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Freezing Point Determination of Water and Sucrose Solution




  • Insert funnel tube in the vertical portion of T-tube at one side of the apparatus and pour 400 mil of either, cooled to 10 0 C close the vertical tube with cork and connect the pressure pump to the inlet tube of the air drying attachment.

    Adjust the pump so as to pass air through the apparatus at moderate rate, as may be judged by the agitation of conc. Sulphuric acid in the drying tube. Continuous vaporization in the flask from temperature to 0 0 C within 5 to 10 min. continue lowering of temp. Until control thermometer register near 3 0 C.

    At this stage lowering the gauge tube into the bath then closing the top by means of the fore finger and raising to a suitable height an estimate in to the larger tube. A small quantity of alcohol, sufficient to till the lower space between the two pour in the propose of restoring the 400 ml. An additional 10 to 15 ml. is sufficient for each succeeding determination.

    Pour into freezing tube sufficient distilled water (30-35 ml) which was boiled and cooled to 0 C or lower to submerge the thermometer bulb. Insert the thermometer bulb. Insert the thermometer, together with the stirrer and lower the test tube can be made as to the quantity of ether necessary to two test tubes, will serve to complete the conduction medium between the freezing both and the liquid to be tested.

    Keep the stirrer in steady up and down motion at a rate of one stock each 1-2 seconds, provided the cooling proceeds satisfactory maintain a passage of air through the apparatus until the temperature of the cooling bath reaches 2.5 0 C at which time the top of mercury column in thermometer usually reaches to a position near the freezing point of water.

    Maintain the temperature of the cooling bath at 2.5 0 C and continuous the manipulation of the stirrer until a super cooling of the sample of 1.0 to 1.2 0 C is observed. At this stage the liquid will being to freeze as may be noted by rapid rise to mercy. Manipulate the stirrer slowly and carefully three to four times as the mercury column should remain its highest point.

    The top of the mercury column should remain stationary for at least one minute. Not the exact reading on the thermometer scale, taking necessary precaution to avoid parallax and estimate 1/100.001 0 C.

    When the observation has been satisfactorily completed make a duplicate determination in the similar manner then remove the thermometer and stirrer and empty the water from freezing tube.

    Example:

    Two tested thermometer give intervals of 0.199 0C and 0.200 0 C respectively between the freezing point depression reading of the two sucrose solutions. One thermometer gave freezing point depression 0.422 0 C (0.779 and 0.343 and 0.621 0 C while the other gave 0.422 and 0.622 0 C).

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