Oct. 5, 2001
NAME________Chemist__________________12:10-1:30 exactly
Chemistry 103 Section 1
EXAM #1--60 min.
IMPORTANT NOTE--For partial credit be sure to show your reasoning. Sometimes your instructor may go to heroic lengths to give you partial credit if you show work that is both legible logical. If you need more paper, write on the back of the page and indicate clearly that you have done so. Units and significant figures are important!
Look over all questions before starting and plan your time wisely.
There will be no partial credit on Problem 1.
(Possibly Useful )Physical Constants
NA = 6.022 x 1023
Mass of an electron 9.1 x 10-28 g
Mass of a proton 1.67 x 10-24 g
Mass of a neutron 1.67 x 10-24 g
Density of water 1.00 g/cm3 Specific heat of water 4.18 J/g °C
Solubility Table Activity Series
Periodic Table
Problem 1________/20
Problem 2________/20
Problem 3________/20
Problem 4________/20
Problem 5________/20
Total _________
Very approximate grading scale (average about 76)
Based on 24 points of Basic material, 63 points of HW level material, and 23 points of synthetic level. Please check your exam and if it's misgraded return it to me with a note about what's wrong. If you would like to discuss your exam and how to improve your performance, please see me duirng office hours or make an appointment to see me.
0-24 0.0
25-56 1.3, 1.7 Serious work is needed. Semester 2 will be hard.
57-69 2.0 More work and different strategies needed.
70-79 2.3, 2.7 More work and different strategies needed.
80-89 3.0, 3.3, 3.7 Keep on practicing.
90-100 4.0 Congratulations! Keep up the good work.
NAME
____________________________Problem 1 (20 points)
Indicate whether the quantity in Column A is greater than (>), equal to (=), or less than (<) the quantity in column B. You may write the words, the symbols or both. No partial credit will be awarded on the parts of this Problem. Part (a) is done for you as an example.
Column A Column B
|
(a) The yield of crops per hectare receiving no fertilizer. |
is less than < |
The yield of crops per hectare receiving ammonium sulfate |
|
(b). The molar mass of (NH 4)2SO4
|
> |
The molar mass of Mg SO 4 |
|
< |
The number of moles produced when 2 moles of HNO 3 completely dissolves. |
|
(d) The heat required to sublimate 100 g of "water" at 25°C. ice to vapor |
> |
The heat required to evaporate 100 g "water" at 25°C. Water to vapor |
|
(e) The absolute value of the amount of heat given off by a chemical reaction Z in a bomb calorimeter. |
= |
The absolute value of the amount of heat absorbed by the bomb calorimeter following reaction Z. |
|
(f) The number of mass spectrometer peaks for H 2O if we have isotopes 1H, 2H, 16O and 18O, |
= 5 each |
The number of mass spectrometer peaks for CCl 4 if we have isotopes 12C, 35Cl, and 37Cl. |
NAME
____________________________Problem 2-- (20 pts)
a) In Rutherford's famous experiment alpha particles were shot at a piece of thin gold foil. What important conclusion was about the structure of the atom was reached based on this experiment?
Most of the mass of the atom is concentrated in the nucleus. The atom is mostly empty space.
b) C
6O6H12 (s) + 6O2 (g) à 6CO2(g) + 6H2O (l) DH/mole glucose =?What are the values that you need to know ahead of time and the values that you need to measure in order to calculate the enthalpy of the combustion reaction above? You may use words or words and symbols (but not symbols alone). Assume you have a water jacketed bomb colorimeter similar to that shown in the text and in lecture.
|
Know ahead of time |
Measure |
|
Mass of glucose |
Initial and final temperatures. |
|
Heat capacity of calorimeter |
|
|
Specific heat of water |
|
|
Mass water |
|
|
|
|
|
|
NAME
____________________________Problem 3 (20 points)
In order to make a buffered solution, a biochemist weighs out 40.0 grams of glycine , C
2O2NH4 and dissolves it in a liter of water. She then removes 5.00 mL of the solution and mixes it with 95.0 mL of water. Finally she removes 5.00 mL of this second solution and mixes it with 95.0 mL of water.What is the glycine concentration of the final solution?
This is a dilution problem.
To 3 s. f.
Molar mass of glycine is 74.0 g/mol
40.0 g ( 1 mole/ 74.0 g ) / 1 Liter = 0.54 M Solution 1
0.54 M ( 5mL / (5 + 95 mL) = 0.027 M Solution 2
0.027 M (( 5mL / (5 + 95 mL) = 0.00135 M Solution 3
NAME
____________________________Problem 4 (20 points)
The reaction below uses highly pure reagents to produce silicon for silicon chips used for computers and calculators.
