A 1.994 g sample of gypsum, a hydrated salt of calcium sulfate, CaSO4, is heated at a temp. above 170 C in a crucible until a constant mass is reached. The mass of anhydrous CaSO4 salt is 1.577 g.
Calculate the percent by mass of water in the hydrated calcium sulfate salt.
This is what I did....
1.577/1.944 * 100 = 79.09%
100-79.09 = 20.91% water.
Is this correct? Thanks for your help!
Yes, it's correct. Another way you could have done it (but no more correct than the way you did it) is
1.994 g = hydrated CaSO4
-1.577 g = anhydrous material
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0.417 g = mass water driven off
%H2O = (0.417/1.944)*100 = 20.913 which I would round to 20.9%.
Thank you!
To determine the percent by mass of water in the hydrated calcium sulfate salt, you need to consider the following:
1. Begin by calculating the mass of water lost during heating:
Mass of water = Mass of hydrated salt - Mass of anhydrous salt
Mass of water = 1.994 g - 1.577 g
Mass of water = 0.417 g
2. Next, calculate the percent by mass of water in the hydrated salt:
Percent by mass of water = (Mass of water / Mass of hydrated salt) * 100
Percent by mass of water = (0.417 g / 1.994 g) * 100
Percent by mass of water = 20.91%
Therefore, your calculation is correct. The percent by mass of water in the hydrated calcium sulfate salt is indeed 20.91%.