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Acid–base titration

Add base in a burette and compare the pH curve and indicator end point.

    C10 · Acid–base titrationReady
    Add base in a burette and compare the pH curve and indicator end point. You can also experiment with the numbers and controls below.

    Chemistry · Acid · Base / Principles and Exploration

    Acid–base titration — principles and investigation

    Neutralizing an acid with a base of known concentration allows you to estimate the concentration of the acid in the volume used in the reaction. Compare the pH change and indicator color using a sample of hydrochloric acid and a standard sodium hydroxide solution. This is a titration experiment that examines the difference between the equivalence point determined by stoichiometry and the end point determined by an indicator.

    How does it work?

    At 25℃, Kw=10⁻¹⁴. The equivalence point pH is 7, and the concentration right next to the equivalence point is also calculated using the concentration of excess moles divided by the total volume and the auto-ionization of water. The estimated acid concentration is c base V terminal/V acid.

    Key relationship

    D=(n acid−n base)/V total · [H⁺]−Kw/[H⁺]=D

    Try this investigation

    1. Add NaOH using the burette and drop button. Change the indicator and compare the color and final volume. The concentration input is a learning reference value that changes the correct answer for estimating unknown concentration.
    2. Run and record 0, 24.9, 25.0, and 25.1 mL of NaOH at a standard concentration of 0.1 mol/L and 25 mL of HCl, respectively.
    3. Record the value when only the indicator is changed from 24.9 mL and the value when only the standard concentration is changed from 25 mL of NaOH to 0.20 mol/L.

    Interpreting your results

    Are the equivalence point and an indicator’s endpoint always identical?

    The equivalence point is the point where n(H⁺)=n(OH⁻). The end point is a color change standard that is observed, so it varies for each indicator. The curve is the same even if you change the indicator.

    Assumptions and limitations

    Assume 25℃ monovalent strong acid HCl·strong base NaOH, complete dissociation·volume addition·activity 1. Carbon dioxide absorption, mixing delay, and droplet size errors are excluded. The discoloration range is a representative value for educational purposes, and the end point is a model defined as the pH in the middle of the range (9.10 or 3.75). It may differ from the actual visual endpoint. Indicators do not change pH.