1798f_PChem Rev 1 Qn and Ans

1798f_PChem Rev 1 Qn and Ans - 1 Raffles Junior College H2...

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Unformatted text preview: 1 Raffles Junior College H2 Chemistry 2008/9 Physical Chemistry Revision Part 1 (Chemical Bonding, Chemical Kinetics, Chemical Energetics) Prepared by Mrs Chung-Chong Ai Lin and Dr Wong Poh Lee Instructions : For your revision of Stoichiometry and The Gaseous State, please attempt all questions in Chemistry / Focus Exercises. Chemical Bonding 1(a) State the two main features of the Valence-Shell Electron-Pair Repulsion (VSEPR) model for accounting for the shapes of molecules. [2] (b) The H- N- H bond angles of the three nitrogen-containing species, NH 3 , NH 2- and NH 4 + are different. Draw the dot-and-cross diagram for each of the species. What is the order, arranged in ascending magnitude, of the H- N- H bond angle in these species? Explain your answer. [5] (c) Ethylene glycol, HOCH 2 CH 2 OH, is the major substance in antifreeze. It is a slightly viscous liquid that is not very volatile at room temperature. Acetone, (CH 3 ) 2 CO, is a substance widely used as an industrial solvent. At room temperature, it is a liquid that is not viscous but is volatile. (i) Describe both the intramolecular and intermolecular bonding in each of ethylene glycol and acetone, relating the bonding to the differences in their viscosity and volatility where appropriate. [The resistance of a liquid to flow is called viscosity. A viscous liquid flows slowly] (ii) Compare the boiling points of ethylene glycol and 1-propanol giving your reasons. [7] [Modified from TJC/2003/P1/1] 2. Fluorine is the most electronegative and reactive of all elements. It is a pale yellow, corrosive gas, which reacts with practically all organic and inorganic substances. (a) LiF, HF and NF 3 are three different fluoride compounds, arranged in decreasing order of boiling points. Explain the statement in italics in terms of structure and bonding of the compounds. [3] (b) Phosphorus can form different fluoride compounds like PF 3 and PF 5 while nitrogen formed only NF 3 . Explain. [2] (c) Difluorodiazine, N 2 F 2 , is a colourless gas which can exist in two isomeric forms having different boiling points of - 106 C and - 111 C. (i) By considering the arrangement of the lone pairs and bond pairs of electrons on the nitrogen atoms, draw the structures of N 2 F 2 molecule in its two isomeric forms. In your diagram, you should clearly illustrate the general shapes of the isomers. (ii) Account for the difference in boiling points of the two isomers. [6] [NYJC/2003/P3] 2 3(a) A sample of stained glass, as used in church windows, is known to contain lead(II) oxide and silicon(IV) oxide. (i) Describe the bonding in silicon(IV) oxide and explain why it contributes to the hardness of the glass. (ii) Describe the bonding in lead(II) oxide and explain why it does not contribute to the electrical conductivity (if any) of the glass....
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1798f_PChem Rev 1 Qn and Ans - 1 Raffles Junior College H2...

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