Download Chemistry 515 Name: L. S. Curtin Soc. Sec. #: February 8, 1999

Chemistry 515
L. S. Curtin
February 8, 1999
Name: ___________________________
Soc. Sec. #: _______________________
EXAM I
INSTRUCTIONS:
1) This exam consists of six pages. If any of the pages are missing bring your exam to me immediately.
2) Make sure to print your name and social security number in the top right hand corner of the answer
sheet as well as this page of the exam.
3) Answers to multiple choice questions must be legible and written only on the answer sheet provided
with the exam. DO NOT REMOVE THE ANSWER SHEET FROM THE EXAM. Each multiple choice
question is worth four points.
4) You must show all your work in order to receive credit on non-multiple choice questions.
5) Answers must be expressed with the proper units and units must be carried through in your
calculations.
6) Budget your time for each question and answer the questions which you know how to work first. After
you have finished the entire exam it is a good practice to review and check your work.
7) A periodic table will be given to you before the exam. DO NOT WRITE ON THE PERIODIC
TABLE! Scratch paper will be supplied if you need it.
8) Good luck.
1) Which of the following is an incorrect statement?
a)
b)
c)
d)
e)
Elements in a compound combine in fixed percentages by volume.
Salt dissolved in water is an example of homogeneous matter.
Elements cannot be broken down into simpler substances via chemical means.
Boiling water is an example of a physical change.
None of the above are incorrect statements.
Elements in compounds combine in fixed percentages by mass not volume.
2) Which of the following statements is correct?
a) The number of protons and neutrons in the nucleus of an atom are always equal.
b) The mass of an atom is contained primarily in the nucleus and the volume of an atom is primarily
determined by the size of the electron cloud.
c) Isotopes of a given element have very different chemical reactivities because they have the same
number of protons in the nucleus.
d) Alkaline earth elements generally form +1 ions when combining to form compounds.
e) None of the above are correct statements.
Protons and neutrons reside in the nucleus of the atom and are about 10,000 times more massive than
electrons. The diameter of a typical nucleus is about 105 times smaller than that of the atom. Thus, the
mass of the atom is primarily contained in the nucleus and the volume is primarily determined by the size
of the electron cloud.
3) CH3NH2 reacts with O2 to produce CO2, H2O and N2. What is the coefficient in front of the CH3NH2
in the correctly balanced chemical reaction?
a)
b)
c)
d)
e)
1
2
3
4
None of the above.
The balanced chemical reaction is:
4 CH3NH2(l) + 7O2(g) → 2CO2(g) + 10H2O(g) + 2N2(g)
4) A measurement made with an improperly calibrated balance is an example of the following:
a)
b)
c)
d)
e)
A systematic (determinate) error that affects the accuracy of a measurement.
A systematic (determinate) error that affects the precision of a measurement.
A random (indeterminate) error that affects the accuracy of a measurement.
A random (indeterminate error that affects the precision of a measurement.
None of the above.
Systematic errors affect the accuracy of a measurement (how close is the measured value to the true value)
and random errors affect the precision of a measurement (how closely spaced the measurements are).
5) Which of the following elements is an alkali metal?
a)
b)
c)
d)
e)
Ca.
Fe.
F2.
Rb
None of the above is an alkali metal.
The alkali metals are the elements in group IA. Rb is the correct response.
6) How many protons, neutrons and electrons are there in a barium-117 (117Ba) ion?
a)
b)
c)
d)
e)
56 protons, 61 neutrons and 56 electrons.
117 protons, 56 neutrons and 56 electrons.
56 protons, 61 neutrons and 54 electrons.
56 protons, 117 neutrons and 56 protons.
None of the above.
The atomic number of barium is 56 and so there are 56 protons in the nucleus of any barium atom or ion.
Since the question is asking about the barium ion (Ba2+) there are 54 electrons in the ion. The number of
neutrons is determined by the atomic number and the mass number.
mass number = number of protons + number of neutrons
117 = 56 + number of neutrons
number of neutrons = 61
7) What is the correct molecular weight of the compound Na2S2O3? (Round off atomic masses to two
places to the right of the decimal point)
a)
b)
c)
d)
e)
71.06 a.m.u.
126.05 a.m.u.
135.13 a.m.u.
158.12 a.m.u.
None of the above.
atomic mass Na2S2O3 = (2)(atomic mass of Na) + (2)(atomic mass of S) + (3)(atomic mass of O)
atomic mass Na2S2O3 = (2)(22.99 a.m.u.) + (2)(32.07 a.m.u.) + (3)(16.00 a.m.u.)
atomic mass Na2S2O3 = 158.12 a.m.u.
8) What is the coefficient in front of the oxygen in the correctly balanced equation for the combustion of
butane (C4H10)?
a)
b)
c)
d)
e)
5
8
13
26
None of the above.
The correctly balanced equation is:
C4H10(g) + 13O2(g) → 8CO2(g) + 10H2O(g)
9) Which of the following is an example of a chemical change?
a)
b)
c)
d)
e)
Boiling water.
