CHEM 114: Mid-course TEST Wednesday 23 rd March pm Answer ALL QUESTIONS

Transcription

1 NAME:. STUDENT ID N o. CHEM 114: Mid-course TEST Wednesday 23 rd March pm Answer ALL QUESTIONS TIME MANAGEMENT: This examination is marked out of 60. An approximate marking scheme is provided to help you allocate your time effectively. You are encouraged to spend approximately 1 minute per mark allocated. Section 1 is multiple choice. There are 15 questions each worth 1 mark (15 marks total) Section 2 contains discursive questions. There are 3 multi-part questions each worth a total of 15 marks (45 marks total). ANSWERS: Section 1: Please complete the provided answer sheets. Use a 2B pencil and only fill in 1 circle or your answer will be invalid. Section 2: Fill in your answers in the spaces provided on the test sheet. If you need more space (e.g. for calculation workings) please use the blank paper on the back of the preceding page. Write in sentences and show your working where appropriate. PERIODIC TABLE: A detachable Periodic Table is included at the end of the test. Detach it and use it. Please leave blank. For Staff use only. Section 1 Section 2 Q1-15 Q1 /15 Q2 /15 Q3 /15 Machine Marked

2 Section 2 Question 1 [15 marks total] (a) The rationalization of shape of small covalent molecules is called the VSEPR model. i. State what VSEPR stands for? [1 mark] Define what is meant by a lone pair of electrons? [1 mark] i Define what is meant by a dipole? [1 mark] (b) Use the VSEPR model to predict the shape of one molecule of hydrogen sulphide (H 2 S) in the gas phase. Show your full working including electron counting and clearly state the number of bonding pairs and lone pairs (if any). [4 marks] 2

3 (c) Would you expect a molecule of H 2 S to be polar or non-polar? Explain your answer, giving at least two reasons. (d) Draw the Lewis symbols for [2 marks] i. S H (e) Draw the complete dot-cross diagram for H 2 S. 3

4 Question 2 [15 marks total] (a) With reference to the periodic table, name an element between Z = 1 and Z = 20 that is: i. An alkali metal An alkaline earth metal i A noble gas (b) The first and second ionization energies of potassium (K) are 419 kj/mol and 3052 kj/mol. Explain why the second ionization energy of potassium is much higher than the first. (c) Complete the following statements: [2 marks] i. Reduction is of electrons Oxidation is of electrons 4

5 Ionization Energy (kj/mol) (d) Which of the elements listed below has the following pattern for its first six ionization energies? Ionization A. Al B. B C. C D. Li E. O Circle the correct answer [2 marks] (e) Write out the electron configurations for the following neutral atoms: [2 marks] i. Potassium Chlorine 5

6 (f) State the octet rule. [1 mark] (g) Classify the following intramolecular bonds as ionic, polar covalent or covalent: [2 marks] i. The bond in NaCl The bond in KF i The bond in H 2 iv. A CCl bond in CCl 4 6

7 Question 3 [15 marks total] (a) Consider a neutral atom of the element potassium (K) shown below K i. How many electrons does the atom contain? [1 mark] How many neutrons does the atom contain? [1 mark] (b) Chlorine-35 and Chlorine-37 differ in their number of Protons Electrons Neutrons Circle the correct answer(s) [1 mark] (c) The isotopic composition of a bulk sample of chlorine gas was found to be 75.8% chlorine-35 and 24.2% chlorine-37. The relative atomic mass of chlorine-35 is g/mol, while that of chlorine-37 is g/mol. Calculate the atomic weight of chlorine in this bulk sample. Show your full working. [2 marks] (d) Potassium (K) reacts with elemental chlorine gas to form a salt. Write a balanced equation for this reaction, including the physical states of the reactants and products. [4 marks] 7

8 (e) How many moles of potassium are present in 30 g of potassium chloride? Show your full working. (f) How many moles of chlorine gas would be needed to prepare a 30 g sample of potassium chloride by reaction with potassium? Explain how you obtain your answer. END OF SECTION 2 END OF PAPER (Periodic Table on following page) 8

9 Periodic Table 1 2 H Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe (99) Cs Ba see Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn below (210) (210) (222) Fr Ra see Rf Db Sg Bh Hs Mt Ds Rg Cn (223) (226) below (257) (260) (263) (262) (265) (266) He La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu (147) Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr (227) (231) (237) (242) (243) (247) (245) (251) (254) (253) (256) (254) (257)