Acid · Base · Stoichiometry

Neutralization calculator: how much base neutralizes an acid

Order the right amount of caustic before the tank goes over pH.

Last updated 2026-09-28. Math runs in your browser, no data leaves your computer.

Start with the chemical sitting in the tank, then pick what you will add to neutralize it. It works both ways round, so an acid spill neutralized with soda ash and a caustic rinse neutralized with sulfuric acid run through the same form.

The chemical you have

Pick the pure substance, not the trade name, because the math runs on the molecule and its molar mass.

Presets are summed from the IUPAC CIAAW 2024 atomic weights, and you can type over them.

The hydrogen ions each mole gives up or takes up, so 2 for sulfuric acid and 1 for caustic soda.

Pick whatever the drum label, the tank gauge, or the lab report actually gives you.

Use the weighbridge ticket or the net weight on the drum, since tare left in the number overstates the charge.

Read it off the tank gauge or strapping table at the working level, not the nameplate capacity.

Take it from the COA or a titration, because a spent bath rarely sits at the strength it was made up to.

Take the relative density from SDS Section 9; the tool treats it as kg per liter to turn volume into mass.

Lab reports often give normality instead, and for sulfuric acid 1 N is only 0.5 mol/L, so check the unit.

What you will add

Pick the neutralizer and the strength you buy it at. Leave the strength at 100 for a dry solid such as soda ash or hydrated lime, and add an SG when you want the answer as a volume to pump.

It has to be the opposite type to the chemical above, an acid against a base or a base against an acid.

Filled from the preset, and editable for a hydrate or a grade the list does not carry.

Soda ash counts 2 when it goes all the way to carbon dioxide, and 1 if you stop at bicarbonate.

Enter 50 for 50 percent caustic lye so the answer is the weight of liquid you actually order.

Only needed for a liquid, so the tool can return the volume to meter in as well as the weight.

Every weight and volume in the result table below uses this unit pair.

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General guidance only. Verify against the cited primary sources before you commit to a shipment, declaration, or contract.

How the stoichiometry works

Neutralization pairs hydrogen ions from the acid with hydroxide or carbonate from the base. The tool turns what you entered into moles of chemical, multiplies by the H+ each mole gives or takes, and divides by the H+ per mole of the neutralizer. In one line, mol neutralizer = mol chemical × H+ chemical ÷ H+ neutralizer, then the mass follows from the molar mass and the strength you buy it at.

Moles come from the mass of pure chemical divided by its molar mass. For a solution that is mass × % w/w ÷ 100, and for a volume it is liters × SG × % w/w ÷ 100 in kg, or liters × mol/L directly. The US gallon of 3.785411784 L and the pound of 0.45359237 kg are the exact definitions in NIST Handbook 44.

Every preset molar mass below is summed from the IUPAC CIAAW Abridged Standard Atomic Weights 2024 (H 1.0080, C 12.011, N 14.007, O 15.999, Na 22.990, Mg 24.305, P 30.974, S 32.06, Cl 35.45, K 39.098, Ca 40.078). The result is the stoichiometric charge, the amount for a complete reaction; real tanks carry buffers and dissolved metals, so trim the last few percent against a pH probe.

Preset g/mol H+ per mole
Hydrochloric acid, HCl 36.458 1
Sulfuric acid, H2SO4 98.072 2
Nitric acid, HNO3 63.012 1
Phosphoric acid, H3PO4 97.994 3
Acetic acid, CH3COOH 60.052 1
Sodium hydroxide, NaOH 39.997 1
Potassium hydroxide, KOH 56.105 1
Calcium hydroxide, Ca(OH)2 74.092 2
Magnesium hydroxide, Mg(OH)2 58.319 2
Sodium carbonate, Na2CO3 105.988 2
Sodium bicarbonate, NaHCO3 84.006 1
Ammonia, NH3 17.031 1

Worked example: spent sulfuric acid and caustic soda

The booking. A plant has 2,000 lb of spent acid at 10% w/w sulfuric acid, which is 200 lb or 90.72 kg of H2SO4. The operator divides by 98.072 g/mol to get 925.0 mol, orders the same number of moles of NaOH, and books 925.0 × 39.997 g = 81.6 lb of caustic, which looks fine on paper.

The failure. Sulfuric acid gives up two hydrogen ions per molecule, so the reaction needs 2 mol of NaOH per mol of acid. With 81.6 lb in the tank only half the acid is gone, the pH is still far too low to discharge, and the batch waits for a second delivery. Either the order changes, or the tank sits.

The fix. Leave H+ per mole at 2 for sulfuric acid and the tool returns 1,850.0 mol of NaOH, or 163.1 lb pure. Bought as 50 percent lye, that is 326.3 lb of liquid, and the tank reaches neutral on one delivery with a pH probe to trim the end.

Working from a lab result in mol/L or normality rather than % w/w? The molarity calculator turns grams, liters, and moles into each other at /tools/chemicals/molarity-calculator.

Need the molar mass of a salt or hydrate the presets do not carry? The molar mass calculator sums any formula from the same IUPAC atomic weights at /tools/chemicals/molar-mass-calculator.

Frequently asked

How much sodium hydroxide neutralizes sulfuric acid?

Two moles of NaOH for every mole of H2SO4, because sulfuric acid gives up two hydrogen ions. By mass that is 2 × 39.997 = 79.994 g of NaOH per 98.072 g of acid, or about 0.816 kg of NaOH per kg of pure sulfuric acid. The molar masses come from the IUPAC CIAAW 2024 abridged atomic weights.

What is the molar ratio in a neutralization reaction?

It is the number of hydrogen ions the acid gives per mole divided by the number the base takes per mole. HCl with NaOH is 1 to 1, H2SO4 with NaOH is 1 to 2, and HCl with Ca(OH)2 is 2 to 1, so half a mole of lime handles each mole of HCl. The tool shows both numbers so you can change either one when your reaction stops at a different end point.

Does the tool assume phosphoric acid loses all three hydrogens?

Yes, the preset counts all three acidic hydrogens, which is full stoichiometric neutralization. The third hydrogen of phosphoric acid is very weak, so a process that stops near pH 7 uses less base than the preset returns. Change the H+ per mole box to 1 or 2 to match the end point your procedure actually targets, and confirm it with a titration on a real sample.

Why does the calculator ask for % w/w and specific gravity?

Moles come from the mass of pure chemical, and a drum label gives you volume and strength instead. The tool multiplies volume by SG to get the mass of solution, then by the percent w/w to get the mass of pure acid or base. Take both values from SDS Section 9 or the certificate of analysis for the lot, since strength drifts between batches.

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