Download Here are the answers and work for your summer packet.

Here are the answers and work for your summer packet.
NOTE: This is to be used to check your work, and to help you understand
things that you are struggling with.
If you are simply copying the answers from this packet, you should consider
whether you actually want to take AP Chemistry and remember that you will
be given a formal test on this material in the first week of school.
Practice Problems
CHAPTER 1
1. For each of the following pieces of glassware, provide a sample measurement at arrow and discuss the
number of significant figures and uncertainty.
4.0 mL
10.25 mL
15 mL
2. A student performed an analysis of a sample for its calcium content and got the following results:
14.92%, 14.91%, 14.88%, and 14.91%
The actual amount of calcium in the sample is 15.70%. What conclusion can you draw about the
accuracy and precision of these results?
The student was very precise but not accurate.
3. Calculate the percent error for the following measurements.
a. The density of an aluminum block determined in an experiment was 2.64 g/cm3. (Accepted
value = 2.70 g/cm3)
b. The experimental determination of iron in ore was 16.48%. (Accepted value was 16.12%)
2.64g /cm 3 − 2.70g /cm 3
× 100 = −2.2%
2.70g /cm 3
16.48% −16.12%
b.
× 100
16.12%
a.
€
€
4. How many significant figures are in each of the following?
a. 12 = 2
b. 1098 = 4
c. 2001 = 4
d. 2.001 x 103 = 4
e. 100 = 1
f.
g.
h.
i.
0.0000101 = 3
1000. = 4
22.04030 = 7
1.00 x 103 = 3
5. Round of each of the following numbers to two significant figures, and write the answers in
scientific notation.
a. 0.00031254 = 0.00031
c. 35,900 = 36,000
b. 31,254,000 = 31,000,000
d. 0.00000399= 0.0000040
6. Use scientific notation to express the number 480 to
1
a. One significant figure = 5 x 102
b. Two significant figures = 4.8 x 102
c. Three significant figures = 4.80 x 102
7. Perform the following mathematical operations, and express each result to the correct number of
significant figures.
a. 97.381 + 4.2502 + 0.99195 = 102.62315 = 102.623
b. 171.5 + 72.915 – 8.23 = 236.185 = 236.2
c. 0.102 x 0.0821 x 273.5
= 1.9
1.2
d. (9.04 – 8.23 + 21.954 + 81.0) / 3.1416
= 38.26 (tricky, multi step sig. figs.)
8. Precious metals and gems are measured in troy weights in the English system:
24 grains = 1 pennyweight (EXACT)
20 pennyweights = 1 troy ounce (EXACT)
12 troy ounces = 1 troy pound (EXACT)
1 grain = 0.0648 gram
1 carat = 0.200 gram
a. Diamonds are measured in carats. If a lucky girl receives a 5 carat diamond how many
pennyweights is it?
b. What is the mass of 2.3 troy ounces of gold in grams?
c. The density of gold is 19.3 g/cm3. What is the volume of a troy pound of gold?
.200gram
1grain
1pennyweight
×
×
= .6 pennyweights
1carat
.0648gram
24grains
20 pennyweights
24grains
.0648grams
×
×
= 72grams
b. 2.3troyounces ×
1troyounce
1pennyweight
1grain
19.3g
1grain
1pennyweight
1troyounce
1troypound
×
×
×
= .0517 troypounds 3
c.
3 ×
cm
cm
0.0648grams
24grains
20 pennyweights 12troyounces
troypound
troypound
.0517
=1
mL
V
1troypound
V=
.0517troypound
mL
V = 19.3mL
a.
€
€
€
5carat ×
9. Apothecaries (druggists) use the following set of measures:
20 grains ap = 1 scruple (EXACT)
3 scruples = 1 dram ap (EXACT)
8 dram ap = 1 oz. ap (EXACT)
1 dram ap = 3.888 g
a. An aspirin table contains 5.00 x 102 mg of active ingredient. How many grains ap of
active ingredient does it contain?
b. From (a) how many scruples?
c. What is the mass of 1.00 scruple in grams?
