School of Chemistry and Physics UNIVERSITY OF KWAZULU-NATAL, WESTVILLE NOVEMBER 2012 EXAMINATION CHEM199: FOUNDATION CHEMISTRY

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1 School of Chemistry and Physics UNIVERSITY OF KWAZULU-NATAL, WESTVILLE CHEM199: FOUNDATION CHEMISTRY DURATION: 3 HOURS TOTAL MARKS: 100 Internal Examiner: External Moderator: Mrs R Moodley, Mrs R Oosthuizen, Dr A Langlois Westville Campus Mr M Rasalanavho, Ms P Bhujrajh Pietermaritzburg Campus Mrs K-L Barry (Pietermaritzburg Campus) NOTE: This paper consists of 18 pages including a Periodic Table and Electronegativity Table. Please check that you have them all. Each question is marked out of 20 marks. Marks for individual sub-questions are given in brackets after each question. Students are requested, in their own interests, to write legibly. ANSWER ALL FIVE QUESTIONS IN THE EXAMINATION ANSWER BOOKLET PROVIDED 1

2 Question 1 For the questions below (1.1 to 1.20), write the number in your answer book and the letter (A, B, C or D) corresponding to the most appropriate answer. Note that there is only one correct answer for each question Work out the answer of the following expression to the correct number of significant figures: A. 18 B C. 1.8 x 10 3 D (1) 1.2. Calculate the number of moles in 1.58 x atoms of Na. A mol B mol C mol D mol (1) 2

3 1.3. Which formula represents dinitrogen pentoxide? A. N 2 P 2 O 5 B. N 2 O 5 C. NO 5 D. N 2 PO 5 (1) 1.4. Using IUPAC rules, give the name for CuCl 2. A. Cuprous chloride B. Copper(II) chloride C. Copper chloride D. Copper dichloride (1) 1.5. Which block in the periodic table do the halogens belong to? A. s B. p C. d D. f (1) 3

4 1.6. The mass of one molecule of the painkiller codeine, C 18 H 21 NO 3, is: A g B x g C x g D x g (1) 1.7. Which of the following has a polar covalent bond? A. O 2 B. NaCl C. HCl D. PH 3 (1) 1.8. Which pair of particles has the same number of electrons? A. Cl, Ca 2+ B. Br, Se C. Ne, F D. Al 3+, P 3 (1) 4

5 1.9. Which pair(s) of particles have the same valency? i. Na and Mg; ii. Na and Ne; iii. Na and K; iv. Na and F A. i and iii B. i and ii C. iii and iv D. ii and iv (1) The smallest unit of a covalent compound is called a/an: A. Formula unit B. Atom C. Molecule D. Ion (1) Vacuum or pressure filtration uses one of the following glassware: A. Round bottom flask B. Volumetric flask C. Büchner flask D. Conical flask (1) 5

6 1.12. Laboratory equipment used for heating a solid substance during a combustion reaction is a: A. funnel B. crucible C. watch-glass D. desiccator (1) Graduation marks on this glassware run from bottom to top: A. Graduated pipette B. Burette C. Bulb pipette D. Measuring cylinder (1) When aqueous lead nitrate, Pb(NO 3 ) 2, reacts with aqueous potassium iodide, KI, the product lead iodide, PbI 2 settles out of solution. Pb(NO 3 ) 2 (aq) + 2KI(aq) PbI 2 (s) + 2KNO 3 (aq) The above reaction can be classified as a: A. Neutralisation reaction B. Decomposition reaction C. Precipitation reaction D. Combustion reaction (1) 6

7 1.15. A g sample of purple crystals of hydrated cobalt(ii) chloride gives a blue coloured solid, CoCl 2, and gaseous water when heated strongly. What percentage of the solid product (blue coloured solid) was obtained if g of the gaseous water was released? A % B % C % D % (1) Pure copper may be produced by the reaction shown below: Cu 2 S(s) + O 2 (g) 2Cu(s) + SO 2 (g) What mass of Cu 2 S is required in order to prepare kg of copper metal? A kg B kg C kg D kg (1) 7

8 1.17. Consider the following reaction: 2KHCO 3 (s) K 2 CO 3 (s) + CO 2 (g) + H 2 O(l) How many moles of potassium carbonate will be produced if 476 g of potassium hydrogen carbonate are heated? (Note: Molar mass of KHCO 3 = g mol -1 ) A moles B moles C moles D moles (1) Using the chemical equation and statement given in number above, what volume of the gaseous product will be formed if this reaction is carried out at 25 C and 1 atm? A dm 3 B dm 3 C. 116 dm 3 D. 264 dm 3 (1) 8

9 1.19. What theoretical mass of carbon tetrachloride will be formed when moles of CHCl 3 react with excess chlorine? CHCl 3 + Cl 2 CCl 4 + HCl A g B g C g D g (1) The products of the combustion of propyl alcohol with oxygen gas are shown in the equation below: C 3 H 7 OH + O 2 CO 2 + H 2 O When properly balanced, the equation indicates that moles of oxygen gas are required for each mole of C 3 H 7 OH: A. 4.5 B. 6.0 C. 7.5 D. 9.0 (1) [20] 9

10 Question Quinine is a chemical compound that has been effectively used for the treatment of malaria. A sample of quinine was found to contain 74.05% C, 7.46% H, 8.63% N and the remainder oxygen, by mass. a) Determine the empirical formula for quinine. (7) b) Calculate the mass of nitrogen in a 381 g sample of quinine. (3) 2.2 Quinine is sometimes used as a cutting agent (diluting agent) in street drugs such as cocaine (C 17 H 21 NO 4, M= g mol -1 ). a) Does the combination of quinine and cocaine produce a compound or a mixture? Explain your answer. (2) b) Determine the mass percentage composition of oxygen in cocaine. (2) c) What is the mass of 1 mole of cocaine? (1) d) How many oxygen atoms are there in g of cocaine? (5) [20] 10

