.
Houston Community
College System
Chemistry 1411
EXAM # 1A
The Periodic table of the Chemical Elements
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CHEM 1411 Sample Exam #1A (1,2, and 3)
Part I. Multiple choice questions. ( 4 points each)
Direction- Please write your correct choice in space provide.
____1. The distance between carbon atoms in ethylene is 134 picometers. Which of the
following express the distance in meters?
A. 1.34x10-13 m
B. 1.34x10-10 m
C. 1.34x10-7 m
D. 1.34x10-6 m
____ 2. Acetic acid boils at 244.2 0F. What is boiling point in degrees celsius?
A. 167.7 0C
B. 153.4 0C
C. 117.8 0C
D. 103.7 0C
____ 3. Which of the following expressed measurement 52,030.2 m in correct scientific
notation?
A. 5.20302x104 m
B. 5.203x104 m
C. 5.20x104 m
D. 5.2x104 m
____ 4. Select the answer with correct number of decimal places for the following sum.
4.65 g + 2.0 g + 19.6442 g =
A. 26.2942 g
B. 26.29 g
C. 26 g
D. 26.3 g
C. Os
D. I
____ 5. Which of the following is a non-metal?
A. Li
B. Be
____ 6. Bromine is the only non-metal that is liquid at room temperature. Consider the
isotope bromine-81, 3581 Br. Select the combination which list the correct atomic
number, neutron number , and mass number respectively.
A. 35,46,81
B. 35,81,46
C. 81,46,35
D. 46,81,35
____ 7. Which of the following name is correct for given chemical formula?
A. I2O5 , iodine pentoxide
C. PbO , lead(I) oxide
B. LiNO3 , lithium nitrate
D. H2SO4 , hydrosulfuric acid
____ 8. Which of the following chemical formula is not correct for given chemical name?
A. ferric oxide , Fe2O3
B. calcium hydroxide , Ca(OH)2
C. tetrasulfur dinitride , S4N2
D. potassium chlorite , KClO3
____9. What is the mass in grams of 0.250 mole common antiacid, calcium carbonate?
A. 4.00x102 g
B. 25.0 g
C. 4.00x10-2 g
2
D. 2.50x10-3 g
____ 10. Which one of the following reactions is not balanced?
A. 2C6H6(l) + 15O2(g)  12CO2(g) + 6H2O(g)
B. B2O3(s) + 6HF(l)  2BF3(g) + 3H2O(l)
C. UO2(g) + 4HF(l)  UF4(s) + 4H2O(l)
D. 2B5H9(l) + 12O2(g)  5B2O3(s) + 9 H2O(g)
____11. Which identification is INCORRECT for the element?
A. Na, sodium
B. S, sulfur
C. P, potassium
D. Zn, zinc
____12. Which of the following is not a chemical change?
A. burning coal
C. boiling an egg
B. making bread rise using baking soda
D. boiling water
____13. Which ion has a -1 charge?
A. CO3
B. HSO3
C. NH4
D. SO4
____14. Which of the following is improperly labeled?
A. Cu- transition metal
C. Br- halogen
B. Mg- alkaline earth metal
D. U- noble gas
____15. How many carbon atoms are in CH3-CH2-COO-CH3
A. 1
B. 2
C. 3
D. 4
Part II. Show all your work for complete credit.
16. The density of mercury , the only metal to exist as liquid at room temperature, is 13.6
g/cm3 . What is the density in pounds per cubic inch (lb/in3) ? ( 1 lb=454 g , 1 in =2.54 cm)
( 8 points)
17. The speed needed to scape the pull of earth,s gravity is 11.3 km/s. What is this speed in
mi/hr ? ( 1 mi=1.6094 km) ( 6 points)
18. Lithium , is used in dry cells and storage batteries and in high temperature lubricants, it
has two naturally occurring isotopes, 6Li and 7Li. Calculate the atomic mass of lithium.
( 8 points)
isotopes isotopic mass(amu) abundance(%)
6
Li
6.01521
7.50
7
Li
7.016003
92.50
19. Terphthalic acid , used in the production of polyester fibers and films, is composed of
carbon, hydrogen, and oxygen. when 0.6943 g of acid is subjected to combustion analysis
it produced 1.471 g CO2 and 0.391 g H2O. What is its empirical and molecular formula if
its molar mass is 172 g/mol. ( 8 points)
20. Aluminum reacts with oxygen to produce aluminum oxide which can be used as an
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absorbent, desiccant or catalyst for organic reactions. ( 10 points)
4 Al(s) + 3 O2(g)  2 Al2O3(s)
A mixture of 82.4 g of aluminum (M=26.98 g/mol) and 117.65 g of oxygen (M=32.00 g/mol)
is allowed to react.
a) Identify the limiting reactant.
b) Calculate the mass of aluminum oxide formed.
c) Determine the mass of the excess reactant present in the vessel when the reaction is
complete.
d) What is the percentage yield for the reaction if reaction mixture produce 120 g of
aluminum oxide?