€
1g
= .500g
1000mg
a.
1dramap 3scruples 20grainsap
.500g ×
×
×
= 7.72grainsapothecary
3.888g
1dramap
1scruple
1g
500mg ×
= .500g
1000mg
b.
1dramap 3scruples
.500g ×
×
= .386scruples
3.888g
1dramap
500mg ×
€
2
€
c.
1.00scruple ×
1dramap
3.888g
×
= 1.30g
3scruples 1dramap
10. The world record for the hundred meter dash is 9.79 s. What is the corresponding speed in
units of m/s, km/hr, ft/s, and mi/hr?
a. At this speed how long would it take to run a mile (5,820 ft)?
€
€
100m
= 10.2m /s
9.79s
10.2m
1km
60s 60min
×
×
×
= 36.7km /hr
s
1000m 1min 1hour
10.2m 100cm
1in
1 ft
×
×
×
= 33.5 ft /s
s
1m
2.54cm 12in
10.2m 100cm
1in
1 ft
1mi
60s 60min
×
×
×
×
×
×
= 22.8mi /hr
s
1m
2.54cm 12in 5280 ft 1min 1hour
V
D=
t
1mile = 22.8miles /hr × time
a.
1mile
= .0439hours
22.8 mi hour
or2.63min
time =
€
11. You’re planning to buy a new car. One model that you’re considering gets 32 miles per gallon of
gasoline in highway travel. The one that your spouse likes gets 14 kilometers to the liter. Which
car has the better gas mileage? (1 gal = 4 qt., 1.057 qt = 1 L)
Convert so that the speeds are the same
14km 1000m 100cm
1in
1 ft.
1mi
1L
4qt
×
×
×
×
×
×
×
= 33mi /gallon
L
1km
1m
2.54cm 12in 5280 ft 1.057qt 1gallon
About the same mi/gallon but your spouses is slightly higher
12. You pass a road sign saying “New York – 112 km.” If you drive at a constant speed of 65 mi/hr.,
how long should it take you to reach New York?
a. If your car gets 28 miles to the gallon, how many liters of gasoline are necessary to travel
112 km?
€
1000m 100cm
1in
1 ft
1mi
×
×
×
×
= 69.6mi
1km
1m
2.54cm 12in 5,280 ft
69.6miles
= 1.07hours
65 miles hour
28miles 5280 ft 12in 2.54cm
1m
1km
1gal 1.057qt
×
×
×
×
×
×
×
= 12km /L
gallon
1mi
1 ft
1in
100cm 1000m 4qt
1L
a.
112km
= 9.3L
12 km L
112km ×
€
€
13. You have a 1.0 cm3 sample of lead and a 1.0 cm3 sample of glass. You drop each in separate
beakers of water. How do the volumes of water displaced by each sample compare? Explain.
Density of lead = 11.35 g/cm3
Density of glass = 3.00 g/cm3
They would displace the same volumes of water as they both have the same volumes (1.0cm3) and
both of their densities are greater than water (1.0 g/cm3) so they will sink.
14. A person has a temperature of 102.5 F. What is this temperature on the Celsius scale?
a. On the Kelvin scale?
3
5
C = (102.5 − 32) = 39.17C
9
K = 39.17 + 273.15 = 312.32K
€
a
b
c
d
15. Convert the following Celsius temperatures to Kelvin and to Fahrenheit degrees.
a. The boiling-point temperature of ethyl alcohol, 78.1 C
b. A cold winter day, -25 C
c. The lowest possible temperature, -273 C
d. The melting-point temperature of sodium chloride, 801 C
Original temp
K=C+273.15
F=(9/5)(C)+32
78.1
351.25
172.6
-25
248.15
-13
-273
.15
-459
801
1074.15
1473.8 = 1470 with s.f.
