Ch. 4 & 13 solution test (75 points) AP Chem

Show you work in an organized manner, include any relevant equation / formula used, proper units in your work / answer, and the proper number of significant figures in your answer.


1. Experimental design: determination of the molar mass of a compound. [HW problem; solution 2000; 15 points]

a. list the experimental measurements (not calculations) to determine the molar mass of a nonvolatile nonelectrolyte using freezing point depression.

b. describe the data analysis (i.e. show equations) using the above information.

c. what is the effect on the determination of the compound’s molar mass if the solvent is volatile (i.e. some of the solvent evaporated) ? Justify your response.

2. The formula and the molecular weight of an unknown hydrocarbon compound are to be determined by elemental analysis and the freezing-point depression method. [HW problem; solution 1985; 25 points]

(a) The hydrocarbon is found to contain 93.46 percent carbon and 6.54 percent hydrogen. Calculate the empirical formula of the unknown hydrocarbon.

(b) A solution is prepared by dissolving 2.53 grams of p-dichlorobenzene (molecular weight 147.0) in 25.86 grams of naphthalene (molecular weight 128.2). Calculate the molality of the p-dichlorobenzene solution.

(c) The freezing point of pure naphthalene is determined to be 80.2 °C. The solution prepared in (b) is found to have an initial freezing point of 75.7 °C. Calculate the molal freezing-point depression constant of naphthalene.

(d) A solution of 2.42 grams of the unknown hydrocarbon dissolved in 26.7 grams of naphthalene is found to freeze initially at 76.2 °C. 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?

3. A solution of 80.5 g of vitamin C (C 6H 8O 6) in 210. g of water has a density of 1.22 g / mL. Calculate ___ of vitamin C in the solution. [HW problem; ch. 13.21; 20 points]

a. mass percent

b. mole fraction

c. molality

d. molarity

4. For each of the following reactions, in part (i) write the BALANCED equation and in part (ii) answer the question about the reaction. Coefficients should be in terms of lowest whole numbers. Assume that solutions are aqueous unless otherwise indicated. Represent substances in solutions as ions if the substances are extensively ionized. [15 points]

a. mix solutions of calcium fluoride and lithium phosphate

ii. how many moles of the product would be formed by mixing 5 moles of calcium fluoride and 5 moles of lithium phosphate ?

b. sodium metal is added to water

ii. what is / are the chemical name(s) of the product(s) in the above reaction ?

c. add zinc metal to a solution of concentrated ammonia

ii. identify the Lewis acid in the above reaction