Last modified: Wed 12/31/1969 06:00:00 pm ACA

Oklahoma State University

It is OK to use your textbook or lecture notes from class, but if you can answers the questions without it that is OK too.

Do not press the RETURN or ENTER key while you are answering these questions. Your browser will interpret either the same as clicking on the Submit key.

Answer all of the questions below. If you do not know an answer enter CNA. However, it will help me the most if you answer each question with your best intuition/idea about what would be a reasonable answer.

First Name:

Last Name:


1. What is the atomic mass (in amu) for phosphorus?


2. What is the atomic mass (in amu) for chlorine?


3. What is the formula mass (in amu) for PCl3?


4. What is the name of the compound with the formula PCl3?

5. What is the mass (in grams) of one molecule of PCl3? (Remember 1 amu = 1.66054 x 10-24 grams)


6. What is the mass, in grams, of 6.02 x 1023 molecules of PCl3?


7. What is the mass, in grams of 6.02 x 1023 molecules of Br2?


In chemistry a mol is the term used to describe an amount of substance that contains 6.023 x 1023 units (atoms/molecules/formula units) of that substance. For example, 1 mol of PCl3 molecules contains 6.023 x 1023 molecules of PCl3. A mole of PCl3 molecules has a mass equal to its formula weight expressed in units of grams. The term molar mass is used to describe the mass of 1 mol of a substance.

8. What is the molar mass of PCl3? (Hint: look at the definition of molar mass above and your answer in Q6.)

grams mol-1

9. How many mol of PCl3 are there in 13.74 grams of PCl3?


10. Complete the following table.


Molar Mass (g mol-1)



number of atoms, molecules or formula units






OK, how about one fun problem?

11. How many oxygen atoms in a sample of Al(NO3)3 with a mass of 1.415 x 10-21 grams? O atoms

12. Is there anything about the questions that you feel you do not understand? List your concerns/questions.

13. If there is one question you would like to have answered in lecture, what would that question be?