16. The density of diamond is 3.51 g/cm3. What is the volume of a 4.5 carat diamond? 1 carat =
0.200 g
4.5carat ×
.200g
= .90g
1carat
m
V
g
.90g
3.51 3 =
cm
V
.90g
V=
= .26cm 3
g
3.52 3
cm
D=
17. The volume of a diamond is found to be 2.8 mL. What is the mass of the diamond in carats?
(See question #16)
€
€
€
g
m
3 =
cm
2.8cm 3
g
m = 3.51 3 × 2.8cm 3 = 9.8g
cm
1carat
9.8g ×
= 49carat
.200g
3.51
Really impressive diamond!!
18. A sample containing 33.42 g of metal pellets is poured into a graduated cylinder initially
containing 12.7 mL of water, causing the water level in the cylinder to rise to 21.6 mL. Calculate
the density of the metal.
V = 21.6mL −12.7mL = 8.9mL
33.42g
g
D=
= 3.8
8.9mL
ml
19. Two spherical objects have the same mass. One floats on water; the other sinks. Which object
has the greater diameter? Explain your answer.
Whichever object floats must have a large diameter, which causes a larger volume thus lowering
the density
20. What are some of the differences between a solid, a liquid, and a gas?
Answers vary
21. What is the difference between homogeneous and heterogeneous matter?
Homogeneous –mixture in which you cannot see the boundary between phases ex. Koolaid
Heterogeneous – mixture with at least two distinct reactions
22. Classify each of the following as homogeneous or heterogeneous.
4
a.
b.
c.
d.
e.
f.
Soil - heterogeneous
the atmosphere - homogeneous
a carbonated soft drink - heterogeneous
gasoline - homogeneous
gold - homogeneous
a solution of ethanol and water - homogeneous
23. Classify each of the following as a mixture or a pure substance. Of the pure substances, which
are elements and which are compounds?
a. Water – PS (compound)
f. Uranium – PS (element)
b. Blood - M
g. Wine – could be either
c. The oceans - M
h. Leather – could be either
d. Iron – PS (element)
i. Table salt (NaCl) – PS
e. Brass – M (Alloy of metals)
(compound)
24. Distinguish between physical and chemical changes.
Physical – only alters the shape or form of substance, includes all phase changes
Chemical – changes how atoms are bonded
25. List four indications that a chemical change (reaction) has occurred.
Energy is transferred (light and heat), gas is produced, solid (precipitate) is produced, color
change
26. If you place a glass rod over a burning candle, the glass appears to turn black. What is
happening to each of the following (physical change, chemical change, both, or neither) as the
candle burns? Explain each answer
a. the wax – both, melting and burning
b. the wick – chemical, burning
c. the glass rod – physical, soot is being deposited
27. The properties of a mixture are typically averages of the properties of its components. The
properties of a compound may differ dramatically from the properties of the elements that
combine to produce the compound. For each process described below, state whether the
material being discussed is most likely a mixture or a compound, and state whether the process
is a chemical change or a physical change.
a. An orange liquid is distilled, resulting in the collection of a yellow liquid and a red solid.
b. A colorless, crystalline solid is decomposed, yielding a pale yellow-green gas and a soft,
shiny metal.
c. A cup of tea becomes sweeter as sugar is added to it.
a. physical, mixture
b. chemical, compound
c. physical, mixture
CHAPTER 2
1. Describe Dalton’s atomic theory.
All matter is made up of atoms, all atoms of an element are the same, compounds form when
atoms join together, atoms cannot be broken down into smaller parts
2. What discoveries were made by J.J. Thomson, Henri Becquerel, and Lord Rutherford? How did
Dalton’s model of the atom have to be modified to account for these discoveries?
