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Acid-Base Titration Calculator

Calculate the molarity or volume of an acid or base solution in a 1:1 ratio titration using Ma*Va = Mb*Vb.

Titration Params

Acid Solution

M
mL

Base Solution

M
mL

Calculated Value

Molarity of Acid (Mₐ)0.122M
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What is Acid-Base Titration & the Equivalence Point?

Titration is the gold-standard laboratory technique for determining the unknown concentration of an acid or base. A solution of known concentration (the titrant) is slowly added to the unknown solution (the analyte) until the reaction reaches its equivalence point, where the moles of acid exactly equal the moles of base and the reaction is complete.

Mathematical Foundation

Titration Stoichiometry (1:1 Ratio)
Ma⋅Va=Mb⋅VbM_a \cdot V_a = M_b \cdot V_b
MaM_a= Molarity of the acid solution (mol/L).
VaV_a= Volume of the acid solution (mL or L).
MbM_b= Molarity of the base solution (mol/L).
VbV_b= Volume of the base solution (mL or L).

Laws & Principles

  • Equivalence Point: At the equivalence point, the moles of H+ ions donated by the acid exactly equal the moles of OH- ions donated by the base. For a strong acid-strong base titration, the equivalence pH is 7.0.
  • Indicator Selection: Phenolphthalein (colorless to pink, pH 8.2-10.0) is the most common indicator for strong acid-strong base titrations. Methyl orange (red to yellow, pH 3.1-4.4) is used for strong acid-weak base titrations.
  • Volume Units Must Match: Both Va and Vb must use the same units (both mL or both L). The units cancel in the equation, so mismatched units produce answers that are off by a factor of 1000.

Step-by-Step Example Walkthrough

" A chemistry student titrates 25.0 mL of an unknown HCl solution with 0.100 M NaOH. The endpoint is reached after adding 18.5 mL of NaOH. What is the molarity of the HCl? "

  1. 1. Write the equation: Ma * Va = Mb * Vb.
  2. 2. Substitute known values: Ma * 25.0 = 0.100 * 18.5.
  3. 3. Calculate the right side: 0.100 * 18.5 = 1.85 mmol.
  4. 4. Solve for Ma: 1.85 / 25.0 = 0.0740 M.
Final Result: The unknown HCl solution has a concentration of 0.0740 mol/L (74.0 mM).

Quick Answer: What does this titration calculator solve?

It solves for any one of the four variables in the titration equation Ma*Va = Mb*Vb. Given three known values (two concentrations and one volume, or two volumes and one concentration), it calculates the missing fourth value. This is the standard technique for determining unknown acid or base concentrations in analytical chemistry.

The Core Titration Equation

Ma * Va = Mb * Vb

This equation states that the moles of acid (Ma * Va) must equal the moles of base (Mb * Vb) at the equivalence point. It only applies to 1:1 stoichiometric reactions such as HCl + NaOH or HNO3 + KOH. For reactions with different stoichiometric ratios (like H2SO4 + 2NaOH), the equation must be modified to include the molar ratio.

Common Acid-Base Pairs

Acid Base Ratio Equivalence pH
HCl (Hydrochloric)NaOH (Sodium Hydroxide)1:17.0
HNO3 (Nitric)KOH (Potassium Hydroxide)1:17.0
H2SO4 (Sulfuric)NaOH1:27.0
CH3COOH (Acetic)NaOH1:18.7 (basic)

Laboratory Scenarios

Strong Acid + Strong Base

The pH curve rises sharply at the equivalence point, jumping from roughly pH 3 to pH 11 within a single drop. Phenolphthalein works well here because its color change range (8.2-10.0) falls within this steep transition zone.

Weak Acid + Strong Base

The equivalence point pH is above 7 (typically 8-10) because the conjugate base of the weak acid hydrolyzes in water. The buffer region before the equivalence point makes the pH change more gradual, requiring careful indicator selection.

Calculation Best Practices (Pro Tips)

Do This

  • ✓Record the buret reading at the endpoint, not the total volume poured. The volume used (Vb) equals the final buret reading minus the initial reading. Forgetting to subtract the initial reading is the most common lab error.
  • ✓Verify the stoichiometric ratio before applying Ma*Va = Mb*Vb. The 1:1 formula only works for monoprotic acid-monobasic base pairs. For H2SO4 + NaOH (1:2 ratio), you must multiply one side by the molar coefficient.

Avoid This

  • ✗Do not confuse endpoint with equivalence point. The endpoint is when the indicator changes color. The equivalence point is the theoretical exact stoichiometric balance. A well-chosen indicator makes these nearly identical, but they are not the same concept.
  • ✗Do not mix mL and L volumes. If your acid volume is in mL (25.0 mL), your base volume must also be in mL. The units cancel in the equation, but only if both sides use the same scale.

Frequently Asked Questions

Why does Ma*Va = Mb*Vb only work for 1:1 reactions?

The equation equates moles of acid to moles of base. In a 1:1 reaction like HCl + NaOH, one mole of acid reacts with exactly one mole of base. For H2SO4 + 2NaOH, each mole of sulfuric acid requires two moles of NaOH. The corrected equation becomes Ma*Va = (1/2)*Mb*Vb to account for the 1:2 stoichiometric coefficient.

What indicator should I use for a weak acid-strong base titration?

Use phenolphthalein (transition range pH 8.2-10.0). The equivalence point of a weak acid-strong base titration falls above pH 7 (typically around pH 8.7 for acetic acid + NaOH). Phenolphthalein changes color right in this zone. Methyl orange would change color too early (pH 3-4), far before equivalence is reached.

What is a back titration and when is it used?

A back titration is used when the analyte reacts too slowly, is insoluble, or does not produce a clear endpoint. You add a known excess of reagent to the analyte, let the reaction go to completion, then titrate the leftover excess with a second standard solution. The difference tells you how much reacted with the original analyte.

Why does the pH jump so sharply at the equivalence point?

Before the equivalence point, the excess acid (or base) acts as a buffer, resisting pH change. At the equivalence point, all the acid has been neutralized, so the buffer capacity drops to zero. A single additional drop of titrant has no buffer to resist it, causing the pH to swing several units in one step. This sharp transition is what makes the indicator color change visible.

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