THE UNIVERSITY OF THE SOUTH PACIFIC SEMESTER 1 EXAMINATION 2009 CHP02 PRELIMINARY CHEMISTRY A

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1 THE UNIVERSITY OF THE SOUTH PACIFIC SEMESTER 1 EXAMINATION 2009 CHP02 PRELIMINARY CHEMISTRY A INSTRUCTIONS TO CANDIDATES Time Allowed: 3 hours plus 10 minutes reading time. Total Marks: There are three sections in this paper. All sections are compulsory. 2. Answer ALL questions in blue or black ink. 3. Section A is worth 20 marks, Section B is worth 30 marks, and Section C is worth 50 marks. 4. Section A consists of 20 multiple-choice questions. Circle the letter that represents the best answer to each question on the answer grid provided. 5. Sections B and C consists of numerical type questions requiring calculations. Write your answers in the spaces provided on the question paper. If you need additional space, use the facing page. 6. Show all working clearly. Marks will be allocated on the basis of logical working. 7. Calculators are permitted, provided they are not programmed before the start of the examination. 8. Periodic Table and Fundamental Constants are provided at the end of this paper. 9. You are required to fill in your details below. STUDENT NAME: STUDENT ID. NO: CAMPUS:

2 Section A Multiple Choice (20 marks) There are 20 multiple-choice questions. Circle the letter that represents the best answer in the answer grid provided. Each question is worth 1 mark. 1. What is the first step of the scientific method? A. Propose a hypothesis B. Develop a theory C. Establish a law D. Make reproducible observations 2. While performing an experiment in lab, a student records a physical measurement 4.45 in the lab notebook. This value is best described as A. highly precise B. accurate C. meaningless D. imprecise 3. Which of the following numbers has the fewest number of significant figures? A B C D Which one of the following corresponds to the greatest mass? A x 10 2 g B kg C. 500 g D. 6.5 x 10 2 mg 5. Which individual is credited with developing the atomic theory? A. Democritus B. Aristotle C. Dalton D. Rutherford 6. Which one of the following does not naturally exist as a diatomic molecule? A. Helium B. Hydrogen C. Nitrogen D. Flourine 2

3 7. Which one of the following statements does not characterize all gases? A. They are invisible. B. They have neither a definite shape nor a definite volume. C. They completely fill the container in which they are placed. D. Their fundamental particles move independently of one another. 8. A freshly opened can of soda poured over ice is classified as substance A. a pure B. a homogeneous C. an elemental D. a heterogeneous 9. How many elements are there in the 6 th period of the periodic table? A. 2 B. 18 C. 32 D Which of the following is not a match? A. 2 PO 4, phosphite ion B. OH -, hydroxide ion C. 2 CrO 4, chromate ion D. ClO, chlorate ion Having one mole of carbon dioxide means that you have A x moles of carbon. B x atoms of oxygen. C x molecules of carbon dioxide. D x molecules of carbon. 12. Which one of the following is not a major point of the kinetic molecular theory? A. Temperature of a gas is proportional to its average kinetic energy. B. Gas molecules exhibit negligible intermolecular forces. C. Gases completely fill the container they occupy. D. Gas molecules are in rapid, random motion. 13. Gases mix rapidly and thoroughly due to A. the low density of gases. B. the rapid and random motion of the molecules. C. the small nature of the molecular species. D. the temperature dependence of gas molecules. 3