J.J. Thomson – discovered electrons and protons, came up with the plum pudding atomic theiry,
atoms are made up of smaller things
Henri Becquerel – radioactivity, elements can be transferred into other elements
Lord Rutherford – nucleus, different regions of an atom
Dalton’s model has to change to account for the fact that atoms are divisible, elements can
transform into other elements
3. What is the distinction between atomic number and mass number?
Atomic number = number of protons
Mass number = protons + neutrons
4. What is the difference between atomic mass and average atomic mass?
Atomic mass = specific to one atom, protons + neutrons
5
Average atomic mass = weighted average of all isotopes
5. What is an isotope?
Isotopes are atoms of the same element that have different numbers of neutrons. All elements
have isotopes, and all elements have at least one isotope which is radioactive.
6. How many protons and neutrons are contained in the nucleus of each of the following atoms?
a. 22Ti42
d. 36Kr86
b. 30Zn64
e. 33As75
c. 32Ge76
f. 19K41
Element
Protons
Neutrons
Titanium
22
20
Zinc
30
34
Germanium
32
44
Krypton
36
50
Arsenic
33
42
Potassium
19
22
7. Write the isotopic symbol for each of the isotopes below.
a. Atomic number = 8, number of neutrons = 9
b. The isotope of chlorine in which mass = 37
c. Atomic number = 27, mass = 60
d. Number of protons = 26, number of neutrons = 31
e. The isotope of I with a mass number of 131
f. Atomic number = 3, number of neutrons = 4
a.
17
8
O b.
37
17
Cl c.
60
27
57
Co d. 26
Fe e.
131
53
I f. 37 Li
8. The element copper has naturally occurring isotopes with mass number of 63 and 65. The
relative abundance of the isotopes are 69.2% for mass = 62.93 amu, and 30.8% for mass = 64.93
amu. Calculate the average atomic mass of copper.
€
€
€
.692(62.93amu)
+ .308(64.93)
€
€
€
€ = 63.55amu
€
9. An element consists of 1.40% of an isotope with mass 203.973 amu, 24.10% of an isotope with
mass 205.9745 amu, 22.10% of an isotope with mass 206.9759 amu, and 52.40% of an isotope
with mass 207.9766 amu. Calculate the average atomic mass and identify the element.
.0140(203.973amu) + .2410(205.9745amu) + .2210(206.9759amu) + .5240(207.9766amu) = 207.217,LEAD
10. Distinguish between the terms family and period in connection to the periodic table. For which
of these terms is the term group also used?
Family – vertical column, also called group
Period – horizontal column
11. In the periodic table, what is the name of the following groups
a. Group (2)
b. Group (18)
a. Alkaline Earth b. Noble Gases
12. An ion contains 50 protons, 68 neutrons, and 48 electrons. What is its symbol and charge?
118
50
€
Sn +2
13. Which of the following sets of elements are all in the same group in the periodic table?
a. N, P, O
c. Rb, Sn
b. C, Si, Ge
d. Mg, Ca
B (C, Si, and Ge) and D (Mg + Ca)
14. Identify each of the following elements:
a. A member of the same family as oxygen whose most stable ion contains 54 electrons
b. A member of the alkali metal family whose most stable ion contains 36 electrons
c. A noble gas with 18 protons in the nucleus
d. A halogen with 85 protons and 85 electrons
a. Te b. Rb c. Ar d. At
15. Would you expect each of the following atoms to gain or lose electrons when forming ions? What
ion is the most likely in each case?
6
a. Na
d. Ba
g. Al
b. Sr
e. I
h. S
c. P
f. O
a. lose, Na+1 b. lose, Sr+1 c. gain, P-3 d. lose, Ba+2 e. gain I-1
f. gain O-2 g. lose, Al+3 h. gain, S-2
16. For each of the following ions, indicate the total number of protons and electrons in the ion. For
the positive ions, predict the formula of the simplest compound formed between itself and oxide.
