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School of Chemistry UNIVERSITY OF KWAZULU-NATAL JUNE 2008 EXAMINATION CHEM099/CHEM199 : FOUNDATION CHEMISTRY DURATION : 3 HOURS TOTAL MARKS : 100 External Examiner: Dr C Southway University of KwaZulu-Natal, Pietermaritzburg Internal Examiner: Mrs R Moodley, Ms T Naicker, Ms R Robb University of KwaZulu-Natal, Westville Mr M Rasalavavho University of KwaZulu-Natal, Pietermaritzburg Instructions to Candidates: This paper consists of 12 pages including a Periodic Table and a Table of Relative Atomic Masses. Please check that you have them all. Answer all 5 questions on the paper provided and show your working clearly. Marks are given in brackets after each question and all questions are marked out of 20. QUESTION ONE 1.1 Select from the table below the formula/word/phrase that best matches the following statements or definitions a) to j) Note: The formula/word/phrase can be used more than once or not at all in the answers. Some questions may have more than one answer or no answer, in which case you will write ‘No answer’ The mark will only be awarded if the complete answer is provided. 1 School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb CHEM099/CHEM199 : FOUNDATION CHEMISTRY JUNE 2008 EXAMINATION KBr Solubility Conductivity Liquid Diffusion Volatile Solid HF Sr(OH)2 Ar Compressibility Fe/V Li2O Boiling point CO Mass a) Acetone has a high vapour pressure and therefore evaporates readily b) Contains the most reactive halogen c) Macroscopic properties of matter d) An inert gas e) Classified as a mixture f) Molecule/s g) Formula Units h) Pure substance i) Contains an alkali metal j) Matter having a fixed shape (10) 1.2 Camphor is an organic compound which is used in some mothballs. At room temperature this solid compound vapourises. This process is known as sublimation. a) Give another example of a substance which undergoes this process. (1) b) What is the reverse transition/process called? (1) c) Explain the process of sublimation with the help of the kinetic (particulate) theory of matter, using camphor as an example. (4) 2 School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb CHEM099/CHEM199 : FOUNDATION CHEMISTRY JUNE 2008 EXAMINATION 1.3 Classify the following as physical (quantitative or qualitative) or chemical properties. Give a reason for your answer. a) Silver jewellery turns black due to continuous exposure to air. (1) b) The molecule hexane is a colourless liquid at 25 °C. (1) c) At 20 °C, 37 g of NH4Cl is soluble in 100 g of H2O. (1) d) Zinc reacts with hydrochloric acid solution to produce hydrogen gas and a water solution of zinc chloride. (1) [20] QUESTION TWO 2.1 Select from the table the formula/word/phrase that best matches the following statements a) to h) Note: The formula/word/phrase can be used more than once or not at all in answering the question. Some questions may have more than one answer or no answer, in which case you will write ‘No answer’ The mark will only be awarded if the complete answer is provided. 3 School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb CHEM099/CHEM199 : FOUNDATION CHEMISTRY JUNE 2008 EXAMINATION Mixture Sterling silver KMnO4 (aq) Chemical change Brass Concrete Closed system Isolated system Physical change Endothermic Exothermic Glass a) Examples of homogeneous mixtures. b) An alloy. c) When 2 colourless solutions are mixed together a blood red solution forms. d) The reaction that has heat as a product. e) A closed thermos bottle or flask. f) The transformation that occurs when a lump of iron is stretched into a wire. g) The reaction whereby the energy of the products is higher than that of the reactants. h) The type of change(s) that obeys the Law of Conservation of Mass. (8) 2.2 As a chemist working in the forensics department of the SAPS, you were called upon to identify an unknown powder that was found at 3 different crime scenes. Your preliminary examination of the powder samples obtained from Scene 1 and Scene 2 might suggest it being an illegal drug (a date-rape drug). However, you were uncertain about the powder found at Scene 3. After separating the powder into its elements, you obtain the data presented in the table below. Scene Mass of Sample (g) Mass of C (g) Mass of H (g) Mass of N (g) Mass of