Exam Review #20

20) Use stoichiometry to solve the following complex problems:

A.   If a sample of K₂S is known to contain 8.418x10²⁴ atoms of K, what mass of potassium sulfide is present?

8.418x10²⁴ atoms K x          1 mol K           x  1 mol K₂S x 110 mol K₂S =  769 mol K₂S

                                    6.022x10²³ atoms K     2 mol K       1 mole K₂S

B. How many chloride atoms can be found in 38.0L of CCl₄ gas at STP?

38.0 L CCl₄ x 1 mol CCL₄ x   4 mol Cl x 6.022x10²³ atoms Cl = 4.10 atoms CL

                       22.4 L CCl₄   1 mol CCL₄  1 mol Cl

C. If a sample of carbon monoxide gas has a volume of 20.8L at STP, how many grams of oxygen are present?

20.8L CO x 1 mol CO x 1 mol O  x 16.0g O = 14.9g O

                     22.4L CO    1 mol C     1 mol O