For the negative ions predict the simplest compound formed between itself and aluminum.
a. Fe+2
d. Cs+1
g. Br-1
+3
-2
b. Fe
e. S
h. N-3
+2
-3
c. Ba
f. P
a. FeO, 26 p, 24 e
b. Fe2O3, 26 p, 23 e
c. BaO, 56 p, 54 e
d. Cs2O, 55p, 54e
e. Al2S3, 16p, 19e
f. AlP, 15p, 18e
g. AlBr3, 35p, 36e
h. AlN, 7p, 10e
17. An element’s most stable ion forms an ionic compound with bromine, having the formula XBr2.
If the ion of element X has a mass number of 230 and 86 electrons, what is the identity of the
element, and how many neutrons does it have?
Radium, 144 neutrons
Writing Formulas and Naming Compounds – Do WITHOUT an ion chart! You need to have these
memorized.
1. Name each of the following
a. NaCl
b. Rb2O
c. FeBr3
d. Cr2O3
e. CaBr2
f. CsF
g. CaS
a. sodium chloride
b. rubidium oxide
c. iron (III) bromide
d. chromium (III) oxide
e. calcium bromide
f. cesium fluoride
g. calcium sulfide
h. aluminum iodide
2. Name each of the following
a. NI3
b. PCl3
c. SO2
a. nitrogen triodide
b. phosphorus trichloride
c. sulfur dioxide
d. iodine trichloride
3. Name each of the following
a. HCl
b. H3PO4
c. HIO3
a. hydrochloric acid
b. phosphoric acid
c. iodic acid
4. Name each of the following
a. HgO
b. CuI
c. CuI2
d. CoI2
e. Na2CO3
compounds:
h. AlI3
o. BaSO3
i. Al2O3
p. KMnO4
j. ZnCl2
q. Sr3P2
k. Li3N
r. Ca3(PO4)2
l. Ag2S
s. Pb(NO3)2
m. KClO4
t. NaNO2
n. Al2(SO4)3
u. K2Cr2O7
i. aluminum oxide
p. potassium
j. zinc chloride
permanganate
k. lithium nitride
q. strontium phosphide
l. silver sulfide
r. calcium phosphate
m. potassium
s. lead (II) nitrate
perchlorate
t. sodium nitrite
n. aluminum sulfate
u. potassium
o. barium sulfite
dichromate
compounds:
d. ICl3
g. P2S5
e. SF2
h. N2O4
f. N2F4
e. sulfur difluoride
f. dinitrogen tetrafluoride
g. diphosphorous pentasulfide
h. dinitrogen tetraoxide
compounds:
d. HNO2
e. HI
f. H2SO3
d. nitrous acid
e. hydroiodic acid
f. sulfurous acid
compounds:
f. NaHCO3
k. Pb3(PO4)2
g. HC2H3O2
l. KIO3
h. NH4NO2
m. Ca(OH)2
i. Co2S3
n. CoS
j. ICl
o. S3N4
7
p. SF6
t. H2SO4
q. NaClO
u. Sr3N2
r. BaCrO4
v. Al2(SO3)3
s. NH4NO3
w. SnO2
a. mercury (II) oxide
j. iodine monochloride
b. copper (I) iodide
k. lead (II) phosphate
c. copper (II) iodide
l. potassium iodate
d. cobalt (II) iodide
m. calcium hydroxide
e. sodium carbonate
n. cobalt (II) sulfide
f. sodium bicarbonate
o. trisulfur tetranitride
g. acetic acid
p. sulfur hexafluoride
h. ammonium nitrite
q. sodium hypochlorite
i. cobalt (III) sulfide
r. barium chromate
5. Write the formula for each of the following compounds:
a. Cesium bromide
k.
b. Barium sulfate
l.
c. Chlorine trifluoride
m.
d. Ammonium chloride
n.
e. Beryllium oxide
o.
f. Chlorine monoxide
p.
g. Magnesium fluoride
q.
h. Sulfur difluoride
r.
i. Sulfur hexafluoride
s.
j. Sodium dihydrogen phosphate
t.
