Unit IV Homework Set General Chemistry I

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1 Unit IV omework Set General hemistry I Oxidation number problems from previous homework assignments, plus other relevant problems carried over from Unit III: 5. (Unit II) Earlier in semester we considered the Earth-saving chemistry of selenium, including some of the compounds listed below, and we introduced the selenate ion, SeO.. For each of the compounds shown, assign the oxidation numbers and write them in the spaces provided. SeO 2 Se O K 2 Se K Se 2 Se Se SeO 4 2 SeO 3 Se Se. In part, the last compound is formed from the first compound according to the following chemical equation: SeO O 2 SeO 3 Is the above reaction a redox reaction? Explain your reasoning. 7. (Unit II) ppendicitis is caused by inflammation of the appendix.... The gases used in this procedure have advantages and disadvantages relative to each other. For example, N 2 O gas has a mild analgesic effect. On the other hand... During prolonged laparoscopic procedure N 2 O should not be a preferred gas for pneumoperitoneum because it supports combustion better than air. onsider this reaction with methane. 4N 2 O(g) + 4 (g) 4N 2 (g) O(g) + O 2 (g) 2. ssign oxidation numbers for all of the atoms in this reaction. Write the oxidation numbers in parentheses above the formula. \ / \ / \ / \ / 4N 2 O(g) + 4 (g) 4N 2 (g) O(g) + O 2 (g) Which element is oxidized? Which is reduced? 14. (Unit II) The proper assignments of oxidation numbers (ON) are necessary for recognizing and balancing redox reactions (e.g. questions IV and V on page 3), but they are also useful for understanding other aspects of chemical reactivity. For example, I mentioned in class that oxidation numbers allow one to deduce the relative strength of analogous acids.. ssign the requested oxidation numbers for the following pairs of acids: 1. NO 2 NO 3 ON of N ON of N

2 Unit IV omework Set page SO 4 2 SO 3 ON of S ON of S 3. lo 4 lo 2 ON of l ON of l. ircle the stronger acid in each of the above pairs.. What is the general relationship between oxidation number and acid strength? D. On October 12, 2008, an oleum spill at a chemical plant in western Pennsylvania forced about 2,500 residents to evaluate. Oleum also known as fuming sulfuric acid, 2 SO 4 xso 3 is especially dangerous because the sulfur trioxide escapes as a gas and reacts with moisture in the air to form sulfuric acid according to the reaction SO 3 (g) + 2 O(g) 2 SO 4 (g). Is this a redox reaction? Explain your reasoning. 16. (Unit II) Titration with an aqueous solution of potassium dichromate is a useful procedure for determining the amount of iodide in solution. The unbalanced chemical equation for this reaction is given below. ssign the oxidation number of the atoms indicated below (all atoms except and O). K 2 r 2 O 7 (aq) + I(aq) ri 3 (aq) + I 2 (s) + KI(aq) + 2 O(l) Identify the oxidizing agent and the reducing agent in the above reaction. oxidizing agent reducing agent 18. (Unit II) Several years ago an undergraduate working in my lab needed acetylene gas, (g), for an experiment. Normally acetylene is purchased in a tank like other gases, but in the published experiment he was trying to repeat, the researchers generated acetylene by adding calcium carbide to a large volume of water and collecting the acetylene gas, according to this reaction a 2 (s) + 2 O(l) (g) + ao(s). Is this a redox reaction? Explain your reasoning. 3. (Unit III) We carried out the thermite reaction.... Write the oxidation numbers in the spaces provided. \ / \ / 2l(s) O(s) l 2 O 3 (s) (g) 9. (Unit III) Yttrium is also a useful starting material for making other yttrium compounds... D. ircle the one that is larger? 1. O F 2. O 2 F 3. l F E. Why would picking the larger between oxygen and chlorine be more difficult?

3 Unit IV omework Set page (Unit III) Write ground-state electronic configurations for the following atoms or ions and give the number of unpaired electrons: P(g) Ti(g) Pt(g) unpaired electrons unpaired electrons unpaired electrons 21. (Unit III) TOMI PROPERTIES. ircle the atom expected to have the larger radius. 1. a e 2. S Si 3. l I P Sb. Which of the following has the largest radius: F, O 2, Na +, Ne? Explain your reasoning.. ircle the atom expected to have the higher first ionization energy. 1. l P 2. s N Energy 3. Ge O Se D. Using the coordinates provided, show the expected shape for a plot of sequential ionization energies for nitrogen. IE 1 IE 2 IE 3 IE 4 IE 5 IE 6 IE 7 IE (Unit III) TOMI PROPERTIES. For the following sets of atoms, write an L above the one that is largest, and an S above the one that is smallest. 1. O S Se Te 2. s r Ge Se 3. S Se Si Sn. Give an example of a monoatomic ion that is smaller than an argon atom but has the same number of electrons.. Would you expect the following reaction to be more favored towards the left (reactants) or towards the right (products)? (g) + O + (g) + (g) + O(g) Explain your reasoning.

