Download ECE final exam_fall 2013

CHEMISTRY 1127
Name
FINAL EXAMINATION
______________________
Signature
December 14, 2013
Section _____________________
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TA
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PLEASE READ THE FOLLOWING INSTRUCTIONS
Do NOT begin the exam until asked to do so.
There are 12 numbered pages in this exam. Check to see they are all here before you begin the exam. Return
all these papers when you are finished. A separate packet has a page of equations, a periodic table, and a
phase diagram. Make sure that you have both packets. Use a pen with blue or black ink for the entire exam.
Be sure to follow ALL directions. In working the problems, you MUST SHOW ALL WORK. Write your
answers in the space provided. Use correct significant figures and units throughout. No credit will be given
unless all work is clearly shown and the method of solution is logically correct.
For those who have an excused absence from an hourly exam, and are using part of this final as credit
for that exam:
Part I corresponds to Exam I.
Part II corresponds to Exam II.
Part III corresponds to Exam III
You may want to spend extra time on the particular portion of this exam that corresponds to the hourly
exam that you missed.
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Grader
Grader
CHEM 1127, Final Exam
December 14, 2013
Name _______________________
I. (74 points)
A.
(15 points) Answer the following questions on the blanks provided.
_______________ 1. A solution is made up of 12.0 g of sugar and 112 g of water. What is the
mass % of sugar in the solution?
_______________ 2. How many grams of water are required to dissolve a mixture made up of
28 g of A (solubility = 14 g/100 g H2O) and 28 g of B
(solubility = 25 g/100 g H2O)?
_______________ 3. What is the molar mass of Na2CO3.10H2O?
_______________ 4. What is the mass percent of oxygen in CaCO3?
_______________ 5. The edge of a cube, made up of an alloy is 2.00 cm. The cube has a mass
of 12.0 g. What is the density of the alloy?
B.
(18 points) Answer the following questions by writing your answers on the blanks provided.
_______________ 1.
Write the chemical formula of sodium chlorite?
_______________ 2.
Write the chemical formula of iron(III) carbonate?
_______________ 3.
What is the name of the compound HNO2 (aq)?
_______________ 4.
What is the name of the compound CH4?
_______________ 5.
Write the chemical formula of silver sulfate?
_______________ 6.
What is the name of the compound N2O5?
Consider nuclear symbol of nickel ion which is given as
answers in the blanks provided.
C.
60
28
_______________ 7.
How many protons are there?
_______________ 8.
How many electrons are there?
Ni 2+ to answer questions 7 - 9 Write your
_______________ 9. How many neutrons are there?
(5 points) A solution is prepared using 10.00 mL chloroform (d =1.492 g/cm3) and 10.00 mL of
benzene (d = 0.879 g/cm3). What is the density of the final solution? (Volumes are additive)
____________________
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CHEM 1127, Final Exam
December 14, 2013
D.
Name _______________________
(5 points) An element has three naturally occurring isotopes with the following abundances and
masses:
Abundance
mass (amu)
90.48%
19.992440
0.27%
20.993846
9.25%
21.991385
Determine the molar mass of the element.
____________________
E.
(8 points) In each of these questions, PRINT, in capital letters (i.e. A, B, C, etc. and not a, b, c,
etc.) in the blanks the letter corresponding to the best answer. Circled letters will not be
considered. There is no penalty for guessing.
________ 1. The element found in Group 3, Period 4 in the periodic table is
A) Ga
B) Na
C) Sc
D) K
E) None of the above
________ 2. Which of the following is not a metallic element?
A) Sc
B) F
C) Ag
D) Cu
E) Zn
________ 3. Which of the following can be considered a simplest formula?
A) K2Cr2O4
B) H3P3O3
C) N2O4
D) C2H6
E) KMnO4
________ 4. Consider a solution of ethyl alcohol and water. Ethyl alcohol is completely soluble in
water. The combination is best described as
A.
B.
C.
D.
