per kilogram of solvent. Temperature-independent. Used in colligative-property calculations.
- Oxidation state
- Formal electron count relative to the elemental state, assigning all bonding electrons to the more electronegative atom. Tracked by the Redox Balancer.
- Le Chatelier's principle
- A system at equilibrium shifts to partially counteract an applied disturbance (concentration, pressure, temperature). The qualitative version of the Q vs K comparison.
- Half-equivalence point
- In a weak-acid titration, the point where exactly half the acid has been neutralized. At this point [HA] = [A⁻] and pH = pKa. Marked on the Titration Curve Simulator.
- ICE table
- Initial / Change / Equilibrium bookkeeping for solving equilibrium problems. The framework behind the Ka/Kb arithmetic on the pH Calculator.
- Equilibrium constant (K)
- Ratio of product activities to reactant activities at equilibrium, each raised to its stoichiometric coefficient. Temperature-dependent via the van't Hoff equation. Computed in the Gibbs Free Energy Calculator.
- Reaction quotient (Q)
- Same expression as K but evaluated at the current (non-equilibrium) state. Q < K means forward shift, Q > K means reverse, Q = K means at equilibrium. The Q vs K Checker does the comparison.
- van't Hoff factor (i)
- Number of particles per dissolved formula unit. i = 1 for glucose, 2 for NaCl, 3 for CaCl₂. Real solutions show i below the ideal value at high concentration because of ion pairing. Used in the Colligative tool.
- Ebullioscopic constant (Kb)
- Solvent constant linking molality to boiling-point elevation. For water, Kb = 0.512 °C·kg/mol.
- Cryoscopic constant (Kf)
- Solvent constant linking molality to freezing-point depression. For water, Kf = 1.86 °C·kg/mol, roughly 3.6× larger than Kb because the enthalpy of fusion is smaller than the enthalpy of vaporization.
- Activity coefficient (γ)
- Correction factor that turns concentrations into effective activities in non-ideal solutions. Drifts from 1 above ~0.1 M total ionic strength. The reason most calculators understate Ksp/Ka shifts in concentrated systems.
- Standard state
- Reference condition for thermodynamic data. 1 bar pressure for gases (IUPAC; older sources use 1 atm), 1 M for solutes, pure liquid or solid for condensed phases, 25 °C unless stated otherwise.
- Limiting reagent
- The reactant that runs out first in a balanced reaction, setting the theoretical yield. Identified by the Stoichiometry Calculator using mole ratios.
- Theoretical yield
- Maximum product mass from a balanced reaction at 100% conversion of the limiting reagent. Compared against actual yield to get percent yield.
- Enthalpy (ΔH)
- Heat exchanged at constant pressure. Negative ΔH means exothermic. Combined with ΔS in ΔG = ΔH − TΔS, which is what the Gibbs calculator uses to predict spontaneity.
When the calculator is wrong
Every calculator on this site runs an idealized model. The output is only as honest as the assumptions, and the assumptions break under predictable conditions. Knowing where they break is what separates a working chemist from a calculator-trusting student.
Ideal-gas behavior fails above about 10 atm and near each gas's condensation temperature. PV = nRT assumes no intermolecular forces and zero molecular volume. CO₂ at 50 atm and 25 °C deviates from the ideal-gas prediction by roughly 5%. Water vapor near saturation deviates much more. For most undergraduate problems (1 to 5 atm, room temperature, common gases like N₂/O₂/Ar) the deviation stays under 1%. For industrial-scale gas blending or cryogenic mixtures, the Peng-Robinson or van der Waals equations of state replace the ideal-gas relation. The Ideal Gas Calculator flags the regime in its limitations panel.
Activity coefficients deviate from 1 above about 0.1 M total ionic strength. A 1 m NaCl solution doesn't depress water's freezing point to the textbook −3.72 °C; the measured value is closer to −3.37 °C, giving an effective van't Hoff factor of 1.81 instead of the ideal 2.0. The Debye-Hückel limiting law and its extensions correct for this, but no general-chemistry calculator applies the correction by default. Concentrated buffer prep, colligative-property work on saline solutions, and Ksp predictions in seawater all need the activity correction or they're systematically wrong.
