Download chemistry log: solutions

Learning Log -Solutions-2010/11
I. PROBLEMS: Solve the following problems. Show all work
concentration problems (31, 35a , 37a)
vapor pressure (47)
freezing and boiling points (51)
Molar Mass from osmotic pressure (61)
Molar Mass by freezing point depression(59)
II. CONCEPTS: Explain the following concepts and give an example
a). Solution Process-- explain the solute-solvent interactions that cause polar and ionic
solutes to dissolve in a polar solvent like water and nonpolar solutes to dissolve in nonpolar
solvents like CCl4. Answer question 3
b) What happens to the following colligative properties of a liquid when a non-volatile
solute is added:
1) vapor pressure
3) freezing point
2) boiling point
4) osmotic pressure
PROBLEM: The formula and the molecular weight of an unknown hydrocarbon compound are
to be determined by elemental analysis and the freezing point depression method.
a) The hydrocarbon is found to contain 93.46 % carbon and 6.54 % hydrogen. Calculate
the empirical formula of the unknown hydrocarbon.
b) A solution is prepared by dissolving 2.53 grams of p-dichlorbenzene (MM=147.0) in
25.86 g of naphthalene (MM = 128.2) . Calculate the molality of the p-dichlorobenzene solution.
c) The freezing point of pure naphthalene is determined to be 80.2oC The solution
prepared in “b” is found to have an initial freezing point of 75.7oC. Calculate the molal freezing
point constant of naphthalene.
d) A solution of 2.43 grams of the unknown hydrocarbon is dissolved in 26.7 g of
naphthalene is found to have an initial freezing point of 75.7oC. Calculate the apparent
molecular weight of the unknown hydrocarbon on the basis of the freezing point depression
experiment above.
e) What is the molecular formula of the unknown hydrocarbon?