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Preparation of pH buffer solutions

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    Phosphate and Acetate buffers
    The different names for phosphate salts. Standardization buffers pH 4 and pH 7. Ph range of some buffer systems. Making up buffer solutions by adding an adjuster solution (acid or base) to a known volume and concentration of a primary salt solution. Potassium hydrogen phosphate, potassium dihydrogen phosphate, disodium hydrogen phosphate, potassium hydrogen phthalate, sodium acetate,sodium tetraborate, tris aminomethane.
    Related link:
    For EDTA titrations
    For Fluoride (TISAB)
    For Determination of Fe.
    On this page: Click the links below to jump to the relevant info:

    Phosphates
    Phosphate salts are known by several names and the correct phosphate must be used to prepare buffer solutions.
    One phosphate cannot be substituted for another phosphate. Check formula of salt to be certain.


    Formula
    Name of salt
    Other names
    KH2PO4
    potassium dihydrogen
    phosphate
    potassium dihydrogen orthophosphate
    monobasic potassium phosphate
    monopotassium phosphate
    acid potassium phosphate
    potassium biphosphate
    K2HPO4
    potassium hydrogen
    phosphate
    dipotassium hydrogen orthophosphate
    dipotassium hydrogen phosphate
    dibasic potassium phosphate
    dipotassium phosphate
    K3PO4
    potassium phosphate
    tribasic potassium phosphate
    tripotassium phosphate



    Standardization buffers
    For pH=7.00 :
    Add 29.1 ml of 0.1 molar NaOH to 50 ml 0.1 molar potassium dihydrogen phosphate.

    Alternatively :
    Dissolve 1.20g of sodium dihydrogen phosphate and 0.885g of disidium hydrogen phosphate in 1 liter volume distilled water.

    For pH= 4.00 :
    Add 0.1 ml of 0.1 molar NaOH to 50 ml of 0.1 molar potassium hydrogen phthalate .

    Alternatively :
    Dissolve 8.954g of disodium hydrogen phosphste.12 H2O and 3.4023g of potassium dihydrogen phosphate in 1 liter volume distilled water.


    Range of common buffer systems ¹

    Buffering system


    Useful buffering pH range @ 25°C

    Hydrochloric acid/ Potassium chloride
    1.0 - 2.2
    Glycine/ Hydrochloric acid
    2.2 - 3.6
    Potassium hydrogen phthalate/ Hydrochloric acid
    2.2 - 4.0
    Citric acid/ Sodium citrate
    3.0 - 6.2
    Sodium acetate/ Acetic acid
    3.7 - 5.6
    Potassium hydrogen phtaalate/ Sodium hydroxide
    4.1 - 5.9
    Disodium hydrogen phthalate / Sodium dihydrogen orthophospate
    5.8 - 8.0
    Dipotassium hydrogen phthalate / Potassium dihydrogen orthophospate
    5.8 - 8.0
    Potassium dihydrogen orthophosphate / sodium hydroxide
    5.8 - 8.00
    Barbitone sodium / Hydrochloric acid
    6.8 - 9.6
    Tris (hydroxylmethyl) aminomethane / Hydrochloric acid
    7.0 - 9.00
    Sodium tetraborate/ Hydrochloric acid
    8.1 - 9.2
    Glycine/ Sodium hydroxide
    8.6 - 10.6
    Sodium carbonate/ Sodium hydrogen carbonate
    9.2 - 10.8
    Sodium tetraborate/ Sodium hydroxide
    9.3 - 10.7
    Sodium bicarbonate / Sodium hydroxide
    9.60 - 11.0
    Sodium hydrogen orthophosphate / Sodium hydroxide
    11.0 - 11.9
    Potassium chloride/ Sodium hydroxide
    12.0 - 13.0
    Preparing a Buffer Solution ²
    This page gives tabulated info on the preparation of buffers by mixing adjusters
    with a known volume of the primary salt solution, and made up to 200ml with distilled water.

    BUFFERS 1.00 - 9.00


    Buffer A :
    pH 1.0 - 2.2

    Buffer B :
    pH 2.2 - 4.00

    Buffer C :
    pH 4.10 - 5.90

    Buffer D :
    pH 5.8 - 8.00

    Buffer E :
    pH 7.0 - 9.00

    50 ml 0.2 M KCl + mls of 0.2 M HCl

    100 ml 0.1 M potassium hydrogen phthalate + mls of 0.1 M HCl.