O (g) 1 94.46 72.07 4.800 11.19 6.403 2 24.97 19.05 1.268 2.960 1.693 3 29.30 21.60 1.500 1.400 4.800 4 School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb CHEM099/CHEM199 : FOUNDATION CHEMISTRY JUNE 2008 EXAMINATION a) State the Law of Constant Composition. (2) b) Explain, using calculations, how you could use the data above to show that the powder found at Scene 1 could be the same compound as the powder found at Scene 2 . (5) c) Calculate the mass of carbon that would be found in a sample that contains 45.67 g of oxygen. (3) d) Explain, without using calculations, how you could possibly use the data above to verify that the substance found at Scene 3 is not the same compound. (2) [20] QUESTION 3 3.1 When octane (C8H18) vapour undergoes combustion (reacts with oxygen) in the car engine, water vapour and carbon dioxide are produced. a) Write a word equation for this reaction. (1) b) Write a balanced chemical equation for the reaction including state symbols. (2) c) State whether the enthalpy change, ∆H, for the above reaction is positive or negative AND give a reason for your answer. (1) 5 School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb CHEM099/CHEM199 : FOUNDATION CHEMISTRY JUNE 2008 EXAMINATION d) Explain how you could test for the carbon-containing gas liberated AND provide a chemical equation as part of you explanation. (2) 3.2 Classify the chemical reactions below by selecting the term(s) from the table below that best matches with the reactions a) to d). Note: The term can be used more than once or not at all in answering the reactions. Some reactions may have more than one answer or no answer, in which case you will write ‘No answer’ The mark will only be awarded if the complete answer is provided. Combination reaction Displacement reaction Synthesis reaction Neutralisation reaction Precipitation reaction Gas forming reaction Decomposition reaction Combustion reaction Dehydration reaction a) HCl (aq) + NaOH (aq) NaCl (aq) + H2O (l) b) 2Hg (l) + O2 (g) 2HgO (s) c) PbCl2 (aq) + CuSO4 (aq) PbSO4 (s) + CuCl2 (aq) d) 2H2O2 (aq) 2H2O (l) + O2 (g) (4) 6 School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb CHEM099/CHEM199 : FOUNDATION CHEMISTRY JUNE 2008 EXAMINATION 3.3 The graph shows the solubility curves for several substances. Answer the following questions based on the graph. a) Which substance is the most soluble at 60oC? (½) b) Which substance is the least soluble at 10oC? (½) c) Define the term saturated solution. (1) d) If 45 g of ammonia gas (NH3) was dissolved in 100 g of water at 20oC, would the solution be unsaturated, saturated or supersaturated? Explain your answer? (2) 7 School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb CHEM099/CHEM199 : FOUNDATION CHEMISTRY JUNE 2008 EXAMINATION e) What mass of ammonium chloride (NH4Cl) will precipitate out of 250 g saturated NH4Cl solution it is cooled from 90oC to 50oC? (3) f) How much more KNO3 would need to be added to make the solution saturated if 108 g of solution, containing 20 g of the salt, is heated to 50oC? (4) [20] QUESTION 4 A 250.0 ml solution of potassium dichromate (Solution A), was prepared in the laboratory by dissolving 31.25 g of the salt (K2Cr2O7) in water. 4.1 Explain clearly how you would go about preparing this solution in the laboratory. (2) 4.2 Calculate the concentration of Solution A in g/dm3. (3) 4.3 Determine how many milliliters of water was added to Solution A if the density of Solution A is 1.02 g/ml. (Density of water = 1.00 g/ml). (3.5) 4.4 Would you consider this to be a concentrated solution or a dilute solution? Explain your answer. (2) 8 School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb CHEM099/CHEM199 : FOUNDATION CHEMISTRY JUNE 2008 EXAMINATION 4.5 How many milliliters of water would need to be added to 90 ml of Solution A to decrease the concentration to 69.44 g/dm3? (3.5) 4.6 If a mass of 8.75 g of K2Cr2O7 was added to Solution A and the volume increased by 3.27 ml, what would the concentration of the new solution be in g/ml? (3) 4.7 Determine the volume in milliliters of Solution A needed to make 100 ml of Solution B with a concentration of 9.54 g/dm3. (3) [20] QUESTION 5 5.1 Name each of the pieces of laboratory apparatus, A to L, shown below. NOTE: Half a mark will only be awarded if