Gypsum, used for wallboard, has the formula CaSO_4 2H_2 O. What is the percent b
ID: 1024688 • Letter: G
Question
Gypsum, used for wallboard, has the formula CaSO_4 2H_2 O. What is the percent by weight of water in this hydrate? If 15.000 grams of this hydrate is heated, what mass of water would be lost? Describe and given an example of how a drying agent works. A freshman chemistry student collected the following data during an experiment similar to yours. If the anhydrous salt is CuCl_2. Make the requested calculations. Mass of dried crucible 34.0000 g Mass of crucible and hydrate 34.2350 g Mass of crucible and anhydrous salt 34.1850 g Mass of hydrate_____Mass of anhydride_______Mass of water lost_____Percent water in hydrate________Moles of anhydride_______Moles of water in hydrate______Formula of hydrate_______SHOW CALCULATIONS ON BACK TO RECEIVE ANY CREDIT.Explanation / Answer
Atomic weights : Ca=40, S= 32, O= 16 and H=1
Molecular weight of CaSO4= 40+32+4*16= 136
Molecular weight of 2 moles of water= 2*(2+16)=36
Basis :1 mole of CaSO4.2H2O
Moles= mass/molecular weight
Molecular weight = mass = 136+36= 172
Mass % of H2O= 100*36/172=20.93%
Moles of CaSO4.2H2O in 15 gm = 15/172 =0.087
1 mole CaSO4.2H2O contains 2 mole of water
0.087 moles of CaSO4.2H2O contains 2*0.087/1=0.174 moles of water =0.174*2= 0.348 gm of water
2. drying agents form hydrates at low temperature according to the reaction
x(drying agent)+ nH2O----->x(H2O)n
in the above example of CaSO4.2H2O
CaSO4 is drying agent and mixes with water CaSO4+2H2O-----> CaSO2(H2O)2
Mass of hydrate= mass of crucible+hydrate- mass of crucible
=34.2350-34= 0.2350gm
Mass of anhydrous salt= mass of crucible+anhydrous salt- mass of dried crucible= 34.1850-34=0.1850gm
Mass of water lost= mass of hydrate- mass of anhydrous salt= 0.2350-0.1850=0.05 gms
Percent of water= 100*0.05/0.2350 =21.28%
Moles of anhydride = mass/Molecular weight of CuCl2=0.1850/134=0.001381 moles
Moles of water= 0.05/18= 0.0028
Moles of anhydride: moles of water= 0.001381:0.0028 = 1:2
So formulais CuCl2.2H2O
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.