E.
E.
A heterogeneous mixture
A homogeneous compound
A pure element
A homogeneous mixture
None of the above
(2 points) Balance the following equation using the smallest whole numbers as stoichiometric
coefficients. Calculate the sum of the coefficients of the reactants and the products?
C2H2 (g) + O2 (g) → CO2 (g) + H2O (ℓ)
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CHEM 1127, Final Exam
December 14, 2013
F. (4 points) What is the mass (in grams) of a tin (Sn) atom?
G.
Name _______________________
____________________
(5 points) Magnesium atoms react with bromine in a ratio of 1 atom to 2 atoms respectively
according to the following reaction.
Mg (s) + Br2 (ℓ) → MgBr2 (s)
If 1.00 g of magnesium reacts with 10.0 g of Br2, how many grams of product are produced?
H.
____________________
(8 points) An Erlenmeyer flask contains 125.0 mL of a solution of 0.450 M CoCℓ3.
1.How many moles of chloride ions are present?
____________________
2.What volume of 0.450 M CoCℓ3 must be taken to obtain 0.00250 mol of Co3+ ions?
____________________
I. (4 points) Polyethylene is a polymer consisting of only carbon and hydrogen. If 2.300 g of the
polymer is burned in oxygen it produces 2.955 g H2O and 7.217 g CO2. What is the empirical
formula of polyethylene? (Circle the correct answer)
A. CH
B. CH2
C. C2H3
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D. C5H8
E. C7H8
CHEM 1127, Final Exam
December 14, 2013
Name _______________________
II. (59 points)
A. (6 points) Write the appropriate letter in the blank provided.
_______ 1. What volume of CH4 at 0°C and 1.00 atm contains the same number of molecules as
0.50 L of N2 measured at 27°C and 1.50 atm?
A. 0.37 L
B. 0.46 L
C. 0.50 L
D. 0.82 L
E. 0.68 L
_______ 2. At 25ºC, a molecule of pentane, C5H12, effuses more slowly than a molecule of
propane, C3H8. This is principally because,
A. pentane is heavier than propane.
B. pentane has more H atoms.
C. rate and effusion are directly proportional
D. at 25ºC, the kinetic energy of pentane is smaller than the kinetic energy of
propane.
_______ 3. Which of the following is insoluble in water?
B.
C.
A. KNO3
B. CuSO4
C. NaOH
D. HCℓ
E. BaSO4
(12 points) Write the products obtained when aqueous solutions of the following compounds react.
If there is not any reaction between the species write NR. Do not include the spectator ions, or you
will lose points.
1. HF and NaOH
_____________________________
2. CuCl2 and Na2SO4
_____________________________
3. NH3 and NaOH
_____________________________
4. CH3NH2 and HBr
_____________________________
(10 points) Consider the reaction between K2S and CoCℓ3 for the following two questions.
2Co3+ (aq) + 3S2- (aq) → Co2S3 (s)
1. How many moles of K2S are required to react completely with 0.125 moles of CoCℓ3?
____________________
2. Calculate the mass of Co2S3 that forms from the reaction of 0.125 moles of CoCℓ3
with 1000.0 mL of 0.100 M K2S.
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CHEM 1127, Final Exam
December 14, 2013
Name _______________________
C. (14 points) Write your answer in the blank provided.
Examine the following balanced half-reaction:
2H2O + CrO2- → CrO42- + 3e- + 4H+
__________ 1. (2 points) Is this an oxidation or a reduction?
__________ 2. (2 points) What element is oxidized or reduced?
Balance the following half-equation in acid.
ClO3 → Cl2
__________ 3. (4 points) What is the coefficient of H+ in your balanced equation?
The above reaction occurs along with the reaction given above before Part 1 of this problem.
Write a balanced equation for the overall reaction that occurs.
__________ 4. (4 points) What is the coefficient of water in the balanced overall equation?
__________ 5. (2 points) Which reactant is the oxidizing agent?
D.
