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Tutorial4-Solutions.pdf

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Department
Chemistry
Course
CHEM 1A03
Professor
David Brock
Semester
Summer

Description
CHEM 1A03 TUTORIAL #4 Oct 1 – Oct. 5, 2012 Solutions – Chapter 10 _____________________________________________________________________ The following problems (1-8) are based on material from Chapter 10 and class notes. 1. Arrange the following in terms of increasing electronegativity: (a) Mg, N, O, Si, (b) F, Se, Sn, Te (a) Mg < Si < N < O EN increases left to right across a period and bottom to (b) Sn < Te < Se < F top of a group. 2. For the following anions: SO , CO , NO , ClO , and ClO : - 3 3 3 3 2 a) Draw Lewis structures and resonance forms b) What are the average bond orders for the central-atom-to-oxygen bonds in these species? c) What is the average formal charge on the oxygen atoms in each of these species? d) Indicate whether the species is an exception to the octet rule (i.e. it has more than an octet of electrons around one of the atoms). e) Give the VSEPR AB Enclmsses f) Predict the shapes of the anion. Note that the figures used to illustrate the shapes in point f) do not indicate the bond orders and the formal charges. SO 2- 3 a) 26 valence electrons O S O O S O O S O O O O 2- b) For SO3, the average bond order is 4/3. c) The average formal charge on oxygen in S32-is -2/3. d) The charge-minimized resonance structures do not follow the octet rule. e) AB 3 f) triangular pyramidal S O O O Page 1 of 9 CHEM 1A03 TUTORIAL #4 Oct 1 – Oct. 5, 2012 Solutions – Chapter 10 _____________________________________________________________________ CO 2- 3 a) 24 valence electrons O O O C C C O O O O O O b) For CO , the average bond order is 4/3. 3 2- c) The average formal charge on oxygen3iis -2/3. d) The resonance structures do follow the octet rule. e) AB 3 f) triangular planar or trigonal planar O O C O NO - 3 a) 24 valence electrons O O O N N N O O O O O O b) For NO, the average bond order is 4/3. 3 - c) The average formal charge on oxygen3in NO is -2/3. d) The resonance structures do follow the octet rule. e) AB 3 f) triangular planar or trigonal planar O O N O ClO - 3 a) 26 valence electrons O Cl O O Cl O O Cl O O O O - b) For Cl3, the average bond order is 5-3. c) The average formal charge on oxygen3in ClO/3. d) The charge-minimized resonance structures do not follow the octet rule. e) AB3E f) triangular pyramidal or trigonal pyramidal Page 2 of 9 CHEM 1A03 TUTORIAL #4 Oct 1 – Oct. 5, 2012 Solutions – Chapter 10 _____________________________________________________________________ Cl O O O ClO 2- a) 20 valence electrons Cl Cl O O O O - b) For Cl2 , the average bond order is 3/2. c) The average formal charge on oxygen in2ClOis -1/2. d) The charge-minimized resonance structures do not follow the octet rule. e) AB2E2 f) bent (or angular or v-shape) Cl O O 3. Oxalic acid, (COOH)2 has two ionizable hydrogens and contains a carbon-carbon single bond. When one mole of oxalic acid reacts with one mole of calcium hydroxide,Ca(OH) 2, the salt C2C 4 is formed. 2- a) Draw adequate Lewis structures to represent the bonding in the oxalate 2on4 C O . There are 34 valence electrons. O O O O O O O O C C C C C C C C O O O O O O O O b) What is the average carbon-oxygen bond order in oxalate ion? Average bond order = (1 + 2 + 1 + 2)/4 = 1.5 c) What is the average formal charge on each oxygen atom in oxalate ion? Average formal charge on oxygen = (-1 + 0 + (-1) + 0)/4 = -1/2 d) Give the shape around each C atom in the oxalate ion. Each C atom is AX3 trigonal planar (triangular planar). Page 3 of 9 CHEM 1A03 TUTORIAL #4 Oct 1 – Oct. 5, 2012 Solutions – Chapter 10 _____________________________________________________________________ O O C C O O 4. Phosphoric acid, H 3O ,4contains three oxygen-hydrogen single bonds. When one mole of phosphoric acid reacts with one mole of sodium hydroxide, the salt sodium dihydrogen phosphate, NaH P2 , 4esults. - a) Draw adequate Lewis structures for H PO3and4H PO .2 4 H PO has 32 valence electrons. H PO has 32 valence electrons. 3 4 2 4 O O O HO P OH HO P O HO P O OH OH OH - b) Calculate bond orders for all the phosphorus-oxygen bonds of H PO3and4H PO 2 4 In H PO , there is one P-O bond of bond order 2, and three P-O bonds of bond order 1. In 3 - 4 H 2O ,4there are two P-O bonds of bond order 1.5, and two P-O bonds of bond order 1. - c) Calculate the formal charges on each oxygen atom in H 3PO 4nd H PO2. 4 In H3PO 4 all oxygen atoms have a formal charge of zero. In H2PO 4 two oxygen atoms (bonded to H) have a formal charge of zero, while the other two have a formal charge of -1/2. 5. A gaseous molecule "X" is made by burning sulfur in air. "X" is converted to "Y" by reaction with oxygen in the presence of a catalyst. "Y" reacts vigorously with water to produce "Z" which turns litmus red. a) Identify "X", "Y", and "Z". "X" = SO 2, "Y" is SO3, and "Z" is2H S4 . b) Write a balanced equation for each reaction. S8(s) + 8 O2(g) --> 8 S2 (g) or S(s) + O2(g) --> SO2(g) 2SO 2g) + O 2g) --> 2SO 3g) SO 3(g) + H2O(l) --> 2 SO4(aq) c) Draw Lewis diagrams of the molecules "X" and "Y". Determine their AB nEmVSEPR classes and name the molecular shapes. Indicate the bond angles, and if they are ideal or less than ideal. Are the "X" and "Y" molecules polar or non-polar? Page 4 of 9 CHEM 1A03 TUTORIAL #4 Oct 1 – Oct. 5, 2012 Solutions – Chapter 10 _____________________________________________________________________ SO 2as 18 valence electrons. Its Lewis structure is (2 double bonds) INCORRECT: CORRECT: .. S S .. S .. O O O O O O .. .. Petrucci does not show the charge-minimized structure, as seen on the right-hand side. We will draw this structure. SO 3as 24 valence electrons. Its Lewis structure is O S O O For SO 2 (b) its VSEPR class is2AX E. The shape is bent (or angular, or v-shape). The O-S-O bond angle will be less than the ideal angle of 120, because of the influence of
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