Problem Set 17
This will NOT be collected. Answers are posted on the web site
Midterm Review Problems Remember that doing this sheet alone is NOT enough for a review.
Go over all of the problem sets AND all quizzes for a full review. The answers will be published on the web
page so you can check your work.
A. Equations Write each equation in words and balance. Label with the type of reaction. Choices are
single replacement, double replacement, composition/synthesis, decomposition
1 __2___H2 +_____ O2   2____H2O type: composition or synthesis
2. ___2__KClO3  ___2__KCl + __3___O2 type: decomposition
3. _2____K + __2___H2O  ___2__KOH + _____H2 type: single replacement
4. _____Cl2 + __2___LiI  ___2__LiCl + _____I2 type: single replacement
5. If we reacted acetic acid and sodium bicarbonate to form carbon dioxide, water and sodium hydroxide, what
would the chemical equation be? Balance it.
CH3COOH + NaHCO3  NaCH3COO + H2CO3  CO2 + H2O + NaCH3COOH
B. Gram to Mole and Mole to Gram
2Na + 2H2O  2NaOH + H2 (gas) Use this equation
7. If we begin this reaction with 75.0 g of water, how many moles of water do we start with?
75.0 g H2O
mole
=
4.17
mole
18.0 g
8. Since the molar ratio of water to sodium hydroxide is 2:2, we will produce the same number of moles of
sodium hydroxide as we put in of water (if sodium is in excess).
How many grams of sodium hydroxide do we produce? 4.17 mole
C. Density
9. A student has a lump of clay that sinks. The student rolls the clay into a thin, flat rectangle and finds the clay
now floats. Explain.
The mass is clearly the same: no clay has been lost nor gained by changing shape. Density is mass divided by
volume. If the mass is the same, the volume must have changed. The volume has increased by using a different
shape. This reduces the overall density to less than that of water so that the clay can float. The same principle
is used in making aircraft carriers out of cement and steel.
10. Mark wants to send his sister a bookcase shelf full of books. He feels airmail would be best because she
needs the books for the new term at school. He stacks the books on the floor and measures the stack at 1.0 m X
30 cm X 15 inches. There are 15 books and each has an average mass of 5.25 lbs. What is the density (in g/cm3)
of the books?
Density = mass/volume = 5.25 lbs 15 books
1 book
1 inch
1.0 m
30 cm
15 inch 2.5 cm
1m
1 kg
100 cm
2.2 lb
D. Classification of Matter
11. Compare a solution to a mixture.
All solutions are mixtures but only some mixtures are solutions. Any time something is dissolved in water it is
a mixture. Mixtures, however, can also be a combination of solids or gases.
12. Compare a compound to a mixture.
Mixtures are when two or more substances are combined physically but not chemically. A compound is when
two or more substances are combined chemically. Zinc and copper making brass is a mixture. Salt in water is a
mixture. Sodium and chlorine making salt is a compound.
E. Solubility
13. What is the relationship between solubility of solids and temperature? What causes this? Is this the same for
gases? Why or why not?
For most ionic compounds, as temperature increases so does solubility. As temperature increases molecules
move faster thus creating more space between molecules for other atoms/molecules/salts to fit.
Gases are the opposite: as the temperature increases, more come out of solution. Think about a soda. Warm
soda holds less carbonation than cold soda.
14. You have 25 g of KNO3 in 150 g of water at 90 C. How can you make this solution saturated?
170 g = 25 + x
100 g
= 170 x 150 = 100x + 25 x 100;
150 g
25500 = 2500 + 100x; 23000 = 100x;
x = 230 ; so add 230 g of KNO3
15. Is 25 g of NaCl in 50 g of water at 30 C saturated? If not, how can it be made saturated?
29 = x
100
100x = 29 x 50; 100x = 1450 = 100x; x = 14.5 so yes it is saturated
50
F. Physical vs. Chemical Changes
16. Label each as chemical or physical
a. boiling water
physical
b. lighting a match chemical
c. adding sodium to a fire chemical
d. distilling water physical
e. making coffee or tea physical
G. Percent Error
17. We are expecting to produce 257.50 g of compound X in an experiment. However, we collect only
243.55 g. What is our percent error?
Expected – actual
X 100% = 257.50 – 243.55 x 100% =
Expected
257.50
Note: the subtraction is to establish the distance between the values and so is an absolute value
15. What is the relationship between percent error and percent yield?
Percent error is how much is “lost” in an experiment: percent yield is what one gets. Thus, they are
opposites. For example, if percent error is 35 %, then percent yield is 64%.
H. Stoichiometry
2H2 + O2  2H2O
If you begin this reaction with 845.00 g of H2
18. How many moles of H2 did you begin with?
845 g H2
1 mole
=
422.5 mol
2.o g
19. How many moles of H2O do you produce?
422.5 mol H2 2 = 422.5 mol H2O
2
20. How many g of H2O do you produce?
422.5 mol H2O
18 g
=
7605 g of H2O
1 mol
21. If one starts with 62.3g of aluminum oxide and excess hydrochloric acid how many grams of aluminum
chloride is made?
Al2O3 + 6 HCl  3H2O + 2AlCl3
62.3 g Al2O3
1 mol
2
133.7g =
101.96 g
1
1 mol
I. Ionic Compounds
Write the formula and name for the compound made of
22. barium and fluorine
Barium fluoride Ba
+2
. . . .
-1
F ; BaF2;
: F : Ba : F :
. .
23. lithium and oxygen
Lithium oxide
Li
+1
..
..
O
-2
Li2O
. .
..
..
..
: Li : O : Li :
. .
..
..
163 g
J. Name or write the formula
18. Potassium chromate
K +1 CrO4-2
so, K2SO4
19. potassium and sulfate
K+1 SO4 -2
so, K2SO4
20. Ba(OH)2
Barium hydroxide
21. Fe2(SO4)3
Iron (III) sulfate: you need the 3 (III) because iron is a transition metal and the oxidation state varies