Asked by Jenna
How do I "determine the mass percent of H2O in the hydrate Cr(NO3)3 * 9H2O to 3 significant figures"?
Answers
Answered by
bobpursley
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.
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.
Answered by
DrBob222
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
[9*molar mass H2O/molar mass Cr(NO3)3*9H2O]*100 = %H2O