Download Chem 150 - Fall 2015 Exam I

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Chem 150 - Fall 2015
Exam I
•
There is periodic table for you to use on the last page of the exam.
•
Be certain that what you hand in represents your own work.
1. For each of the following elements, indicate their number of valence electrons and the number of
covent bonds they would normally form as part of molecules.
No. valance electrons
No. of bonds
Se
P
C
Br
H
2. Draw the Lewis dot structures for the following molecules
Lewis dot structure
PH3
CH2O
HCN
3. Which of the following compounds has the strongest dispersion force between its molecules in its
pure form (circle one)?
a.!
b.!
c.!
!1
Chem 150
Exam I
4. Which Period 3 element has the lowest affinity
for valence electrons?
Fall, 2015
Electronegativities
a. Si
b. P
c. S
d. Cl
5. Formaldehyde is toxic because it is highly
reactive with biological molecules. The
molecular formula for formaldehyde is CH2O
a. Draw the Lewis dot structure for hydrogen
formaldehyde:
b. Is formaldehyde a polar molecule? (circle one)
yes / no
c. If so, which atom is the more negatively charged?
_______
6. Identify each of the following compounds as either ionic or molecular (circle one).
a. PF3
ionic / molecular
b. (NH4)2C2O4
ionic / molecular
c. BaO
ionic / molecular
d. NaF
ionic / molecular
e. CH2O
ionic / molecular
7. The following molecules all have approximately the same molar mass, which is expected to have the
lowest boiling point (circle one)?
a. !
b. !
c. !
8. Identify whether each of the described energies below are an example of kinetic or potential energy
(circle one)
a. The dispersion force that exists between molecules
kinetic / potential
b. When a ball is thrown straight up into the air, the energy it has as it just leaves kinetic / potential
your hand
c. The nutritional energy in a slice of pizza
kinetic / potential
d. When a ball is thrown straight up into the air, the energy it has when it reaches kinetic / potential
its highest point before returning back to earth.
2
Chem 150
Exam I
Fall, 2015
9. As you cool 252 mL of water from 80°C to 24°C,
a. Do the average velocities of the water molecules,
speed up / slow down / remain the same
b. If the density of water is 1.0 g/mL, and the specific heat of water is 1.0 cal/°C-g, how many
calories of heat are required to cool the 252 mL of water from 80°C to 24°C?
!
c. Describe what will happen to the water if you continue to remove heat (thermal energy) from the
water after it reaches 24°C
d. Water (H2O) has a very high melting point compared to other molecules of similar size and
composition, e.g., H2S, CH4, NH3, HF, which unlike water are all gases at room temperature.
Explain why water stands out among this group
10. Which of the following compounds has the strongest dispersion force between its molecules when in
its pure form (circle one)?
a.!
b.!
c.!
11. Which of the following compounds contains a covalent bond that is strongly polar (circle one)?
a. !
b. !
c. !
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Chem 150
Exam I
Fall, 2015
12. Shown below is the structural formula for the amino acid cysteine?
!
a. Circle all of the hydrogen atoms that can participate in hydrogen bonds.
b. Draw a square around each of the atoms that can serve as an acceptor in a hydrogen bond.
c. Draw one example of a water molecule hydrogen bonding to cysteine with the water molecule
serving as the acceptor.
d. Draw one example of a water molecule hydrogen bonding to cysteine with the water molecule
serving as the donor.
13. Which of the following compounds is expected to be the most soluble in water (circle one)?
a. !
b. !
c. !
14. When hydrochloric acid reacts with potassium monohydrogen phosphate in solution to form
potassium dihydrogen phosphate, and potassium chloride, 28.2 kcal of heat are absorbed from the
surroundings per mole of potassium monohydrogen phosphate that reacts.
a. If this reaction is carried out in a beaker, how does the beaker feel to the touch (circle one)?
warmer / cooler / unchanged
b. Using chemical formulas, write the net ionic equation for this reaction, which also includes the
heat that is absorbed in the reaction.
c. This is an acid base reaction. For each species in your balance chemical equation, use labels to
identify the acid, the base, the conjugate acid, and the conjugate base.
