SOLUCIONARIO 1. A 2. C. 3. acid is a proton/h + donor and base is a proton/h + acceptor; H 2 CO 3 /CH 3 COOH and NaOH/KOH/Ba(OH) 2 ;

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1 SOLUCIONARIO 1. A. C. acid is a proton/h donor and base is a proton/h acceptor; H CO /CH COOH and NaOH/KOH/Ba(OH) ; Accept any suitable examples. 4. Chemical [ max] reaction with reactive metal/mg/zn/carbonate/hydrogen carbonate; hydrochloric acid would react faster/more vigorously / ethanoic acid would react slower/less vigorously; OR react with alkali; temperature change will be more for hydrochloric acid / temperature change will be less for ethanoic acid; Physical [ max] conductivity; hydrochloric acid will conduct more/higher / ethanoic acid will conduct less/lower; Accept other suitable examples. 5. black coffee; 10 /1000 times; 6. C 7. D 8. D 9. (i) [CH CH COOH]: ( =) 0.8 (mol dm ); [CH OH]: ( =) 1. (mol dm ); [H O]: 0.80 (mol dm ); [CH CH COOCH ][H O] (ii) (K c =) ; [CH CH COOH][CH OH] IB Questionbank Chemistry 1

2 [(0.80) ] (K c = =) 0.7; [(1. 0.8)] Allow Award [1 max] for (i) Acid: proton/h donor and Base: proton/h acceptor; Do not accept OH for base. Weak base: (base/electrolyte) partially dissociated/ionized (in solution/water) and Strong base: (base/electrolyte assumed to be almost) completely/100% dissociated/ionized (in solution/water) / OWTTE; NH / CH CH NH ; Allow either name or formula or other suitable example. (ii) sulfurous acid/h SO ; corrodes marble/limestone buildings/statues / leaching in soils / harms/kills plants; OR nitrous acid/hno ; corrodes marble/limestone buildings/statues / leaching in soils / harms/kills plants; OR carbonic acid/h CO ; corrodes marble/limestone buildings/statues / acidification of lakes; Do not allow oxides (e.g. CO etc.). Do not accept just corrodes or damages. 11. Volume of KOH: 0 (cm ); Allow any value between 0 and 1 (cm ). ph at the equivalence point: ; 1. (i) HIn is a weak acid / weak base; HIn H In ; colour 1 colour required. Award [] for M alone. in base equilibrium moves to right / in acid equilibrium moves to left; (ii) phenolphthalein; indicator colour change occurs in range of ph at the equivalence point / OWTTE; M can be scored independently even if indicator is incorrect. 1. acidic; [Fe(H O) 6 ] [Fe(H O) 5 (OH)] H / [Fe(H O) 6 ] H O [Fe(H O) 4 (OH) ] [Fe(H O) 5 (OH)] H O ;Accept equations indicating the formation of IB Questionbank Chemistry

3 [Fe(H O) (OH) ] [Fe(H O) (OH) 4 ] Do not penalize. 14. n(hcl) = ( ) = (mol); n(naoh) = ( ) = 0.00 (mol); n(hcl) remaining = ( ) = 0.00 (mol); 0.00 [HCl] = = 0.10 (mol dm ); 0.0 ph = 1.0; Award [ max] for just ph = 1.0 without working. 15. C 16. A 17. A 18. a Lewis acid can accept a pair of electrons; it is a Lewis base as it can donate the lone/non-bonding pair of electrons (on the N atom); Do not award second mark for simply stating it is a Lewis base with no reason given. 19. (measuring) the ph / the strong acid solution will have a lower ph; conductivity (measurement) / the strong acid will be a better conductor; the strong acid will react more vigorously with metals/carbonates / the reaction with metals/carbonates; the heat change when it is neutralized with a base will be different / heat of neutralization / OWTTE; 0. water can act as a Brønsted-Lowry acid by donating a proton/h to form OH ; water can act as a Brønsted-Lowry base by accepting a proton/h to form H O ; Accept equations showing the above clearly labelling the acid and basic behaviour and the conjugate acid or base. Award [1 max] for correct definition of how water can act as a Brønsted- Lowry acid or base. 1. A. B. C [OH ] 4. K b = = / ; [NH ] [OH 4.75 ] = ( ) = (mol dm ); IB Questionbank Chemistry

