CHM2045 Exam 3 Review Fall 2015

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1 The steps to solving any chemistry problem 1) Read Question 2) Re-read Question 3) Write down everything you are given 4) Write down what you are trying to find CHM2045 Exam 3 Review 1) Write out the following Lewis Structures a) NO 3 - b) SeCl 4 c) ClF 4 + d) NI 3 e) COCl 2

2 2) In which of the following is it necessary to use an expanded octet to represent a Lewis structure which has a zero formal charge of the central atom? I. SO 4 2 II. SeO 2 III. CO 3 2 IV. PO 4 3 V. SO 3 (a) I and II only (b) III, IV, and V only (c) I, II, IV, and V only (d) IV and V only (e) V only 3) Which of the following species have resonance? (There could be more than one answer) a) NO 3 b) 2 SO 3 c) 3 PO 3 d) O 3 e) H 2O

3 4) Determine the molecular shape of the following molecules a) CO 3 2- b) CS 2 c) I 3 - d) XeF 4 5) Which of the following molecules show net dipole moments? (I.e. Which of the molecules are polar?) (More than one answer) a) CH 4 b) O 3 c) CH 2Br 2

4 6) Which of the following is true regarding molecular orbital theory? (a) Antibonding orbitals have no effect on bond order (b) Molecular orbitals are hybridizations of atomic orbitals (c) Molecular orbital theory can be used to predict the relative stability of molecules (d) Molecular orbital theory cannot be used to predict the magnetic properties of molecules (e) The overlap of p orbitals always forms pi bonds 7) What are the hybridizations of all the atoms in the molecule? (For c, identify the labeled atoms only) a) BF 3 b) CO 2 c)

5 8) The active ingredient in super-glues is methylcyanoacrylate. How many sigma (σ) and pi (π) bonds are in one molecule of methylcyanoacrylate? (hint : don t forget to consider the carbon-hydrogen bonds in the molecule) (a) 7 σ, 3 π (b) 7 σ, 4 π (c) 12 σ, 3 π (d) 12 σ, 4 π (e) 16 σ, 4 π 9) Indicate the hybridization change of sulfur during the reaction: SF 4 + 2H 2O SO 2 + 2HF (a) From sp 3 d to sp 2 (b) From sp 3 to sp 2 (c) From sp 3 d to sp 3 (d) From sp 4 to sp 2 (e) From sp 3 d 2 to sp

6 10) Consider 3.00 moles of Xenon, considered an ideal gas, at a density of 5.00 g/l and a pressure of 5.00 atm. What is the closest value to the temperature of this gas? 11) A g sample of a gas occupies a volume of 3.34 L at 28 C and 745 mmhg. What is the most likely formula for the gas? a) NO 2 b) BCl 2 c) CO 2 d) Xe

7 12) When a 5.00 L flask containing 1.35 atm of gas A is joined with a 2.00 L flask containing 1.00 atm of gas B, and the stopcock between the flasks is opened, the gases mix at constant temperature. What is the total pressure of gases in the now-joined flasks? (assume no reaction between the gases) 13) A gas mixture consists of equal masses of methane (CH 4; molecular weight 16.0) and argon (Ar; atomic weight 40.0). If the partial pressure of argon is 200 mm Hg, what is the pressure of methane, in mmhg?

8 14) When an evacuated 50.0 ml glass bulb is filled with a noble gas at 22 C and 747 torr, the bulb gains g in mass. Which of the following is the noble gas? (a) Xe (b) Kr (c) Ar (d) Ne (e) He 15) Select the pair of substances in which the one with the lowest normal boiling point is listed first. (a) C 7H 16, C 5H 12 (b) Xe, Kr (c) H 2O, H 2S (d) CH 3CH 2OH, CH 3OCH 3 (e) CF 4, CCl 4 16) Circle which member in each pair has the highest vapor pressure at a given temperature? A: C 2H 6 or C 4H 10 B: CH 3CH 2OH or CH 3CH 2F C: NH 3 or PH 3

9 17) Which of the following substances exhibits hydrogen-bonding intermolecular forces in its liquid state? (a) CH 3NH 2 (b) CH 3OCH 3 (c) CH 3F (d) H 2S (e) (CH 3) 3N 18) Select the correct statement for the given phase diagram: (a) The solid has a lower density than the liquid. (b) The triple point is higher than the normal melting point. (c) As one follows the line from C to D the substance changes from a solid to a liquid. (d) As one follows the line from C to D the substance changes from a liquid to a gas. (e) The temperature corresponding to Point E is the normal boiling point. 19) Which of the following properties of water is not related to hydrogen-bonding intermolecular forces in water? (a) Relatively high surface tension (b) Relatively low vapor pressure (c) Relatively high ΔH vap (d) Relatively high molecular polarity (e) Solid water is less dense than liquid water

10 20) Nickel crystallizes in a face-centered cubic structure with an edge length a = 388 pm. Based on this information, calculate the approximate density of nickel. 21) A cylinder with a frictionless movable piston contains an ideal gas at 400K. After the temperature of the cylinder is increased to 800K at constant barometric pressure, which of the following will not be true? a) The volume of the gas in the cylinder at 800K will be twice the volume of the gas in the cylinder at 400K b) The average kinetic energy of the gas in the cylinder at 800K will be greater than it was at 400K c) The frequency and force of the gas particle collisions in the cylinder at 800K will be greater than at 400K d) The root-mean-square velocity (urms) of the gas in the cylinder at 800K will be greater than at 400K e) The pressure of the gas inside the cylinder at 800K will be twice the pressure of the gas at 400K 22) A certain gaseous oxide of sulfur has an effusion rate that is times the effusion rate of oxygen gas. What is the most likely molecular formula of this oxide? (a) SO (b) SO 2 (c) SO 3 (d) SO 4 (e) S 2O

11 23) Non-ideal behavior for a gas is most likely to be observed under conditions of (a) High temperature and low pressure. (b) High temperature and high pressure. (c) Low temperature and low pressure. (d) Standard temperature and pressure. (e) Low temperature and high pressure. GOOD LUCK ON THE EXAM! -Broward Teaching Center

3. Which of the following elements is primarily responsible for the photochemical smog? Chemistry 12, Exam III, Form A, April 4, 2001

3. Which of the following elements is primarily responsible for the photochemical smog? Chemistry 12, Exam III, Form A, April 4, 2001 Chemistry 12, Exam III, Form A, April 4, 2001 In all questions involving gases, assume that the ideal-gas laws hold, unless the question specifically refers to the non-ideal behavior. 1. It takes 21.3