GENERAL PRINCIPLES OF CHEMISTRY, CHEM110

Transcription

1 University of Kwa-Zulu Natal, Westville Campus, Durban Class Test 3: Friday, 8 May 2009 GENERAL PRINCIPLES OF CHEMISTRY, CHEM110 Duration: 45 minutes Total Marks: 25 Internal Examiners: Dr V. Nyamori and Dr B. Moodley IMPORTANT: Complete this part immedidately Student No: Name: Tutorial Venue: Tutor: INSTRUCTIONS: 1. Student should note that there is no negative marking in the multiple choice questions. Please answer the MCQs on the MCQ answer sheet. 2. Answer ALL questions. 3. Calculators may be used but all working must be shown. 4. Your answers must be written on the question paper in spaces provided. The left-hand pages may be used for extra space or for rough work and must be indicated as such. 5. Marks will be deducted for the incorrect use of significant figures and the omission of units. 6. You must write legibly in black or blue ink. Tipp-Ex is not allowed. Pencils are only allowed for the MCQ answer sheet (section A) 7. A periodic table is provided.

2 Section A MCQ: Answer on the MCQ answer sheet by colouring in the correct answer. 1.1 Choose the preferred Lewis structure for NOCl. a) Cl O N b) Cl N O c) Cl N O d) N Cl O 1.2 The following Lewis structure N C O represents one of the resonance forms of the cyanate ion. The formal charges on the N, C and O atoms, respectively, are: a) -2, +4, -1 b) -2, 0, +1 c) 0, 0, -1 d) +2, 0, Which of the following molecules has the highest boiling point under same conditions other than temperature? a) NH 3 b) H 2 O c) HF c) CH 4

3 1.4 Which one of the following properties does not determine the physical state of a substance? a) Pressure b) Chemical identity c) Solubility d) Temperature 1.5 A chemical reaction that absorbs heat from the surroundings is said to be and has a ΔH at constant pressure. a) endothermic, positive b) endothermic, negative c) exothermic, negative d) exothermic, positive 1.6 The following reaction occurs at room temperature and pressure: 2Cl (g) Cl 2 (g) ΔH = kj Which statement is correct? a) 2Cl (g) has the higher enthalpy. b) Cl 2 (g) has the higher enthalpy. c) 2Cl (g) has the lower enthalpy. d) the energy of both 2Cl (g) and Cl 2 (g) are the same.

4 1.7 The temperature of a sample of gas is increased from 330 K to 500 K whilst the pressure is kept constant. Which statement is correct? a) the volume of the gas decreases. b) the volume of the gas increases. c) the number of moles of the gas decreases. d) the number of moles of the gas increases. 1.8 Which property listed below is INCORRECT for gases? a) pressure b) volume c) temperature d) energy

5 Section B: Answer on the question paper in ink in the spaces provided. 2. Draw Lewis structures of the following compound a) Na 2 O b) H 2 NOH 3. Arrange the following substances in order of increasing magnitude of their London dispersion forces SiCl 4, CCl 4, GeCl 4 4. a) Which of the following compound would you expect to have the highest melting point? KBr, CH 3 Cl, CH 3 OH (½ mark)

6 b) Show the trend, from highest to lowest melting point, in question (a) and explain your choice for the lowest and highest melting point compound (4 marks) 5) Using VSEPR theory, draw the shape and name the molecular geometry of the following molecules. Include bond angles in your structures. a) BeH 2 (1½ mark) b) PF 5 (2 marks)

7 6) A sample of a compound (5.04 x 10-3 mole) is dissolved in 41.0 g of water and then placed into a Styrofoam cup. The temperature of the solution changes from C to C. What is the heat of solution of the compound expressed in kj/mol? (Note: Assume the specific heat of the solution is 4.18 J g -1 0 C -1 ). (1½ marks) 7) Use the data given to calculate ΔH for the reaction of ethylene, C 2 H 4, with F 2 shown in the following reaction; Data: C 2 H 4 (g) + 6F 2 (g) 2CF 4 (g) 4HF (g) H 2 (g) + F 2 (g) 2HF (g) C (s) + 2F 2 (g) CF 4 (g) 2C (s) + 2H 2 (g) C 2 H 4 (g) ΔH = kj ΔH = kj ΔH = kj (2 marks)

8 8) A sample of air occupies 3.82 L at a pressure of 1.25 atm. What volume, in litres, does it occupy if the pressure is increased to 5016 mmhg? (1½ marks) 9) Which gas law is used to explain why hot air balloons rise? Give an explanation for your answer.