Bonus question( 10 points)- show all your work.
a) When 11.2 g CaCO3 reacts with excess hydrochloric acid, as below, 4.61 g of CO2 is
produced. What is the percent yield of CO2? Do not type the units with your answer.
CaCO3(s) + 2 HCl(aq)  CO2(g) + CaCl2 (aq) + H2O(l) (not balanced)
b) Calcium reacts with oxygen to make calcium oxide, CaO. What is the theoretical yield
of CaO(s) that could be prepared from 7.63 g of Ca(s) and 2.56 g of O2(g)?
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CHEM 1411 SAMPLE EXAM # 1A - KEY (1, 2, and 3)
PART-I
1. B (pico = 10 -12 , 134 x 10 -12 m = 1.34 x 10 -10 m)
2. C
C = 5/ 9(F-32) = 5/ 9(244.2 - 32) = 5/ 9(212.2) = 117.9 oC
3. A
4. D sum = 26.2942 g , round off to the least number of decimal point (one), sum = 29.3 g
5. D
6. A
7. B
LiNO3 is Lithium nitrate
8. D potassium chlorate, KClO3
9. B
CaCO3 = 1(40) + 1(12) + 3(16) = 100 g/ml
11. C
P is the symbol for phosphorous
13. B
HSO3‾ (bisulfite)
10. C
2H2O(l)
12. D boiling water is a phase change from liquid to vapor
14. D Uranium is an inner transition metal
15. D four carbon atoms
PART-II
1 lb
------------ x
454 g
(2.54 cm)3
------------------ = 0.491 lb/ in3
1 in3
16.
13.6 g
----------- x
cm3
17.
11.3 km
------------- x
sec
18.
Ave. atomic wt. of Li = (7.50/100) (6.01521) + (92.50/100) (7.016003) = 6.95 a.m.u.
19.
mc = (3/11) mCO2 = (3/11)(1.471) = 0.4012 g , mH = (1/9) mH2O = (1/9) (0.391) = 0.0434 g
1 mi
3600 sec
---------------- x ---------------- = 2.53 x 104 mi/hr
1.6094 km
1 hr
mO = m - (mc + mH) = 0.6943 - (0.4012 + 0.0434) = 0.2497 g
C = 0.4012/12 = 0.0334
, 0.0334/0.01561 = 2.14 = 2
H = 0.0434/1 = 0.0434
, 0.0434/0.01561 = 2.78 = 3
O = 0.2497/16 = 0.01561 , 0.01561/0.01561 = 1 = 1
empirical formula is C2H3O = 2(12) + 3(1) + 1(16) = 43
X = ( 172/ 43) = 4
,
(C2H3O)4
or
C8H12O4
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20a)
(4x27) g
(3x32) g
4 Al
+
(2x102) g
3 O2

2Al2O3
82.4 g
117.65 g
Xg
(82.4) (2) (102)
Al2O3 from Al =
------------------------ = 155.64 g = 156 g
4 x 27
(117.65) (2) (102)
Al2O3 from O2 =
------------------------ = 250.00 g
3 x 32
So, Al produce smaller amount of Al2O3. Al is the limiting reagent.
b)
156 g Al2O3 formed
c)
(4x27) g
4 Al
(3x32) g
+
82.4 g
3 O2

2Al2O3
Xg
(82.4) (3) (32)
O2 used up in the reaction = -----------------------4 x 27
O2 (excess) = 117.65 - 73.2 g = 44.4 g
=
73.2 g
120
% yield = ----------- x 100 = 77%
156
BONUS QUESTION:
d)
a) CaCO3(s) + 2 HCl(aq)  CO2(g) + CaCl2 (aq) + H2O(l)
(11.2 g, CaCO3) x ( 1 mole CaCO3 / 100 g Mwt. ) ( 1mole CO2 /1 mole CaCO3) (44 g CO2 / 1 mole CO2)
= 4.928 g CO2
% yield = ( g, actual value / g, theoretical value) x 100 = 93.5 %
b)
2 Ca + O2  2 CaO
(7.63 g Ca) (1 mol Ca / 40 g) ( 1 molO2 /2 mol Ca) ( 32 g O2 / 1 mol O2) = 3.052 g O2
3.052 g O2 requried to react woth 7.63 g Ca. Since have only 2.56 g O2 in the reaction, therefore O2 is
limiting reagent.
