Percent by weight of substance in hydrate

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To find the percent by weight of water in gypsum (CaSO4·2H2O), calculate the mass of CaSO4 and the mass of 2H2O using atomic masses from the periodic table, then determine the percentage of water in the total mass of the hydrate. For part (b), it is assumed that all water is lost upon heating, allowing the use of the percentage calculated in part (a) to determine the mass of water lost from a 15.000-gram sample. The discussion emphasizes the importance of accurate mass calculations for both components of the hydrate. Overall, understanding the composition of the hydrate is crucial for solving the problem effectively.
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Q: Gypsum, used for wallboard, has the formula CaSO4 2H2O. (a) What is the percent by weight of water in this hydrate? (b) If 15.000 grams of this hydrate is heated, what mass of water would be lost?

I'm thinking that I have to find out the mass of the CaSO4 and then the mass of 2H2O, then calculate the percentage of 2H2o to CaSO4. I just don't know how to find out the mass of either one..

For part (b) i guess i assume that all water is lost in heating? Then use the percentage from (a) to calculate the water lost?

thanks for any help,
hairy_grape
 
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The percentage should be of H2O in the entire hydrate CaSO4·2H2O
You use the atomic masses from the periodic table to find the masses...

For (b) it sounds like you're on the right track.
 
Bohrok said:
The percentage should be of H2O in the entire hydrate CaSO4·2H2O
You use the atomic masses from the periodic table to find the masses...

For (b) it sounds like you're on the right track.

ok thanks
 
Thread 'Confusion regarding a chemical kinetics problem'

Thread 'Confusion regarding a chemical kinetics problem'

TL;DR Summary: cannot find out error in solution proposed. [![question with rate laws][1]][1] Now the rate law for the reaction (i.e reaction rate) can be written as: $$ R= k[N_2O_5] $$ my main question is, WHAT is this reaction equal to? what I mean here is, whether $$k[N_2O_5]= -d[N_2O_5]/dt$$ or is it $$k[N_2O_5]= -1/2 \frac{d}{dt} [N_2O_5] $$ ? The latter seems to be more apt, as the reaction rate must be -1/2 (disappearance rate of N2O5), which adheres to the stoichiometry of the...
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