Chapter 16 Redox chemistry and corrosion

Transcription

1 Worked solutions to textook questions 1 Chpter 16 Redox hemistry nd orrosion Q1. Identify eh of the following hlf equtions s involving either oxidtion or redution: N(s) N + (q) + e Cl 2 (g) + 2e 2Cl (q) S(s) + 2e S 2 (q) d Zn(s) Zn 2+ (q) + 2e A1. d Q2. oxidtion redution redution oxidtion Blne the following hlf equtions nd then identify eh s representing either n oxidtion or redution retion: Fe(s) Fe 3+ (q) K(s) K + (q) F 2 (g) F (q) d O 2 (g) O 2 (q) A2. d Q3. Fe(s) Fe 3+ (q) + 3e oxidtion K(s) K + (q) + e oxidtion F 2 (g) + 2e 2F (q) redution O 2 (g) + 4e 2O 2 (q) redution Iron rets with hydrohlori id ording to the ioni eqution: Fe(s) + 2H + (q) Fe 2+ (q) + H 2 (g) Wht hs een oxidised in this retion? Wht is the produt? Write hlf eqution for the oxidtion retion. Identify the oxidnt. d Wht hs een redued in this retion? Wht is the produt? e Write hlf eqution for the redution retion. f Identify the redutnt. A3. Fe(s) hs een oxidised to Fe 2+ (q) Fe(s) Fe 2+ (q) + 2e H + (q) d H + (q) hs een redued to H 2 e 2H + (q) + 2e H 2 (g) f Fe(s)

2 Worked solutions to textook questions 2 Q4. When strip of mgnesium metl is pled in lue solution ontining opper(ii) ions (Cu 2+ (q)), rystls of opper pper nd the solution soon eomes pler in olour. Show tht this retion is redox retion y identifying the sustne tht is oxidised nd the one tht is redued. Write hlf eqution for the oxidtion retion. Write hlf eqution for the redution retion. d Write n overll redox eqution. e Identify the oxidnt nd the redutnt. f Explin why the solution loses some of its olour s result of the retion. A4. Mgnesium is oxidised, opper ions re redued. Mg(s) Mg 2+ (q) + 2e Cu 2+ (q) + 2e Cu(s) d Mg(s) + Cu 2+ (q) Mg 2+ (q) + Cu(s) e oxidnt Cu 2+ ; redutnt Mg f The solution loses some of its lue olour due to the loss of Cu 2+ (q), whih ret to form Cu(s). Q5. Some ions, suh s the Cu 2+ ion, n e either oxidised or redued. Write the formul for the produt of the oxidtion of the Cu 2+ ion. Write the formul for the produt of the redution of the Cu 2+ ion. Nme one other ion tht n e either oxidised or redued. A5. Cu 2+ Cu Fe 2+ Q6. Clium tht is exposed to the ir forms n oxide oting. Wht is the formul of lium oxide? Wht hs een oxidised in this retion? Write hlf eqution for the oxidtion retion. d Wht hs een redued in this retion? e Write lned hlf eqution for the redution retion. f Write n overll eqution for this redox retion. g Copy the following sttement nd fill in the lnk spes with the pproprite words: Clium hs een y to lium ions. The hs gined eletrons from the. The oxygen hs een y to oxide ions. The hs lost eletrons to the. A6. CO C(s)

3 Worked solutions to textook questions 3 C(s) C 2+ (s) + 2e d O 2 (g) e O 2 (g) + 4e 2O 2 (s) f 2C(s) + O 2 (g) 2CO(s) g oxidised, oxygen, oxygen, lium, redued, lium, lium, oxygen Q7. Assign n oxidtion numer to the underlined element in eh the following moleules or ions: NiO 2 CO CO 2 d Br 2 e N 2 H 4 f H 2 SO 4 g NO 3 h CH 4 i O 2 3 j PO 4 k H 2 S l Cr 2 O 3 A7. Ni +4 C +2 C +4 d Br 0 e N 2 f S +6 g N +5 h C 4 i O 0 j P +5 k S 2 l Cr +3 Q8. In eh of the following redox retions, use oxidtion numers to identify the element tht hs een oxidised nd the one tht hs een redued. P 2+ (q) + Mg(s) P(s) + Mg 2+ (q) 2HgO(s) 2Hg(l) + O 2 (g) 2H 2 O(l) + 2F 2 (g) 4HF(q) + O 2 (g) d MnO 4 (q) + 8H + (q) + 5Fe 2+ (q) Mn 2+ (q) + 4H 2 O(l) + 5Fe 3+ (q) A8. led redued (+2 to 0), mgnesium oxidised (0 to +2) merury redued (+2 to 0), oxygen oxidised ( 2 to 0) oxygen oxidised ( 2 to 0), fluorine redued (0 to 1) d mngnese redued (+7 to +2), iron oxidised (+2 to +3)

