Neutralization Reaction Calculator
Mix a specific amount of acid with a specific amount of base and find out what is left over: excess acid, excess base, or an exact match. A live 3D beaker and charts show the H+ vs OH- balance as you adjust the amounts.
Reviewed by the ToolNestr Editorial Team — July 2026
Acid
Base
Two ideas that trip students up
1. Acid and base streams merge into one mixture
The red acid stream and blue base stream pour into the same beaker. In this snapshot there is slightly more H⁺ than OH⁻, so the mixed liquid settles on the reddish side — leftover acid, not a 50/50 blend.
2. Whichever bar is taller is left over
For 0.050 L of 0.20 M HCl mixed with 0.030 L of 0.25 M NaOH: mol H⁺ = 0.010, mol OH⁻ = 0.0075. The taller H⁺ bar means 0.0025 mol of acid remains once all the OH⁻ has reacted away.
Neutralization graphs
How it works
The core idea in one line: neutralization is a race between moles of H+ and moles of OH- — whichever side brings more, wins, and the leftover decides whether the mixture ends up acidic or basic.
mol H⁺ = Macid × Vacid × nacid
moles of hydrogen ion available
mol OH⁻ = Mbase × Vbase × nbase
moles of hydroxide ion available
excess = |mol H⁺ − mol OH⁻|
leftover reagent once reaction goes to completion
Because moles depend on concentration, volume, and how many H⁺ or OH⁻ each formula unit supplies (n), two solutions that look similar by volume can still neutralize very differently. Once mol H⁺ and mol OH⁻ are found, whichever is larger is left over after the smaller amount is fully consumed forming water.
Worked example 1 — strong acid + strong base, excess acid
Given: 50 mL of 0.20 M HCl (n = 1) is mixed with 30 mL of 0.25 M NaOH (n = 1). What is left over?
H⁺ is in excess, so the resulting solution is acidic — there is unreacted HCl beyond what the NaOH could neutralize.
Worked example 2 — diprotic acid, excess base
Given: 20 mL of 0.15 M H₂SO₄ (n = 2, diprotic) is mixed with 40 mL of 0.20 M NaOH (n = 1). What is left over?
Each mole of H₂SO₄ supplies two moles of H⁺, so n = 2 is essential here — using n = 1 would wrongly predict excess acid instead of excess base.
Common neutralization reactions and their salts
The salt identity depends only on the acid and base used — not on how much of each you mix.
| Reaction | Salt formed | Resulting pH (stoichiometric mix) |
|---|---|---|
| HCl + NaOH → NaCl + H₂O | Sodium chloride | ≈ 7 (strong + strong) |
| H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O | Sodium sulfate | ≈ 7 (strong + strong) |
| HNO₃ + KOH → KNO₃ + H₂O | Potassium nitrate | ≈ 7 (strong + strong) |
| CH₃COOH + NaOH → CH₃COONa + H₂O | Sodium acetate | > 7 (weak acid + strong base — salt hydrolyzes basic) |
Only strong acid + strong base pairs land at pH ≈ 7 when mixed in exact stoichiometric amounts. Weak-acid or weak-base pairs form salts that themselves shift the pH away from 7.
Where neutralization actually matters
💊 Antacids
Antacid tablets contain a mild base (like calcium carbonate or magnesium hydroxide) that neutralizes excess stomach acid (HCl), relieving heartburn by consuming H⁺ until the excess acid is used up.
🏭 Wastewater treatment
Industrial and municipal wastewater is often acidic or basic before discharge. Plant operators dose acid or base by the mole to bring effluent pH into a safe range, using the same H⁺/OH⁻ balance this calculator computes.
🌱 Soil pH correction
Agricultural lime (a base) neutralizes excess acidity in soil, while sulfur-based amendments can neutralize overly alkaline soil — both are large-scale acid-base stoichiometry problems, just spread across a field instead of a beaker.
🧯 Lab spill neutralization
Spilled acids and bases in a lab are neutralized with a counter-reagent before cleanup. Knowing the moles of acid or base spilled lets responders add just enough neutralizer without overshooting into the opposite extreme.
