Practice Exam AP Chemistry Midterm 1st 9 weeks Section I - Multiple Choice (50%)

Directions: Each set of lettered choices below refers to the numbered statements immediately following it. Select the one lettered choice that best fits each statement and then blacken the corresponding space on the Scantron. A choice may be once, more than once, or not at all in each set. You must choose 40 out of 50, leave 10 blank. Wrong answers have a 0.25 point penalty, so no guessing! Questions 1-3 A. phosphorus B. beryllium C. sodium D. magnesium E. sulfur 1. Which of the above is a chalcogen? 2. Which of the above has a nonmetal with an oxidation number of +6? 3. Which of the above forms salts that are all soluble in water? Questions 4-6

A. CrO4-2

B. SO3-2 C. H+ D. SO4-2

E. Mn+2

4. In a reaction between potassium chromate and sodium sulfite in acidified

solution, which of the above will serve as the oxidizing agent? 5. Which of the above is added to the reactants side to denote that the reaction is

occurring in acidic solution? 6. Forms a yellow color in solution

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Questions 7-10 A. HNO3 N2O5 + H2O

B. Zn + CuSO4 Cu + ZnSO4 C. 2NH4Cl + Ca3(PO4)2 (NH4)3PO4 + CaCl2 D. 2C2H2 + 5O2 4CO2 + 2H2O E. Pb+2 + 2I-1 PbI2 7. Is an example of a single displacement. 8. Is an example of a combustion reaction 9. Is an example of a precipitation reaction. 10. Is a example of a metathesis reaction. 11. The value of the acid-dissociation constant, Ka, for a acetic acid is 2 x 10-5. The

pH of a 0.20M acetic acid solution is closest to? A. 2-3 B. 4-5 C. 5-6 D. neutral E. above 7 12. Carbon dioxide and water are products of this type of reaction: A. synthesis B. single displacement C. metallic chlorate decomposition D. double displacement E. combustion 13. Sodium sulfate reacts with barium chloride to form the insoluble compound: A. chlorine B. water C. potassium nitrate D. sodium chloride E. barium sulfate 14. Which of the following does NOT behave as an electrolyte when it is dissolved

in water: A. CH3CH2OH B. Na2CO3 C. NH4Br D. CH3COOH E. HBr

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15. Which of the following will NOT decompose into an acid anhydride and water: A. H2CO3 B. NaHCO3 C. H2SO3 D. H3PO4 E. HNO3 16. Potassium reacts with an element to form a compound with the general

formula K3X. What would the most likely formula be for the compound formed between the aluminum and element X?

A. K2X B. KX2 C. K3X2 D. K2X3 E. KX 17. Which electro negativity is probable for an alkali metal? A. 1.0 B. 2.0 C. 3.0 D. 4.0 E. 5.0 18. Which of the following describes a chemical property?

A. Sodium chloride crystals are brittle. B. Phosphine combines explosively with oxygen. C. Copper(II) sulfate forms blue crystals. D. Purification of alcohol by distillation. E. Mercury is a liquid at room temperature. 19. For the radioisotope Hydrogen-3, tritium, give the A, Z, protons, neutrons and

electrons in order: A. 0,2,1,1 B. 1,1,2,2 C. 1,1,2,0 D. 1,2,0,1 E. 2,1,0,1 20. The geometrical arrangement of atoms in the sulfate ion is A. Tetrahedral B. Trigonal planar C. Bent 1 D. Bent 2 E. Trigonal pyramidal 21. A flask contains 1.0 gram of methane, 1.0 gram of oxygen, and 1.0 gram of

sulfur dioxide. The partial pressure of methane is 0.50 atm. What is the total pressure in the flask?

