Ch. 3, 4 & 13  stochiometry & solution                       test  [100 points]                                 AP chemistry

Show your work in an organized manner, include (i) any relevant equation (or formula), (ii) conversion factor(s), (iii) put the proper units in your calculations and answer, and (iv) have the proper number of significant figures in your answer. 

Academic Honesty:   The answers on this test are my own and I am using only the allowed set of notes as described in the syllabus.  I have not discussed the test questions with anyone before or during the test nor have I seen the test questions prior to the exam.  If you violate any of the preceding items or do not sign, your semester grade is a F.

                                                                                                Signature:  ___________________

1. 2.78 mg of a hypothetical (?) compound containing carbon, hydrogen, and oxygen was burned in air and generated 6.32 mg of carbon dioxide and 2.58 mg of water.  1.0 g of the compound was dissolved in 25.0 g of benzene; the solution’s freezing point is 6.677 ºC.  The Kb and Kf of benzene is 2.53 ºC / m and 5.12 ºC /  m, respectively.  The boiling and freezing point of benzene is 80.1 ºC and 5.5 ºC . respectively.   [30 points]

a.  What is the molecule’s empirical formula ?

b. What is the compound’s molar mass ?

c.  What is the compound’s chemical formula ?


2.  List the following aqueous solution in order of increasing freezing point:  0.040 m glucose, 0.021 m potassium bromide, and 0.030 m adenosine triphosphate (ATP).  Justify your answer.  [10 points]

3.  The osmolarity of a solution is the number of moles of solute particles per liter of solution.

An isosmotic solution has the same osmolarity as the inside of a cell. 

An isotonic solution would not change the volume of a cell. 

An isosmotic solution of urea is not an isotonic solution to red blood cells, but an isosmotic solution of urea is an isotonic solution for cells in the distal nephron (it’s cells in the kidney). 

Actually, red blood cells would swell / burse in an isosmotic solution of urea. 

Resolve the apparent contradiction; hints:  (i) there’s a difference in urea permeability in these two types of cells, and for simplicity, assume that (ii) the intracellular concentration of urea in both types of cells is zero, and (iii) the intracellular volume (i.e. volume inside of a cell) is much less than the extracellular volume (i.e. volume outside of a cell).  [10 points]

4.  Describe the basis of decompression disease or the bends, which occurs when a diver rapidly returns to the surface.  [15 points]

5. An ionic compound from the below list of possible ionic compounds

BaCl2

CuCl2

Na2CO3

Ba(OH)2

Cu(NO3)2

NaI

 

CuSO4

NaOH

 

 

Na2SO4

is to be identify based on the results of experiments, where the below ionic compounds

are added to the unknown ionic compound.  Design an experiment to confirm that the ionic compound is NaSO4 based on the preceding information, your knowledge of the solubility rules of ionic compounds, and physical properties of the above aqueous solutions, e.g. its color.  There may be more than one correct answer.  [20 points]

6. In a redox titration experiment in the AP biology class used KMnO4 to measure the concentration of hydrogen peroxide; the reaction: 

5 H2O2 +  2 MnO4 -  +  6 H + -->  2 Mn2+  +  5 O2  +  8 H2O. 

KMnO4 was added to the hydrogen peroxide solution, where the color of an aqueous solution of KMnO4 and hydrogen peroxide is purple and colorless, respectively.  As such, as long as there is some hydrogen peroxide in the solution, the solution will remain colorless due to the addition of KMnO4, but once the hydrogen peroxide is gone, the addition of KMnO4 will change the solution’s color to purple; this color change determines the end point.  If it takes 18.0 mL of a 0.125 M KMnO4 solution to reach the end point in titrating a 25.0 mL solution of hydrogen peroxide, what is the concentration of hydrogen peroxide (before the addition of any KMnO4) ?  [15 points]