This is an open book, 22 problem, take home exam. It is due at the next class meeting. Try to work the exam without your book. Then go through it the second time using references. Mail it to Dr. H. Plastas Chemistry Department, Montgomery College, Rockville, MD 20850 if you can not attend that class. Mail it if you are in a distance learning section. By signing below your are attesting, on your honor, that you have completed this exam without help from any other person.

__________________________________________Signature

Balance each of the following equations using the smallest ratio of whole numbers. (2 pts each)
 

1. 6 H₂O + ___Ca₃P₂(s) --> 2 PH₃ + 3 Ca(OH)₂
2. 4 H₂O + 4 Br₂ + ___H₂S --> ___H₂SO₄ + 8 HBr
3. 4 C₉H₁₁ + 47 O₂ --> 36 CO₂ + 22 H₂O
4. 3 TiO₂ + 4 H₃SbO₄ --> ___Ti₃(SbO₄)₄ + 6 H₂O
5. ___Sb₂S₃ + 9 PbO --> ___Sb₂O₃ + 9 Pb + 3 SO₂

Complete and balance (using the smallest whole number ratio) the following equation. If no reaction will take place write "NR". (4 pts each)

6. ___Cl₂O₅ + ___H₂O --> 2 HClO₃
7. 2 Ti(ClO₃)₃(s) > 2 TiCl₃ + 9 O₂
8. ___Sn₃(PO₄)₄ + 6 Ba --> 2 Ba₃(PO₄)₂ + 3 Sn
9. ___P₂O₃ + 6 KOH --> 2 K₃PO₃ + 3 H₂O
10. 3 H₂SO₄(aq) + ___ Fe₂O₃(aq) --> Fe₂(SO₄)₃ + 3 H₂O
11. 2 AlCl₃ + 3 Ba(OH )₂ --> 3 BaCl₂ + 2 Al(OH)₃
12. ___V₂(CO₃)₃(s) > V₂O₃ + 3 CO₂
13. ___C₅H₁₀O₅ + 5 O₂ (in excess) --> 5 CO₂ + 5 H₂O
14. ___(NH₄)₂SO₄(s) > 2 NH₃ + H₂SO₄
15. ___Fe(CN)₃(s) + 3 HCl(aq) --> FeCl₃ + 3 HCN
 

For the remaining problems, show the set up and give the answer to the proper number of significant figures with the correct units. Neatness will be greatly appreciated! Box the answer.
 

16. Convert 0.0991 lb. of zinc to moles. (7 pts)
(0.0991 lb) (453.6 g/lb) (1 mol Zn/65.38 g) = 0.688 mol Zn
 

17. Convert 880 cg of iodine to molecules. (7 pts)
(880 cg) (1g/100 cg) (1 mol I₂/254 gI₂)(6.02 x 10²³ molecules I₂/mol I₂)
= 2.1 x 10²² molecules I₂

18. Calculate the percent by weight of sulfur in arsenic(III)
sulfide, to three significant figits. (7 pts)
As₂S₃; molar mass = 246.02 g per mole
% S = (96.18g  S / 246.02g As₂S₃) (100) = 39.1% S

19. An experimental catalyst used in the polymerization of butadiene is 23.3% Co, 25.3% Mo and 51.4% Cl.  Calculate its empirical formula. (10 pts)

(23.3 g) (1 mole/58.9 g) = 0.3956 mol Co;   1.5

(25.3 g) (1 mol/95.9 g) = 0.2638 mol Mo;    1

(51.4 g) (1 mol/35.5 g) = 1.448 mol Cl;        5.5

                                                                                           Co₃Mo₂Cl₁₁
 

20. What is the molecular formula of a compound
with the empirical formula C₃H₆O₂ and molar
mass of approximately 887 grams per mole. (5 pts)

molar mass of C₃H₆O₂ = 74 g / mol
(887)/(74) = 12; molecular formula C₃₆H₇₂O₂₄
 

21. Suppose a new element is discovered, atomic number
114, consisting of two isotopes. The lighter isotope is
88.444% abundant and weighs 280.91 amu/atom.
The heavier isotope weighs 284.11 amu/atom.
Calculate the atomic weight (atomic mass) to 5 significant figures. (7 pts)

(280.91) (0.88444) + (284.11) (.11556) = 248.448 + 32.832 = 281.28 amu/atom
 

22. If gold is selling for $4700 a pound, how many atoms
of gold can be bought for one cent? (7 pts)

(1 lb)/$4700) (454 g/lb) (1 mol Au/197 g)(6.02 x 10²³ atoms/1 mole) (1$/100 cents)
2.9518 x 10¹⁸ = 3.0 x 10¹⁸ atoms/cent