A. 3.5 atm B. 1.5 atm C. 1.2 atm D. 0.88 atm E. 0.44 atm 22. 20.0 grams of sodium hydroxide are dissolved in enough water to make 2.00

liters of solution? What is the molarity of the solution? A. 0.125 B. 0.250 C. 0.750 D. 1.00 E. 2.00 23. What is the maximum quantity of water that can be made from a mixture of

10.0 g hydrogen and 16.0 g of oxygen? A. 9.00 B. 10.0 C. 18.0 D. 36.0 E. 74.0

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24. Elements M and fluorine react to form two different compounds. IN the first

reaction0.490 g of M reacts with 1.000 g of fluorine. In the second 0.55 g of M reacts with 1.000 g of fluorine. Which are possible formulas for the two compounds?

25. What is the molarity of chloride ion, in 100.0 mL of a 0.500 M barium chloride

solution? A. 0.050 B. 0.100 M C. 0.250 M D. 0.500 M E. 1.00 M 26. Which of the following experimental procedures is used to separate two

substances by taking advantage of their differing solubilities? A. distillation B. filtration C. decantation D. crystallization E. precipitation 27. Which element reacts most readily with chlorine? A. lithium B. carbon C. nitrogen D. iodine E. Neon 28. Within a family or group in the Periodic Chart, metallic character generally A. increases with increasing atomic number B. decreases with increasing atomic umber C. shows no trend with increasing atomic number D. increases with increasing ionization energy E. none of the above

First compound Second compound A. MF M2F2 B. MF2 MF C. MF2 M2F3 D. M2F MF2 E. M2F3 M3F

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29. Consider 210Po+2. How many protons, neutrons, and electrons does this ion have?

A. 84 protons, 126 neutrons, 82 electrons B. 84 electrons, 84 protons, 126 neutrons C. 84 neutrons, 126 protons, 82 electrons D. 84 neutrons, 84 electrons, 126 protons E. 84 electrons, 126 neutrons, 82 protons 30. The apparatus below is used for which method of physical separation: A. decantation B. extraction C. distillation D. filtration E. chromatography 31. The diagram below is an illustration of which scientist’s work: A. Thompson B. Lavoisier C. Rutherford D. Milliken E. Dalton

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32. Club soda is a(n) A. homogeneous mixture D. pure substance B. heterogeneous mixture E. element C. compound 33. Which of the following has the highest vapor pressure? A. silver acetate B. aluminum phosphate C. magnesium iodide D. sodium dichromate E. zinc carbonate 34. The oxidation number of the phosphorus atom in the phosphate ion is: A. +1 B. +3 C. +5 D. -3 E. -1 35. How many grams of calcium nitrate contains 24 grams of oxygen atoms: A. (24) (164) B. (6) (164) (24) C. (24) (16) (5) () (16) (16) 164 D. (164) (6) (16) E. (24) (164) (6) (16) 36. The molar mass is determined by dissolving 5.00 g of a compound in 50.0 g of

benzene. The freezing point was lowered by 2.5oC. The freezing point constant, Kf, for benzene is 5.0oC/m. What is the molar mass of the compound?

A. 20.0 B. 50.0 C. 100.0 D. 150.0 E. 200.0 37. What is the formula of a compound formed by combining 50.0 grams of

element X (atomic mass = 100.0) and 32.0 grams of oxygen gas? A. XO2 B. XO4 C. X4O D. X2O E. XO 38. Element Q occurs in compounds X, Y, and Z. The mass of element Q in one

mole of each compound is as follows: Compound Grams of Q in compound X 38.00 Y 95.00 Z 133.00 Element Q is mostly likely: A. N B. O C. F D. Ir E. Cs

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39. Which of the following does NOT show hydrogen bonding? A. Ammonia, NH3 B. Hydrazine, N2H4 C. Hydrogen peroxide, H2O2 D. Dimethyl ether, CH3OCH3 E. Methyl alcohol or methanol, CH3OH 40. An oxide is known to have the formula X2O7 and to contain 76.8% X by mass.

Which of the following would you use to determine the atomic mass of X?