the full name of the apparatus is given. (6) 100 ml 100 ml 150 ml 250 ml A 5.2 B C D E F G H I J K L Give the letter(s) identifying the picture(s) for each answer. NOTE: The letters A to L can be used more than once in answering questions a) to f). Some questions have more than one answer and some may have no answer. Each question a) to f) is worth one mark. The mark will be assigned only if the complete answer is given. Which of the above A to L: 9 School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, Pmb CHEM099/CHEM199 : FOUNDATION CHEMISTRY JUNE 2008 EXAMINATION a) has a single graduation mark? b) is used in a distillation experiment? c) can be used to measure out variable volumes of a liquid? d) is used in an experiment to separate out a mixture of two immiscible liquids? e) is used in a filtration experiment? f) has a tap which controls the outflow of liquid? (6) 5.3 Correct the following statements without using the word “NOT”. Your correct statement should include all the underlined words. a) Simple distillation is preferred to use when separating liquids with boiling points close to each other. In such a case a fractionating column should be attached to the mouth of the collecting container/receiver. (2) b) Differential measuring, also known as measuring directly, is preferred. For this method, students are required to tare/zero the mass balance before adding sample to the container. (2) c) During a physical change, the composition of the reactants change and their masses often increase. (2) d) The least unit of measurement gives the maximum volume glassware can hold and is determined by taking a reading at the bottom of the meniscus of the liquid contained. (2) [20] 10 School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, WESTVILLE CHEM099/CHEM199 : FOUNDATION CHEMISTRY JUNE 2008 EXAMINATION 11 School of Chemistry, UNIVERSITY OF KWAZULU-NATAL, WESTVILLE CHEM099/CHEM199 : FOUNDATION CHEMISTRY JUNE 2008 EXAMINATION TABLE OF RELATIVE ATOMIC MASSES (Based on Carbon-12) Symbol Actinium Aluminium Americium Antimony Argon Arsenic Astatine Barium Berkelium Beryllium Bismuth Boron Bromine Cadmium Caesium Calcium Californium Carbon Cerium Chlorine Chromium Cobalt Copper Curium Dysprosium Einsteinium Erbium Europium Fermium Fluorine Francium Gadolinium Gallium Germanium Gold Hafnium Helium Holmium Hydrogen Indium Iodine Indium Iron Krypton Lanthanum Lawrencium Lead Lithium Lutetium Magnesium Manganese Mendelevium Ac Al Am Sb Ar As At Ba Bk Be Bi B Br Cd Cs Ca Cf C Ce CI Cr Co Cu Cm Dy Es Er Eu Fm F Fr Gd Ga Ge Au Hf He Ho H In I Ir Fe Kr La Lr Pb Li Lu Mg Mn Md Atomic No. 89 13 95 51 18 33 85 56 97 4 83 5 35 48 55 20 98 6 58 17 24 27 29 96 66 99 68 63 100 9 87 64 31 32 79 72 2 67 1 49 53 77 26 36 57 103 82 3 71 12 25 101 Atomic Mass [227] 26.98 [243] 121.75 39.95 74.92 [210] 137.34 [247] 9.012 208.98 10.81 79.90 112.41 132.91 40.08 [251] 12.01 140.12 35.45 52.00 58.93 63.55 [247] 162.50 [252] 167.26 151.96 [257] 19.00 [223] 157.25 69.72 72.61 196.97 178.49 4.00 164.93 1.01 114.82 126.90 192.22 55.85 83.60 138.91 [260] 207.2 6.94 174.97 24.31 54.94 [258] Symbol Mercury Molybdenum Neodymium Neon Neptunium Nickel Niobium Nitrogen Nobelium Osmium Oxygen Palladium Phosphorus Platinum Promethium Plutonium Polonium Potassium Praseodymium Proctactinium Radium Radon Rhenium Rhodium Rubidium Ruthenium Samarium Scandium Selenium Silicon Silver Sodium Strontium Sulfur Tantalum Technetium Tellurium Terbium Thallium Thorium Thulium Tin Titanium Tungsten Uranium Vanadium Xenon Ytterbium Yttriium Zinc Zirconium Hg Mo Nd Ne Np Ni Nb N No Os O Pd P Pt Pm Pu Po K Pr Pa Ra Rn Re Rh Rb Ru Sm Sc Se Si Ag Na Sr S Ta Tc Te Tb Tl Th Tm Sn Ti W U V Xe Yb Y Zn Zr A value given in brackets denotes the mass of the longest-lived or best known isotope 12 Atomic No. 80 42 60 10 93 28 41 7 102 76 8 46 15 78 61 94 84 19 59 91 88 86 75 45 37 44 62 21 34 14 47 11 38 16 73 43 52 65 81 90 69 50 22 74 92 23 54 70 39 30 40 Atomic Mass 200.59 95.94 144.24 20.18 [237] 58.69 92.91 14.01 [259] 190.20 16.00 106.42 30.97 195.08 [147] [244] [209] 39.10 140.91 231.04 226.03 [222] 186.21 102.91 85.47 101.07 150.36 44.96 78.96 28.09 107.87 22.99 87.62 32.07 180.95 [98] 127.60 158.93 204.37 232.04 168.93 118.71 47.88 183.85 238.03 50.94 131.29 173.04 88.91 65.39 91.22