(2.56 g, O2) ( 1 mol / 32 g O2) ( 2 mol CaO / 1 mol O2) (56 g CaO / 1 mol CaO )
= 8.96 g CaO , theoretical value of CaO
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Houston Community College System
Chemistry 1411
EXAM # 1B
Comparison of Temperature Scales
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CHEM 1411 Exam #1B (1,2, and 3)
Directions- please answer the following multiple-choice questions next to each number. Please show all your
work for bonus question and part (II) questions in the space provided.
Part (I) - Multiple Choice - (3 points each)
_____ 1. Which number definitively distinguishes one element from another element?
A. charge number
B. number of neutrons
C. number of protons
D. number of electrons
_____ 2. A 239.5g sample of Benzene is found to occupy a volume of 274ml. What is its density?
A. 0.874
B. 1.99
_____ 3. Convert 3.50 ft to cm.
A. 107 cm
B. 2.9 x 102 cm
C. 0.788
D. 1.58
C. 381.0 cm
D. 503 cm
_____ 4. How many electrons, protons, and neutrons are in an atom of
A. 77 electrons, 79 protons, 117 neutrons
C. 76 electrons, 79 protons, 118 neutrons
197Au3+ ?
B. 80 electrons, 78 protons, 116 neutrons
D. 80 electrons, 80 protons, 115 neutrons
_____ 5. Which name is incorrect?
A. HBr hydrobromic acid
C. MgS, magnesium sulfide
B. AlCl3, aluminum (III) chloride
D. Mg3N2, magnesium nitrite
_____ 6. Which one of the following is improperly labeled?
A. He (noble gas)
B. K (alkali metal)
C. Ca (transition metal) D. Br (halogen)
_____ 7. Calculate the formula weight of aniline, C6H7N.
A. 93.g
B. 85g
C. 62g
D. 49g
_____ 8. Forty centimeters is equal to how many nanometers(nm)?
A. 4.00 x 108nm
B. 4.00 x 10-10nm
C. 4.00 x 1012nm
D. 4.00 x 10-15nm
_____ 9. The state of matter with the highest measure of entropy or disorder is
called _______ state.
A. solid
B. gas
C. liquid
_____ 10. Octane burns according to the following equation:
D. mixed
2C8H18 + 25O2  16CO2 + 18H2O
How many grams of CO2 are produced when 5.00 g of C8H18 are burned?
A. 0.351 g
B. 1.93 g
C. 15.4 g
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D. 40.0 g
_____11. The elements with the same atomic number but different atomic masses are called____.
A. reactants
B. isotopes
C. anions
D. molecules
C. SO3
D. all of these
C. 185.3
D. 104.2
_____ 12. Which of these compounds is not ionic?
A. Li2SO4
B. NaF
_____ 13. What is the molar mass of cryolite (Na3AlF6)?
A. 205.0
B. 210.0
_____ 14. How many Magnesium atoms are in 3.00 moles of Mg3(PO4)2 ?
A. 5.42 x 1024
B. 1.48 x 1022
C. 2.99 x 1021
D. 2.40 x 1022
_____ 15. An oxide of iron has the formula Fe3O4. What mass percent of oxygen does it contain?
A. 0.72%
B. 60%
C. 27.6%
D. 72.6%
_____ 16. Determine the empirical formula of a compound that has (by mass) 85.7% carbon, 14.28%
hydrogen.
A. CH
B. CH2
C. C2H
D. C3H6
_____ 17. The empirical formula of styrene is CH, its molecular weight is 104.1. What is the molecular
formula of styrene?
A.C8H8
B. C4H4
C. C10H10
D. none of these
_____ 18. Give (in order) the correct coefficients to balance the following reaction:
C2H4 + O2  CO2 + H2O
A. 1,2,2,4
B. 1,1,1,2
C. 2,2,2,2
D. 1,3,2,2
_____ 19. The melting point of Sulfur is 115 0C. What is this on the Fahrenheit scale?
A. 116 0F
B. 621 0F
C. 2032 0F
D. 239 0F
_____ 20. When 125.0 g of ethylene ( C2H4) burns in oxygen to give carbon dioxide and water, how
many grams of CO2 are produced?
A. 250.0 g
B. 393.0 g
C. 425.6 g
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D. 57.50 g
Part (II) - Show all your work. (8 points each)
21.
A hypothetical pure metallic cube has a side of 3.00 cm and a mass of 9.0 grams. What is the
density of this cube in ounces per cubic inch (oz/in3)? (Remember, 16oz equal 1 pound, 2.2lbs = 1kg)
22. A substance, NxOy, has the composition by mass 69.57% O. Calculate the molecular formula of this
substance if its molecular mass is 92 grams.
