chemistry exam

Last Name: ID # # on the signature list: First Name: (to be entered by the teacher) Professor: Dr. G. DÉNÈS Chem242-FE.W2012

CHEMISTRY 242/4 -51 Winter 2011 Final Examination Thursday April 16, 2012 Total number of pages: 26 14:00-17:00 ************************************************************************************* Enter your name and your Concordia ID number on the top of this page, in the space provided, and your Concordia ID number on the top of each subsequent page, in the space provided. Answer all questions on this questionnaire. Balance all equations. Explain your answers, starting from the periodic table, whenever possible. No booklet No book, note or periodical table allowed. No scrap paper allowed. Use the back of the questionnaire sheets for scrap. Printed translation dictionaries are allowed. No scientific, technical, definition, or electronic dictionary is allowed This final examination counts for 50 marks, out of a total of 100 marks. If you do better in % in the final exam than in the midterm exam, the midterm exam will not count and the final exam will count for 75% instead of 50%. When the question asks to compare values, such as distances, radii, energies, etc..., you are expected to tell whether numbers are larger, smaller, or about the same, and explain why if an explanation is requested. No numerical value is expected, unless requested. This exam is made of two parts:

- Part I requires only short answers - Part II requires full explanations

Answer all questions in the space provided on the questionnaire. You can use the back of the pages for scrap if you wish; it will not be graded.

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Chem 242, Winter 2012, Final examination Your ID # Part I starts here. Give only short answers in the space provided. No explanation required unless requested. 1: Give the name of the scientists who did the following:

- designed a method to determine the electron pair geometry and molecular shape by evaluating repulsion between electron :

- designed a rule to show the variation of health response of nutrient with intake dose:

- determined the electron distribution and the electron spin within a set of degenerate orbitals :

- established the most commonly used electronegativity scale that assigns a 4.0 electronegativity to the most electronegative element :

- established rules to explain the polarization of some ions: 2: 2.1. Draw the electron dot diagram of the [IF4]- ion (no explanation required):

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Chem 242, Winter 2012, Final examination Your ID # 2.2. Answer the following questions regarding the [IF4]- ion :

- Formal charge on I: - Formal charge on F:

- Oxidation number on I: - Oxidation number on F:

2.3. The formal charges found above violate a rule. Give the following about the rule that is violated:

- name of the inventor of the rule:

- name of the rule:

- tell in 2 or 3 lines what the rule says regarding the above violation:

- Tell what is the other statement of the same rule:

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Chem 242, Winter 2012, Final examination Your ID # 2.4. Give the following structural information about the [IF4]- ion :

- Electron pair geometry :

- Molecular geometry : - Polarity: is the ion polar or nonpolar? - Hybridization of iodine :

3: Give the valence electronic structure of the element located in group 15, period 5: Give the symbol and name of the same element: Give the expected oxidation number(s) of the same element: 4: Give the most important interatomic interaction responsible for the following :

- Boiling point of anhydrous HF :

- Boiling point of anhydrous HCl : - Hydration of the barium ion : - Hydration of the beryllium ion : - Bonding in CaH2 :

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Chem 242, Winter 2012, Final examination Your ID # 5: Compare qualitatively (using the sign < and the ions symbol) the ionic radius of the ion obtained when Te, I, Cs and Ba achieve the nearest noble gas configuration. Explain in 2 or 3 lines only. 6: Circle the letter a, or b, and/or c, or... for the answer that applies best to the properties of most molecular compounds in the given conditions in each question below (MORE than one answer may apply): 6.1 At ambient temperature, most molecular compounds are:

a. Hard and brittle b. Hard but not brittle c. Soft d. Malleable e. Ductile

6.2 At ambient temperature, most molecular compounds are:

a. Good electrical conductors b. Semiconductors c. Insulators

6.3 At ambient temperature, most molecular compounds are:

a. Gases b. Liquids c. Low melting point solids d. High melting point solids

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Chem 242, Winter 2012, Final examination Your ID # 6.4 At ambient temperature:

a. Most molecular compounds dissolve in non-polar solvents and the solution does not conduct electricity.

b. Most molecular compounds dissolve in non-polar solvents and the solution conducts electricity.

c. All molecular compounds dissolve in high polarity solvents and the solution does not conduct electricity.

d. All molecular compounds dissolve in high polarity solvents and the solution conducts electricity.

6.5 When heated to the molten state in a non-reactive atmosphere, most molecular compounds behave as follows:

a. They decompose. b. They do not decompose and they conduct electricity. c. They do not decompose and they do not conduct electricity.