a. CsBr
k. SiCl4
b. BaSO4
m. Li3N
c. ClF3
n. SnF2
d. NH4Cl
o. NH4C2H302
e. BeO
p. NH4HSO4
f. ClO
q. Co(NO3)3
g. MgF2
r. Cu2S
h. SF2
s. KClO4
i. SF6
t. Li2C4H4O6
j. NaH2PO4
6. Write the formula for each of the following compounds:
a. sodium oxide
b. Sodium peroxide
c. Potassium cyanide
d. Copper (II) nitrate
e. Silicon tetrafluoride
f. Lead (II) sulfide
g. Lead (IV) sulfide
h. Copper (I) chloride
i. Cadmium selenide
a.
b.
c.
d.
e.
f.
g.
h.
i.
j.
NaO
NaO2
KCN
Cu(NO3)2
SiF4
PbS
PbS2
CuCl
CdSe
ZnS
j.
k.
l.
m.
n.
o.
p.
q.
x. Na2CrO4
y. HClO
z. NO
s. ammonium nitrate
t. sulfuric acid
u. strontrium nitride
v. aluminum sulfite
w. tin (IV) oxide
x. sodium chromate
y. hypochlorous acid
z. nitrogen monoxide
Silicon tetrachloride
Lithium nitride
Chromium (III) carbonate
Tin (II) fluoride
Ammonium acetate
Ammonium hydrogen sulfate
Cobalt (III) nitrate
Copper (I) sulfide
Potassium chlorate
Lithium tartrate
Zinc sulfide
Ammonium hydrogen phosphate
Hydrobromic acid
Bromous acid
Perchloric acid
Silicon dioxide
Sodium sulfate
Aluminum hydrogen sulfate
k. (NH4)2HPO4
l. HBr
m. HBrO2 (BrO2 is not on the sheet,
sorry!!)
n. HClO4
o. SiO2
p. Na2SO4
q. Al(HSO4)3
8
CHAPTER 3 – Stoichiometry
1. Balance the following equations:
a. 2 CO + O2 → 2 CO2
b. 2 N2O5 + 2 H2O → 4 HNO3
c. PCl5 + 4 H2O → H3PO4 + 5 HCl
d. CH4 + 4 Br2 → CBr4 + 4 HBr
e. C5H10O2 + 9 O2 → 5 CO2 + 5 H2O
f. Cr(OH)3 + 3 HClO4 → Cr(ClO4)3 + 3 H2O
g. 2 KNO3 → 2 KNO2 + O2
h. La2O3 + 3 H2O → 2 La(OH)3
i. NCl3 + 3 H2O → NH3 + 3 HOCl
j. Mg3N2 + 8 HCl → 3 MgCl2 + 2 NH4Cl
k. 2AgNO3 + K2SO4 → Ag2SO4 + 2 KNO3
l. 2 Al(OH)3 + 3 H2SO4 → Al2(SO4)3 + 6 H2O
m. 2 CH3NH2 + 3 O2 → 2 CO2 +2 H2O + N2
n. (NH4)2Cr2O7 → Cr2O3 + 2 N2 + 4 H2O
2. Write balanced chemical equations to correspond to each of the following descriptions.
a. When solid potassium chlorate is heated it decomposes to form solid potassium chloride
and oxygen.
b. Solid zinc metal reacts with sulfuric acid to form hydrogen gas and an aqueous solution
of zinc sulfate.
c. When liquid phosphorous trichloride is added to water, it reacts to form aqueous
phosphorous acid, and hydrochloric acid.
d. When hydrogen sulfide gas is passed over solid hot iron (III) hydroxide, the resultant
reaction produces solid iron (III) sulfide and water vapor.
€
€
€
€
a.
b.
c.
d.