11 Question Aluminium reacts with hydrochloric acid to give hydrogen gas and aluminium chloride, according to the following balanced equation: 2Al(s) + 6HCl(aq) 3H 2 (g) + 2AlCl 3 (aq) a) Calculate the mass, in grams of aluminium needed to react with ml of a M HCl solution. (3½) b) After all the HCl (given in part a) above) has reacted, what will be the molar concentration of AlCl 3 in the solution? (Assume there is negligible (no) change in the volume of the resulting solution.) (2½) c) What volume, in ml, of the gas will be produced if the reaction was carried out at 25 C and 1 atm? (3) 11

12 3.2 Potassium superoxide, KO 2, is found in a self-contained breathing apparatus used by emergency personnel as a source of oxygen. A reaction vessel contains mol KO 2 and g of H 2 O to generate oxygen, according to the following balanced equation: 4KO 2 (s) + 2H 2 O(l) 4KOH(s) + 3O 2 (g) a) Determine which reactant is limiting. (3½) b) Is this the most economically sensible limiting reagent for this reaction? Explain your answer. (1½) c) Calculate the mass of excess reactant that remains upon completion of the reaction. (2) d) What mass of KOH can be produced in the above reaction? (2) e) Calculate the percentage yield of KOH, if g was recovered experimentally. (2) Question 4 [20] 4.1 Consider the isotope Sr-88 and its 2+ cation. a) Define the term isotope. (1) b) Determine the number of each type of subatomic particle in the cation of this isotope. (3) c) Write down two other isotopic notations for the neutral atom of this isotope. (2) d) Discuss the similarities and differences, with reasons, in terms of properties, that the Sr-88 isotope would have with another isotope of Sr. (2) 12

13 4.2 a) State Pauli s Exclusion Principle. (1) b) State Hund s Rule. (1) 4.3 Find the element which is in period 4 and group 13 and write the: a) Name and symbol of this element. (1) b) Spectroscopic full electronic configuration. (1) c) Abbreviated spectroscopic electronic configuration. (1) d) Number of unpaired electrons in the outermost principle energy level. (1) 4.4 Write the Lewis electron dot structure for: a) an anion of phosphorus. (1½) b) ammonia (NH 3 ) (1½) 4.5 Correct the following statements: a) Transition metals are collectively called the p-block elements, because their valence electrons are in the p-sublevel. (1½) b) The excited state of sodium has an electronic configuration of 1s 2 2s 2 2p 6 3s 1 because it has less energy than the ground state. (1½) [20] 13

14 Question 5 A technician working in the Foundation Chemistry Laboratory found an unlabelled reagent bottle containing a white powder on a shelf. The technician suspected that it might be potassium hydrogen phthalate (KC 7 H 4 O 2 COOH) or benzoic acid (C 6 H 5 COOH). Both these acids are called monocarboxylic acid (-COOH) and react in a similar way. To determine its identity, s/he measured a sample from this reagent bottle and carried out a titration reaction using a standard solution of sodium hydroxide. HO O O O O H O - K + Potassium hydrogen phthalate Benzoic acid The molar mass of KC 7 H 4 O 2 COOH = g mol -1 and of C 6 H 5 COOH = g mol Define the underlined words/phrase in the paragraph above. (1) 5.2 Explain why the technician should rinse the burette with the solution it will hold. (1) 14

15 5.3 Suppose that the technician had measured g of the acid sample and made a solution of this acid sample with a total volume of ml. S/he then measured successive 20.0 ml aliquots of this solution and carried out titrations with a suitable indicator. The titration results were tabulated as shown below: Title:.... Titration Trial 1 Trial 2 Trial 3 Trial 4 2 nd reading ml ml ml ml 1 st reading 0.64 ml 0.35 ml 0.58 ml 0.48 ml a) Name the appropriate glassware the technician should use when measuring 20.0 ml aliquots of the acid solution. (1) b) Describe the purpose of an indicator while carrying out a titration reaction. (1) c) Give a suitable title/description for the table given above. (1) d) Which trial s result shouldn t be used by the technician when carrying out further calculations? Give an explanation to your answer. (1) e) Calculate the average volume of the titre from the appropriate results. (2) f) If the concentration of the standard solution is M NaOH, determine the number of moles of NaOH used to neutralise the acid. (3) g) If the reaction ratio between the acid and the base (NaOH) is 1:1, how many moles, in the 20.0 ml aliquot of the acid, were neutralised? (1) 15

16 h) Calculate the total number of moles of the acid in the ml solution prepared by the technician. (2) i) Calculate the molar mass of the acid from the mass used. (3) j) Identity the acid found in the unlabelled reagent bottle. Explain how you reached this conclusion. (1) 5.4 Besides spillage, give two possible errors that can result in a lower molar mass than expected. (2) [20] 16

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Students are requested, in their own interests, to write legibly.

Students are requested, in their own interests, to write legibly. School of Chemistry UNIVERSITY OF KWAZULU-NATAL, PIETERMARITZBURG CHEM 099/CHEM 199: FOUNDATION CHEMISTRY DURATION: 3 HOURS TOTAL MARKS: 100 Internal Examiner: External Moderator: Mrs R Moodley, Mrs R