6.6 Find the incorrect statement(s).

a. Molecular compounds cannot be composed of only non-metals b. Molecular compounds can be made of metals and non-metals. c. Molecular compounds cannot be made of metals only. d. An ionic bond is extreme case of a polar bond. e. A small and highly charged cation can make covalent a bond that would otherwise be

ionic

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Chem 242, Winter 2012, Final examination Your ID # 7: The combustion reaction of hydrogen in oxygen to give hydrogen peroxide has a negative Gibbs free energy. 7.1 Write the balance equation for the above reaction. 7.2 However, the above reaction does not take place. Write the balanced equation for the combustion reaction of hydrogen in oxygen that actually takes place. 7.3 Compare qualitatively the Gibbs free energy of the reaction that actually takes to that of the reaction that gives hydrogen peroxide. 7.4 Using the position of oxygen in the periodic table, justify why the compound obtained by combustion of hydrogen in oxygen is the compound shown in your answer to question 7.2, rather than hydrogen peroxide.

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Chem 242, Winter 2012, Final examination Your ID # 8. Fill in the missing word in the following sentences: 8.1 A semiconductor doped with impurity is called an semiconductor or an semiconductor.

8.2 The theory that explains bonding and the electrical properties of metals based on the presence of a very large number of molecular orbitals very close to one another to form a continuum is called the

theory.

9. Answer the following questions regarding the fcc structure of a metal: 9.1 Tell what fcc stands for: 9.2 Tell what is the radius of a metal atom versus the fcc unit-cell edge a: 9.3 Tell how many number of metal atoms there are in a fcc unit-cell: 9.4 Tell what is the coordination number of each metal atom in a fcc unit-cell:

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Chem 242, Winter 2012, Final examination Your ID # 10: Answer the following questions about acids and bases. 10.1 An acid stronger than 100% sulfuric acid is called a . 10.2 Magic acid is made of . 10.3 Magic acid is used in the petroleum industry for breaking bonds between and . 11. Write two balanced equations for reactions used for the production of hydrogen in the two following cases. For each, give the physical states of reactants and products, and the reaction conditions. 11.1 Preparation in the laboratory: 11.2 Preparation in the industry:

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Chem 242, Winter 2012, Final examination Your ID # 12. Answer the following questions about metallic hydrides: 12.1 They contain hydrogen in the following form(s) (circle your answer(s)):

H H2 H+ H- Not well defined 12.2 In addition to hydrogen, they contain one of the following element:

a. An alkali metal or an alkaline earth metal

b. A transition metal

c. A metalloid

d. A non-metal 12.3 Their structure is:

a. Similar to the metal, with similar electrical and magnetic properties

b. Molecular

c. Similar to a halide salt

d. Polymeric

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Chem 242, Winter 2012, Final examination Your ID # 12.4 Choose the correct statement about their physical state and properties:

a. At ambient temperature, they are gases, liquids or soft solids

b. They melt at high temperature to give stable electrically non-conducting melts.

c. They melt at high temperature to give stable electrically conducting melts.

d. They decompose at high temperature, releasing hydrogen gas and the metal. 12.5 Choose the correct statement about their stoichiometry:

a. All are stoichiometric compounds with an expected oxidation state of the metal.

b. All are stoichiometric compounds with unexpected oxidation states of the metal

c. Most are non-stoichiometric 12.6 Choose the method used for their preparation:

a. Reaction of an ionic hydride with a metal-containing compound. b. Reaction of an ionic hydride with a non-metal or a metalloid.

c. Decomposition of another hydride at high temperature.

d. Heating a metal under flow oh hydrogen.

e. Heating a metal under high pressure hydrogen.

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Chem 242, Winter 2012, Final examination Your ID # 13. Circle the following species that do NOT have an octahedral molecular geometry in the gas phase:

[IF6]- [PF6]- SF6 XeF6

14. Tell what is obtained when each alkali metal is burned in an excess of oxygen. Justify any difference of behavior of each in no more than 3 or 4 lines.

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Chem 242, Winter 2012, Final examination Your ID # 15. Circle in the following list the mixed-oxidation state compounds:

PbO PbO2 Pb2O3 Pb3O4 In2O3 InO 16. Comparing group 1 and group 11 elements: 16.1 Give the list of the elements of group 11 and their electronic structure. 16 .2 Compare the reactivity of group 1 and group 11 elements with water, and use their electronic structure to explain the similarities/differences.

