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Chem 123
PRACTICE QUESTIONS FOR EXAM I
Fall 2014
This has been updated after Monday’s lecture (9/15/14)
I am not providing answers to most of these questions. Please review your textbook and lecture
notes if you don’t know the answers.
Please note that these practice questions are provided just to show you what your exam questions
may look like. They do not cover all the material you should know for Exam I. You should know the
answers of all questions here but there will certainly be questions on your exam not shown here.
These are practice questions. This is not meant to show you the length of the exam. Obviously
there are more questions here than you can answer in a one-hour exam.
THESE ARE THE EQUATIONS AND CONSTANTS THAT WILL BE PROVIDED ON THE
EXAM.
As usual, a periodic table will also be provided.
R = 8.314 J mol 1 K 1
R = 0.08206 atm L mol 1 K 1
Ideal gas law equation will not be provided...you should know it.
Equations provided on exam (no need to memorize):
P1 ΔHvap 1 1
ΔHvap 1
ln =
ln P=
+C
P2
R
T2 T1
R
T
Gen Chem I review material (about 15% of exam)
Nomenclature (about 10% of exam)
Organic Molecules, Logarithm, & Chapter 12 (about 75% of exam)
Practice questions on nomenclature are not provided here. Refer to Nomenclature Reviews A, B, C and
Quizzes #1 through 4.
1. When comparing atoms of two elements the one with the higher first ionization energy should be …
A. smaller in size
B. larger in size
2. Which atom is larger?
A. phosphorus
B. sulfur
3. Which is more electronegative?
A. sulfur
B. nitrogen
4. Which of the following is a molecule? (Circle as many as applies.)
A. Hf
B. P4
C. PO3
D. He
E. Fe2O3
5. Which has a higher ionization energy?
A. metals B. nonmetals
6. What are alloys?
A. They are the elements along the border between metals and nonmetals in the periodic table.
B. They are compounds of metals.
C. They are homogeneous mixtures of metals.
D. They are compounds of aluminum.
7. The following questions concern selenium (atomic number 34).
A. Give its full electron configuration. Circle its valence electrons in the configuration.
B. Give it electron configuration using the Core Method.
C. Give its electron dot symbol.
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8.
.. H H
H N C C C N:
H
A
B C
Give the hybridization, the bond angle and state the geometry at each of the above atoms:
*Hybridization Bond Angle
Geometry (name in one or two words)
A ___________ ___________ ______________________
B ___________ ___________ ______________________
C ___________ ___________ ______________________
What is the total number of bonds in this molecule? Ans. _____
What is the total number of bonds in this molecule? Ans. _____
*We did not review this, but you should know hybridization from Gen Chem I. You can review with
Chap.10 Sec 2 and/or using this link:
Handout on Geometry & Hybridization from Gen Chem I.
9. Draw the resonance structures of CO32–.
Draw the resonance hybrid of CO32–.
If we were able to measure its dipole moment, would you expect it to be zero or larger than zero?
Ans. _________
10. Give the full structure of (showing all atoms, bonds and lone pairs)
a) benzene
b) acetic acid
c) acetone
11. Which has the higher viscosity? (Assume they are of comparable size.)
A. CH3CH2CH2CH2CH2CH2CH3
B. CH3CH2CH2CH2CH2CH2OH
12. Which do we expect to have the higher boiling point?
A.
B.
H3C N CH3
CH3
H
H3C C CH3
NH2
13. Which should have the higher surface tension?
A. substance with a higher vapor pressure
B. substance with a lower vapor pressure
14. Which is a better solvent for CH3CH2CH2CH2CH2CH2CH3
A. H2O
B. benzene
C. CH3CH2CH2CH2OH
Pressure
15. Which has the higher vapor pressure at a given temperature?
A. H2O (l) B. H2S (l)
16. Which of the following affects the vapor pressure of a liquid?
A. the surface area of the liquid
B. the volume of the liquid
C. the temperature of the liquid
D. all of the above
E. none of the above
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17. In the graph shown on the right showing the vapor pressure of acetic acid and ether.
Temperature
Acetic acid is CH3CO2H and ether is CH3CH2OCH2CH3 and considered similar in molecular weight.
Which curve corresponds to acetic acid?
A. Curve A Curve B
P
A
B
T
18 Which pair of solute and solvent is most likely to form a solution?
A. CCl4 in H2O
B. NaCl in benzene C. benzene in C6H14
19. Ethanol (C2H5OH) and water (H2O) are both liquids at or near room temperature. When a sample
of ethanol is poured into a beaker containing water, the two liquids are…
A. immiscible because organic and non-organic compounds cannot mix.
B. immiscible because each has strong hydrogen bonds that cannot be broken.
C. miscible because both are liquids and all liquids are miscible.
D. miscible because each can hydrogen bond with the other.
20. State what forces are broken when these substances melt.
If there is more than one, state all of them.