(5 points) Hydrogen gas bubbled into a solution of barium hydroxide that has sulfur in it. The
balanced equation for the reaction that takes place is
2OH-(aq) + H2(g) + S(s)  S2-(aq) + 2H2O
What volume of 0.350 M of Ba(OH)2 is required to react completely with 2.50 g of sulfur?
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CHEM 1127, Final Exam
December 14, 2013
E.
Name _______________________
(12 points) Consider oxygen gas:
1. A 6.00 L flask contains oxygen gas at a certain temperature and pressure. What is the volume
of a flask that would contain the same amount of oxygen gas at a pressure twice that of the
original pressure and a temperature, a third that of the original temperature in K.
____________________
2. A certain amount of oxygen gas effuses out of a pinhole in 45 seconds. How long will it take
for the same amount of N2O4 to effuse out of the same pinhole?
____________________
3. Oxygen gas is a product of the electrolysis of Aℓ2O3
2Aℓ2O3 (s) → 4Aℓ (s) + 3O2 (g)
What volume of oxygen gas measured at 25ºC and 1.00 atm is produced from the electrolysis
of 1.000 x 103 kg (1 metric ton) of Al2O3?
____________________
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CHEM 1127, Final Exam
December 14, 2013
Name _______________________
III. (68 points)
A.
(10 points) Answer the following questions, using Y if the statement is true and N if the statement
is false. Write your answers in the blanks provided.
_________ 1. A molecule that follows the octet rule has a central atom and 4 surrounding
atoms. The geometry must be tetrahedral.
_________ 2. A photon’s energy is directly proportional to its wavelength.
_________ 3. In the hydrogen atom a transition from n = 2 to n = 3 requires the same amount of
energy as a transition from n = 3 to n = 4.
_________ 4. For the following reaction, ΔH° = ΔHf° for CH3OH (ℓ):
2 C (s) + 4H2 (g) + O2 (g) → 2CH3OH (ℓ)
_________ 5. At constant pressure
ΔHsystem + ΔHsurroundings = 0
B.
(8 points) Write your answers in the blanks provided:
1. What is the abbreviated ground state electron configuration for Mn?
________________________
_________ 2. How many unpaired electrons are there in Mn3+?
_________ 3. How many electrons can an atom have with quantum numbers n=5, ℓ= 3, mℓ= +2.
_________ 4. What element has the abbreviated electron configuration of [Kr]5s2 4d6?
C.
(6 points) Write your answers to the blanks provided. Consider the atoms: Na, Si, Rb, and Sn.
_________ 1. Which atom is the smallest?
_________ 2. Which atom has the highest first ionization energy?
_________ 3. Which atom has the lowest electronegativity?
D.
(4 points) How much energy is associated with a transition from n = 10 to n = 5?
__________________
In this transition is energy absorbed or given off? _____________
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CHEM 1127, Final Exam
December 14, 2013
E.
Name _______________________
(6 points) Write the Lewis structure of each of the following species in the box provided and the
molecular geometry in the blank provided.
1. IO4Lewis Structure:
Molecular geometry: ____________________
2. NO3Lewis structure:
Molecular geometry: ____________________
(10 points) SeCl4 has the following Lewis structure. Using the Lewis structure given answer the
questions below.
:
:Cl :
Cl :
: :
Se
: :
:
F.
:
:Cl : Cl
:
___________ 1.
What is the total number of valence electrons?
___________ 2.
What is the hybridization of the central atom?
___________ 3.
What is the molecular geometry?
___________ 4.
Is the molecule polar or nonpolar
___________ 5.
What is the formal charge on the central atom?
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CHEM 1127, Final Exam
December 14, 2013
G. (8 points) Consider the following thermochemical data:
2P (s) + 3Cℓ2 (g) → 2PCℓ3 (ℓ)
PCℓ3 (ℓ) + Cℓ2 (g) → PCℓ5 (s)
Name _______________________
ΔH° = -636 kJ
ΔH° = -138 kJ
1. Write a balanced chemical equation for the formation of one mole of PCℓ5 (s) from its
elements.
