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    Titration analysis method-acid-base titration method (3)

    • Last Update: 2021-09-21
    • Source: Internet
    • Author: User
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    3.
    Application of acid-base titration-determination of alkalinity

    (1) Alkalinity composition
    .
    The alkalinity of water refers to the total amount of substances in the water that can quantitatively react with strong acids

    .
    More alkalinity sources of water, natural water alkalinity is substantially carbonates,
    bicarbonates function and hydroxide content, it can be divided into alkalinity hydroxide (OH - ) alkalinity, carbonate salt (CO.
    's
    2 3- ) alkalinity and bicarbonate (HC03 .
    3
    - ) alkalinity
    .
    We can not assume the presence of water while OH
    - and HC03 .
    3
    - , may constitute five kinds of combinations: (OH - ), (OH - , CO.
    'S
    .
    3
    2- ), (CO.
    'S
    .
    3
    2- ), (CO.
    'S
    .
    3
    2- , HC03 .
    3
    - ), (HCO 3 - )
    .

    For example, a large number of algae thrive in natural water bodies, which strongly absorb CO 2 in the water, so that the water has a higher pH value, mainly carbonate alkalinity.
    Generally, natural water with a pH value of <8.
    3 mainly contains bicarbonate alkalinity, which is slightly higher than The weakly acidic natural water of 8.
    3 can contain bicarbonate and
    carbonate alkalinity at the same time .
    When the pH value is greater than 10, it is mainly hydroxide breakage

    .
    The total alkalinity is taken as the sum of the concentrations of these components

    .
    When the water contains borate,
    phosphate, or silicate , the measured value of total alkalinity also includes their role
    .

    (2) Determination of alkalinity
    .
    The alkalinity is determined by acid-base titration

    .
    Using HCl and H
    2 SO 4 as standard solutions, phenolphthalein and methyl orange as indicators, according to the volume of acid consumed by the discoloration of different indicators, various alkalinity contained in water samples can be measured
    .

    Determination of alkalinity available continuous titration: taking up a volume of water sample, phenolphthalein indicator was added standard solution was titrated to a strong acid, to the solution from red to colorless, the amount of the standard solution of the acid represented by P
    .
    Then add methyl orange indicator to the water sample, continue to titrate the solution from yellow to orange, and use M to denote the volume of the standard solution for titration

    .
    According to the relative size of P and M, the composition of alkalinity in water can be judged and its content can be calculated

    .
    The reaction of various alkalinities in titration is as follows

    .

    Phenolphthalein discoloration:

    Methyl orange discoloration:

    The total alkalinity of water: T = OH - + CO.
    'S
    .
    3
    2- + HC03 .
    3
    - = P + M

    The relationship between various alkalinity and acid-base titration results is shown in Table 2.
    2.
    4

    .

    Table 2.
    2.
    4 Composition and calculation of alkalinity in water

    (3) Alkalinity calculation
    .

    1) First judge the composition of alkalinity by the values ​​of P and M (see Table 2.
    2.
    4)

    .

    For example, the result of the titration is P=11.
    05ml, M=8.
    90ml, check table 2.
    2.
    4, since P>M, the alkalinity components in the water are OH
    - and CO 3 2-
    .

    The OH-content is PM=2.
    15ml, meaning that the OH
    - consumable acid standard solution in water is 2.
    15ml,
    and the CO
    3 2- content is 2M=19.
    80ml, meaning that the CO
    3 2- consumable acid standard solution in water is 19.
    80ml

    .

    The total alkalinity is P+M=19.
    95ml, which means that the total alkalinity in the water can consume 19.
    95ml of the acid standard solution

    .

    2) The expression method of alkalinity
    .
    In mg/L, in mol/L or mmol/L, in mgCaO/L or mgCaCO
    3 /L
    .

    3) Commonly used molar mass for alkalinity calculation
    .

    4) Expression for alkalinity calculation
    .

    [Example 2.
    2.
    1] The titration result of continuous titration is P=11.
    05ml, M=8.
    90ml; known V water sample=100ml, CHCl=0.
    1mol/L

    .

    After analysis, the alkalinity components in the water are OH - and CO 3 2- , the content of OH- is PM =2.
    15ml, the content of
    CO
    3 2- is 2M=17.
    80ml, and the total alkalinity is P+M=19.
    95ml

    .

    The result of alkalinity calculation can be expressed as

    Related links: Titration analysis method-acid-base titration (2)

     

     

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