pH Neutralization Dosing Calculator

Neutralizing a strong acid with caustic soda is a one-to-one mole reaction: one mole of H⁺ needs one mole of NaOH. The H⁺ concentration is 10⁻ᵖʰ moles per litre, so the caustic needed is volume (L) × 10⁻ᵖʰ × 40 grams of 100 % NaOH. A 5 m³ tank at pH 2 — 0.01 mol/L — needs 50 moles, or 2000 g of NaOH, which is 2.67 L of the commercial 50 % solution (density about 1.5 kg/L).

The calculator applies exactly this, then divides by your dosing window to give the L/h the dosing pump must deliver.

The arithmetic above is exact for strong acids like HCl and H₂SO₄, which fully dissociate. Weak acids — acetic, citric, phosphoric — hold H⁺ in equilibrium and need more caustic, and the curve is not a simple function of pH. For those, size from a titration and control the dose with a pH loop rather than a fixed formula.

Real plants also dose in steps: neutralization is a batch process in ETP, often with mixing and a second correction dose after the first settles.

With the L/h rate, pick a diaphragm dosing pump sized for mid-stroke operation, add a calibration column, and protect the caustic line — 50 % NaOH crystallizes below about 12 °C and must be kept warm and dry. Teflow supplies and services the dosing pumps for these skids across Gujarat — call +91 98251 62709 for a quote.