4 Unit IV omework Set page 4 New and/or expanded problems for Unit IV: 9. (Fall 2008) onsider the following gas phase reaction: F 2 (g) + I 2 (g) 2FI(g). You will note from the data provided that the bond energy for FI(g) is greater than the bond energies of either F 2 (g) or I 2 (g). 1. Speculate on why the bond enthalpy of FI(g) is greater than the bond enthalpies of either F 2 (g) or I 2 (g). 2. ased on the bond energies, do you expect the above reaction to be endothermic or exothermic? Explain your reasoning.. Now use bond energies to estimate for the above reaction. Does your answer agree with your prediction in I..1 above?. Fluorine and iodine form a number of other compounds, including IF 3 and IF 5. In the space below, draw dot structures for these molecules and sketch the expected shape of the molecule. IF 3 IF 5 dot structure IF 3 dot structure IF 5 molecular shape molecular shape 11. (Fall 2015) Draw dot structures as instructed below, and answer any associated questions. e sure to show all nonzero formal charges.. Draw the best dot structure you can for OF 2.. Draw the best dot structure you can for NN, where the atoms are connected as written.. Draw the best dot structure you can for the hypothetical molecule NOF which contains all of the nonmetal elements from the second row of the periodic table, except neon. Which bond in NOF do you expect to be the strongest? Why? D. Draw two dot structures for SeO 2 : 1. best dot structure you can that obeys the octet rule, and 2. best dot structure you can that exceeds the octet rule to minimize formal charge. Would the molecular geometries corresponding to the two dot structures you drew above be the same or different? Explain why or why not.

5 Unit IV omework Set page (Fall 2015) onsider the fluorine compounds shown below.. Which of these molecules contain polar bonds?. Which of these molecules are polar? 13. (Fall 2012) Write the best dot structure you can and assign all non-zero formal charges for the following molecules/ions. Draw a box around the structure you consider to be the best (i.e. the one you want graded). OrF (r is the central atom) PF (Fall 2012) I really botched the question on the last exam involving the partial oxidation of hydrocarbons as a route to make hydrogen gas. Let s see if I can get it right this time. We ll keep things simple by considering the partial oxidation of ethane as shown in the following reaction: 2 6 (g) + O 2 (g) 2O(g) (g) nd I do not want to leave out any important reactions and values, so instead of using ess s law, let s use the bond enthalpy data provided on the last page of the info sheet.. First, write dot structures for 2 6, O 2, O, and 2. You will need these dot structures for parts and. 2 6 O 2 O 2. Now calculate for the partial oxidation of ethane.. Was ethane really oxidized in this reaction? ssign oxidation numbers 2 6 (g) + O 2 (g) 2O(g) (g) Was 2 6 oxidized? If so, did oxidation occur at or or both? 15. (Fall 2012) Throughout the semester we considered the combustion of fuel and the analogous reaction the food undergoes as part of the metabolic processes: fuel/food + O 2 (g) O 2 (g) + 2 O(l)

6 The reverse of this reaction that occurs during photosynthesis is also pretty important: O 2 (g) + 2 O(l) fuel/food + O 2 (g). Is this reaction endothermic or exothermic? Explain your reasoning.. recent Science Q& feature in the New York Times began as follows: Unit IV omework Set page 6 Q. My family owns a 40-acre woodlot of relatively mature deciduous trees. ow many pounds of carbon dioxide does such a forest absorb in a typical year? nd how many pounds of oxygen are emitted?. "n approximate value for a 50-year-old oak forest would be 30,000 pounds of carbon dioxide sequestered per acre," said Timothy J. Fahey, professor of ecology in the department of natural resources at ornell University. "The forest would be emitting about 22,000 pounds of oxygen." Let s assume that the carbon dioxide is sequestered as 6 12 O 6. onvert 30,000 pounds of carbon dioxide to moles of O 2 and 22,000 pounds of oxygen to moles of O 2. Now balance the chemical equation O 2 (g) + 2 O(l) 6 12 O 6 (s) + O 2 (g) ased on your calculation, if 30,000 pounds of carbon dioxide was sequestered would 22,000 pounds of oxygen be emitted? Explain your reasoning or support your answer with a calculation. 16. (Fall 2015) Iodine is an important element. While its percent abundance on Earth is less than 0.05%, iodine is an essential element in biology, and iodine compounds have found numerous applications in industry and medicine.. Dot structures are given below for several compounds containing iodine (lone pairs are shown only for the central atom). Draw the structure and name the molecular geometry from the following list: linear, bent, T- shaped, see-saw, trigonal pyramidal, trigonal planar, trigonal bipyramidal, square planar, square pyramidal, tetrahedral, and octahedral. name: name: name: name:

