Name:
AP Chemistry: Unit 10: Intermolecular Forces & Solubility: Homework
Date:
1. What is the strongest intermolecular force present for each of the following compounds?
a. water _____________________________________
b. carbon tetrachloride _____________________________________
c. ammonia _____________________________________
d. carbon dioxide _____________________________________
e. phosphorus trichloride _____________________________________
f.
nitrogen _____________________________________
g. ethane (C2H6) _____________________________________
h. acetone (CH2O) _____________________________________
i.
methanol (CH3OH) _____________________________________
j.
borane (BH3) _____________________________________
2. Hydrogen bonding is a significant intermolecular force and is responsible for many important chemical
and physical properties associated with life processes. Shown in Figure 1 are the boiling points for
various hydrogen compounds of the p-block elements.
Figure 1. Boiling points of compounds containing hydrogen and p-block elements.
Based on your understanding of the three intermolecular forces, Van der Waals, dipole-dipole and Hbonding, explain the following.
a. What is the molecular shape of HF, HCl, HBr and HI?
b. What is the molecular shape of H2O, H2S, H2Se, and H2Te?
c. What is the molecular shape of NH3, PH3, AsH3, and SbH3?
d. Based on your understanding of Van der Waals forces explain why there is a general increase in
the boiling points for HCl, HBr and HI.
e. Based on your understanding of Van der Waals forces explain why there is a general increase in
the boiling points for H2S, H2Se, and H2Te.
f.
Based on your understanding of Van der Waals forces explain why there is a general increase in
the boiling points for PH3, AsH3, and SbH3.
g. Why is the boiling point for water so much higher than what would be estimated based on the
periodic trend for the other group 16 compounds?
h. Why is the boiling point for ammonia so much higher than what would be estimated based on the
periodic trend for the other group 15 compounds?
i.
Why is the boiling point for HF so much higher than what would be estimated based on the
periodic trend for the other group 17 compounds?
j.
What is the ratio of lone pair to covalently bonded hydrogens in water, ammonia and hydrogen
fluoride? How does this effect the extent of the hydrogen bonding network that is possible in
these molecules? Why is the boiling point of water so much higher than either NH3 or HF?
k. Based on your understanding of dipole-dipole forces, why is the boiling point of HF higher than
NH3?
l.
Based on your understanding of intermolecular forces and molecular shape, predict the trend in
boiling points for the group 14 compounds, CH4, SiH4, GeH4, and SnH4.
m. Based on your understanding of intermolecular forces, predict the trend in boiling points for the
Noble gases, Ne, Ar, Kr, and Xe.
3. Explain why ethyl alcohol (C2H5OH) has a higher boiling point (78.40 C) than methyl alcohol (CH3OH;
64.70 C).
4. Rank the following by from lowest to highest anticipated boiling point: C2H4, CH4, Ne, H3COCH3.
5. Motor oil largely consists of molecules that consist of long chains of carbon atoms with hydrogen atoms
attached to them. Using your knowledge of intermolecular forces, why wouldn’t it be better to use a
compound like glycerol. The formula of glycerol is CHOH(CH2OH)2.
6. Using your knowledge of the “like dissolves like” principle of solubility, determine which compound will
dissolve best in each of the following problems. Explain your reason for having made this determination.
a. Liquid: methanol (CH3OH)
Compounds: carbon diselenide and oxygen dichloride
b. Liquid: carbon disulfide
Compounds: methanol (CH3OH) and lithium chloride
c. Liquid: water
Componds: carbon tetrachloride and ammonia
d. Liquid: isopropanol (C3H8O)
Compounds: water and methane
7. What is the molarity of a solution made when you dilute 35 grams of sodium carbonate to a volume of
3,400 mL?
8. If I add 45 grams of sodium chloride to 500 grams of water, what will the melting and boiling points be of
the resulting solution? Kb(H2O) = 0.52 0C/m and Kf(H2O) = 1.86 0C/m
9. What is the vapor pressure of the solution in problem #8 at 250 C? The vapor pressure of pure water at
250C is 3.17 kPa.
10. How does the energy of attraction between particles compare with their energy of motion in a gas and in a
solid? As part of your answer, identify two macroscopic properties that differ between a gas and a solid.
11. Liquid propane, a widely used fuel, is produced by compressing gaseous propane at 20°C. During the
process, approximately 15 kJ of energy is released for each mole of gas liquefied. Where does this energy
come from?
12. A liquid has a ΔHvap of 35.5 kJ/mol and a boiling point of 122°C at 1.00 atm. What is its vapor pressure at
113°C?