4 poh = log 10 ( ) =.7 / [H ] = = ; ph = 14.7 = 10.6; Award [ max] for correct final answer if no working shown (a) initial amount of HCl = = mol and initial amount of NH = = mol; 1000 final amount of NH 4 and NH both = mol; 4 final [NH ] and [NH ] both = =. 10 mol dm ; [OH [NH ] ] = K b = K b = / ; [NH 4 ] poh = 4.75 hence ph = 9.5; Award final two marking points if half-equivalence method used. 14 (b) a buffer solution resists a change in ph when small amounts of acid or base are added to it; Do not accept description in terms of composition of buffer. when H is added it reacts with NH to form NH 4 ; when OH is added it reacts with NH 4 to form NH and H O;Accept equations for last two marking points. 6. (i) NaCl is the salt of a strong acid and a strong base / no hydrolysis with (Na and C1 ion); the CO ions combine with H from water to form a weak acid leaving OH ions / CO H O HCO OH / OWTTE; (ii) Fe has a small radius and a high charge / Fe has a high charge density; it forms bonds with the OH ions from water leaving H ions / it increases the polarity of the O H bond (in the water ligands) / [Fe(H O) 6 ] [Fe(H O) 5 (OH)] H etc; 7. C 8. C 9. D 0. B 1. A. A IB Questionbank Chemistry 4

5 . (a) (i) CH COOH(aq) H O(l) CH COO (aq) H O (aq); OR CH COOH(l) H O(l) OR CH COOH(aq) Must include. Ignore state symbols. CH COO (aq) H O (aq); CH COO (aq) H (aq); (ii) K a = / [H ] = / [H ] = ; 0.00 ph =.7; Award [] for correct final answer, allow mark for correct conversion of [H ] to ph even if [H ] incorrect. (b) (initial)[ch COOH] = mol dm and) eqm [CH COOH] = 0.00 mol dm ; (initial)[ch COO ] = 0.00 mol dm and) eqm [CH COO ] = 0.00 mol dm ; Allow 0.0 moles and 0.0 moles instead of 0.00 and 0.00 mol dm. [H [CH COOH] ] = K a = mol dm [SALT] / ph = pk a log ; [CH COO ] [ACID] ph = 4.94; Award [ max] for correct final answer if no working shown. (c) (if acid added) CH COO H CH COOH; (if alkali added) CH COOH OH CH COO H O; Explanation marks cannot be awarded without equations. Accept H OH H O as OH reacts with H in the buffer to form water. 4. D 5. A [H ][OH ] [H O ][OH ] 6. (i) K c = / K / K w = [H ][OH ]/K w = [H O ][OH c = ]; [H O] [H O] Do not award mark if [ ] are omitted or other brackets are used. Expression must be consistent with K c /K w. (ii) [H ] increases, [OH ] decreases but still some present (K w / K c constant) / [OH ] cannot go to zero as equilibrium present / [OH K w K c[h O] ] = /, thus [OH ] [H ] [H ] cannot be zero / OWTTE; Accept equilibrium present. (iii) (changing T disturbs equilibrium) forward reaction favoured / equilibrium shifts to the right; IB Questionbank Chemistry 5

6 to use up (some of the) heat supplied; (K w / K c ) increases (as both [H ] and [OH ] increase); (iv) ph =, [H ] = 0.01 mol dm and ph = 6, [H ] = 10 6 mol dm / [H ] = 10 ph ; [H ] decreased/changed by 10000/10 4 ; Award [] for correct final answer. 7. C 8. C 9. A 40. C 41. (i) (K w ) = [H ][OH ] / (K w ) = [H O ][OH ]; Do not award mark if [ ] omitted or other brackets are used. (ii) [H ] increases, [OH ] decreases but still some present (K w constant) / [OH ] cannot go to zero as equilibrium present / [OH K w ] =, [H ] thus [OH ] cannot be zero / OWTTE; (iii) (changing T disturbs equilibrium) endothermic reaction / forward reaction favoured / equilibrium shifts to the right; to use up (some of the) heat supplied; K w increases (as both [H ] and [OH ] increase); (iv) (as [H ] increases) ph decreases / ph < 7; No mark for more acidic. inverse relationship between ph and [H ]/ph = log[h 1 ]/ph = log 10 ; [H ] Accept [H O ] in place of [H ]. 4. (i) Acid: H PO 4 ; (Conjugate) base: HPO 4 ; No mark for NaH PO 4 or Na HPO 4. H PO 4 (aq) H (aq) HPO 4 (aq); Accept reverse equation or reaction with water. Ignore state symbols, but equilibrium sign is required. Accept OH (ions) react with H (ions) to form H O. (ii) strong base/oh replaced by weak base (H PO 4, and effect minimized) / strong base reacts with acid of buffer / equilibrium in (i) shifts in forward direction; OH (aq) H PO 4 (aq) H O(l) HPO 4 (aq); Ignore state symbols, accept equilibrium sign. Accept OH added reacts with H to form H O. IB Questionbank Chemistry 6

