Stoichiometry Worksheet (with key)

Liberal Arts Chemistry

Dr. Susan Campbell

1.  Silver sulfide (Ag₂S) is the common tarnish on silver objects.  What weight of silver sulfide can be made from 1.23 mg of hydrogen sulfide (H₂S) obtained from a rotten egg?  The reaction of formation of silver sulfide is given below:

4Ag   +  2 H₂S   +   O₂  ------->   2 Ag₂S   +  2 H₂O (Equation must first be balanced.)

1.23 mg H₂S  x  1g/1000mg  x 1 mole H₂S/ 34.0 g H₂S  x  2moles Ag₂S/2 moles H₂S  x 

248 g/1mole Ag₂S  = .00897 g silver sulfide

2.  A somewhat antiquated method for preparing chlorine gas involves heating hydrochloric acid with pyrolusite (manganese dioxide), a common manganese ore.  (Reaction given below.)  How many kg of HCl react with 5.69 kg of manganese dioxide?

4HCl(aq)   +   MnO₂(s) ------->   2 H₂O(l)    +    MnCl₂ (aq)   +   Cl₂(g) (Equation must first be balanced.)

5.69 kg MnO₂  x  1000g/1 kg   x  1 mole MnO₂/ 86.9 g MnO₂  x  4moles HCl/1 mole MnO₂

x  36.5 g HCl/ 1 mole HCL  x  1kg/1000g  =   9.56 kg HCl

3.  What is the weight (IN GRAMS) of one atom of Zn?

First, you need to realize that one atom of zinc weighs 65.4 amu's (not 65.4 grams).  However, one mole of Zn atoms does weight 65.4 grams.

65.4 g Zn/1 mole Zn atoms  x  1 mole Zn atoms/6.02 x 10²³ Zn atoms = 1.09 x 10^-22 grams/atom of Zn