Chemistry 111 – 2014 Name: ________________________
Exam #1
N
A
= 6.022 x 10 23
1. How many protons, neutrons and electrons are found in an ion of the isotope
27 Al 3+
.
13 protons because Al is element #13
14 neutrons because the mass number = 27 = #p + #n; # n = 27 - 13
10 electrons because neutral Al would have 13 but this has a +3 charge
2. Define:
Isotopes: Two atoms that have the same atomic number but different masses. Also, same number of protons but different numbers of neutrons.
Allotropes: Two different molecular forms (that is shapes) of the same element.
3. Elements in the same GROUP of the periodic table tend to have similar properties.
4. Give formulas for the following:
Ammonium carbonate: (NH
4
)
2
CO
3 tetraphosphorus decaoxide: P
4
O
10
Aluminum permanganate: Al(MnO
4
)
3 sodium sulfide: Na
2
S
5. What is the formula of the ionic compound formed between iron(III) ion and hydroxide ion?
Fe(OH)
3
because iron(III) ion has a +3 charge and hydroxide has a -1 charge.
6. How many atoms of nitrogen are found in 4.60 mol N
2
O
5
? ________________________
4.60 mol N O
2 5
 
 23
2 mol N 6.022 10 N atoms
1 mol N O
2 5
1 mol N
  24
5.54 10 atoms

7. Balance the following reaction:
1 Al
2
(CO
3
)
3
+ 6 HCl  2 AlCl
3
+ 3 CO
2
+ 3 H
2
O
The initial “1” is generally omitted.
8. Copper (Cu) has two isotopes. Their masses are:
63 Cu = 62.93 aum 65 Cu = 64.93 amu
Which isotope is present in greater abundance?
63 Cu or 65 Cu
9. Consider the reaction of ethane with oxygen:
2 C
2
H
6
+ 7 O
2
 4 CO
2
+ 6 H
2
O
If 3.8 mol C
2
H
6
are reacted with excess oxygen, what amount (in moles) of H
2
O can be formed?

2 mol C H
6

10. What does the “mole” represent in chemistry?
Avogadro’s number of particles. The particles are typically atoms, ions, or molecules.
11. What is the molar mass of (NH
4
)
2
SO
3
?
116.13 g/mol
12. Well mixed, filtered salt water represents: (circle all that apply) element compound
homogeneous mixture pure substance heterogeneous mixture
Although the sample contains two compounds, it would not be considered a compound.

Long Answer Questions: You MUST Show All Work
Some molar masses: CaSO
4
: 136.13 g/mol
Fe
2
O
3
: 159.69 g/mol
13. Calculate the percent composition of oxygen in CaSO
4
.
Assume 1 mol of compound. mass O
%O = mass CaSO
4

100

4 mol O

16.00 g O
1 mol O
= 47.0%
136.13 g CaSO
4
14. What is the weight of one gallon of gasoline (in pounds)?
1 gal

1 gal

1 L
3

1 cm3

454 g
= 6.00 pounds
Density = 0.72 g/cm3
1 gallon = 3.785 L
1 pound = 454 g
15. Gypsum is used in drywall to make walls. It is a hydrate of calcium sulfate, CaSO
4
 x H
2
O. If 4.68 g of gypsum is heated to drive off the waters of hydration, the resulting anhydrous calcium sulfate has a mass of 3.70 g. What is the value of x?
Mass lost = mass H
2
O = 4.68 g – 3.70 g = 0.98 g
0.98 g H
2
O x 1 mol H
2
O/18.02 g = 0.05438 mol H
2
O
3.70 g CaSO
4
x 1 mol CaSO4/136.13 g = 0.02718 mol CaSO
4
Mol H
2
O/mol CaSO
4
= 0.05438/0.02718 = 2

16. Potassium (1.350 g) reacts with oxygen under controlled conditions. The resulting compound has a mass of 2.455 g. What is the formula of the compound formed? (NOTE: do not base your answer on expected ion charges from the periodic table.)
You know the mass of K and the final mass. The mass of K is used to find the moles of K.
Mass gained = mass O added to form the compound = 2.455 g – 1.350 g = 1.105 g O
1.105 g O x 1 mol O/16.00 g = 0.06906 mol O
2.455 g K x 1 mol K/39.098 g = 0.03453 mol K
Mol O/mol K = 0.6906/0.03453 = 2
Formula = KO
2
(this kind of compound is called a “superoxide” and they sometimes form between Group 1A metals and oxygen).
17. Metallic iron is made by the reaction of iron oxide with carbon:
2 Fe
2
O
3
(s) + 3 C(s)  4 Fe(s) + 3 CO
2
(g)
If 200 g Fe
2
O
3
are reacted with excess C, what mass of CO
2
is formed?
The path is g Fe
2
O
3

mol Fe
2
O
3

mol CO
2

g CO
2
200 g Fe
2
O
3
x 1 mol Fe
2
O
3
/159.69 g = 1.252 mol Fe2O
3
1.252 mol Fe
2
O
3
x 3 mol CO2/2 mol Fe
2
O
3
= 1.879 mol CO
2
1.870 mol CO
2
x 44.01 g CO
2
/1 mol CO
2
= 82.7 g CO
2