    100 ml 0.1 M potassium hydrogen phthalate + mls of 0.1 M NaOH

    . 100 ml 0.1 M KH2PO4 + mls of 0.1 M NaOH.

    100 ml 0.1 M tris (hydroxymethyl) aminomethane + mls of 0.1 M HCl.

    pH
    mls of 0.2M HCl added
    pH
    mls of 0.1M HCl added
    pH
    mls of 0.1M NaOH added
    pH
    mls of 0.1M NaOH added
    pH
    mls of 0.1 M HCl added
    1.00
    134.0
    2.20
    99.0
    4.10
    2.6
    5.80
    7.2
    7.00
    93.2
    1.10
    105.6
    2.30
    91.6
    4.20
    6.0
    5.90
    9.2
    7.10
    91.4
    1.20
    85.0
    2.40
    84.4
    4.30
    9.4
    6.00
    11.2
    7.20
    89.4
    1.30
    67.2
    2.50
    77.6
    4.40
    13.2
    6.10
    13.6
    7.30
    86.8
    1.40
    53.2
    2.60
    70.8
    4.50
    17.4
    6.20
    16.2
    7.40
    84.0
    1.50
    41.4
    2.70
    64.2
    4.60
    22.2
    6.30
    19.4
    7.50
    80.6
    1.60
    32.4
    2.80
    57.8
    4.70
    27.2
    6.40
    23.2
    7.60
    77.0
    1.70
    26.0
    2.90
    51.4
    4.80
    33.0
    6.50
    27.8
    7.70
    73.2
    1.80
    20.4
    3.00
    44.6
    4.90
    38.8
    6.60
    32.8
    7.80
    69.0
    1.90
    16.2
    3.10
    37.6
    5.00
    45.2
    6.70
    38.6
    7.90
    64.0
    2.00
    13.0
    3.20
    31.4
    5.10
    51.0
    6.80
    44.8
    8.00
    58.4
    2.10
    10.2
    3.30
    25.8
    5.20
    57.6
    6.90
    51.8
    8.l0
    52.4
    2.20
    7.8
    3.40
    20.8
    5.30
    63.2
    7.00
    58.2
    8.20
    45.8


    3.50
    16.4
    5.40
    68.2
    7.10
    64.2
    8.30
    39.8


    3.60
    12.6
    5.50
    73.2
    7.20
    69.4
    8.40
    34.4


    3.70
    9.0
    5.60
    77.6
    7.30
    74.0
    8.50
    29.4


    3.80
    5.8
    5.70
    81.2
    7.40
    78.2
    8.60
    24.4


    3.90
    2.8
    5.80
    84.6
    7.50
    82.2
    8.70
    20.6


    4.00
    0.2
    5.90
    87.4
    7.60
    85.6
    8.80
    17.0






    7.70
    88.4
    8.90
    14.0






    7.80
    90.6
    9.00
    11.4






    7.90
    92.2








    8.00
    93.4




    BUFFERS 08 - 13

    Buffer F: pH 8.0 - 9.10

    Buffer G :
    pH 9.2 - 10.80

    Buffer H :
    pH 9.60 - 11.00

    Buffer I :
    pH 10.90 - 12.00

    Buffer J :
    pH 12.00 - 13.00

    100 mL 0.025 M Na2B4O7.10H2O (borax) + mls of 0.1 M HCl.

    100 mL 0.025 M Na2B4O7.10H2O (borax) + mls of 0.1 M NaOH.

    100 mL 0.05 M NaHCO3 + mls of 0.1 M NaOH.

    100 mL 0.05 M Na2HPO4 + mls of 0.1 M NaOH.

