Finding Percents in Chemical Equations?

Question

1)heating 100.0 grams of copper(ii) sulfate pentahydrate and obtaining 58.2 grams of anhydrous copper(ii) sulfate. What percent yield was obtained in this experiment? CuSO4 x 5H2o + heat --> CuSO4 + 5H2O
2)Find the percent composition by mass of phosphoric acid, H3PO4
3) Find the emperical formula for a compound that has the following percentage composition by mass: 10.04% carbon; .84% hydrogen; 89.12% chlorine.


Any help would be thankful. I just do not understand how to do these specific types of problems.

Answer 1

1) Atomic weights: Cu=63.5 S=32 O=16 CuSO4=143.5 H=1 H2O=18 CuSO4*5H2O=233.5

Let CuSO4 be called CS. Let CuSO4*5H2O be called CSP.

100.0gCSP x 1molCSP/233.5gCSP x 1molCS/1molCSP x 143.5gCS/1molCS = 61.46gCS

58.2gCS/61.46 x 100% = 94.7% yield

2) Atomic weights: H=1 P=31 O=16 H3PO4=98

3/98 x 100% = 3.1%

31/98 x 100% = 31.6%

64/98 x 100% = 65.3%

3) Atomic weights: C=12 H=1 Cl=35.5

10.04/12 = 0.84

0.84/1 = 0.84

89.12/35.5= 2.51

0.84/0.84 = 1

2.51/0.84= 2.99 ~ 3

CHCl3 chloroform