1. Dichloroethane, a compound that is often used for dry cleaning, contains carbon, hydrogen, and chlorine. It has a molar mass of 99g/mol
Analysis of a sample shows that it contains 24.3%
carbon and 4.1%
hydrogen. What is its molecular formula?

2. When rubidium ions are heated to high temperature, two lines are observed in its line of spectrum at wavelengths of (a) 7.9× 10^{-7}m
and (b) 4.2× 10^{-7}m
. What are the frequencies of the two lines? (hint: use electromagnetic spectrum)

3. Draw the orbital diagram for the valence shell of each of the following atoms:
(a) C
(b) N
(c) P
(d) V
(e) Si

4. What is the molarity of an automobile battery acid, H2SO4
solution if 22.53 mL of the acid neutralizes 42.11 mL of 1.923 M sodium hydroxide, NaOH?


5. Determine oxidation states of the elements in the following compounds or ions listed below
(a) NaBH4
(b)( HPO4)2
(c) Mg2Si
(d) RbO2

6. Predict the result of mixing reasonably concentrated solutions of the following ionic compounds. If precipitation is expected write a balanced net ionic equation for the reaction

(a) Potassium sulfate and barium nitrate
(b) Lithium chloride and silver acetate

7. 5.6g of iron metal, Fe, are heated strongly and mixed with 8 g of sulfur, S, to form 4.4 g of iron (II) sulfide, FeS.

a. Identify the limiting and excess reactants
b. Calculate the mass of FeS formed
c. calculate the percent yield of FeS
8. The three naturally occurring isotopes of magnesium have masses of 23.985 (Mg-24), 24.986(Mg-25)
, and 25.983 (Mg-26 ) amu. Their abundances are 78.70%,10.13%
, and 11.17%
, respectively. Calculate the average atomic mass of magnesium.

And show the formulas.