4 14. Arrange the following four gases in order of increasing average velocity, assuming they all exist at the same temperature: Kr, Cl 2, N 2 O, SO 3 A. Kr < Cl 2 < N 2 O < SO 3 B. Cl 2 < N 2 O < Kr < SO 3 C. N 2 O < Cl 2 < SO 3 < Kr D. Kr < SO 3 < N 2 O < Cl As one descends from the top of a mountain, A. the atmospheric pressure increases. B. the atmospheric pressure decreases. C. the atmospheric pressure increases, then decreases. D. the atmospheric pressure remains constant. 16. What volume does a gas occupy if 2.5 moles exert a pressure of 977 torr at 32 0 C? A. 49 dm 3 B. 6.7 cm 3 C. 5.1 dm 3 D. 64 cm Which one of the following materials would not be classified as an amorphous solid? A. A glass window B. Bicycle tire C. A sandwich plastic bag D. Table salt 18. The reason that metals are good conductors of electricity is that A. they have more electrons than nonmetals. B. they have a higher number of negative charges. C. their valence electrons are free to move about the crystal lattice. D. they have fewer electrons than nonmetals. 19. At the equilibrium vapor pressure of an enclosed liquid, A. the rate of condensation > the rate of evaporation B. the rate of condensation = the rate of evaporation C. the rate of condensation < the rate of evaporation D. no molecules either evaporate or condense 4

5 20. A liquid with a higher equilibrium vapor pressure than another liquid can be attributed to A. weaker intermolecular forces. B. a larger density. C. a higher surface tension. D. a higher boiling point. 5

6 SECTION A: Multiple Choice (20 marks) ANSWER SHEET Circle the letter in the answer grid that represents the best answer to each question. 1 A B C D 2 A B C D 3 A B C D 4 A B C D 5 A B C D 6 A B C D 7 A B C D 8 A B C D 9 A B C D 10 A B C D 11 A B C D 12 A B C D 13 A B C D 14 A B C D 15 A B C D 16 A B C D 17 A B C D 18 A B C D 19 A B C D 20 A B C D 6

7 Section B Short Answer Questions (30 marks) There are 10 questions. Each question is worth 3 marks. 1) (a) Students in different class sections attempted to measure the mass of a g object. Describe the series of measurements as precise, precise and accurate, or neither. (1½ marks) Class 1: 94.2 g, 93.8 g, 94.4 g, 94.0 g Class 2: 94.3 g, 89.7 g, g, 97.8 g Class 3: g, g, 99.8 g, 99.8 g (b) Round off each of the following numbers to the number of significant figures indicated in brackets. (1½ marks) (i) 115 (2) (ii) (3) (iii) 1.45 (2) 2) (a) Identify the following as either a physical or a chemical property. (1½ marks) (i) (ii) (iii) Diamond is one of the hardest known substances Soap is slippery Gold does not rust (b) Identify the following as homogeneous or heterogeneous matter. (1½ marks) (i) Gasoline (ii) Air (iii) Alcohol 3) (a) Name the following compounds. (1½ marks) (i) LiF (ii) AlCl 3 (iii) Mg(OH) 2 7

8 (b) Write down the formulas for the following compounds. (1½ marks) (i) Copper (II) sulfide (ii) Lead (II) chloride (iii) Sulfur trioxide 4) What is the percent composition of all of the elements in limestone (CaCO 3 )? 5) A balloon can hold 1000 cm 3 of air before busting. The balloon contains 875 cm 3 of air at 8 0 C. Will it burst when it is taken to another place with a temperature of 30 0 C? (Assume that the pressure of the gas in the balloon remains constant). 8

9 6) (a) When a fuel tank is filled up no more fuel can be added. But when a car tyre is filled, more air can be added. Explain. (1½ marks) (b) (i) State the Boyle s Law of gases. (½ marks) (ii) Explain Boyle s Law of gases using kinetic molecular theory. (1 mark) 7) A sample of gas occupies 500 cm 3 at STP. Calculate its volume at 45 o C and 1.5 atm pressure. 9

10 8) How much water needs to be added to 25.0 cm 3 of 15.6 M HNO 3 in order to dilute it to a 2.5 M solution? 9) Classify each of the following crystalline solids as ionic, molecular, or metallic. (2 marks) (i) (ii) (ii) (iv) Zinc Zinc oxide Phosphorous Iodine monobromide (b) State 2 ways in which the rate of dissolving can be increased. (1 mark) 10) Predict whether each of the following solvents is miscible or immiscible with water. Also state which is polar and which is non polar. (i) Methanol (CH 3 OH) (ii) Carbon tetrachloride (CCl 4 ) (iii) Lithium carbonate (Li 2 CO 3 ) 10

