Part II Semester Exam Practice

A.P. CHEMISTRY Part II Semester Exam Practice

Part A Problem Solving

CLEARLY SHOW THE METHOD USED AND THE STEPS INVOLVED IN ARRIVING AT YOUR ANSWERS. It is to your advantage to do this, since you may obtain partial credit if you do and you will receive little or no credit if you do not. Attention should be paid to significant figures.

Be sure to write all your answers to the questions on your answer sheet. Do NOT write your answers on the test.

1. 115.0 mL of 0.500 M hydrochloric acid reacts with 42.0 g of magnesium metal.

(a). Write a complete balanced equation for the reaction.

(b). Calculate the number of moles of each reactant.

(c). Find the limiting reactant and calculate the amount in grams of each of the products involved in the reaction.

(d). Assuming STP, calculate the volume of hydrogen gas produced from the reaction.

(e). How does the produced volume of hydrogen change at 1000 mm Hg of pressure and 20 degrees centigrade?

2. An unknown compound is composed of carbon, hydrogen, and oxygen in the following percentages: C - 57.8% H - 3.65% and O - 38.5%

(a). Find the empirical formula of the compound.

(b). The change in the freezing point of a solution with the unknown compound in benzene is 4.14oC. What is the molecular mass when 6.73 g of the unknown is

dissolved in 50.0 g of benzene. (kf for benzene is 5.10).

(c). What is the mole fraction of benzene, C6H6?

(d). The vapor pressure of benzene is 25.6 mm Hg at a certain temperature. What is the vapor pressure of the solution?

. 3. CuSO4 x H2O A 0.755g sample of hydrated copper (II) sulfate xhydrate was heated carefully until it had change completely to anhydrous copper (II) sulfate (CuSO4) with a mass of 0.483 g. Determine the value of x. 4. Using the bond energies given, estimate the enthalpy, ∆H, for the following reaction:

N2 + 3 H2 ----> 2 NH3 N-N 163 H-H 436 Units: kJ/mol N=N 418 N-H 391 N=N 941

5. A 1.37 M solution of citric acid in water has a density of 1.10 g/cm3. Calculate the mass percent,

molality, and mole fraction of the citric acid. Citric acid is H3C6H5O7.

Part B Reactions and Essay NO CALCULATORS MAY BE USED IN THIS SECTION

Question 4 REACTIONS: For each of the following three reactions, in part I write a balanced equation and in part II answer the question about the reaction. In part I, coefficients should be in terms of lowest whole numbers. Represent substances in solution as ions if the substance is extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction.

Example: A strip of magnesium is added to a solution of silver nitrate I. Mg + 2 Ag+  Mg2+ + 2 Ag II. Which substance is oxidized in the reaction? Ans. Magnesium (Mg) metal is oxidized to Mg2+.

(a) A strip of zinc is placed in a solution of nickel (II) nitrate. Identify the spectator ion(s) in this reaction.

(b) Solid aluminum hydroxide is added to a concentrated solution of potassium hydroxide. Give the correct name for the product in this reaction.

(c) Ethyne is burned in air. How many molecules of product is formed when 4 molecules of ethyne react?

(d) Solid calcium carbonate is added to a solution of ethanoic (acetic) acid. Describe the result expected when the gas is tested using a glowing splint

(e) An acidified solution of potassium permanganate is added to sodium oxalate. What is the oxidation number of manganese before and after the reaction?

(f) Boron trifluoride gas is added to ammonia gas. Which substance acts as the Lewis acid in the reaction? Explain

(g) Sulfur trioxide gas is bubbled into a solution of sodium hydroxide. Describe the change in pH of the solution as the sulfur trioxide is added.

(h) Equal volumes of 0.1 M solutions of lead (II) nitrate and magnesium iodide are combined. 5. Answer the following questions that relate to laboratory observations and procedures.

(a) An unknown gas is one of three possible gases: nitrogen, hydrogen, or oxygen. For each of the three possibilities, describe the result expected when the gas is tested using a glowing splint (a wooden stick with one end that has been ignited and extinguished, but still contains hot, glowing, partially burned wood).

(b) The following three mixtures have been prepared: CaO plus water, SiO2 plus water, and CO2 plus water. For each mixture, predict whether the pH is less than 7 (acidic), equal to 7 (neutral), or greater than 7 (basic). Justify your answers.

(c) Each of three bakers contains a 0.10 M solution of one of the following solutes: potassium chloride, silver nitrate, or sodium sulfide. The three beakers are labeled randomly as solution 1, solution 2, and solution 3. Shown below is a partially completed table of observations made of the results of combining small amounts of different pairs of the solutions.

Solution 1 Solution 2 Solution 3

black Solution 1 precipitate Solution 2 no reaction Solution 3

(i) Write the chemical formula of the black precipitate. (ii) Describe the expected results of mixing solution 1 with solution 3. (iii) Identify each of the solution 1, 2, and 3.

- + GeCl4 SeCl4 ICl4 ICl4

6. The species represented above all have the same number of chlorine atoms attached to the central atom. (a) Draw the Lewis structure for each of the four species. Show all valence electrons in your structure.

(b) On the basis of the Lewis structures drawn in part (a), answer the following questions about the particular species indicated.

(i) What is the Cl-Ge-Cl bond angle in GeCl4? (ii) Is SeCl4 polar? Explain. - (iii) What is the hybridization of the I atom in ICl4 ? + (iv) What is the geometric shape formed by the atoms in ICl4 ?

7. Account for each of the following observations in terms of atomic theory and/or quantum theory.

(a) Atomic size decreases from Na to Cl in the periodic table.

(b) Boron commonly forms molecules of the type BX3. These molecules have a trigonal planar structure. (c) The first ionization energy of K is less than that of Na. (d) Each element displays a unique gas-phase emission spectrum.