How does a titration find the unknown concentration of an acid or base?
Titration: use titration data and the Table T titration relationship to calculate the unknown concentration of an acid or base.
A focused Regents Chemistry answer on titration: the laboratory procedure, the role of the indicator and the endpoint, and the Table T relationship M_A V_A = M_B V_B for a one-to-one acid-base reaction, with a worked calculation.
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What this topic is asking
The Core Curriculum asks you to use titration to find an unknown concentration, applying the Table T relationship for a one-to-one acid-base reaction. This is both a laboratory skill (part of the required lab work) and a Part C calculation, so the Regents tests the procedure and the math.
The titration procedure
Accurate technique matters: read the buret at the bottom of the meniscus, add the solution slowly near the endpoint, and swirl to mix. The endpoint is where the indicator just changes color, indicating that the acid and base have reacted in the proportion set by the balanced equation.
The Table T relationship
This relationship holds when the acid and base react in a one-to-one ratio (such as with ). To use it, identify the three known quantities and solve for the fourth. Volumes can stay in milliliters because they appear on both sides and the units cancel, but molarity must be in mol/L.
The laboratory equipment and sources of error
Titration is one of the required laboratory skills, and Part C often asks about the apparatus or how to reduce error. The known solution (the titrant) is delivered from a buret, which measures volume precisely; the unknown solution is measured with a pipet or volumetric flask into a flask, and the indicator is added there. A common source of error is misreading the buret: you must read the volume at the bottom of the meniscus at eye level to avoid a parallax error. Other errors include overshooting the endpoint (adding titrant past the color change) and an unrinsed buret diluting the titrant. Repeating the titration and averaging the volumes improves reliability, and the percent error of a result can be found with the percent-error formula on Table T.
Solving a titration problem
The steps are always the same:
- Write .
- Substitute the three known values.
- Rearrange to make the unknown the subject.
- Solve and attach the unit (mol/L).
Try this
Q1. State what the endpoint of a titration indicates. [1 point]
- Cue. That the acid and base have reacted in the correct proportion (neutralization is complete), shown by the indicator color change.
Q2. A mL acid is neutralized by mL of M base (one-to-one). Find the acid molarity. [2 points]
- Cue. M.
Exam-style practice questions
Practice questions written in the style of NYSED exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Regents (Part C style)3 marksIn a titration, mL of hydrochloric acid is exactly neutralized by mL of M sodium hydroxide. Using the Table T titration relationship, (a) state the equation, (b) show the numerical setup and (c) calculate the molarity of the acid.Show worked answer →
A 3-point Part C titration calculation using from Table T.
(a) Equation (1 point): (valid for a one-to-one acid-base reaction such as with ).
(b) Setup (1 point): , so .
(c) Calculation (1 point): M.
Markers reward stating the titration relationship, substituting the volumes and known molarity, and the answer M. Volumes can stay in milliliters because they appear on both sides and cancel.
Regents (Part B-2 style)2 marksDuring an acid-base titration, (a) state the purpose of the indicator and (b) describe what is observed at the endpoint.Show worked answer →
A 2-point constructed-response item on titration technique.
(a) Indicator (1 point): the indicator signals when the acid has been neutralized by the base (or vice versa) by changing color, so the volume needed can be recorded.
(b) Endpoint (1 point): at the endpoint the indicator changes color, showing that the acid and base have reacted in the correct proportion (the point of neutralization).
Markers reward describing the indicator as a color signal of neutralization and identifying the endpoint as the color change marking the reacted proportion.
Related dot points
- Acids, bases and the pH scale: identify Arrhenius acids and bases, interpret the pH scale, and relate a change in pH to a change in hydrogen ion concentration.
A focused Regents Chemistry answer on Arrhenius acids and bases, the pH scale, and how each pH unit means a tenfold change in hydrogen ion concentration, using Table K and Table L of the Reference Tables.
- Neutralization and salts: write neutralization reactions of an acid with a base to form a salt and water, and identify the salt produced.
A focused Regents Chemistry answer on neutralization: how an acid and a base react to form a salt and water, how to predict the salt from the acid's anion and the base's cation, and the role of the hydrogen and hydroxide ions.
- Concentration and molarity: calculate molarity, parts per million and percent by mass using the concentration formulas on Table T.
A focused Regents Chemistry answer on solution concentration: molarity as moles of solute per liter of solution, parts per million, and percent by mass, all from the Table T formulas, with worked calculations and the dilution idea.
- Stoichiometric calculations: use mole ratios from a balanced equation to convert between moles and masses of reactants and products.
A focused Regents Chemistry answer on stoichiometry: using the mole ratios from a balanced equation together with gram-formula mass to convert between moles and masses of reactants and products, with worked mole-mole and mass-mass examples.
- Equilibrium and Le Chatelier's principle: describe dynamic equilibrium and predict the shift in a system when concentration, temperature or pressure is changed.
A focused Regents Chemistry answer on dynamic equilibrium and Le Chatelier's principle: equal forward and reverse rates, and how a change in concentration, temperature or pressure shifts the equilibrium to relieve the stress.
Sources & how we know this
- Physical Setting/Chemistry Core Curriculum — New York State Education Department (2002)
- Reference Tables for Physical Setting/Chemistry, 2011 Edition — New York State Education Department (2011)