chem help for acid titration?

NetherCraft 0

1.Why is equivalent mass determined and not molar mass?

2. Why must the KHP and the acid samples be dried? If they are not dried, how would the results change (high or low)?

3. Why must NaOH be standardized? Why can’t an exact solution of NaOH be prepared?

i need it in five hours. please hurry

1 Answer

  • 1.Why is equivalent mass determined and not molar mass?

    equivalent mass is determined for unknown acids when we do not know how many H+ ions it has per molecule.

    we can calculate the moles of our standard base.

    but without knowing the # of H+ ions / molecule,

    we can not balance an equation for our acid vs. NaOH

    so we can’t find moles of acid without an equation

    so we can’t find molar mass

    but we can find equiv of base

    we know equiv of base = equiv of acid

    so we can calculate equiv weight

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    2. Why must the KHP and the acid samples be dried? If they are not dried, how would the results change (high or low)?

    a standard must be of known purity,

    if it hasn’t been dried of absorbed moisture,

    then we do not know its grams per equivalent

    but if it has moisture, it will be weaker that we thought it should be

    it will take more KHP to neutralize the NaOH

    we will think that NaOH is stronger than it really is

    when we use that NaOH which has a molarity higher than it should be

    we will calculate unknown as stronger than they really are

    with normalities that are too High

    & more equivalents per gram (which is a lower equivalent mass… less grams per equivalent)

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    3. Why must NaOH be standardized? Why can’t an exact solution of NaOH be prepared?

    because NaOH hasn’t a known purity

    as soon as we open the bottle it absorbs moisture & CO2 out of the air

    its grams become less concentrated in NaOH not only because of the excess weight it absorbs

    but also because the CO2 & H2O combine to make carbonic acid which destroys some of the NaOH

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