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Chem 242, Winter 2012, Final examination Your ID # 17. Zinc oxide dissolves in both acids and bases. 17.1 This ability to dissolve in both acids or bases has two names. Give the two names:

17.2 The formula and name of the zinc ion obtained in an acid are: 17.3 The formula and name of the zinc ion obtained in a base are:

18. Answer the following questions regarding spinels.

18.1 Give the formula of the spinel mineral: 18.2 Give the name of spinels that contain sulfide ions: 18.3 Give the formula of the three kinds of spinels, including metal ion site occupation:

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Chem 242, Winter 2012, Final examination Your ID # 18.4 For the spinel containg zinc and iron(III), with a ratio Fe/Zn = 2/1, give the formula and the magnetic

property for each kind of spinel, such as defined in above question 18.3. Do NOT justify your answers. 19. Give the formula of each borate anion. Draw each anion, including three variations for one of them, and for each, give the ratio of bridging oxygen over terminal oxygen

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Chem 242, Winter 2012, Final examination Your ID #

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Chem 242, Winter 2012, Final examination Your ID # 20. Answer the following question regarding graphite:

20.1 Most reliable method of preparation from amorphous carbon at a large scale. Give the name of the method and a brief description

20.2 Give the bonding type observed in graphite: 20.3 Tell whether graphite is molecular, ionic, metallic or a covalent polymeric network

20.4 Give the hybridization of carbon in graphite

20.5 Tell whether graphite is hard or soft, and give a practical application of its harness or softness.

20.6 Give its electrical property, and whether that property is isotropic or anisotropic.

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Chem 242, Winter 2012, Final examination Your ID # 21. Answer the following regarding nitrogen dioxide : 21.1 Give its formula:

21.2 Draw all its Lewis structure(s) and tell whether there is resonance in that molecule.

21.3 Give the hybridization of nitrogen:

21.4 Give the approximate bond angle, with a short explanation:

21.5 Give the bond order in the real nitrogen dioxide molecule:

21.6 Give the magnetic property of the molecule with a short explanation:

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Chem 242, Winter 2012, Final examination Your ID # 22. 22.1 Explain briefly, using balanced equations, what happens to the sulfur contained in coals and natural gas when these are burned, and the resulting damage to the environment: 22.2 Describe briefly, using a balanced equation, what is the method used in industry to reduce the emission of the sulfur compound formed in power plants that burn coal or natural gas. Explain briefly why such a reaction to neutralize the sulfur compound formed works.

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Chem 242, Winter 2012, Final examination Your ID # 23. Group 17 elements: 23.1 Give the name of group 17:

23.2 Given the expected oxidation states for group 17 elements, and explain briefly why the first element of the group behaves differently from the rest of the group with respect to oxidation states:

23.3 Give the main natural source of fluorine :

See Part II of this exam on the next page

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Chem 242, Winter 2012, Final examination Your ID # Part II starts here. Give your answers in the space provided. Detailed explanation required 2x: Explain, using balanced equations, how caved are formed underground and how columns of material grow up from the floor of the caves and down from their ceiling. Give the names of these columns of material.

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Chem 242, Winter 2012, Final examination Your ID # 25: The structure of rubidium calcium fluoride, RbCaF3 has the following characteristics:

- simple (primitive) cubic unit-cell, with a unit-cell edge a = 3.905 Å - atomic positions: Ca in 0 0 0 Rb in 2 2 2 F in 2 0 0

25.1. Give the list of lattice translations present in a primitive lattice (No redundant ones):

25.2. Derive the list of all ions contained in the unit-cell (show calculation, do NOT give

redundant ones): 25.3. Draw a three-dimensional picture of the unit-cell and place all the ions inside.

Draw all the bonds on the same picture. Also draw one example of the shortest distance for the following: Rb-Rb, Rb-Ca, Rb-F, Ca-Ca, Ca-F and F-F.

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Chem 242, Winter 2012, Final examination Your ID # 25.4. Determine the number of each kind of ions in the unit-cell (explain)

25.5. Check that the stoichiometry of the unit-cell is in agreement with that of the compound formula.

25.6. Determine the number of unit formulas in the unit-cell; show the formula used.

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Chem 242, Winter 2012, Final examination Your ID # 25.7. Just using the position of the three elements in the periodic table, i.e. without using the

figure, tell which elements form bonds to one another in RbCaF3, and give, with justifications, the mode of bonding.

25.8. Give the coordination number (for Rb, Ca and F) and shape (for Ca and F only) of the

polyhedron of coordination of the ions, as shown on the figure.

25.9. Determine the values of the nearest Rb-Rb, Ca-Ca, F-F, Rb-Ca, Rb-F and Ca-F distances and. Show the detail of the calculations, and give the coordinates of the pair of ions used to calculate each interionic distance.

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Chem 242, Winter 2012, Final examination Your ID # 25.10. On the above figure, draw all the bonds for one Cu, and the same for one Cl, showing the

three-dimensionality of the coordination of each ion. Use the figure to give the coordination number and shape of the polyhedron of coordination for

both ions. 25.11. Show on the figure one of each of the nearest Cu-Cu, Cl-Cl, and Cu-Cl distances and

determine their numerical values. Show the detail of the calculations.

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Chem 242, Winter 2012, Final examination Your ID #

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