AVOGADRO EXAM 2004 UNIVERSITY OF WATERLOO DEPARTMENT OF CHEMISTRY 20 MAY 2004 TIME: 75 MINUTES

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1 VGR XM 24 UNIVRSIY F WRL PRMN F HMISRY 2 MY 24 IM: 75 MINUS his exam is being written by several thousand students. Please be sure that you follow the instructions below. We'll send you a report on your performance. op performers are eligible for a prize. 1. Print your name here: 2. Print your school name and city on your SUN RSPNS sheet.. Select, and enter on the SUN RSPNS sheet, one of the following numbers: ode 1 ode 2 ode ode 5 ode 6 ode 8 ntario, now studying grade 11 hemistry in a nonsemestered school ntario, now studying grade 11 hemistry in a semestered school ntario, grade 11 hemistry already completed Manitoba or Saskatchewan high school student Québec high school student lberta or ritish olumbia high school student ode 9 New runswick, Newfoundland, Nova Scotia or Prince dward Island high school student ode 1 Northwest erritories, Nunavut, or Yukon high school student ode 11 High school student outside anada ode 12 eacher 4. Print your name (last name, first name and optional middle initial) on the SUN RSPNS sheet. lso fill in the corresponding circles below your printed name. 5. Now answer the exam questions. Questions are not in order of difficulty. Indicate your choice on the SUN RSPNS sheet by marking one letter beside the question number. Mark only one answer for each question. Questions are all of the same value. here is a penalty (1/4 off) for each incorrect answer, but no penalty if you do not answer. 6. ake care that you make firm, black pencil marks, just filling the oval. e careful that any erasures are complete make the sheet white again H 1.8 Li Na K Rb s Fr (22) e Mg a Sr a Ra (226) 21 Sc Y (5771) LaLu (891) clr i Zr Hf Rf V Nb a b r Mo W Sg Mn c (98) 75 Re h 8 26 Fe Ru s Hs o Rh Ir Mt 1 28 Ni Pd Pt Uun u g u Uuu 12 2 Zn d Hg Uub l Ga In l Uut Si Ge Sn Pb N P.97 s Sb i S Se e Po (29) F l r I t (21) He 4. 1 Ne r Kr Xe Rn (222)

2 VGR XM 24 NSWRS 1 How many neutrons, protons and electrons are there in one 25 Mg + ion? 25 neutrons, 25 protons, 24 electrons 12 neutrons, 1 protons, 12 electrons 4 For which of the following processes is the energy change equal to the second ionization energy of X(g)? X (g) + e X 2 (g) 1 neutrons, 12 protons, 1 electrons X(g) + 2e X 2 (g) * 1 neutrons, 12 protons, 11 electrons 25 neutrons, 12 protons, 11 electrons 2 n element, Z, has only two isotopes, with relative masses of 8.1 and 8.2. naturally occurring sample of this element has a relative mass of What is the percentage abundance of the lighter isotope? X 2+ (g) X + (g) + e X(g) X 2+ (g) + 2e * X + (g) X 2+ (g) + e 5 What is the correct Lewis symbol for the oxygen atom? % * 4% 5% 6% 7% What is the correct burette reading? * 24.4 ml ml * ml ml 24.5 ml 6 Which ion of magnesium is stable in magnesium compounds? * Mg 2+ Mg Mg + Mg + Mg 24 UNIVRSIY F WRL VGR XM /2

3 7 What is the mass of one oxygen molecule? g g g vogadro constant: N = mol 1 11 Which one of the following is the major cause of hardness in natural groundwater? iron ions * calcium ions * g sodium ions g chloride ions 8 Which of the following bonds has the least ionic character? fluoride ions * H H KH F lectronegativity values H, 2.1, 2.5,.5 F, 4. K,.8 r, he reaction 2 Na(s) + 2 (g) Na 2 2 (s) is an example of * a synthesis reaction a decomposition reaction a single displacement reaction 9 In what region of the periodic table are the least metallic elements found? a double displacement reaction an addition reaction upper centre lower centre * upper right lower left IUP defines an addition reaction as a chemical reaction of two or more reacting molecular entities, resulting in a single reaction product containing all atoms of all components, with formation of two chemical bonds and a net reduction in bond multiplicity in at least one of the reactants. n example of an addition reaction is the addition of Hr across the double bond of ethene. upper left 1 When zinc metal is treated with dilute aqueous sulfuric acid, H 2 S 4 (aq), the products are 1 What is the correct formula for bismuth (III) sulfide? i S is i S 2 ZnS 4, 2 and H 2 Zn(H) 2 and S Zn(H) 2 and S 2 * i 2 S is * ZnS 4 and H 2 ZnS, H 2 and 2 24 UNIVRSIY F WRL VGR XM /

4 14 What are the spectator ions in the reaction below? Pb(N ) 2 (aq) + 2 KI(aq) PbI 2 (s) + 2 KN (aq) Pb 2+, N and I Pb 2+ and I * K + and N K + and Pb 2+ Pb 2+ and K + 17 What is the percentage, by mass, of nitrogen in the compound N 2 5? 1.% * 25.9% 28.6% 5.% 4.% 15 alance the equation below using the smallest whole number coefficients. r 2 + KH + 2 K 2 r 4 + H 2 What is the coefficient of 2 when the equation is balanced? 18 Which combination of solutions would produce a precipitate upon mixing? Na 2 S 4 (aq) and (NH 4 ) 2 S(aq) NaN (aq) and Mgr 2 (aq) 2 g 2 S 4 (aq) and KN (aq) * 4 6 * us 4 (aq) and al 2 (aq) (NH 4 ) 2 (aq) and KN (aq) 8 19 onsider the equation below. 16 particular compound has the following mass composition. 2.4% Na.71% H 21.8% P 45.1% What is the empirical formula of the compound? NaH 2 P Na 2 HP Na 2 H P NaH 2 P 4 * Na 2 HP 4 2 NaH + l 2 Nal + Nal + H 2 What is the maximum mass of Nal that can be obtained from a reaction mixture containing 5. grams of NaH and 71 grams of l 2? * 46.5 g 9.1 g 74.5 g 186 g 121 g 24 UNIVRSIY F WRL VGR XM /4

