Chapter 7 Homework - 20 points total

 

Naming and writing ionic formulas: 

     Remember:   -The first symbol is positive and called the name it is on the chart

                            -The second symbol is negative and changes its name to –ide

                            -If the second symbol is a POLYATOMIC ion, its name ends in –ate

    or -ite

    (with the only exception being OH-1 which is called Hydroxide)

 

Section #1:

(indicate on your homework paper which section and page number you are doing!)

  Do practice problems #1-2 on p. 207

  Do practice problems #1-2 on p. 209

  Do practice problems #1-2 on p. 211

  Do practice problems #1-2 on p. 213

  Copy the names of the following acids onto your homework.:  HF, HCl, H3PO4, HNO3, H2SO4, CH3COOH.  You will find them in table 7-5 on p. 214

 

Assigning Oxidation Numbers to Compounds:  (look at the rules on p. 216 for help!)

  Do practice problem #1 on p. 218  (remember to write the section and page number)

  Do Section review problem #1 p. 219

---------------------------------------------End of Section #1--------------------------------------

 

Section #2:

Percent Composition: (a good sample problem is on p. 227 of your book)

Find the Percent composition of each element in the following compounds’ empirical formulas:

1.  NaCl                                                                       4.  C6H12O6    

2.  H2O                                                                        5.  CH3OH

3.  Mg3(PO4)2

 

Empirical Formulas:  (a good sample problem is on p. 229-230 of your book)

Use the percent composition of these compounds to determine the empirical formula (Hint:  You can figure out many of these by balancing the ionic charges.  Do that to check your work.  Realize that the ones on the test will be all covalent, not ionic)

6.    11.0% H and 89.0% O                               7.    39. % Na and 60.7% Cl

8.    27.7% Mg  and 72.3% PO4  (Hint:Keep PO4 together, eg. molar mass = 95.0 g/mol)

9.    32.4% Na and 67.6% SO4 (Hint:  Keep SO4 together)

10.  40.0% C,  6.67% H,  and 53.3% O            11.  37.5% C,  12.5% H and 50.0% O

12.  66.0% Ca and 34.0% P                              13.  82.4% N  and 17.6% H

 

Molecular Formulas: Use the empirical formulas you found in questions #6-13 of the Empirical Formulas section to answer these questions.  NOTE:  I made up these compounds, they do not exist in real life - it is just an example of how to do these type of problems.

(see p. 232-233 for a great sample problem)

6.   Molecular mass =  54.0                   Empirical Formula Mass = 18.0

7.   Molecular mass =   117                 Empirical Formula Mass = 58.5

8.   Molecular mass =    1320                Empirical Formula Mass =  263

9.   Molecular mass =     568               Empirical Formula Mass =  142

 

 

Hydrates:  Find the formulas for the following hydrates

(see sample problem 7-11 on p. 227-228 for help on these)

 

                                                                   Answers in mole ratio of compound to water

10.  0.391 g Li2SiF6,  0.0903 g H2O               (1:2)

11.  0.737 g MgSO3,  0.763 g H2O                (1:6)

12.  95.3 g LiNO3,  74.7 g H2O                      (1:3)

13.  76.9 g CaSO3,  23.1 g H2O                      (1:2)

14.  89.2 g BaBr2, 10.8 g H2O                         (1:2)

 

Answers to % comp. Problems                                

 

1.            39.3:60.7                                                        

2.         11:89                                                                          

3.            27.7:23.6:48.7                                                            

4.            40:6.7:53                                                                   

5.            37.5:12.5:49.9                                                

 

Answers to empirical problems

6.         H2O          

7.         NaCl

8.         Mg3 (PO4) 2

9.         Na2 SO4

10.       CH2O

11.       CH4O

12.       Ca3P2

13.       NH3

 

Answers to molecular formulas

 

6.         H6O3

7.         Na2Cl2

8.            Mg15(PO4) 10

9.            Na8(SO4) 4