23. A reaction that produces crude iron from iron ore is shown below:
Fe3O4 (s) + 4CO (g)
 3 Fe (s) + 4CO2 (g)
How many moles of iron could be produced from the reaction of 2.5 mol Fe3O4 and 3.0 mol of
CO? Identify limiting reactant and determine how many moles of unreacted substance remained in
the reaction.
24. A 0.9301 g sample of a compound known to contain C,H, and O was burned in oxygen to
yield 1.729 g of CO2 and 0.3535 g of H2O. What is the molecular formula of the compound if the
molar mass of compound is approximately 140 g.
25. Perform the following calculations and round off the answers to the proper significant figures.
a) 14.86 ml + 15.0 ml + 14.980 ml =
b) (42.927 g/ml)(9.00 ml) =
BONUS question-Show all your work.(10 points)
Naturally occurring element “Y” exists in two isotopic forms: Y-57 ( 57.977 amu ) , Y-58 ( 58.977amu)
Calculate the percentage of each isotope if the average atomic weight of X is 58.776 amu.
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CHEM 1411 SAMPLE EXAM # 1B - KEY (1, 2, and 3)
Part (I)
1.
2.
3.
4.
5.
C
A
A
C
D
6. C
7. A
8. A
9. B
10. C
11.
12.
13.
14.
15.
B
C
B
A
C
16.
17.
18.
19.
20.
B
A
D
D
B
Part (II)
21.
D = m/v = (9.0 g/27.00 cm3) = 0.33 g/cm3
(0.33 g/cm3) ( 10-3kg/ 1g) ( 2.2lb/ 1kg) ( 16 oz / 1lb) ((2.54cm)3/1in3 )= 0.19oz/ in3
22.
N = 30.43%
O = 69.57%
moles N = (92g/14g)(0.3043) = 1.99  2
moles O = (92g /16g)(0.6957) = 4.00 , So the molecular formula is = N2O4
OR: N = 30.43/14 = 2.174  2/174/2.174 = 1
O =69.57/16 = 4.348  4.348/2.174 = 2; (empirical formula is NO2)
(NO2)X  (14 + 32)X = (46)X = 92; X = 2; (NO2)2  N2O4
23.
1.0 mole 4.0 mole
3 mole
4 mole Stoichiometric Relations
Fe3O4 (s) + 4CO (g)  3 Fe (s) + 4CO2 (g)
2.5 mole 3.0 mole
X mole
Stoichiometric molar ratio of reactants  Fe3O4/4CO =1/4 = 0.25
Given 2.0 mole Fe3O4 to 2.5 mole CO; molar ratio is 2.5/3.0 = 0.833  Fe3O4 is in excess and CO is limiting
reagent. So use CO for stoichiometric relations to other reactant and products.
X (from Fe3O4)
X (from CO)
(2.5)(3.0)
= ---------------------- = 7.5 moles Fe
1.0
(3.0)(3.0)
= ---------------------- = 2.25 moles Fe (CO is limiting reagent)
4.0
mol CO used in the reaction = ( 3.0 mol CO)( 1 mol Fe3O4 mol/ 4 mol CO) = 0.75 mol
2. 5 – 0.75 = 1.75 mol Fe remain in the reaction
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24.
mC = 3/11(1.729) = 0.4715 g , C
mH = 1/9 (0.3535) = 0.03927 g, H
mO = 0.9301 – ( 0.4715 + 0.03927) = 0.4194 g, O
C  (0.4715/0.9301)(140/12) = 5.9 = 6.0
H  (0.03927/0.9301)(140/1) = 5.9 = 6.0
O  (0.4194/0.9301)(140/16) = 3.9 = 4.0 , Therefore the molecular formula is C6H6O4
OR
C = ( 0.4715/12) = 0.03929  ( 0.03929/0.02621) = 1.49 =1.5; 1.5 x 2 = 3
H = (0.03927/1) = 0.03927  (0.03927 /0.02621) = 1.49 = 1.5; 1.5 x 2 = 3
O = (0.4194/ 16)= 0.02621  (0.02621/0.02621) = 1.00 = 1.0; 1 x 2 = 2
The empirical formula is ; C3H3O2
(C3H3O2 ) n = 140 , (71) n = 140 , n = 140 /71 , n = 2  the molecular formula is ; C6H6O4
25.
a) 15.0 ml is the number with the least number of decimal places. Answer is 44.8 ml
b) 9.00 ml is the number with the least number of significant figures(3 sig. Fig.) Answer is 386 g
BONUS
Let fractional abundance of isotope X-57 be A; then
58.776 = 57.977 (Y/100) + 58.977(100 – Y/100)
Y = 20.1% for isotope X-57. and % abundance of isotope X-58 is 79.9%.
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