5 2 If 1. L of.1 mol L 1 NaN (aq) and 1. L of.2 mol L 1 Mg(N ) 2 (aq) are mixed, what are the final concentrations of Na +, Mg 2+ and N? [Na + ] =.5 mol L 1, [Mg 2+ ] =.1 mol L 1, [ N ] =.2 mol L 1 2 Which of the following does not show any significant hydrogen bonding? * ethyne, 2 H 2 hydrazine, N 2 H 4 ethanol, 2 H 5 H * [Na + ] =.5 mol L 1, [Mg 2+ ] =.1 mol L 1, [ N ] =.25 mol L 1 hydrogen fluoride, HF water, H 2 [Na + ] =.5 mol L 1, [Mg 2+ ] =.2 mol L 1, [ N ] =.2 mol L 1 [Na + ] =.5 mol L 1, [Mg 2+ ] =.1 mol L 1, [ N ] =.4 mol L 1 [Na + ] =.1 mol L 1, [Mg 2+ ] =.1 mol L 1, [ N ] =.4 mol L 1 21 Which one of the following substances in aqueous solution is a nonelectrolyte? 24 When three moles of calcium hydroxide, a(h) 2, react completely with two moles of phosphoric acid, H P 4, how many moles of water are produced? one two three four * six NH 4 l * H H LiF HN 2 Note: 2 produces carbonic acid (H 2 ) which ionizes in solution. 25 What is the minimum volume of pure oxygen required to burn 1. L of pure propane, H 8, completely to carbon dioxide and water? (ssume that the volumes of oxygen and propane are measured at the same pressure and temperature.) 22 Which of the following is the poorest electrical conductor? aqueous sulfuric acid graphite * solid anhydrous potassium nitrate 1. L 2. L. L 4. L * 5. L platinum molten sodium bromide 24 UNIVRSIY F WRL VGR XM /5

6 26 What volume of.142 mol L 1 Hl(aq) is required to neutralize 4. ml of.217 mol L 1 a(h) 2 (aq)? 29 Which colour of light has the highest energy per photon? * 12.2 ml red 6.11 ml orange.6 ml yellow 76.4 ml green 17.2 ml * violet 27 sample of gas occupies a volume of 27 L at 2 o and normal atmospheric pressure. What is the volume at 25 o if the pressure remains constant? onsider a sample comprised of 1. moles of an ideal gas. Which graph correctly displays how the product of pressure and volume changes with temperature? 4 L 2.2 L o 27 K * * 48 L 15 L 2 L 28 What volume of ozone,, will have nearly the same number of molecules as 1. L of 2 gas, if both volumes are measured at the same temperature and pressure? 22.4 L ozone 6. L ozone 1.5 L ozone * 1. L ozone.17 L ozone 24 UNIVRSIY F WRL VGR XM /6

7 1 What is the oxidation state of chlorine in l 2? 2 1 * +1 4 How many structural isomers of 4 H 8 are there? two three four five * six +2 2 Use the bond dissociation enthalpies provided to calculate H for the reaction below. H 2 (g) + N 2 (g) 2 NH (g) What is H for the reaction? 5 Which of the following electron attachment processes is/are endothermic? (1) Na(g) + e Na (g) (2) Mg(g) + e Mg (g) () l(g) + e l (g) +122 kj * 8 kj 122 kj 184 kj 177 kj HH 45 kj mol 1 HN 89 kj mol 1 N N 16 kj mol 1 N=N 418 kj mol 1 N N 946 kj mol 1 (4) r(g) + e r (g) (1) and (2) only * (2) and (4) only (4) only (1), (2) and () only (1), (2) and (4) only nergy is always released when an electron is added to a main group atom, except when an electron is added to a group 2 or 18 atom. toms in group 2 have completely filled subshells (s 2 ) and atoms of group 18 have completely filled shells. Which of the following elements has the highest boiling point? 6 xactly 1. g H 2 (s) at o is placed on top of.1 kg u(s) at 1 o. What is the final temperature of the combined system (water plus copper), if no heat is lost to the surroundings? N 2 F 2 * 6.9 o 4 o Heat capacity of u(s) is.9 J g 1 o 1 l 2 r 2 * I 2 21 o 5 o 65 o he heat of fusion of ice is 4 J g 1. Heat capacity of H 2 (l) is 4.18 J g 1 o 1 24 UNIVRSIY F WRL VGR XM /7

8 7 When 5.g of an impure sample of al 2 was treated with excess gn (aq),.5 g of dry gl was obtained. What is the mass percentage of al 2 in the impure sample? 4 What is the ratio x:y when the equation below is properly balanced? x Sn 2+ (aq) + y g + (aq) n Sn 4+ (aq) + m g(s)? 15% 1% 7.7% 5.% *.9% al 2, g mol 1 gl, 14.5 g mol 1 1:1 2:1 * 1:2 :4 4: 8 What is the HNH bond angle in ammonia, NH? (hoose the closest value.) 72 o 9 o * 19 o 12 o 18 o 9 Which of the following is the correct Lewis (i.e., electron dot) structure for the N 2 molecule? * f the choices provided, only has the correct number of valence electrons (16) and gives each atom an octet. he true structure of N 2 is a resonance hybrid of at least three resonance structures. 24 UNIVRSIY F WRL VGR XM /8