Bread dough rising.
Pulverizing sugar cubes into powdered sugar.
Mashing potatoes.
None of the above is an example of a chemical change.
A chemical reaction occurs when a substance is converted into different substance(s). When bread dough
rises the yeast in the bread is converting the sugar present in the dough into carbon dioxide and water,
causing the bread to rise.
10) Al reacts with Cl2 to produce AlCl3. What is the coefficient in front of the aluminum in the correctly
balanced chemical reaction?
a)
b)
c)
d)
e)
1
2
3
4
None of the above.
The correctly balanced equation is:
2Al(s) + 3 Cl2(g) → 2 AlCl3(s)
11) Which of the following statements about Daltons Atomic Theory has been shown to be incorrect?
a)
b)
c)
d)
e)
Matter is neither created or destroyed in chemical reactions, but it can change forms.
Elements generally combine to form compounds in fixed percentages by mass.
Elements are composed of small particles called atoms.
All atoms of a given element are identical to all other atoms of that element, but are different from
those of other elements.
None of the above are incorrect statements.
Isotopes are atoms of a given element that have the same number of protons in the nucleus but different
numbers of neutrons. Thus, not all of the atoms of a given element are identical, some differ in the
number of neutrons in the nucleus.
12) Which of the following answers is expressed to the appropriate number of significant figures?
0.005070x 500÷(6.1 x 104)
a)
b)
c)
d)
e)
-5
4 x 10
4.1 x 10 -5
4.16 x 10 -5
4.166 x 10 -5
None of the above.
This is a muliplication and division problem. The answer to the mathematical problem should be
expressed to the fewest total number of significant figures as are present in the product and quotient in the
above calculation. 0.005070 has four total significant figures, 500 has only one significant figure (500.
would have three) and 6.1 x 104 has two total significant figures. Thus, the answer should only be
expressed to one significant figure.
13) How many µg are there in 250 g?
a)
b)
c)
d)
e)
2.5 x 10 -6 µg.
2.5 x 10-8 µg.
2.5 x 108 µg.
2.5 x 106 µg.
None of the above.
(250 g) x (1 µg/1 x 10 -6g) = 2.5 x 108 µg.
14) Calculate the number of nL in 0.00045 kL.
a)
b)
c)
d)
e)
4.5 x 108 nL.
4.5 x 10 -8 nL.
4.5 x 1010 nL.
4.5 x 10 -10 nL.
None of the above.
(0.00045 kL)x(1 x 103L/kL)x(1 nL/1 x 10-9 L) = 4.5 x 108 nL
15) Given that the density of lead is 11.3 g/mL, calculate the mass of 5.0 L of lead.
a)
b)
c)
d)
e)
4.4 x 10 -4 g.
5.6 x 10 -2 g.
4.4 x 102 g.
5.6 x 104 g.
None of the above.
(5.0 L)x(1 mL/1 x 10-3L)x(11.3 g/mL) = 5.6 x 104 g Pb
On the following part of the examination SHOW ALL OF YOUR WORK, INCLUDING UNITS
WHEN IT IS APPROPRIATE TO DO SO.
16) Suppose that an assistant professor at YSU recently discovered a new element called TarHeelium that
consists of two different isotopes. The isotope occurring in 45.0 % abundance has an isotopic mass of
295 a.m.u. Given that the other isotope occurs in 55.0 % abundance and that the atomic mass of the
element was determined to be 298 a.m.u., calculate the isotopic mass of the isotope that occurs in 55.0
% abundance.
atomic mass = (fractional abundance of 295 isotope)(mass of 295 isotope) + (fractional abundance of other isotope)(mass of other isotope)
298 a.m.u. = (0.45)(295 a.m.u.) + (0.55)(atomic mass of other isotope)
atomic mass of other isotope = 300.0 a.m.u.
17) Give the correct chemical formula for the following compounds.
a)
b)
c)
d)
e)
a)
b)
c)
d)
e)
Ferrous Phosphate.
Perchloric acid
Hydrosulfuric acid.
Dinitrogen tetraoxide.
Ammonium hydrogen sulfite.
Fe3(PO4)2
HClO4
H2S
N2O5
NH4HSO3
18) Give the correct name for the following compounds or ions.
a)
b)
c)
d)
e)
a)
b)
c)
d)
e)
Ca3N2.
NaCN.
PBr5.
Co(H2PO4)3.
IO -.
Calcium nitride.
Sodium cyanide
Phosphorus pentabromide
Cobaltic dihydrogen phosphate or cobalt (III) dihydrogen phosphate
Hypoiodite ion
19) Given that there 1 inch = 2.54 cm, calculate the number of kg/in3 in 65.00 g/cm3.
1 in = 2.54 cm
(1 in)3 = (2.54 cm)3 = 16.4 cm3
(65.0 g/cm3)x(16.4 cm3/1 in3)x(1 kg/1 x 103g) = 1.07 kg/in3