7 Unit IV omework Set page 7 name:. Resonance structure for the molecule IN are given below. ssign nonzero formal charges for these dot structures. Which dot structure is the best resonance structure for IN? 17. (Fall 2012) For each of the following n molecules, give one of the following descriptive names for the molecular geometry (atoms only): linear, bent, T-shaped, see-saw, trigonal pyramidal, trigonal planar, trigonal bipyramidal, square planar, square pyramidal, tetrahedral, octahedral. To the right of the name, sketch the molecular geometry, using wedges for bonds coming out of the paper and dashed lines for bonds going into the plane of the paper. You only need to show the lone pairs on the central atom. Use arrows to show any expected distortions from the idealized geometry. Finally, assuming the bonds are polar, indicate whether the molecule will polar or nonpolar. 18. (Fall 2009) ssign the oxidation numbers for all of the carbon and oxygen atoms in the following organic reagent: O O O

8 Unit IV omework Set page (Fall 2009) The previous question allowed you to demonstrate your ability to write dot structures and use them to deduce geometries and hybridization. The next two examples, drawn from the recent literature, are a bit more interesting, but the fundamental tools used to describe the electronic structure and physical geometry are the same.. ydrazine borane, N 2 N 2 3, has been proposed as a material for storing hydrogen (J. m. hem. Soc. 2009, 131, ). In combination with lithium hydroxide, hydrogen gas is released according to the reaction N 2 N 2 3 (s) + Li(s) LiN (s) + 2 (g) Write a dot structure for N 2 N 2 3 and assign all nonzero formal charges.. When N 2 N 2 3 reacts to form N 2 N 3, why is the hydrogen ion lost from the middle nitrogen instead of the outer nitrogen? 20. (Fall 2009) DOT STRUTURES 1. Write the best dot structure you can and assign all non-zero formal charges for each of the following molecules/ions. Draw a box around the structure you consider to be the best (i.e. the one you want graded). 2. Sketch the molecular geometry, using wedges for bonds coming out of the paper and dashed lines for bonds going into the plane of the paper. You only need to show the lone pairs on the central atom. Use arrows to show any expected distortions from the idealized geometry. 3. Give a descriptive name for the molecular geometry (atoms only): bent, T-shaped, see-saw, trigonal pyramidal, trigonal planar, trigonal bipyramidal, square planar, square pyramidal, tetrahedral, octahedral. 4. Give the hybridization about the central atom.. OrF (r is the central atom). NO 3 1. dot structure 1. dot structure 2. molecular geometry 2. molecular geometry 3. name: 3. name: 4. hybridization: 4. hybridization:

9 Unit IV omework Set page 9. PF 4 1. dot structure 1. dot structure 2. molecular geometry 2. molecular geometry 3. name: 3. name: 4. hybridization: 4. hybridization: 21. (Fall 2009) Xenon forms bonds with oxygen and fluorine, but compounds containing Xe-N bonds are rare (J. m. hem. Soc. 2009, 131, ). The cation F 3 S NXeF was investigated and found to rearrange to form F 4 S=NXe. In both ions the atoms are connected as S N Xe, and the multiplicity of the bonding between sulfur and nitrogen is indicated in the formulas.. Write a good dot structure for F 3 S NXeF and give the molecular geometry and hybridization of the sulfur, nitrogen, and xenon atoms. sulfur: molecular geometry hybridization nitrogen: molecular geometry hybridization xenon: molecular geometry hybridization. Write a good dot structure for F 4 S=NXe and give the molecular geometry and hybridization of the sulfur and nitrogen atoms. sulfur: molecular geometry hybridization nitrogen: molecular geometry hybridization 22. (Fall 2009) dot structure for methyl amide is shown on the right. O Draw a resonance structure for this dot structure. N Which structure do you think is the better resonance structure: the one given above, or the one you drew? Why?

10 Unit IV omework Set page (Fall 2015) Most explosive compounds are nitrogen rich, but an exception to this rule is diacetone diperoxide (DDP) shown on the right. This compound is fairly easy to make, and because it does not contain nitrogen, it is not easily detected. DDP and chemically similar compounds are the reason bottles larger than 3.4 ounces (100 ml) are not allowed in our carry-on items when we fly.. balanced chemical equation for the combustion of DDP is given below O 4 + 7O 2 6O O Use bond enthalpies to estimate for this reaction.. The hydrocarbon analog of DDP is 1,1,4,4-tetramethylcyclohexane (TM). 1. Write a balanced chemical equation for the combustion of TM. The formula for TM is One mole of DDP combusts more violently than one mole of TM. Do you expect the enthalpy of combustion for DP to be more or less exothermic than the enthalpy of combustion for TM? TM 3. onsidering the bond enthalpies, explain why DDP is more reactive than TM.