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41. The volume of a liquid is to be measured. Which of the following cylindrical

flasks would take the most accurate measurement? A. A flask with 1 mL graduations and a diameter of 1 cm B. A flask with 1 mL graduations and a diameter of 3 cm. C. A flask with 5 mL graduations and a diameter of 1 cm. D. A flask with 5 mL graduations and a diameter of 3 cm. E. A flask with 10 mL graduations and a diameter of 1 cm. 42. The empirical formula of a compound is CH2 and its molecular mass is 70. What is the molecular formula of the compound? A. C2H2 B. C2H4 C. C4H10 D. C5H10 E. C6H10

43. 2 H2O + 4 MnO4– + 3 ClO2– ® 4 MnO2 + 3 ClO4– + 4 OH–

Which species acts as an oxidizing agent in the reaction represented above?

A. H2O B. ClO4– C. ClO2– D. MnO2 E. MnO4–

44. When an aqueous solution of NaOH is added to an aqueous solution of potassium dichromate, K2Cr2O7, the dichromate ion is converted to

A. CrO42– B. CrO2 C. Cr3+ D. Cr2O3 E. Cr(OH)3

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45. Which of the following has the lowest conductivity? A. 0.1 M Copper (II) sulfate B. 0.1 M potassium hydroxide C. 0.1 M Barium chloride, D. 0.1 M hydrofluoric acid E. 0.1 M nitric acid

46. To determine the molar mass of a solid monoprotic acid, a student titrated a weighed sample of the acid with standardized aqueous sodium hydroxide. Which of the following could explain why the student obtained a molar mass that was too large? I. Failure to rinse all acid from the weighing paper into the titration vessel II. Addition of more water than was needed to dissolve the acid III. Addition of some base beyond the equivalence point A. I only B. III only C. I and II only D. II and III only E. I, II, and III

47. The molecular formula for hydrated iron III) oxide, or rust, is generally written as

Fe2O3 . xH2O because the water content in the hydrate can vary. If a 1 molar sample of hydrated iron (() oxide is found to contain 108 g of water, what is the molecular formula for the sample?

A. Fe2O3 . H2O B. Fe2O3 . 3H2O C. Fe2O3 . 6H2O D. Fe2O3 . 10H2O

E. Fe2O3 . 12H2O 48. If 16.0 g of methane reacts with 16.0 g of oxygen gas. Which of the following

will be true? A. The mass of water formed will be twice the mass of carbon dioxide formed. B. Equal masses of water and carbon dioxide will be formed. C. Equal umbers of moles of water and carbon dioxide will be formed. D. The limiting reagent will be methane. E. The limiting reagent will be oxygen.

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49. How many grams of carbon are present in 270 g of glucose? A. 12.0 g B. 18.0g C. 67.5 g D. 72.0 g E. 108 g 50. The concentration of sodium chloride in the ocean is about 0.50 molar. How

many grams of sodium chloride are present in 1 kg of sea water. A. 30 g B. 60 g C. 100 g D. 300 g E. 600 g

STOP

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AP Chemistry Midterm 1st Nine Weeks Section II - Free Response (50%)

PART A - Calculator allowed. (30 points: 10 points each problem)

THE METHOD USED AND THE STEPS INVOLVED IN ARRIVING AT YOUR ANSWERS MUST BE SHOWN CLEARLY. 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. 1. Answer the following questions relating to gravimetric analysis In the first of two experiments, a student is assigned the task of determining the umber of moles of

water in one mole of a magnesium hydrate. The student collects the data shown in the following table:

Mass of empty container 22.347 g Initial mass of sample and container 25.825 g Mass of sample and container after first heating 23.982 g Mass of sample and container after second heating 23.976 g Mass of sample and container after third heating 23.977 g a. Explain why the student can correctly conclude that the hydrate was heated a sufficient

number of times in the experiment. b. Use the data above to i. calculate the total number of moles of water lost when the sample was heated, and, ii. determine the formula of the hydrated compound. c. Annie heats the hydrate in an uncovered crucible, ad some of the solid spatters out of the

crucible. This spattering will have what effect on the calculated mass of the water lost by the hydrate? Explain.