15. The gasoline that is sold today can contains up to 85% ethanol (CH3-CH2-OH) by weight, which is
produced from renewable sources.
a. Write a balanced chemical equation for the complete combustion of ethanol to CO2 and H2O
b. One ounce of ethanol weights 28.4 g. If 331 kcal of heat are released per mole of ethanol that
undergoes combustion, how many kcal of heat are released from the burning of 2 ½ ounces of
ethanol.
!
4
Chem 150
Exam I
Fall, 2015
16. For a 0.080 M solution of potassium dihydrogen phosphate,
a. What is the molar concentration of potassium ions?
!
b. What is the molar concentration of dihydrogen phosphate ions
!
c. What is the concentration of potassium ions in units of mEq/L?
!
d. What is the concentration of dihydrogen phosphate ions in mEq/L?
!
17. A 0.400 M solution of lactic acid (HC3H5O3) is determined to have a pH of 2.15. What are the
concentrations of hydronium ion (H3O+) and hydroxide ion (OH-) in this solution?
a. [H3O+]
=
b. [OH-]
=
c. Is lactic acid a weak or a strong acid (circle one)
weak / strong
d. The conjugate base for lactic acid is the lactate ion.
Write the chemical formula for the lactate ion
!
e. If the pKa for lactic acid is 3.90, what is the pH of a solution made by mixing equal amounts of
lactic acid and sodium lactate?
pH
= !
f. Explain what this solution could be used for?
5
2.1
1.0
1.2
0.9
K
0.8
37
6
1.0
0.8
1
0.7
0.7
0.9
[226]
Ra
ytterbium
thulium
erbium
holmium
dysprosium
terbium
gadolinium
europium
samarium
promethium
neodymium
[294]
—
[293]
[288]
[289]
[284]
[285]
[280]
[281]
173.054(5)
nobelium
102
168.93421(2)
mendelevium
101
167.259(3)
fermium
100
164.93032(2)
einsteinium
99
162.500(1)
californium
98
158.92534(2)
berkelium
97
157.25(3)
curium
96
151.964(1)
americium
95
150.36(3)
plutonium
94
[145]
neptunium
93
144.24(3)
uranium
92
91
[227]
Pa
U
231.03588(2) 238.02891(3)
[237]
[244]
[243]
[247]
[247]
Np Pu Am Cm Bk
[251]
Cf
[252]
[257]
[258]
[259]
Es Fm Md No
Element symbols and names: symbols, names, and spellings are recommended by IUPAC (http://www.iupac.org/). Names are not yet proposed for the elements beyond 111 - those used here are IUPAC’s temporary systematic names (Pure & Appl. Chem., 1979, 51, 381–384). In the USA and some other countries, the spellings
aluminum and cesium are normal while in the UK and elsewhere the usual spelling is sulphur.
Atomic weights (mean relative masses): Apart from the heaviest elements, these are IUPAC 2007 values (Pure & Appl. Chem., 2007, in press). Elements with values given in brackets have no stable nuclides and are represented by integer values for the longest-lived isotope known at the time writing.
The elements thorium, protactinium, and uranium have characteristic terrestrial abundances and these are the values quoted. The last significant figure of each value is considered reliable to ±1 except where a larger uncertainty is given in parentheses.
Periodic table organisation: for a justification of the positions of the elements La, Ac, Lu, and Lr in the WebElements periodic table see W.B. Jensen, “The positions of lanthanum (actinium) and lutetium (lawrencium) in the periodic table”, J. Chem. Ed., 1982, 59, 634–636.
Group labels: the numeric system (1–18) used here is the current IUPAC convention. For a discussion of this and other common systems see: W.C. Fernelius and W.H. Powell, “Confusion in the periodic table of the elements”, J. Chem. Ed., 1982, 59, 504–508.
©2007 Dr Mark J Winter [WebElements Ltd and University of Sheffield]. All rights reserved. For updates to this table see http://www.webelements.com/nexus/Printable_Periodic_Table. Version date: 21 September 2007.