1 metric ton = 1000 kg
Si Cl
4 (s) + H2 (g) à Si (s) + HCl (g)Redox --Si goes from +4 to 0 and is reduced. H goes from 0 to +1 and is oxidized.
_
________reactantsEnergy exothermic.
__________ products
Limiting reagenat problem--you are given information to calculate the number of moles of both reactans.
2.3 tons SiCl4 x (1mole/170.1 g) = 13500 moles
2.00 tons H2 x (1 mole / 2 g) = 10^6 moles
SiCl4 is the limiting reagent
13500 moles SiCl4 x 28.1 g /mole = 0.38 tons Si produced same number of moles of SiCl4 and Si).
4 x 13500 moles HCl = 54000 moles HCl
54000 mole x 36.5 g /mole = 1.97 tons HCl
Problem 5 (20 pts)
The United States Environmental Protection Agency, US EPA, in now deciding whether to lower the current standard of 50 ppb arsenic in drinking water. They have reanalyzed their epidemiological data and found that when using appropriate control comparisons a level of 10 ppb causes 1.3 to 3.7 extra cancer cases per 1000 people.
1 billion = 109
10 ppb = 1- x 1 g As / 10^9 g H2O x 1 mole As/ 74.9 g As x 1 g H2O/ 1 mL H2O x 1 mL H2O / 10 ^-3 L = 1.33 x 106-7 M
1.33 x 106-7 M x 6.02 x 10^23 atoms/ mole = 8.01 x 10^16 atoms.
|
1 H 1.008 |
2 He 4.003 |
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|
3 Li 6.941 |
4 Be 9.012 |
5 B 10.81 |
6 C 12.01 |
7 N 14.01 |
8 O 16.00 |
9 F 19.00 |
10 Ne 20.18 |
||||||||||
|
11 Na 22.99 |
12 Mg 24.30 |
13 Al 26.98 |
14 Si 28.09 |
15 P 30.97 |
16 S 32.07 |
17 Cl 35.45 |
18 Ar 39.95 |
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|
19 K 39.10 |
20 Ca 40.08 |
21 Sc 44.96 |
22 Ti 47.88 |
23 V 50.94 |
24 Cr 52.00 |
25 Mn 54.94 |
26 Fe 55.85 |
27 Co 58.93 |
28 Ni 58.69 |
29 Cu 63.55 |
30 Zn 65.39 |
31 Ga 69.72 |
32 Ge 72.61 |
33 As 74.92 |
34 Se 78.96 |
35 Br 79.90 |
36 Kr 83.80 |
|
37 Rb 85.47 |
38 Sr 87.62 |
39 Y 88.91 |
40 Zr 91.22 |
41 Nb 92.91 |
42 Mo 95.94 |
43 Tc (98) |
44 Ru 101.1 |
45 Rh 102.9 |
46 Pd 106.4 |
47 Ag 107.9 |
48 Cd 112.4 |
49 In 114.8 |
50 Sn 118.7 |
51 Sb 121.7 |
52 Te 127.6 |
53 I 126.9 |
54 Xe 131.3 |
|
55 Cs 132.9 |
56 Ba 137.3 |
71 Lu 175.0 |
72 Hf 178.5 |
73 Ta 181.0 |
74 W 183.9 |
75 Re 186.2 |
76 Os 190.2 |
77 Ir 192.2 |
78 Pt 195.1 |
79 Au 197.0 |
80 Hg 200.6 |
81 Tl 204.4 |
82 Pb 207.2 |
83 Bi 209.0 |
84 Po (209) |
85 At (210) |
86 Rn (222) |
|
87 Fr (223) |
88 Ra (226) |
103 Lr (260) |
104 Unq (261) |
105 Unp (262) |
106 Unh (263) |
107 Uns (262) |
108 Uno (265) |
109 Une (266) |
|
57 La 138.9 |
58 Ce 140.1 |
59 Pr 140.9 |
60 Nd 144.2 |
61 Pm (145) |
62 Sm 150.4 |
63 Eu 152.0 |
64 Gd 157.3 |
65 Tb 158.9 |
66 Dy 162.5 |
67 Ho 164.9 |
68 Er 167.3 |
69 Tm 168.9 |
70 Yb 173.0 |
||||
|
89 Ac (227) |
90 Th 232.0 |
91 Pa 231.0 |
92 U 238.0 |
93 Np (237) |
94 Pu (244) |
95 Am (243) |
96 Cm (247) |
97 Bk (247) |
98 Cf (251) |
99 Es (252) |
100 Fm (257) |
101 Md (258) |
102 No (259) |