13. Use these data to draw a qualitative phase diagram for ethylene (C2H4). Is C2H4(s) more or less dense than
C2H4(l)? Explain.
bp at 1 atm:
-103.7°C
mp at 1 atm:
-169.16°C
Critical point: 9.9°C and 50.5 atm
Triple point:
-169.17°C and 1.20 x10-3 atm
14. Which member of each pair of compounds forms intermolecular H bonds? Draw the H-bonded structures in
each choice.
a. CH3CHCH3 or CH3SCH3
|
OH
b. HF or HBr
15. Which has the greater polarizability? Explain.
a. Br- or Ib. CH2=CH2 or CH3-CH3
c. H2O or H2Se
16. Which member in each pair of liquids has the higher vapor pressure at a given temperature? Explain.
a. C2H6 or C4Hio
b. CH3CH2OH or CH3CH2F
c. NH3 or PH3
17. Which substance has the lower boiling point? Explain.
a. LiCl or HCl
b. NH3 or PH3
c. Xe or I2
18. Small, equal-sized drops of oil, water, and mercury lie on a waxed floor. How does each liquid behave?
Explain.
19. Rank the following in order of increasing surface tension at a given temperature, and explain your
ranking:
a. CH3CH2CH2OH
b. HOCH2CH(OH)CH2OH
c. HOCH2CH2OH
20. A drooping plant can be made upright by watering the ground around it. Explain.
21. Which member of each pair is more soluble in diethyl ether, CH3CH2—O—CH2CH3? Why?
a. NaCl(s) or HCl(g)
O
||
b. H2O(l) or CH3CH(l)
c. MgBr2(s) or CH3CH2MgBr(s)
22. You are given a bottle of solid X and three aqueous solutions of X-one saturated, one unsaturated, and one
supersaturated. How would you determine which solution is which?
23. For a saturated aqueous solution of each of the following at 20°C and 1 atm, will the solubility increase,
decrease, or stay the same when the indicated change occurs?
(a) O2(g), increase P
(b) N2(g), increase V
24. Caffeine is about 10 times as soluble in hot water as in cold water. A chemist puts a hot-water extract of
caffeine into an ice bath, and some caffeine crystallizes. Is the remaining solution saturated, unsaturated, or
supersaturated? Explain.
25. Calculate the molarity of each aqueous solution:
a. 32.3 g of table sugar (C12H22011) in 100. mL of solution
b. 5.80 g of LiNO 3 in 505 mL of solution
26. How would you prepare the following aqueous solutions?
a. 365 mL of 8.55 X 10-2 M KH2PO4 from solid KH2PO4
b. 465 mL of 0.335 M NaOH from 1.25 M NaOH
27. Calculate the molality of the following:
a. A solution containing 85.4 g of glycine (NH2CH2COOH) dissolved in 1.270 kg of H2O
b. A solution containing 8.59 g of glycerol (C3H803) in 77.0 g of ethanol (C2H5OH)
28. How would you prepare the following aqueous solutions?
a. 3.10 X 102 g of 0.125 m ethylene glycol (C2H602) from ethylene glycol and water
b. 1.20 kg of 2.20 mass % HNO3 from 52.0 mass % HNO3
29. A solution consists of 0.35 mol of isopropanol (C3H7OH) dissolved in 0.85 mol of water. (a) What is the mole
fraction of isopropanol? (b) The mass percent? (c) The molality?
30. Calculate the molality, molarity, and mole fraction of NH3 in an 8.00 mass % aqueous solution (d =
0.9651 g/mL).
31. Classify the following substances as strong electrolytes, weak electrolytes, or nonelectrolytes:
a. hydrogen chloride (HC1)
b. potassium nitrate (KNO3)
c. glucose (C6H1206)
d. ammonia (NH3)
32. Which solution has the lower freezing point?
a. 11.0 g of CH3OH in 100. g of H2O or 22.0 g of CH3CH2OH in 200. g of H2O.
b. 20.0 g of H2O in 1.00 kg of CH3OH or 20.0 g of CH3CH2OH in 1.00 kg of CH3OH.
33. Rank the following aqueous solutions in order of increasing (a) osmotic pressure; (b) boiling point; (c)
freezing point; (d) vapor pressure at 50°C:
(I) 0.100 in NaNO3 (II) 0.100 m glucose (III) 0.100 in CaC12
34. An industrial chemist is studying small organic compounds for their potential use as an automobile antifreeze.
When 0.243 g of a compound is dissolved in 25.0 mL of water, the freezing point of the solution is -0.201°C.
a. Calculate the molar mass of the compound (d of water = 1.00 g/mL at the temperature of the
experiment).
b. The compositional analysis of the compound shows that it is 53.31 mass % C and 11.18 mass % H, the
remainder being O. Calculate the empirical and molecular formulas of the compound.
c. Draw two possible Lewis structures for a compound with this formula, one that forms H bonds and one that
does not.
35. A biochemical engineer isolates a bacterial gene fragment and dissolves a 10.0-mg sample of the material in
enough water to make 30.0 mL of solution. The osmotic pressure of the solution is 0.340 ton at 25°C.
a. What is the molar mass of the gene fragment?
b. If the solution density is 0.997 g/mL, how large is the freezing point depression for this solution (Kf of
water = 1.86°C/m)?