11 Section C Long Answer Questions (50 marks) There are 5 questions. Each question is worth 10 marks. 1) (a) A compound consists of magnesium, carbon and oxygen. It has 21.6 % Mg and 21.4 % C. Calculate its empirical formula. (b) A compound of nitrogen with molar mass of 92.0 g was found to have an empirical formula of NO 2. What is its molecular formula? (2 marks) 11

12 (c) How many moles of H atoms will react with 2.5 moles of N to make NH 3? (2 marks) (d) Use the periodic table and write down the symbol of the element that fits each of the following descriptions. (i) The fourth-period alkaline earth metal. (ii) The liquid halogen. (iii) The group IIIA metalloid (iv) The last transition metal of the fifth period. (v) The period 4, group 1A element. (vi) The second noble gas. 12

13 2) (a) Arrange the following items in increasing order of mass. (4 marks) 4.55 x atoms of Pb 8.50 g of C moles Ca (b) Calculate the amount (in grams) of Ca(OH) 2 formed by reacting 17.0 g of CaO with water. The equation for the reaction is CaO + H 2 O Ca(OH) 2 Note: Mr [Ca(OH) 2 ] = 74 g/mol and Mr (CaO) = 56 g/mol 13

14 c) (i) Write down the electron configuration and draw the atomic structure of sodium (Na). (1½ marks) (ii) Using the electron-dot diagram, explain how chemical bonding occurs in sodium chloride (NaCl). (1½ marks) 14

15 3) (a) (i) A container holds two gases, A and B. Gas A has a partial pressure of 325 torr and gas B has a partial pressure of 488 torr. What percent of the molecules in the mixture is gas A? (2 marks) (ii) Which law of gases have you applied when calculating percent of molecules of gas A in part (i) above? (1 mark) (b) (i) What is the pressure (in atmospheres) exerted by a mixture of 12.0 g N 2 and 12.0 g O 2 in a 2.5 L container at 25 0 C? 15

16 (ii) Calculate the partial pressure of N 2 in the mixture of the gases in part (i) above. (2 marks) (c) 4.0 dm 3 of a gas was collected over water at 25 o C at a pressure of 95.6 kpa. Pressure of water is 3.5 kpa at 25 o C. Calculate the pressure of dry gas. (2 marks) 4) (a) (i) The density of a gas was measured at 1.50 atm and 27 0 C and found to be 1.95 g/dm 3. Calculate the molar mass of this gas. 16

17 (ii) Which gas could it most likely be? (1 mark) (b) If you had equal mass of helium (He), methane (CH 4 ) and carbon dioxide (CO 2 ) gas, which gas would exert the highest pressure? (c) Atoms of metallic structures are packed together in 3 geometric arrangements, Name the 3 types of metal crystal packing arrangements and state their coordination number. 17

18 5) (a) The ionic compound, caesium chloride (CsCl), has a crystalline structure. A unit cell of CsCl is illustrated below. Cs + ions Cl - ions (i) How are the caesium and chloride ions arranged in this unit cell? (1 mark) (ii) What is the coordination number of chloride ions? Explain why this is so. (1 mark) (iii) What is the coordination number of caesium ions? (½ mark) (iv) What is the coordination ratio of caesium chloride structure? (1 mark) (v) Compare the sizes of chloride and caesium ions. (½ mark) (vi) State the relationship between the value of the coordination number and the packing of atoms in a crystal. (1 mark) 18

19 (b) Distinguish between intermolecular and intramolecular forces using an example. (2 marks) (c) (i) At C,the vapor pressure of liquid A is 25 kpa where as vapor pressure of liquid B is 50 kpa. Explain relative strengths of their boiling points (ii) heats of vaporisation (iii) intermolecular forces of attraction 19

20 L.Torr mol.k 20

21 21 21/21

b. Na. d. So. 1 A basketball has more mass than a golf ball because:

b. Na. d. So. 1 A basketball has more mass than a golf ball because: Chem I Semester Review All of the following are general characteristics of a substance in the liquid state except a. definite volume. c. not easily compressed. b. able to flow. d. definite shape. In the