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    Phosphorus Acid Titration

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    JoséMaríaMore
    The document describes two experimental methods to determine the concentration of a phosphoric acid solution: 1) Titration using a pH indicator. A 10.0 mL aliquot is titrated with 0.1M NaOH until the color changes from yellow to blue at pH 4.7. 2) Titration using a pH meter. A 10.0 mL aliquot is titrated with 0.1M NaOH and the pH is recorded after adding set volumes. A graph of pH vs volume added is made to find the endpoint and calculate concentration. The concentration found can then be used to calculate the purity of the original phosphoric acid bottle.

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    Download as PDF, TXT or read online from Scribd

    Phosphorus Acid Titration

    Uploaded by

    JoséMaríaMore
    318 views2 pages
    The document describes two experimental methods to determine the concentration of a phosphoric acid solution: 1) Titration using a pH indicator. A 10.0 mL aliquot is titrated with 0.1M NaOH until the color changes from yellow to blue at pH 4.7. 2) Titration using a pH meter. A 10.0 mL aliquot is titrated with 0.1M NaOH and the pH is recorded after adding set volumes. A graph of pH vs volume added is made to find the endpoint and calculate concentration. The concentration found can then be used to calculate the purity of the original phosphoric acid bottle.

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    phosphorus acid titration determination experiment

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    Phosphorus acid titration

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    The document describes two experimental methods to determine the concentration of a phosphoric acid solution: 1) Titration using a pH indicator. A 10.0 mL aliquot is titrated with 0.1M NaOH until the color changes from yellow to blue at pH 4.7. 2) Titration using a pH meter. A 10.0 mL aliquot is titrated with 0.1M NaOH and the pH is recorded after adding set volumes. A graph of pH vs volume added is made to find the endpoint and calculate concentration. The concentration found can then be used to calculate the purity of the original phosphoric acid bottle.

    Copyright:

    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
    Download as pdf or txt
    318 views2 pages

    Phosphorus Acid Titration

    Uploaded by

    JoséMaríaMore
    The document describes two experimental methods to determine the concentration of a phosphoric acid solution: 1) Titration using a pH indicator. A 10.0 mL aliquot is titrated with 0.1M NaOH until the color changes from yellow to blue at pH 4.7. 2) Titration using a pH meter. A 10.0 mL aliquot is titrated with 0.1M NaOH and the pH is recorded after adding set volumes. A graph of pH vs volume added is made to find the endpoint and calculate concentration. The concentration found can then be used to calculate the purity of the original phosphoric acid bottle.

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    © All Rights Reserved
    Download as PDF, TXT or read online from Scribd
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    You are on page 1of 2

    Jose M Morenete

    Conor Cleeton

    February 6th

    DETERMINATION OF A PHOSPHORIC ACID SOLUTION CONCENTRATION BY TWO


    METHODS.
    Background
    The technical staff were asked to prepare a solution of phosphoric acid suitable for
    reversing the toning of metal coins. They prepared a solution from an old bottle of
    phosphoric acid, which was labelled as having a specific gravity of 1.75. They prepared a
    50.0 solution using 340 of the phosphoric acid. However, they are concerned about the
    purity of the phosphoric acid and dont know the exact concentration of the solution they
    have prepared and they have asked that you determine the exact concentration of the
    solution and hence calculate the purity of the old bottle of phosphoric acid. Confirm your
    results by two separate experimental methods.
    Phosphoric acid is a triprotic acid, therefore there are three different equilibria in its
    dissociation equations. Each equilibria has its own Ka and pKa values. Therefore, on a
    titration curve there are three points of inflexion, which is equivalent to three equivalence
    points, as shown below:

    Experimental Objective
    In this experiment you will use a pH meter and appropriate pH indicators along materials
    provided to determine the concentration of a solution of Phosphoric Acid used and therefore
    calculate the purity of the phosphoric acid in the old bottle.
    Experiment 1: Titration using a pH indicator.
    Using a bulb pipette, transfer a 10.0 cm3 aliquot of the phosphoric
    acid solution into conical flask and add 2-3 drops of Bromocresol
    green indicator. Following the diagram below, fill a burette with
    approximately 0.1M NaOH and titrate with the solution in the
    conical flask until three concordant titres are obtained. The end
    point of the titration is when the solution changes colour from
    yellow toblue, at a pH of approximately 4.7.

    Experiment 2: Titration using pH meter.


    Collect a burette and fill it with approximately 0.1 M NaOH, and clamp it to a support, as
    demonstrated in the diagram below. Open the stopcock to let the NaOH occupy the whole

    Jose M Morenete
    Conor Cleeton

    February 6th

    burette, doing so under a beaker to prevent spilling. Using a bulb pipette, transfer 10.0 cm3
    of the phosphoric acid solution to a 250 cm3 beaker. Add 25 cm3 of deionised water to the
    beaker. Insert a magnetic stirrer bar and gently stir the solution to
    ensure the contents are mixed. Then, place the pH meter in contact
    with the solution. Record the value of initial pH and volume of NaOh
    added (0.0 cm3). Then, start adding NaOH to the beaker, and record
    the pH every 1.0 cm3 until 9.0 cm3 of NaOH have been added. From
    this point record the pH every 0.25 cm3 of NaOH, until the pH value
    rapidly changes. When this happens, add 0.10 cm3 of NaOh until the
    pH value change slows down. Return to adding 0.25 cm3 until 11.0
    cm3 have been added, and finish off adding 1.0 cm3 , until
    approximately 15.0 cm3 have been added.
    Draw a graph of pH versus Volume of Titrant Added (cm3). From this
    graph you will be able to determine the end-point of the titration, and thus calculate the
    concentration of the phosphoric acid solution.

    Discussion:

    We can obtain the concentration of from finding the number of moles of NaOH that was
    used and as it is a one to one molar ratio we know the number of moles of NaOH is the
    same as the number of moles of . From that we can calculate the concentration of in the
    sample used which is equal to mol/vol.

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