    50 mL 0.2 M KCl + volume indicated (in mL) 0.2 M NaOH.

    pH
    mls of 0.1M HCl added
    pH
    mls of 0.1M NaOH added
    pH
    mls of 0.1M NaOH added
    pH
    mls of 0.1M NaOH added
    pH
    mls of 0.2M NaOH added
    8.00
    41.0
    9.20
    1.8
    9.60
    10.0
    10.90
    6.6
    12.00
    12.0
    8.10
    39.4
    9.30
    7.2
    9.70
    12.4
    11.00
    8.2
    12.10
    16.0
    8.20
    37.6
    9.40
    12.4
    9.80
    15.2
    11.10
    10.2
    12.20
    20.4
    8.30
    35.4
    9.50
    17.6
    9.90
    18.2
    11.20
    12.6
    12.30
    25.6
    8.40
    33.2
    9.60
    22.2
    10.00
    21.4
    11.30
    15.2
    12.40
    32.4
    8.50
    30.4
    9.70
    26.2
    10.10
    24.4
    11.40
    18.2
    12.50
    40.8
    8.60
    27.0
    9.80
    30.0
    10.20
    27.6
    11.50
    22.2
    12.60
    51.2
    8.70
    23.2
    9.90
    33.4
    10.30
    30.4
    11.60
    27.0
    12.70
    64.4
    8.80
    19.2
    10.00
    36.6
    10.40
    33.0
    11.70
    32.4
    12.80
    82.4
    8.90
    14.2
    10.10
    39.0
    10.50
    35.6
    11.80
    38.8
    12.90
    106.0
    9.00
    9.2
    10.20
    41.0
    10.60
    38.2
    11.90
    46.0
    13.00
    132.0
    9.10
    4.0
    10.30
    42.6
    10.70
    40.4
    12.00
    53.8




    10.40
    44.2
    10.80
    42.4






    10.50
    45.4
    10.90
    44.0






    10.60
    46.6
    11.00
    45.4






    10.70
    47.6








    10.80
    48.5








    Acetate buffer solutions pH 3 - 6 ³
    Make up the following solutions
    (1) 0.1M acetic acid
    (2) 0.1M sodium acetate (tri-hydrate) (13.6g / l)
    Mix in the following proportions to get the required ph



    ph
    vol. of 0.1M
    acetic acid
    vol. of 0.1M
    sodium acetate
    3
    982.3 mls
    17.7 mls
    4
    847.0 mls
    153.0 mls
    5
    357.0 mls
    643.0 mls
    6
    52.2 mls
    947.8 mls

    Phosphate buffer solutions ph 7 - 11

    Make up the following solutions
    (1) 0.1M disodium hydrogen phosphate (14.2g / l)
    (2) 0.1M HCl
    (3) 0.1M NaOH
    Mix in the following proportions to get the required ph


    ph
    vol. of phosphate
    vol. of 0.1M HCl
    vol. of 0.1M NaOH
    7
    756.0 mls
    244 mls

    8
    955.1 mls
    44.9 mls

    9
    955.0 mls
    45.0 mls

    10
    966.4 mls


    11
    965.3 mls



    Addition of acid or base to a salt pH 3 - 11
    Here, the primary salt is a solid and is weighed out in grams. A measured amount of 0.1M HCl or NaOH is added,
    then made up to 1 liter to give the relevant buffer solution 4.


    pH
    Salt mixture
    Dilute each mixture to 1 liter solution with distilled water
    3
    10.21g potassium hydrogen phthalate and 223ml of 0.10M HCl
    4
    10.21g potassium hydrogen phthalate and 1ml of 0.10M HCl
    5
    10.21g potassium hydrogen phthalate and 226ml of 0.10M NaOH
    6
    6.81g potassium dihydrogen phOsphate and 56ml of 0.10M NaOH
    7
    6.81g potassium dihydrogen phosphate and 291ml of 0.10M NaOH
    8
    6.81g potassium dihydrogen phosphate and 467ml of 0.10M NaOH
    9
    4.77g sodium tetraborate and 46ml of 0.10M HCl
    10
    4.77g sodium tetraborate and 183ml of 0.10M NaOH
    11
    2.10g sodium bicarbonate and 227ml of 0.10M NaOH

    1. The Physical and Theoretical Laboratory, Oxford University.
    2. "Electrolyte solutions" Robinson, R. A., and Stokes, R. H., 2nd ed., rev. London, Butterworths, 1968.
    3. "Practical chemistry" J. Lambert and T.A. Muir, 3rd. Ed. Heineman, London.
    4. pdf file, www.bc.ca/bcsc/resources/ (Canadian Teachers Federation).

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