Th
232.0381(1)
Ac
70
140.90765(2)
protactinium
69
Er Tm Yb
68
90
67
Dy Ho
66
140.116(1)
thorium
65
89
64
138.9055(2)
actinium
63
Nd Pm Sm Eu Gd Tb
62
Pr
61
Ce
60
La
59
praseodymium
58
cerium
lanthanum
57
[267]
Ds Rg Uub Uut Uuq Uup Uuh Uus Uuo
[268]
Rf
Mt
[276]
[270]
[272]
[271]
118
[262]
Db Sg Bh Hs
[222]
ununoctium
117
Rn
116
At
115
Po
114
Bi
113
Pb
[209]
208.98038(2)
207.2(1)
204.3833(2)
ununtrium ununquadium ununpentium ununhexium
112
200.59(2)
ununbium
111
Tl
86
131.293(6)
radon
54
Xe
110
109
108
107
106
105
195.078(2) 196.96655(2)
darmstadtium roentgenium
Lr
104
Au Hg
85
126.90447(3)
astatine
I
53
Kr
83.798(2)
xenon
[210]
ununseptium
Pt
84
Br
79.904(1)
iodine
36
39.948(1)
krypton
Ar
18
20.1797(6)
argon
Ne
10
4.002602(2)
neon
He
2
helium
18
8.A
Exam I
Actinoids
Lanthanoids
[223]
Fr
0.9
103
Ir
192.217(3)
meitnerium
190.23(3)
hassium
Re Os
186.207(1)
bohrium
W
183.84(1)
seaborgium
Ta
180.9479(1)
dubnium
1.8
88
Hf
1.9
87
Lu
83
1.9
178.49(2)
174.9668(1)
lawrencium rutherfordium
82
127.60(3)
polonium
52
Te
2.0
137.327(7)
radium
Cs Ba
81
80
79
78
77
76
75
74
73
72
71
121.760(1)
bismuth
Se
78.96(3)
tellurium
35
35.453(2)
bromine
Cl
17
18.9984032(5)
chlorine
F
9
fluorine
17
2.2
132.90545(2)
francium
56
1.8
118.710(7)
lead
51
1.9
55
114.818(3)
thallium
112.411(8)
mercury
107.8682(2)
gold
106.42(1)
platinum
102.90550(2)
iridium
101.07(2)
osmium
[98]
rhenium
95.96(2)
tungsten
92.90638(2)
tantalum
91.224(2)
hafnium
88.90585(2)
lutetium
50
Sn Sb
74.92160(2)
antimony
34
32.065(5)
selenium
2.1
87.62(1)
barium
49
In
48
47
46
43
42
41
45
1.7
44
Ru Rh Pd Ag Cd
Nb Mo Tc
40
Zr
39
Y
72.64(1)
tin
Cu Zn Ga Ge As
33
30.973761(2)
arsenic
S
16
15.9994(3)
sulfur
O
8
oxygen
16
7A
2.5
85.4678(3)
caesium
38
Sr
69.723(1)
indium
65.38(2)
cadmium
Ni
58.6934(4)
palladium
Co
58.933200(9)
rhodium
1.6
55.845(2)
ruthenium
1.8
51.9961(6) 54.938049(9)
molybdenum technetium
Cr Mn Fe
63.546(3)
silver
V
50.9415(1)
niobium
Ti
47.867(1)
zirconium
Sc
44.955910(8)
yttrium
32
28.0855(3)
germanium
2.0
Rb
1.0
Ca
31
30
29
28
27
26
25
24
23
22
21
P
15
14.0067(7)
phosphorus
N
7
nitrogen
15
2.4
40.078(4)
strontium
26.981538(2)
gallium
zinc
copper
nickel
cobalt
iron
manganese
chromium
vanadium
titanium
scandium
Si
14
12.0107(8)
silicon
C
6
carbon
14
6A
2.8
39.0983(1)
rubidium
1.5
Al
13
10.811(7)
aluminium
B
5
boron
13
1.8
20
12
2.1
24.3050(6)
calcium
11
5A
2.5
19
10
4A
3.0
22.989770(2)
potassium
EN
12
9
2.0
Na Mg
symbol
8
3A
2.5
2003 atomic weight (mean relative mass)
7
8B
http://www.webelements.com/
7B
1B
2B
3.0
9.012182(3)
magnesium
atomic number
element name
6
5
4
3
Key:
6B
5B
4B
3B
3.5
11
1.5
Be
4
beryllium
2
2A
4.0
6.941(2)
sodium
Li
3
1.00794(7)
lithium
H
1
hydrogen
1
1A
Periodic
Table of
theon
Elements
the world-wide web
table
the periodic
WebElements:
Chem 150
Fall, 2015