Equilibrium constants are temperature-dependent. Always state T when reporting K or Ka. The van't Hoff equation ln(K₂/K₁) = −(ΔH°/R)(1/T₂ − 1/T₁) governs how K shifts with temperature. For Tris buffer, pKa moves by about −0.03 per °C, large enough that a buffer prepared at 25 °C and used at 4 °C in a cold room drifts by ~0.6 pH units. For phosphate buffer, the temperature dependence is much smaller (~−0.003 per °C). Standard practice is to adjust pH at the working temperature, not at the prep bench.
The 5% rule on weak-acid pH calculations breaks above a certain ionization fraction. If [H⁺] from the square-root shortcut exceeds 5% of the initial concentration, the approximation [HA] ≈ C is invalid and the full quadratic is required. The pH Calculator flags this automatically; many textbooks and older calculators don't.
Real reactions don't proceed as cleanly as the balanced equation suggests. Side reactions consume reagent, equilibrium-limited reactions stop short of completion, and transfer losses and water of hydration eat into the recovered mass. A measured yield of 60 to 85% on an organic synthesis is a normal result, not a measurement failure. Yields above 100% mean impurity in the product (water, solvent, starting material), not improvement on the theoretical limit.
Chemistry & Biochemistry Guide
What you can do in Chemistry & Biochemistry
- •Calculate molar mass and percent composition for any chemical formula
- •Balance chemical equations using algebraic and redox methods
- •Determine limiting reagents, theoretical yield, and percent yield in reactions
- •Calculate pH, pOH, Ka, and Kb for acids, bases, and buffer solutions
- •Plan dilutions using C₁V₁=C₂V₂ with serial dilution support
- •Analyze ideal gas problems with PV=nRT and combined gas law calculations
Accuracy, assumptions, and sources
- •Atomic weights use IUPAC 2021 standard values. Isotopically enriched samples may require manual adjustment.
- •pH calculations assume 25°C and dilute aqueous solutions. Ion activity coefficients are approximated as 1.
- •Stoichiometry assumes complete reactions unless percent yield is specified.
- •Ideal gas calculations assume PV=nRT behavior. Real gas deviations occur at high P or low T.
- •Buffer calculations use Henderson-Hasselbalch equation, valid within ±1 pH unit of pKa.
- •Dilution calculations assume volumes are additive (ideal mixing). Concentrated solutions may deviate.
Pick the right calculator fast
- If you need the molecular weight of a compound→Molar Mass Calculator
- If you're balancing a chemical equation→Chemical Equation Balancer
- If you need to find limiting reagent or yield→Stoichiometry Calculator
- If you're calculating pH or working with acids/bases→pH & pOH Calculator
- If you need to prepare a buffer solution→Buffer Maker Calculator
- If you're solving gas law problems→Ideal Gas Law Calculator
- If you need to dilute a stock solution→Dilution Calculator
- If you want elemental composition percentages→Percent Composition Calculator
Common mistakes to avoid
- •Forgetting to balance equations before stoichiometry. Unbalanced equations give wrong mole ratios.
- •Using molality when molarity is needed (or vice versa). Check units: mol/L vs mol/kg solvent.
- •Ignoring significant figures in concentration calculations—propagate precision appropriately.
- •Assuming Henderson-Hasselbalch works outside buffer range (+/- 1 pH of pKa).
- •Confusing strong vs. weak acids: HCl dissociates 100%, but CH3COOH requires Ka calculation.
- •Forgetting temperature effects on equilibrium constants and Kw (Kw changes with temperature).
- •Using wrong stoichiometric coefficients when converting between moles of different species.
- •Ignoring that volumes don't add perfectly for non-ideal mixtures (e.g., ethanol + water).
Editorial policy
- ✓All calculators provide educational estimates, not professional laboratory guidance.
- ✓Atomic weights and constants follow IUPAC standards. Sources are cited in each tool.
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- ✓Results are rounded for display but computed with full precision internally.
- ✓Found an error? Email us at contact@everydaybudd.com and we'll fix it promptly.
- ✓Tools are updated when IUPAC values or chemical education standards change.