Answers to Practice Problems

stoichiometry: 

1) When 26.5 grams of Mg are reacted with hydrochloric acid, how many grams of magnesium chloride are produced?

                              Mg  +   2HCl  -->  MgCl₂  +  H₂

                             104 g MgCl₂

2)  If  147.2 g of hexane combusts at 115C at 101.3KPa, how many liters of carbon dioxide will be produced?

                              2C₆H₁₄  +   19O₂  -->   12CO₂  +  14H₂O

                             327 L CO₂

3) If 24L of oxygen reacts at STP with hydrogen, how many liters of water vapor will be produced?

                         O₂  + 2H₂  -->  2H₂O 

                          48 L H₂O
                                       

gas laws

            Boyles, Charles, combined gas laws

4) My son's "dead" (flaccid) balloon which is 0.76 dm³ at 25C and 103 KPa, is heated it will bounce again.  What temperature is required to restore the balloon to it's original volume at standard pressure, 1.2L ? 

            190 C
          

           ideal gas law

5) An excess of sulfuric acid reacts with 0.24g magnesium to produce hydrogen gas and a salt.  What volume of gas will be produced at 24C and 99.8KPa? 

                                 0.024 dm³ H₂
                   

periodic trends

6) Arrange the following elements and ions in ascending order by size:

Cl^-, Na, O, Ce, Ar.

  By Size:    O, Na, Cl^-,Ce, Ar

Rearrange those same elements (use Cl not Cl-) by reactivity from least reactive to most reactive.

  Ar, Ce, Cl, Na, O

Rearrange those same elements by first ionization energy from least energy to greatest energy.

  Na, Ce, Cl, O, Ar

molecule shapes, bond angles, Lewis dot diagrams

7) What are the bond angles for octahedrals?

     octahedrals have  90^o angles

for irregular trigonal bipyramidal with 2 unshared pairs? 
             90^o angles

What are the bond angles for  a regular tetrahedral?
 109.5^o angles

How many pairs does an irregular trigonal planar have total?
3 total pairs; 1 unshared pair

How many pairs does a regular trigonal bipyramidal have?
5 total pairs; 5 shared pairs

Draw PCl₃ and give shape and bond angles.

            P has 5 e- x 1 atom =  5
            Cl has 7e- x 3 atoms = 21
            total e                       = 26
           
            This forms an irregular tetrahedral.  It has 4 total pairs around the central
            atom and 1 of the pairs is unshared.  The bond angles will be less than
            109.5^o . 

nuclear chem

8) Write a balanced equation for each of the following.

a)  ⁹₃Li-->  ⁹₄ Be +_ ⁰_-1e__
b) ¹⁹⁹ ₈₄ Po + ⁰_-1e --> ¹⁹⁹₈₃Bi (K capture)
c) Beta minus emission by ³⁰₁₃Al  ___  ³⁰₁₃Al --> ⁰_-1e + ³⁰₁₄Si
d) Alpha emission by ²⁴²₉₄ Pu ______ ²⁴²₉₄ Pu --> ⁴₂ He + ²⁴⁰₉₂ U
e)  ¹⁴¹ ₆₂Sm--> ¹₁H + ¹⁴⁰ ₆₁Pm

9) How long will it take 6.00 x 10²⁰ atoms of ¹⁴⁵₆₄Gd to disintegrate to 1.88 x 10¹⁹ atoms if the half life of ¹⁴⁵₆₄Gd  is 25 minutes?

             125 min 
              

10) If the half-life of ¹²⁹₅₅Cs is 32.1 hours, how many atoms will be left after 5 days, 8 hours, 24 minutes if there were initially 1.00 mol of atoms?

     0 .0625 mol atoms remain