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CHEM 15 SAMPLE PROBLEMS (Second Lecture Exam Coverage)
CHEMICAL BONDING
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Write Lewis dot symbols for the following: a. N and N3- , b. S and S2 , c. K and K+
Draw the Lewis structure of the ff: a. magnesium fluoride , b. lithium selenide
Draw the Lewis structure of: a. PCl3 , b. CH2Cl2 , c. HCN , d. BrO3Draw the resonance structures of: a. SO2 , b. NO3Draw the Lewis structures. Indicate the formal charges of each atom. Box the most plausible Lewis structure.a. CO2 , b. NCSWrite the Lewis Structure and assign the formal charges of each atom: a. (NH4)2CO3 , b. Ba(ClO3)2
Which bond is more polar? a. N–O or C–O, b. S–F or O–F , c. O–H or C–H
GEOMETRY AND POLARITY
1. Predict whether each of the following will be polar or non-polar. BeCl2 , BF3 , CCl4 , PCl5
2. Predict whether each of the following will be polar or non-polar. If polar show the NET molecular dipole. H2O , SO2 , NH3
3. Consider the ff. substances: SeF2 , IF3 : a. Draw the Lewis Structure, b. Identify the electron pair geometry, c. Identify the
molecular geometry, d. Identify the type of molecule, d. Polar or nonpolar?
IMFA
1. Which of the following are most likely to exist in the solid state at room temperature?
CH4
CF4
CCl4
CBr4
CI4
MP (oC)
-182
-150
-23
90
171
2. What type(s) of IMFA exist between each of the following molecules? HBr , CH4 , SO2
3. Which of the following exhibits stronger DDF? CH2O (30 g/mol) vs CH3CH3 (30 g/mol), HBr (81 g/mol) vs HCl (36 g/mol)
4. Which of the two polar molecules has a higher boiling point? ethanol or dimethyl ether
5. Which of the following exhibits stronger IMFA? HBr (81 g/mol) vs HCl (36 g/mol), HBr (81 g/mol) vs HF (20 g/mol), HF (20 g/mol) vs
CH3OH (32 g/mol), CH3OH (32 g/mol) vs CH2O (30 g/mol), CH3OH (32 g/mol) vs C6H14 (86 g/mol), CH3OH (32 g/mol) vs H2O (18 g/mol)
6. Predict the boiling points (oC) of the following substances. -70 -90 -112 -162
Molecule
CH4
SiH4
GeH4
SnH4
Estimated MM (g/mol)
16
32
77
123
7. Predict the boiling points of the following substances. -83 -67 -40 20
Molecule
HF
HCl
HBr
HI
Estimated MM (g/mol)
20
36
81
128
8. Rank the substances from strongest to weakest interparticle forces: a) He, NH3, NF3, NaCl b) HF, F2, NaF
GASES
1. A gas occupies a volume of 500 mL at a pressure of 760 torr. What will be its pressure if its volume is reduced to 450 mL?
2. A sample of gas occupies 12 L under a pressure of 1.2 atm. What would its volume be if the pressure were increased to 3.0
atm?
3. A 10.0 mL sample at 25 oC is cooled at constant pressure to 0 oC. What is its new volume?
4. A sample of He is at 760 torr when its volume is 200 mL at 35.0 oC. What must its temperature be if its pressure becomes 740
torr and its volume 300 mL?
5. What will 17.5 g N2 occupy at STP?
6. A sample of chlorine gas is confined in a 5.0-L container at 228 torr and 27 oC. How many moles of gas are in the sample?
7. Calculate the density (in g/L) of NH3 at 752 mmHg and 55.0 oC.
8. A chemical engineer uses waste CO2 from a manufacturing process as a “blowing agent” in the production of polystyrene
containers. Find the density (in g/L) of CO2 and the number of molecules per liter at 20 oC and 0.985 atm.
9. When an evacuated 63.8 mL glass bulb is filled with gas at 22 oC & 747 mmHg, the bulb gains 0.103 g in mass. Is the gas N2,
Ne or Ar?
10. What is the total pressure of a gaseous mixture containing 1.00 g He, 2.00 g H2 & 3.00 g N2 in a 10.0 L container at 300 K?
11. A 355-mL container holds 0.146 g of Ne and an unknown amount of Ar at 35 oC and a total pressure of 626 mmHg.
Calculate the moles of Ar present.
12. Calculate the ratio of the effusion rates of helium and methane (CH4).
13. If it takes 1.25 min. for 0.010 mol of He to effuse, how long will it take for the same amount of ethane (C2H6) to effuse?
MDBAldemita
CHEM 15 Sample Problems
LE2 coverage (page 1 of 1)