7 (iii) strong acid/h replaced by weak acid (H PO 4, and effect minimized) / strong acid reacts with base of buffer / equilibrium in (i) shifts in reverse direction; H (aq) HPO 4 (aq) H PO 4 (aq); Accept reaction with H O. Ignore state symbols. 4. (i) NH weak(er) base/partial dissociation; [OH ] < 0.1(0) /poh > 1 (thus ph < 1 / ph poh = 14); (ii) around ph = 5; Accept a value between 4 and 6. strong acid weak base titration, (thus acidic) / at equivalence point, NH 4 present is acidic / NH 4 NH H ; (iii) NH (aq) H O(l) NH 4 (aq) OH (aq); Ignore state symbols, but equilibrium sign required. [NH 4 ][OH ] K b = ; [NH ] (iv) [NH ] = [NH 4 ]; (v) poh = = 4.75; pk b (= poh) = 4.75; K b = ; Ignore units. Award [] for correct final answer. (vi) optimum/most effective/highest buffer capacity/50 % 50 % buffer/equally effective as an acidic buffer and a basic buffer / OWTTE; 44. B 45. C 46. (a) strong acid completely dissociated/ionized and weak acid partially dissociated/ionized; HNO (aq) H (aq) NO (aq); HNO (aq) H (aq) NO (aq); Allow only arrows as shown. State symbols not needed. Accept H O and H O. (b) With HNO : faster rate of bubble/gas/hydrogen production; faster rate of magnesium dissolving; IB Questionbank Chemistry 7

8 higher temperature change; Accept opposite argument for HNO. Award [1] if observations given but acid is not identified. Reference to specific observations needed. (c) (i) (nitric acid) 7.5 cm ; (ii) not valid as nitrous acid reacts with same volume/ 7.5 cm ; (d) HNO ; (higher conductivity for solutions with same concentration as) there are more ions in solution; 47. A 48. C 49. C 50. C 51. (a) (i) strong acid completely dissociated/ionized and weak acid partially dissociated/ionized; HNO (aq) H (aq) NO (aq); HCN(aq) H (aq) CN (aq); Insist on both arrows as shown. State symbols not needed. Accept H O and H O. (ii) K a = Allow H O instead of H. K a = = ; [H ][CN [HCN] ] (iii) [H 10 ] = K [HCN] / ( ) ; = ; Allow in the range to ph = 5.09; OR a 1 1 ph = (pk a log[hcn]) / (9.1 log 0.108); = 5.09; [H ] = = ; Allow in the range to If expression for [H ] missing but both answers correct, award [], if one answer correct, award []. assume [H ] << / negligible dissociation; IB Questionbank Chemistry 8

9 (b) With HNO : faster rate of bubble/hydrogen/gas production; faster rate of magnesium dissolving; higher temperature change; Accept opposite argument for HCN. Reference to specific observations needed. Award [1] if observations given but acid is not identified. (c) (i) (nitric acid) 7.5 cm ; (ii) not valid as hydrocyanic acid reacts with same volume/ 7.5 cm ; (iii) bromothymol blue / phenol red / phenolphthalein; (d) HNO ; (higher conductivity for solutions with same concentration as) there are more ions in solution; 5. A 5. B 54. (i) donates a proton / H ion; (ii) (acid) (conjugate base) H O OH ; NH ; [1 max] if all four acids and bases given but not clearly paired. NH 4 (iii) Lewis acid accepts an electron pair / Lewis base donates an electron pair; F is the base / BF is the acid; 55. (i) partially dissociated or ionized; CH COOH H O CH COO H O / CH COOH CH COO H ; required for mark. (ii) CH COOH CaCO Ca(CH COO) CO H O Award [1] for correct reactants and products and [1] for balancing. 56. D 57. C 58. C 59. (a) (i) CH CH COOH H O CH CH COO H O / CH CH COOH CH CH COO H ; required for mark. IB Questionbank Chemistry 9

10 (ii) (pk a for propanoic acid = 4.87) [H ] = K a ; [H ] = (mol dm ); (b) sketch to show: indicator range between ph.0 and ph 4.6 (with yellow at ph.0 and blue at ph 4.6); initial ph of acid at.9 ± 1.0 (when no KOH has been added); half-equivalence point (does not need to be named) at ph 4.9 when 1.5 cm of KOH have been added; equivalence point at approx ph when 5.0 cm of KOH(aq) added; upper part of curve from cm added identical to original curve; Award [1] each for any three points. 60. A 61. D 6. A 6. C 64. D 65. A 66. B 67. (i) K a = / ; Accept (ii) weak (acid); K a << 1/ small K a ; (iii) [H O ]/[H ] = K a ; [H O ]/[H ] = (mol dm ); ph =.10/.1/.1; Award [] for correct final answer of ph. assume x << (mol dm )/ ionization of water is insignificant / [C 6 H 5 COOH] initial = [C 6 H 5 COOH] aq / temperature 5 C/98 K; IB Questionbank Chemistry 10

