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    Home > Chemicals Industry > Chemical Technology > Glacial acetic acid for industrial use (5)

    Glacial acetic acid for industrial use (5)

    • Last Update: 2021-11-23
    • Source: Internet
    • Author: User
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    4.
    6.
    2.
    6 Quantitative method

    Internal standard method
    .

    4.
    6.
    2.
    7 Result calculation

    The mass fraction of formic acid w 3 , the value is expressed in %, calculated according to formula (3):

    Where

    m s —The mass of internal standard ethyl acetate , in grams (g);

    A i —formic acid peak area;

    f irelative mass correction factor of formic acid and internal standard ethyl acetate;

    A s —the peak area of ​​the internal standard ethyl acetate ;

    m—The quality of the sample
    .

    Take the arithmetic mean of the two parallel determination results as the determination result, and the difference between the two parallel determination results shall not exceed 0.
    005%

    .

    4.
    7 Determination of acetaldehyde content by titration

    4.
    7.
    1 Method summary

    The acetaldehyde in the sample reacts with excess sodium bisulfite solution, and the remaining sodium sulfite is determined by iodometric method.
    Reaction formula:

    4.
    7.
    2 Reagents

    4.
    7.
    2.
    1 Sodium bisulfite solution: 18.
    2g/L

    .

    Weigh 1.
    66 g of sodium metabisulfite and dissolve it in a 100 mL volumetric flask containing 50 mL of water.
    After dissolution, dilute to the mark with water and mix

    .

    4.
    7.
    2.
    2 Iodine standard solution: c(1/2I
    2 )=0.
    02mol/L

    .

    4.
    7.
    2.
    3
    Sodium thiosulfate standard titration solution: c(Na 2 S 2 O 3 )=0.
    02mol/L

    .

    4.
    7.
    2.
    4 Starch indicator solution: 10g/L

    .

    4.
    7.
    3 Analysis steps

    4.
    7.
    3.
    1 Pipette 10mL sample, place it in a 50mL volumetric flask already filled with 10mL water, add 5mL sodium bisulfite solution, dilute to the mark with water, mix well and let stand for 30min

    .
    It is the test solution

    .

    4.
    7.
    3.
    2 Pipette 50 mL of iodine standard solution into an iodine measuring flask, and place it in an ice water bath to stand still

    .
    Take 20 mL of the test solution in an iodine flask, titrate with sodium thiosulfate standard titration solution until the solution is light yellow, add 0.
    5 mL starch indicator solution, and continue titration until the blue color just disappears as the end point

    .

    4.
    7.
    3.
    3 At the same time of measurement, perform a blank test with the same amount of reagent solution without adding the sample according to the same steps as the measurement

    .

    4.
    7.
    4 Result calculation

    The mass fraction of acetaldehyde w 4 , the value is expressed in %, calculated according to formula (4):

    Where:

    V 0 —The value of the volume of the sodium thiosulfate standard titration solution (4.
    7.
    2.
    3) consumed in the blank test, in milliliter (mL);

    V 1 —The value of the volume of the standard titration solution of sodium thiosulfate consumed by the sample, in milliliters (mL);

    c—The exact value of sodium thiosulfate standard titration solution, the unit is mole per liter (mol/L);

    M— The value of the molar mass of acetaldehyde (1/2C 2 H 4 O), in grams per mole (g/mol) [M(1/2C 2 H 4 O)=22.
    03];

    V—the value of the volume of the sample, the unit is milliliters (mL);

    p—The value of the density of the sample at 20°C, in grams per cubic centimeter (g/cm)
    .

    Take the arithmetic average of the two parallel determination results as the determination result, and the difference between the two parallel determination results shall not exceed 0.
    002%

    .

    Related links: Glacial acetic acid for industrial use (4)

     

     

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