KClO4 →KCl + 2O2
Zn + H 2 SO4 →H 2 + ZnSO4
PCl3 + 3H 2O →H 3 PO3 + 3HCl
3H 2 S + 2Fe(OH) 3 →Fe2 S3 + 6H 2O
3. The molecular formula of aspartame, the artificial sweetener marketed as Nutrasweet, is
C14H18N2O5.
a. What is the molar mass of aspartame?
b. How many moles of aspartame are present in 3769.4 grams of aspartame?
c. How many molecules of aspartame are present in 345.9 grams of aspartame?
d. How many oxygen atoms are present in 23.6 grams of aspartame?
a. 294.0 g/mol
1mol
= 12.821molesC4 H18 N 2O5
294.0g
1mol
6.022x10 23 moleculesaspartame
×
= 7.085x10 23 moleculesaspartame
c. 345.9g ×
294.0g
1mol
1mol
6.022x10 23 molecules 5oxygenatoms
×
×
= 2.42x10 23 oxygenatoms
d. 23.6g ×
294.0g
1mol
1molecule
b.
€
3769.4g ×
4.€ How many moles of ammonium ions are in 0.557 g of ammonium carbonate?
1mol 2ammoniumions
.557g ×
×
= .0114molesammonium
98.0g
1mole
€
5. What is the mass, in grams, of 0.0438 moles of iron (III) phosphate?
.0438mole ×
€
150.8
= 6.61gFePO4
1mol
6. What is the mass, in grams, of 2.69 x 1023 molecules of aspirin, C9H8O4?
2.69x10 23 molecules ×
€
€
1mol
180.0g
×
= 80.4gaspirin
23
6.022x10 molecules 1mol
9
7. What is the molar mass of diazepam (Valium) if 0.05570 mol has a mass of 15.86 g?
15.86g
= 284.7g /mol
.05570mol
8. Determine the empirical formulas of the following compounds.
a. 10.4 % C, 27.8 % S, and 61.7% Cl
b. Monosodium glutamate (MSG), a flavor enhancer in certain foods, 35.51 g C, 4.77 g H,
37.85 g O, 8.29 g N, 13.60 g Na
a. C = 10.4/12=.866moles S = 27.8/32=.868 moles
Cl = 61.7/35.5= 1.738 moles
C=1
S=1
Cl = 2
CSCl2
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b. C = 35.51/12 = 2.959 moles
H = 4.77/1.0 = 4.77 moles
O = 37.85/16 = 2.3656 moles
N = 8.29/14 = .5921 moles
Na = 13.60/23 = .5913
C5H8O4NNa
9. Find the molecular formulas of the following compounds.
a. 73.8% carbon, 8.7% hydrogen, 17.5% nitrogen, molar mass = 166.0 g/mol
b. 80.0% carbon, 20.0% hydrogen, molar mass = 30.0 g/mol
a. C = 73.8/12.0 = 6.15 moles H = 8.7/1.0 = 8.7 moles N = 17.5/14.0 = 1.25
E.F. C5H7N, molar mass = 81 g/mol
M.F. C10H14N2
10. 4 FeCr2O7 + 8 K2CO3 + O2 → 2 Fe2O3 + 8 K2CrO4 + 8 CO2
a. How many grams of FeCr2O7 are required to produce 44.0 g of CO2?
b. How many grams of O2 are required to produce 100.0 g of Fe2O3?
c. If 300.0 g of FeCr2O7 react, how many grams of O2 will be consumed?
d. How many grams of Fe2O3 will be produced from 300.0 g of FeCr2O7?
e. How many grams of K2CrO4 are formed per gram of K2CO3 used?
1molCO2 4molFeCr2O7
271.8g
×
×
= 135.9gFeCr2O7
44.0g
8molCO2
1molFeCr2O7
1molFe2O3
1molO2
32.0g
×
×
= 10.03gO2
b. 100.0gFe2O3 ×
159.6g
2molFe2O3 1molO2
1molFeCr2O7
1molO2
32.0g
×
×
= 8.830gO2
c. 300.0gFeCr2O7 ×
271.8g
4molFeCr2O7 1molO2
1molFeCr2O7
2molFe2O3
159.6g
×
×
= 88.08gFe2O3
d. 300.0gFeCr2O7 ×
271.8g
4molFeCr2O7 1molFe2O3
1molK 2CO3 8molK 2CrO4
194.2g
×
×
= 1.405gK 2CrO4
e. 1gK 2CO3 ×
138.2g
8molK 2CO3 1molK 2CrO4
a.
