Chem 162 Ready for class? Intermoecluar forces : (L) (S) and phase change
1. (a) A sample of hydrogen gas was collected in a large gas buret. The pressure in the buret was
measured as 764.2 torr, the temperature was 23.0 °C, and the buret contained 511 mL of the
collected gas. How many moles of hydrogen were collected?
(b) A sample of hydrogen gas was collected by displacement of water in a large gas buret. The total
pressure in the buret was measured as 764.2 torr, the temperature was 23.0 °C, and the buret
contained 511 mL of the collected gas. How many moles of hydrogen were collected? (At 23.0 °C, the
vapor pressure of water is 21.1 torr.)
2. A gas mixture contains 5.00 liters of a mixture of nitrogen gas and oxygen gas. The total pressure in
the tank is 38.6 atm when the temperature is 25.0 °C, and the mole fraction of oxygen is 0.400. How
much does the oxygen in the tank weigh?
3. In your own words, explain the difference between the bond polarity and molecular polarity.
4. (a) Is CO polar? Show step by step work/logic.
(b) Is CO2 polar? Show step by step work/logic.
(c) Predict the solubility of CO in CO2. Briefly explain your answer.
(d) Predict the vapor pressure of CO and CO2. Briefly explain your answer.
5. Name at least 6 intermolecular forces in increasing strength. For each, give an example of a
compound having that intermolecular force.
6. List all things that are related to polarity. For example, solubility, vapor pressure……
7.
At 1.0 atm pressure, ice (solid H2O) floats in water instead of sinking. Briefly explain this in terms
of intermolecular forces.
8.
Draw a picture (no description please!) showing/explaining
a)
vapor pressure
9.
What is the relationship between (directly, inversely, or not related)
a)
Polarity of molecule and strength of intermolecular forces
b) boiling point
b) strength of intermolecular forces and vapor pressure
c)
vapor pressure and boiling point
d)
polarizability and size of molecule
10. Which compound should have the lowest vapor pressure at a temperature at which all these
substances are in the liquid state? Briefly explain.
a.
CH3CH2F
b.
CH3CH2CH3
c.
CH3CH2CH2CH3
d.
CH3CH2OH
e.
CH3OCH3
11. Given the phase changes: condensation, freezing, fusion, sublimation, deposition, and vaporization.
Which of these phase changes is (are) endothermic?
12. Using the class handout as a guide, come up with density equation for each unit cell. For example,
for simple cubic cell, D = (mass of 1 unit cell) / (volume of 1 unit cell) = (mass of 1 atom)/(2r)^3.
(a) simple (primitive) cubic cell
(b) body centered cubic cell
(c) face centered cubic cell.
13. A new compound, vitellium oxide, has been discovered. X-ray crystallographic studies reveal that it
has a cubic unit cell with a vitellium (Vt) ion at each of the corner lattice points, a vitellium ion at the
geometric center of the unit cell, and an oxide ion in the center of each of the cube faces in the unit
cell. Based on this structure, the correct formula should be… (VtxOy) Show your work.
14. Platinum (atomic mass 195.08 g/mol) crystallizes in a face-centered cubic unit cell. In addition,
platinum has an atomic radius of 139 pm. What is the density (in g/cm3) of platinum?
15. Iron (atomic mass 55.85 g/mol) crystallizes in a body-centered cubic unit cell. If the length of an
edge of the unit cell is 287 pm, what is the density (in g/cm3) of iron?
16. Draw the sketch of phase diagram of water. Label what you think is important.
17. Draw the cooling curve for water including super cooling for water.
a) Label what you think is important.
b) 50.5g of water is cooled from 130.C to 20.0C.
i.
Show this process on the cooling curve.
ii. Calculate the amount of energy associated with this process.
18. p-Xylene, C8H10, has an enthalpy of fusion of 158.3 J g-1 and its melting point temperature is 13.2 °C.
How much heat is required to transform 115 g of solid p-xylene at 13.2 °C into liquid p-xylene, also at
13.2 °C?