Anita conducts a second experiment, and is given 2.94 g of a mixture containing anhydrous magnesium chloride and potassium nitrate. To determine the percentage by mass of magnesium chloride in the mixture she uses excess silver nitrate to precipitate the chloride ion as silver chloride. d. Starting with 2.94 g sample of the mixture dissolved in water, briefly describe the steps

necessary to quantitatively determine the mass of the silver chloride precipitate. e. Anita determines the mass of the silver chloride precipitate to be 5.48 g. On the basis of this

information, calculate each of the following. i. The number of moles of magnesium chloride in the original mixture. ii. The percent by mass of magnesium chloride in the original mixture

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2. The molecular formula of a hydrocarbon is to be determined by analyzing its combustion products and investigating its ideal gas law properties.

(a) The hydrocarbon burns completely, producing 7.2 grams of water and 7.2 liters of carbon dioxide at standard conditions. What is the empirical formula of the hydrocarbon?

(b) Calculate the mass in grams of oxygen required for the complete combustion of the sample of the hydrocarbon described in (a).

(c) The hydrocarbon dissolves readily in chloroform, CHCl3. The freezing point of a solution prepared by mixing 100. grams of chloroform, and 0.600 gram of the hydrocarbon is -64.0˚C. The molal freezing-point depression constant of chloroform is 4.68˚C/molal and its normal freezing point is -63.5˚C. Calculate the molecular weight of the hydrocarbon.

(d) What is the molecular formula of the hydrocarbon?

2 HCOONa + H2SO4 2 CO + 2 H2O + Na2SO4

3. A 0.964 gram sample of a mixture of sodium formate and sodium chloride is

analyzed by adding sulfuric acid. The equation for the reaction for sodium formate with sulfuric acid is shown above. The carbon monoxide formed measures 242 milliliters when collected over water at 752 Torr and 22.0˚C. Calculate the per-centage of sodium formate in the original mixture.

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PART B - No calculator (20 points total)

For each of the following three reactions, first (a) write a balanced equation for the reaction and in part (b) answer the question about the reaction. Initially the coefficients should be in terms of the lowest whole numbers. Assume that solutions are aqueous unless otherwise indicated. Represent substances in solutions as ions if the substances are extensively ionized. Omit formulas for any ions or molecules that are unchanged by the reaction. Box each answer. (6 points)

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? Answer: Magnesium (Mg) metal

1. (i) A solution of tin(II) nitrate is added to a solution of potassium permanganate.

(ii) Which species is the oxidizing agent? How many total electrons are lost in the complete reaction?

2. (i) solid sodium oxide is added to water (ii) How would one test the identity of the product, what would be observed? 3. (i) A solution of hydrogen peroxide is catalytically decomposed

(ii) What is the function of the catalyst?

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Your responses to the rest of the questions in this part of the exam will be graded on the basis of the accuracy and relevance of the information cited. Explanations should be clear and well organized. Examples and equations may be included in your responses where appropriate. Specific answers are preferable to broad, diffuse responses. (each question is worth 7 points) 4. CF4 XeF4 ClF3

(a) Draw a Lewis electron–dot structure for each of the molecules above and identify the shape of each.

(b) Use the valence shell electron–pair repulsion (VSEPR) model to explain the

geometry of each of these molecules. (c) Describe the polarity of each and explain your reasoning. Define dipole

moment. 5. Use the details of modern atomic theory to explain each of the following

experimental observations.

(a) Within a family such as the alkali metals, the ionic radius increases as the atomic number increases.

(b) The radius of the chlorine atom is smaller than the radius of the chloride ion, Cl-. (Radii : Cl atom = 0.99Å; Cl- ion = 1.81Å)

(c) The first ionization energy of aluminum is lower than the first ionization energy of magnesium.

(First ionization energies: 12Mg = 7.6 ev; 13Al = 6.0 ev)

(d) For magnesium, the difference between the second and third ionization energies is much larger than the difference between the first and second ionization energies.

(Ionization energies for Mg: 1st = 7.6 ev; 2nd = 14 ev; 3rd = 80 ev)