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€
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11. Given the reaction: S + O2 → SO2
a. How many grams of sulfur must be burned to give 100.0 g of SO2?
b. How many grams of oxygen must be required for the reaction in part (a)?
€
€
€
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44.0g ×
1molSO2
1molS
32.1g
×
×
= 50.08gS
64.1g
1molSO2 1molS
1molSO2 1molO2
27.0g
×
×
= 49.92gO2
b. 100.0gSO2 ×
64.1g
1molSO2 1molAl
a.
100.0gSO2 ×
12. 6 NaOH + 2 Al → 2 Na3AlO3 + 3 H2
a. How much aluminum is required to produce 17.5 g of hydrogen?
b. How much Na3AlO3 can be formed from 165.0 g of sodium hydroxide?
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c. How many moles of NaOH are required to produce 3 g of hydrogen?
d. How many moles of hydrogen can be prepared from 1 gram of aluminum?
1molH 2 2molAl 27.0g
×
×
= 157.5gAl
2.0g
3molH 2 1molAl
1molNaOH 2molNa3 AlO3
144.0g
×
×
= 198.0gNa3 AlO3
b. 165.0gNaOH ×
40.0g
6molNaOH
1molNa3 AlO3
1molH 2 6molNaOH
×
= 3molNaOH
c. 3gH 2 ×
2.0g
3molH 2
1molAl 3molH 2
×
= .05molH 2
d. 1.0gAl ×
27.0g 2molAl
a.
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€
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17.5gH 2 ×
13. The following unbalanced reaction takes place at high temperatures.
Cr2O3 (s) +
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If 42.7
a.
b.
c.
Al (l) →
Cr
(l)
+
Al2O3
(l)
g Cr2O3 and 9.8 g Al are mixed and reacted until one of the reactants is used up.
Which reactant will be left over?
How much will be left?
How many grams of chromium will be formed?
42.7gCr2O3 ×
a. and c
9.8gAl ×
1molCr2O3
2molCr
52.0g
×
×
= 29.2gCrformed
152g
1molCr2O3 1molCr
1molAl 2molCr 52.0g
×
×
= 18.9gCrformed
127.0g 2molAl 1molCr
so….18.9 g of Cr formed, Al is the limiting reactant, and Cr2O3 is left over
1molAl 1molCr2O3
152.0g
×
×
= 28gCr2O3 used
27.0g
2molAl
1molCr2O3
b.
€
42.7g − 28 = 14.7g →15gleft
9.8gAl ×
14. Calculate the mass of water produced when 42.0 g of propane, C3H8, is burned with 115 g of
oxygen.
€
C3 H 8 + 5O2 →4H 2O + 3CO2
1molC3 H 8 4molH 2O
18.0g
42.0gC3 H 8 ×
×
×
= 68.7gH 2O
44.0g
1molC3 H 8 1molH 2O
1molO2 4molH 2O
18.0g
115gO2 ×
×
×
= 92.0gH 2O
18.0g
5molO2
1molH 2O
So…68.7g of water was formed.
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CONGRATULATIONS, you have made it! Be proud of yourself, and get ready for a fun-filled and
challenging year which will push you to your limits, but make you a better student, get you very
prepared for college, and prove to yourself how brilliant you really are!
Remember, I am on your side, and just want to help! I am trying to give you the tools to succeed, and I
pledge I will not ever give you an assignment or make you learn something that is not necessary for
your success.
If you need anything please do not hesitate to email me! Don’t be a stranger!
See you in the fall!
Mrs. G
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