A. H3C N CH3
_________________________________
CH3
B. CCl4
C. HF
D. CO2 subliming
E. table salt
_________________________________
_________________________________
_________________________________
_________________________________
21. Draw three Lewis structures of ammonia (NH3) and show exactly where the hydrogen bonding is.
22. Carefully explain how a nonpolar molecule such as Br 2 can be attracted to another Br2 molecule.
Use full sentences and Lewis structures in your explanation.
23. NaCl has a molar mass of 58 g/mol and heptane (C7H16) has a molar mass of 100 g/mol. Explain
why NaCl is a solid but heptane is a liquid even though heptane is much larger. Use full sentences.
24. When an ionic compound dissolves in water the ions are surrounded by water molecules. Draw
three water molecules around each ion, showing how the water molecules would be oriented with
H O
respect to the ion. Water is to be drawn thus:
H
+
K
Br
25. NaCl has a molar mass of 58 g/mol and heptane (C7H16) has a molar mass of 100 g/mol. Explain
why NaCl is a solid but heptane is a liquid even though heptane is much larger. Use full sentences.
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26. Give the molecular formula of the following:
O
O
HO
A
B
C
What type of intermolecular forces would you expect these to exhibit?
Which is the dominant intermolecular force for each of these?
27. a) Name the type of organic molecule each of the following belongs: (hydrocarbon? alcohol? etc.)
O
OH
HO
NH2
A
B
C
b) Name the predominant intermolecular forces for each of the above.
28. Draw structures to show where the “ion-dipole force” is in an aqueous solution of KBr.
*******Below are questions pertaining to topics covered on Mon 9/15/14***********
29. What information does X-ray diffraction give us?
A. molecular weight of a substance
B. radioactivity of the substance
C. size of the atom
D. color of the substance
H vap 1
C
30. (4 pts) The Clausius equation is ln P
R
T
3
A graph is plotted for ln P versus 1/T and the slope was determined to be
K. Calculate the
heat of vaporization Hvap in units of kJ/mol. R is 8.3145 J/(K.mol)
Show your setup carefully, including units at every step.
31. Give log 3.15x10–4 to the correct sig. fig.
Ans.–3.502
ln x = 0.0785, what is x? Ans in the correct sig. fig. Ans.1.082
If your answers do not match what is provided here, please review the PowerPoint on logarithm before
you come to ask me.
32. How much heat is needed to warm 78.6g of H2O from 35 C to 130 C?
Given: Specific heat for ice = 2.108 J g–1 C–1
Specific heat for water = 4.18 J g–1 C–1
Specific heat for steam = 1.998 J g–1 C–1
Heat of fusion for H2O = 6.01 kJ/mol
Heat of vaporization for H2O = 40.67 kJ/mol
33. Which compound cannot be liquefied by compression at temperature of 25.0 °C?
A. C2H4, critical point: 9.9 °C, 50.5 atm
B. CH3Cl, critical point: 144.0 °C, 66.0 atm
C. C2H2, critical point: 35.5 °C, 61.6 atm
D. C2H6, critical point: 32.2 °C, 48.2 atm
E. SO2, critical point: 158.0 °C, 78.0 atm
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34. (2 pts) Below is the heating curve of a substance
Temp
E
D
C
B
A
Heat added
a) Which part of the graph shows the substance existing as a liquid and gas at the same time?
(CIRCLE ONE) A
B
C
D
E
b) Explain why the temperature remains constant in section B even though heat is still be added to
the system.
c). Explain in full sentences for Sections B and D on the graph, even though heat is still being added,
why the temperature does not go up. Where did all that energy go?
35. Review energetics of phases changes (as in Example 12.2 & Practice Question posted).
36. A substance has a high melting point and is brittle. Which of the following would fit this
description?
A. Zn B. Br2 C. KBr
37.
P
760 torr
Temp
Carefully label the following on the phase diagram shown above:
solid phase, liquid phase, gas phase
the critical point
the normal boiling point on the x-axis
the normal melting point on the x-axis
What happens to the melting point when the pressure is increased?
A. It is increased
B. It is decreased
For this substance, is the solid or the liquid more dense?
A. the solid
B. the liquid
What happens to the boiling point when pressure is increased?
A. It is increased
B. It is decreased
If the solid is less dense than the liquid would the melting point increase or decrease when the
pressure is increased?
A. MP increases
B. MP decreases
Review questions #38 & 39 have been removed. They will not be on Exam I.