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    Determination of water hardness

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    Water that has non been purified is what is known as “ difficult H2O. ” Difficult H2O can incorporate substances like Ca2+ , Mg2+ , and Fe2+ . These “ difficult ions ” are non ever unhealthy needfully, but there are several good grounds that we take them. First, they can unite with other compounds to organize soap trash. Second, it can take to the buildup of graduated table in pipes which may necessitate dearly-won fixs. Finally, the graduated table and soap trash will take to more expensive energy measures and more fixs needed in the long tally. ( Dean, Reck, Stone, & A ; Robinson, 2009 )

    The sum of difficult ions in H2O can be determined by the procedure of titration. In this instance, the titration is done by adding the chemical EDTA, ethylenediaminetetraacetic acid, to the H2O ( which has a few beads of the index Eriochrome Black T ) until the index alterations from ruddy to blue. The point at which the colour alterations is called the end point. ( Dean, Reck, Stone, & A ; Robinson, 2009 )

    For EDTA to be able to adhere to the difficult ions, it is of import that it remains deprotonated. To make this, a buffer solution is added to maintain the pH at a high degree. This allows EDTA to adhere freely with difficult ions like Ca2+ as shown in the undermentioned reaction:

    EDTA4- + Ca2+ a Ca ( EDTA ) 2-

    In this experiment, the presence of Ca2+ in a H2O sample will be found. The type of titration utilizing EDTA and Eriochrome Black T explained above will be used to find the degree of Ca ions in parts per million. This will so be compared to a graduated table of H2O hardness to see how “ difficult ” the H2O really is. ( Dean, Reck, Stone, & A ; Robinson, 2009 )


    Taking the norm of the differences gives a value of 30.79 milliliter. Using this in concurrence with the reaction listed above, you can find the molar concentration of the EDTA solution.

    Since the mean volume of EDTA used was used, this value is the mean concentration of EDTA. Using Excel to cipher the standard divergence, a value is obtained of 0.008120 A± 0.000003 M EDTA. This has an rsd value of 0.0004 % .

    Using the values from tests 2 and 3 ( test 1 was non within the preciseness needed ) , the concentration of Ca2+ in parts per million ( ppm ) can be calculated. The norm from tests 2 and 3 is 15.12 milliliter.

    Since the mean volume of EDTA used was used, this value is the mean concentration of EDTA. Using Excel to cipher the standard divergence, a value is obtained of 98.4A±0.2 ppm Ca2+ . This has an rsd value of 0.2 % .

    Consequences / Discussion

    Using the graduated table in the lab manual, 98.42ppm corresponds to reasonably soft H2O. The H2O sample used was obtained from the “ Jordan River ” ( of Bloomington, non Israel ) , so it was expected that it might fall under the difficult or really difficult classs. This was because Bloomington has many limestone sedimentations that might reassign difficult ions to the H2O.

    There are a few topographic points in this experiment where mistakes could hold occurred. A calibrated cylinder had to be used alternatively of a volumetric pipette, because the right pump was n’t available, and this is a less accurate instrument. Besides, at some points, it was hard to state when the solution had turned from purple to blue, but the space allowed for the shadiness of blue required for the titration to be “ finished ” to be inactive across the whole experiment.

    Standardization is of import when making a titration experiment since the terminal consequence of the titration depends upon the truth of the concentration of the titrant. Standardization allows for the concentration of the titrant to be confirmed and therefore, increases the truth of the concluding consequence of the titration.

    Difficult H2O has both advantages and disadvantages. Difficult H2O can do rinsing vesture less effectual. It besides causes soap trash to construct up on the organic structure when bathing. Buildups in pipes lead to inefficiency in contraptions that use H2O, which can increase costs. ( “ Hard Water Problems, ” n.d. ) Studies have shown that difficult H2O does n’t look to hold any negative effects on worlds. It is even possible that it could assist support the organic structure against disease. Some surveies have shown that people that drink difficult H2O are less likely to hold bosom disease, but the grounds is n’t complete plenty to do a certain connexion. ( “ Hardness in Drinking-water, ” 2003 )

    This experiment shows a practical application of how chemical science can be used to assist cover with existent universe issues. Testing H2O with chemical methods to find hardness can turn out utile in forestalling the antecedently mentioned issues of inefficiency that difficult H2O can do. Along with the chemical procedures used to sublimate H2O, these constructs can assist to take down costs and heighten efficiency in mundane life.


    • Dean, Norman, Cathrine Reck, Todd Stone, and Jill Robinson. Chemistry C117: Principles of Chemistry and Biochemistry: Laboratory Manual. 8th erectile dysfunction. Plymouth: Hayden-McNeil, 2009. Print.
    • Difficult Water Problems – Limescale Deposits, Reduced Heating Efficiency, Skin Irritation. ( n.d. ) . Retrieved October 07, 2009, from hypertext transfer protocol: //
    • Hardness in Drinking-water. ( 2003 ) . Retrieved October 7, 2009, from hypertext transfer protocol: //

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