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Gen. Chemistry

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How do I "determine the mass percent of H2O in the hydrate Cr(NO3)3 * 9H2O to 3 significant figures"?

  • Gen. Chemistry -

    It depends if you are determining from mass measurements, or a formula calculation.

    I assume you took an experment, measured some of the hydrate, heated it, then measured the unhydrated salt.

    In that case,

    Percenthydrate= 100* (masshydrate-massunhydrated)/masshydrated

    Now, to do this to three sig figures might be a problem, as the number of sig digits might be determined by the subtracation, rather than your wishes.
    For instance, say
    mass hydrated= 10.34 grams
    mass unhydrage= 9.51 grams

    subtracting, one gets .83 grams, and you cannot get three sig figures from this.

  • Gen. Chemistry -

    On the other hand, if you are calculating percent water from the formula, then,
    [9*molar mass H2O/molar mass Cr(NO3)3*9H2O]*100 = %H2O

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