________________________
2. Calculate ΔHf° for PCℓ5 (s).
________________________
H.
(8 points) Using the data provided below answer the following questions.
Specific heat for bromine
ΔHvap° for bromine
Boiling point
0.474 J/g⋅°C
29.6 kJ/mol
59.0 °C
1. Calculate ΔH for 15.0 g Br2 (ℓ, 22.5 °C) → Br2 (ℓ, 59.0 °C)
_____________________
2. Calculate ΔH for 15.0 g of Br2 (ℓ, 59.0 °C) → Br2 (g, 59.0 °C)
____________________
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CHEM 1127, Final Exam
December 14, 2013
I.
Name _______________________
(8 points) The thermochemical equation for the preparation of NH3 from a reaction between HNO3
and hydrogen gas is given below.
HNO3 (g) + 4H2 (g) → NH3 (g) + 3H2O (g)
∆H = -637 kJ
1. Calculate ∆H when one mol of hydrogen gas reacts.
____________________
2. What is ∆H when 10.00 g of NH3 (g) is made to react with an excess of steam to form HNO3
and H2 gases?
_________________________
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CHEM 1127, Final Exam
December 14, 2013
Name _______________________
IV. (49 points)
A.
(8 points) Answer the questions below, using LT (for is less than), GT (for is greater than), EQ
(for is equal to), or MI (for more information required) in the blanks provided.
_________ 1. The boiling point of NH3
_ the boiling point of CH4.
_________ 2. The vapor pressure of compound X is 250 mm Hg at 57°C. Given a sealed flask
that contains some liquid X, the vapor pressure in the flask _ _ 250 mm Hg.
_________ 3. The density of Y (ℓ) is 1.2 g/mL while that of Y (s) is 0.95 g/mL. the melting
point of Y at 1 atm pressure __ the melting point of Y at 10 atm pressure.
_________ 4. Compound A has a vapor pressure of 760 mm Hg at 85°C. Compound B has a
vapor pressure of 760 mm Hg at 40°C. The boiling point of B _ boiling point of
A.
B.
(16 points) Fill in the blanks.
____________ 1. Do dispersion forces exist in all molecules?
____________ 2. Dispersion forces (increase, decrease, do not change) when molar mass
increases.
____________ 3. What intermolecular force(s) is/are present in water?
____________ 4. Which has a higher boiling point, CH4 or CCl4?
For the next four questions, identify the compounds as ionic, molecular, network covalent, or
metallic.
____________ 5. C (graphite)
____________ 6. W
____________ 7. KF
____________ 8. HF
C.
(5 points) Acetic acid has a heat of vaporization of 23.7 kJ/mol. At 35°C, acetic acid has a vapor
pressure of 106 mm Hg. What is the boiling point temperature of acetic acid at 760 mm Hg?
_______________
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CHEM 1127, Final Exam
Name _______________________
December 14, 2013
D. (6 points) Consider 20.0 g of CHCl3 (MM = 119 g/mol) at 45°C (vapor pressure = 448 mm Hg) in
a sealed 5.00 L flask.
1. What is the pressure in the flask?
_______________
2. What is/are the physical state(s) present in the flask?
_______________
E.
(14 points) Consider the phase diagram for CCℓ4 below. Answer the questions about the diagram
by writing your answers on the blanks provided.
__________ 1. Point A represents an equilibrium between _____ phases.
__________ 2. What is CCℓ4 at point C called?
__________ 3. Does the boiling point increase as pressure above the liquid is decreased? (yes
or no)
__________ 4. What point represents CCℓ4 only in the gas phase?
__________ 5. Does the melting point increase as pressure is applied to the solid?
__________ 6. Is the density of liquid is higher than the density of the solid?
__________ 7. Define the phase change going from point B to C.
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