An acid-base titration is a fundamental quantitative laboratory technique used to determine the unknown concentration of an acid or a base by reacting it with a solution of known concentration. Core Concepts of Titration
Titrant: Solution of known concentration (standard solution) placed in the burette.
Analyte (Titrand): Solution of unknown concentration placed in the Erlenmeyer flask.
Equivalence Point: The theoretical point where the moles of acid exactly equal the moles of base (
End Point: The physical point where the chemical indicator permanently changes color, signaling the reaction is complete. Required Laboratory Equipment Burette: Delivers precise, variable volumes of the titrant.
Volumetric Pipette: Transfers an exact volume of the analyte into the flask.
Erlenmeyer Flask: Holds the analyte and allows for splash-free swirling.
pH Indicator: Chemical (like phenolphthalein) that changes color at a specific pH range.
White Tile: Placed under the flask to make the color change easily visible. Step-by-Step Laboratory Procedure 1. Prepare the Equipment
Rinse the burette with distilled water, then with a small amount of the titrant solution. Clamp the burette vertically to a ring stand. Fill the burette with titrant slightly above the
mark, then open the stopcock briefly to fill the tip and remove air bubbles. Record the initial volume reading to the nearest 2. Prepare the Analyte
Use a clean volumetric pipette to measure an exact volume of the analyte solution. Transfer this sample into a clean Erlenmeyer flask. Add
drops of an appropriate pH indicator to the flask and gently swirl to mix. 3. Perform a Rough Titration
Place the flask on a white tile under the burette tip. Rapidly add the titrant while swirling the flask continuously until a permanent color change occurs. Record this final volume. This rough run establishes the approximate volume of titrant required. 4. Perform Precise Titrations
Prepare a fresh analyte flask identical to step 2. Open the stopcock to quickly add titrant until you are within
of the rough endpoint. Slow the addition down to a drop-by-drop rate, swirling constantly. Stop adding titrant the exact moment a single drop causes a permanent color change that persists for at least
seconds. Record the final burette volume reading. Repeat this precise process until you obtain at least three concordant titers (volumes within of each other). Data Analysis and Calculations
To find the concentration of your analyte, use the average volume of your concordant precise titration runs. 1. Write the Balanced Equation
Determine the stoichiometric ratio between the acid and the base. For example, a neutralization reaction between hydrochloric acid ( ) and sodium hydroxide ( ) reacts in a molar ratio:
HCl (aq)+NaOH (aq)→NaCl (aq)+H2O (l)HCl (aq) plus NaOH (aq) right arrow NaCl (aq) plus H sub 2 O (l) 2. Calculate Moles of Titrant
Multiply the average volume of titrant used (converted to liters) by its molarity:
ntitrant=Mtitrant×Vtitrantn sub titrant end-sub equals cap M sub titrant end-sub cross cap V sub titrant end-sub 3. Determine Moles of Analyte
Use the stoichiometric ratio from the balanced equation to convert moles of titrant into moles of analyte:
nanalyte=ntitrant×(moles of analytemoles of titrant)n sub analyte end-sub equals n sub titrant end-sub cross open paren the fraction with numerator moles of analyte and denominator moles of titrant end-fraction close paren 4. Calculate Unknown Concentration
Divide the moles of analyte by the exact volume of analyte originally pipetted into the Erlenmeyer flask:
Manalyte=nanalyteVanalytecap M sub analyte end-sub equals the fraction with numerator n sub analyte end-sub and denominator cap V sub analyte end-sub end-fraction ✅ Summary of Results
An acid-base titration pairs volumetric measurement with chemical stoichiometry to accurately calculate the concentration of an unknown solution. Achieving reliable results relies on eliminating air bubbles, reading the burette at eye level from the bottom of the meniscus, and identifying the sharpest possible endpoint color change.
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