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

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1 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 Oosthuizen, Dr A Langlois Westville Campus Mr M Rasalanavho, Mr M Akerman Pietermaritzburg Campus Mrs H Govender (Westville Campus) NOTE: This paper consists of 13 pages and a Periodic Table and Electronegativity Table. Please check that you have them all. Each question is marked out of 25 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 FOUR QUESTIONS IN THE EXAMINATION ANSWER BOOKLET PROVIDED

2 Question For a 2.35 g sample of ammonia (NH 3 ), determine the following: a) Number of molecules (1½) b) Total number of atoms (1½) c) Volume of the gas at 25ºC and pressure of 1 atm. (1½) d) Molar volume if the density is kg ml -1 (2) 1.2 An analysis of a sample of the well-known pain killer, Aspirin, shows that it has a molar mass of g mol -1. Its composition was found to be 60.0% C, 4.48% H and the remainder oxygen. a) Explain the difference between empirical and molecular formula. (2) b) Determine the empirical formula of Aspirin. (6) c) Determine the molecular formula of Aspirin. (2) d) The technician needs to determine if a batch of tablets is Aspirin. To do so, she analyses g of the tablets and finds that it contains g of C, g of O and H whose mass is obtained by difference. Explain, without the use of calculations, how she would use this data to identify the compound in the tablets. (2) 2

3 1.3 A sample of an unknown compound containing only C, H and O was burned in 5.21 g of oxygen gas as shown in the chemical reaction below. C x H y O z (s) + O 2 (g) CO 2 (g) + H 2 O(g) After the reaction comes to completion, g CO 2 and g H 2 O were formed. a) Identify the type of reaction that is occurring above. (1) b) Calculate the mass of the unknown compound that was burned. (2) 1.4 Determine the percentage composition of waters of crystallization in NiCl 2.6H 2 O. (3½) [25] Question Iron(III) chloride reacts with silver nitrate to produce silver chloride and iron(iii) nitrate according to the following equation: FeCl 3 (aq) + 3AgNO 3 (aq) 3AgCl(s) + Fe(NO 3 ) 3 (aq) a) What volume of a M AgNO 3 solution is needed to react completely with 20.0 ml of a M FeCl 3 solution? (3½) 3

4 b) What mass of AgCl will be formed? (3) 2.2 Copper nitrate is used as a catalyst in solid rocket fuel and can be prepared by reacting copper with nitric acid, according to the following equation: 3Cu(s) + 8HNO 3 (aq) 3Cu(NO 3 ) 2 (aq) + 4H 2 O(l) + 2NO(g) a) How much copper nitrate can be prepared from 75.0 g of each starting material? (7½) b) If the reaction achieves a 95.7% yield, calculate the actual mass of copper nitrate recovered from the reaction. (2) c) Calculate how much of the excess reactant remains unreacted. (3½) 2.3 How many litres of H 2 gas are produced when 1.00 g of Al(s) is consumed in the following reaction if it is performed at a temperature of 25 C and a pressure of 1 atm? 2Al(s) + 6HCl(aq) 2AlCl 3 (aq) + 3H 2 (g) (5½) [25] 4

5 Question The most stable isotope of chromium has 28 neutrons. a) Write down two different isotopic notations for this isotope of chromium. (1) b) How many protons and electrons are found in the +3 ion of this isotope? (1) c) What similarities and differences, in terms of properties, would another isotope of chromium have when compared with this isotope? Explain your reasoning. (2) 3.2 Match each of the items in column A with the most appropriate item(s) in column B. Write down the letters a) to f) and the corresponding numbers 1-9. Some items in column A have more than one answer. The items in column B can be used more than once. Marks will only be awarded if all possible answers are provided. (6) A B a) [Kr]5s 1 1. a p block element b) Z = ns 2 np 5 c) As 3. atomic number 37 d) Cu 4. has no neutrons e) halogen 5. 3 unpaired electrons in the outermost p sub-level f) H valence electrons 7. an element in period 6 and group an element in period 4 and group s 2 2s 2 2p 6 3s 2 3p 6 4s 1 3d 10 5

6 3.3 Answer the following questions: a) Write down the spectroscopic electronic configuration for the cation of sodium. (1) b) Draw the orbital/tabular diagram for the nitride anion. (1) c) Comment on the differences and similarities seen in a) and b) above. (2) 3.4 Draw the Lewis electron dot structure for each of the following substances: a) Cl 2 (1) b) SO 2 (1) 3.5 Which elements in the following ionic compounds have a valency of 1? Write a, b and c and next to each the correct element symbol(s). a) KClO 3 b) sodium sulfate c) nickel(ii) hydroxide (2) 3.6 Which of the following two compounds contains a dipole: bromine gas or carbon monoxide gas? Prove your answer with the aid of a calculation and an explanation. (3) 3.7 Write down the chemical formula and IUPAC name for the compound formed when a) lithium and sulfur react (2) b) calcium and phosphorus react (2) 6 [25]

7 Question A student carried out the following experiment in the laboratory to determine if the sample that he had was glutaric acid [CH 2 CH 2 CH 2 (COOH) 2 ] or malonic acid [CH 2 (COOH) 2 ]. S/he weighed g of the acid and transferred it into a ml volumetric flask. S/he then made it up to the mark with distilled water. S/he titrated ml of the acid solution against a standard mol dm -3 NaOH solution, using phenolphthalein as an indicator. The titration was done in triplicate and the burette readings were recorded in Table 1. Acid(aq) + 2NaOH(aq) Sodium salt(aq) + 2H 2 O(l) Table 1: Titration of ml acid solution against M NaOH solution Titration nd reading (ml) st reading (ml) Titre (ml) a) Define the term standard solution. (1) b) A colour change is observed when the endpoint is reached. Explain what is happening in the reaction vessel. (1) 7

8 c) Why is it important to add an indicator when doing a titration? (1) d) Name 4 pieces of glassware which are essential for this experiment? (2) e) Why should you calculate the volume of the titre immediately after carrying out the titration and before commencing with the next one? (1) f) Calculate which titre values are concordant and then calculate the average titre. (4) g) Calculate the number of moles of NaOH that have reacted with the acid. (2) h) Determine the number of moles of acid in ml of the solution. (2) i) Calculate the concentration of the acid solution. (2) j) Calculate the number of moles in the original prepared solution. (2) k) Calculate the molar mass of the acid in the sample and thereafter decide which acid was in the sample. (3½) l) Which reactant, the acid or the base, is the limiting reagent of the reaction: i) before the endpoint? ii) at the endpoint? iii) after the endpoint? (1½) 4.2 Suppose you are a technician in the Foundation labs and you notice that the NaOH solution is running out in the above experiment. What could you ask the students to do to make the base solution go further? (2) 8 [25]

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

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,