ch. 3, 4, 11, 21.3  stochiometry, solution, reactions     test                              85 points                      AP chemistry

In problems involving any calculation, 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.

1. 90.0 % HNO3 has a density of 1.5 g / mL  (https://en.wikipedia.org/wiki/Nitric_acid).  [15 points]

a. What is the mole fraction of HNO3  ?

b. What is the molality of HNO3  ?

c. What is the molarity of HNO3  ?

2. Describe how to prepare 725 mL of 125 mM potassium chloride using ___ and water.  [10 points]

a. Solid potassium chloride

b. 225 mM potassium chloride

3. A 125 mL aqueous solution of phosphoric acid (hydrogen phosphate) is titrated with 25 mL of 275 mM magnesium hydroxide.  What is the concentration of phosphoric acid prior to the addition of magnesium hydroxide ?  [10 points]

4. Write the net ionic equation for mixing aqueous solutions of  ___; if there is no net ionic reaction, write “no net ionic equation”  [15 points]

a. Sodium carbonate and hydrogen chloride

b. Lead (II) nitrate and lithium bromide

c. Potassium phosphate and barium chloride

d. Sodium hydroxide and silver acetate

e. Lithium sulfide and magnesium bromide

5. In the combustion of 10.0 gallons of octane (FYI; 3.785 L = 1.00 gallon & its density = 0.702 g / mL; which is about a full tank of gas in your car), octane reacts with excess oxygen to produce carbon dioxide and water.  [20 points]

a. Write the balanced chemical equation for this reaction

b. How many pounds of carbon dioxide is produced in the reaction ?  (FYI; 1.00 pounds = 354 grams)

c. If the reaction has a percent yield of 85%, then how much water would be produced in the reaction ?

6. Old topic:  Beer’s law lab.  What is the specific potential effect on the determination of a cobalt due to ___ ;  justify / rationalize your answer.  An aqueous solution of cobalt is a red / pink solution.   [15 points]

a.  The presence of finger prints on the cuvette ?

b. Which color of light, red, green, or blue would have the smallest absorbance ?

c.  Based on the below hypothetical calibration curve, which is the best wavelength ?   justify / rationalize.

calibration curve