11 68. D 69. B 70. (i) acid in both reactions; because it loses a proton/hydrogen ion/h / proton/hydrogen ion/h donor; Second mark can be scored if they do not identify it as an acid in both reactions. (ii) NH ; more readily accepts a proton / equilibrium lies to the right / takes H from H O; If OH chosen award [0] (iii) NH 4 ; donates a proton more readily than NH / equilibrium lies to the left; If NH chosen award [0] 71. (a) solutions of the same concentration; ph meter; strong base has a higher ph / weak base has lower ph; indicator paper/u.i solution; strong base has a higher ph/more purple / weak base has lower ph/blue not purple / OWTTE; measuring conductivity (with conductivity meter); strong base has a higher conductivity / weak base has lower conductivity; comparing heat of neutralization with acid; strong base releases more heat / weak base releases less heat; Award [4 max] for two correct methods with expected results. (b) (i) X; [X] = 10 (mol dm ) and [Y] = 10 6 (mol dm ); (ii) /10 4 :1; Ratio should be in form above. 7. (i) (Lewis acid) electron pair acceptor; appropriate example (such as AlCl, BF etc.); (ii) structural formula of Lewis acid (e.g. BF, AlCl, Transition element etc.); structural formula of Lewis base (e.g. NH, H O etc.); structural formula of product (e.g. F BNH etc.); dative covalent (bond)/coordinate (bond); IB Questionbank Chemistry 11

12 Penalize missing structural formulas once. 7. D 74. B 75. C 76. C 77. A 78. (i) 9.5; Accept any value in the range (ii) titration involves a weak acid and a strong base; salt formed at equivalence point is basic due to hydrolysis; A (aq) H O(l) HA(aq) OH (aq); Ignore state symbols (iii) ; = 0.16 (mol dm ); (iv) at half neutralization point, ph = pk a ; pk a = 5.; Accept any value in the range K a = (mol dm ); Accept calculations based on initial ph or on ph of salt. (v) phenolphthalein; Accept thymolphthalein. Allow ECF from (a)(i). 79. HIn(aq) H (aq) In (aq); colour A colour B in presence of acid/h, equilibrium shifts to left, colour A; in presence of base/oh, equilibrium shifts to right, colour B; 80. (i) buffer solution resists change in ph; on addition of small amount of acid or base; (ii) after mixing [CH COO ] = [CH COOH] = mol dm ; K a = [H ]/ pk a = ph; ph = 4.76; Working must be shown to score []. Award [1] if 4.76 stated with no working. 81. IB Questionbank Chemistry 1

13 14 8. (i) [H ] = = mol dm / poh = log =.90; ph = ( ) = 11.1; Award [] for the correct final answer [NH 4 ][OH ] (ii) K b = ; [NH ] ( ) ( ) = / ; = / ; - 8. A 84. D 85. CH CH NH H O CH CH NH OH ; (ethylamine) more basic/higher basicity/lower pk b ; because of presence of electron-releasing (ethyl or alkyl) group/ N more electron-rich; attracts H (or H from H O) more easily; 86. A 87. A 88. D 89. D 90. (a) (i) acidic and [Fe(H O) 6 ] is a weak acid [Fe(H O) 6 ] (aq) [Fe(OH)(H O) 5 ] (aq) H (aq); FeCl is acidic is not acceptable. (ii) neutral and NaNO / sodium nitrate is formed from strong base and strong acid / ions do not hydrolyse; (iii) alkaline and CO is a weak base / CO (aq) H O(l) HCO (aq) OH (aq); Award [1] only for correct identification of solutions as acidic, neutral and alkaline only, without explanation. (b) nitrogen and sulfur; kills/harms fish/aquatic life in lakes/rivers; leaching of soils damages plant life/trees; IB Questionbank Chemistry 1

14 91. (a) NH (aq) H SO 4 (aq) (NH 4 ) SO 4 (aq); Accept correct equation with NH 4 OH instead of NH n(h SO 4 ) = (mol); n(nh ) = (mol); [NH ] = 0.41 (mol dm ); Award [] for the correct final answer for the concentration calculation. (b) bromocresol green; reaction of weak base and strong acid; ph range of bromocresol green is.8 to 5.4/occurs at ph < 7; (c) (i) K b = = ; K b = [NH 4 [NH ][OH [OH ] = poh =.8; ] ] /[OH 5 ] = [NH Award [4] for the correct final answer. 0.11; K Allow ECF, for example any correct conversion of [OH ] to poh. b ]; (ii) a solution which resists change in ph / changes ph very slightly; when small amounts of acid or base are added; weak acid and its salt / weak acid and its conjugate base; (iii) Award [4] for correct final answer. Accept other valid methods. n(nh ) = (mol) and n(hcl) = (mol); [ NH 4 ] = [NH ]; [OH ] = K b = ; (poh = 4.75 so) ph = 9.5 (allow 9. to 9.); IB Questionbank Chemistry 14