Common misconceptions
"Neutralization always produces a solution with pH exactly 7."
Only true for a strong acid reacting with a strong base in exact stoichiometric amounts. If either partner is weak, the salt produced hydrolyzes in water and shifts the pH above or below 7 — see the acetic acid + NaOH row in the comparison table above.
"The acid and base must be added in equal volumes to neutralize."
What matters is equal moles of H⁺ and OH⁻ (M × V × n on each side), not equal volumes. A small volume of concentrated acid can neutralize a much larger volume of dilute base, or vice versa.
"n is always 1 for every acid and base."
n is the number of H⁺ (for acids) or OH⁻ (for bases) each formula unit supplies. HCl and NaOH have n = 1, but H₂SO₄ and Ca(OH)₂ have n = 2, and H₃PO₄ has n = 3. Forgetting n for polyprotic acids or polybasic bases is a common source of error, as in worked example 2 above.
"Whichever reagent has the bigger volume is automatically in excess."
Excess depends on total moles of H⁺ or OH⁻, which folds in concentration and n as well as volume. A larger volume of a dilute, low-n reagent can still be outweighed by a smaller volume of a concentrated, higher-n reagent.
Formula sources & further reading
The formulas here are standard, traceable to:
- • OpenStax, Chemistry 2e — acid-base reactions and neutralization (free, peer-reviewed). openstax.org
- • Brown, LeMay & Bursten, Chemistry: The Central Science — Chapter 4, Aqueous Reactions and Solution Stoichiometry.
- • Zumdahl & Zumdahl, Chemistry — acid-base neutralization and salt hydrolysis.
mol H⁺ = M_acid × V_acid × n_acid; mol OH⁻ = M_base × V_base × n_base. Results are rounded for display.
How to use this calculator
Enter the acid side
Molarity, volume, and n (H⁺ per formula unit) for the acid.
Enter the base side
Molarity, volume, and n (OH⁻ per formula unit) for the base.
Read the excess
The larger of mol H⁺ / mol OH⁻ tells you which reagent — and how much — remains.
Related tools
Frequently asked questions
What is a neutralization reaction?
A neutralization reaction is the reaction of an acid with a base to form a salt and water: acid + base → salt + water. In aqueous solution, this is really H⁺ (from the acid) combining with OH⁻ (from the base) to form H₂O, while the leftover ions form the salt.
What determines if the mixed solution ends up acidic, basic, or neutral?
It comes down to which species has more moles available: moles of H⁺ (M_acid × V_acid × n_acid) versus moles of OH⁻ (M_base × V_base × n_base). If H⁺ moles are greater, the leftover H⁺ makes the solution acidic. If OH⁻ moles are greater, the leftover OH⁻ makes it basic. If they are exactly equal, all the H⁺ and OH⁻ have combined into water — for a strong acid and strong base, that gives a neutral solution.
What is the salt product in a neutralization reaction?
The salt is whatever is left after the H⁺ and OH⁻ combine into water — the acid's anion paired with the base's cation. For example, HCl + NaOH → NaCl + H₂O: the salt is sodium chloride. The identity of the salt does not change based on how much of each reactant you use, only the leftover acid or base does.
Does neutralization always give exactly pH 7?
No — only when a strong acid reacts with a strong base in exactly stoichiometric amounts. If either the acid or the base is weak, the resulting salt itself reacts with water (hydrolysis) and shifts the pH away from 7. For example, acetic acid + NaOH gives sodium acetate, a salt that makes the solution slightly basic (pH > 7) because acetate is a weak base. This calculator finds the H⁺/OH⁻ mole balance; it does not compute the exact resulting pH for weak-acid or weak-base systems.
How is this different from a titration calculation?
Titration is the step-by-step process of slowly adding a solution of known concentration from a burette until an indicator signals the equivalence point — it is a lab technique for finding an unknown concentration. This calculator instead takes two solutions with amounts you already know and asks a stoichiometry question: given these exact starting quantities, is there leftover acid or leftover base once they react, and how much?