4 Worked solutions to textook questions 4 Q9. Write hlf equtions to represent: the redution of SO 2 4 to SO 2 the oxidtion of H 2 O 2 to O 2 the oxidtion of H 2 S to S d the redution of MnO 4 to MnO 2 e the redution of T 2 O 5 to T f the oxidtion of SO to SO 4 g the redution of IO 3 to I A9. Step 1: Blne ll toms in the hlf eqution exept oxygen. SO 2 4 SO 2 Step 2: Blne the oxygen toms y dding wter moleules. SO 2 4 SO 2 + 2H 2 O Step 3: Blne the hydrogen toms y dding H+ ions (whih re present in idi solution). SO H + SO 2 + 2H 2 O Step 4: Blne the hrge y dding eletrons to the more positive side. SO H + + 2e SO 2 + 2H 2 O Step 5: Add symols of stte. SO 2 4 (q) + 4H + (q) + 2e SO 2 (g) + 2H 2 O(l) Use the sme method to lne the other hlf equtions. H 2 O 2 (q) O 2 (g) + 2H + (q) + 2e (q) H 2 S(g) S(s) + 2H + (q) + 2e (q) d MnO 4 (q) + 4H + (q) + 2e MnO 2 (s) + 2H 2 O(l) e T 2 O 5 (s) + 10H + (q) + 10e 2T(s) + 5H 2 O(l) f SO 2 3 (q) + H 2 O(l) SO 2 4 (q) + 2H + (q) + 2e g IO 3 + (q) + 6e I 2O(l) Q10. Blne the following redox equtions y seprting them into two hlf equtions, lning eh eqution, nd then omining the pir into lned omplete redox eqution. H 2 O 2 (q) + PS(s) PSO 4 (s) + H 2 O(l) I 2 (q) + H 2 S(g) I (q) + S(s) SO 2 3 (q) + MnO 4 (q) SO 2 4 (q) + Mn 2+ (q) d NO(g) + Cr 2 O 2 7 (q) NO 3 (q) + Cr 3+ (q) e Zn(s) + Cr 2 O 2 7 (q) Zn 2+ (q) + Cr 3+ (q) f CuO(s) + NH 3 (q) Cu(s) + NO(g) A10. H 2 O 2 (q) + 2H + (q) + 2e 2H 2 O(l) 4 PS(s) + 4H 2 O(l) PSO 4 (s) + 8H + (q) + 8e 1 4H 2 O 2 (q) + PS(s) PSO 4 (s) + 4H 2 O(l) I 2 (q) + 2e 2I (q) H 2 S(g) S(s) +2H + (q) + 2e I 2 (q) + H 2 S(g) 2I (q) + S(s) + 2H + (q)

5 Worked solutions to textook questions 5 SO 2 3 (q) + H 2 O(l) SO 2 4 (q) + 2H + (q) + 2e 5 MnO 4 (q) + 8H + (q) + 5e Mn 2+ (q) + 4H 2 O(l) 2 5SO 2 3 (q) + 2MnO 4 (q) + 6H + (q) 5SO 2 4 (q) + 2Mn 2+ (q) + 3H 2 O(l) d NO(g) + 2H 2 O(l) NO 3 (q) + 4H + (q) + 3e 2 Cr 2 O 2 7 (q) + 14H + (q) + 6e 2Cr 3+ (q) + 7H 2 O(l) 2NO(g) + Cr 2 O 2 7 (q) + 6H + (q) 2NO 3 (q) + 2Cr 3+ (q) + 3H 2 O(l) e Zn(s) Zn 2+ (q) + 2e 3 Cr 2 O 2 7 (q) + 14H + (q) + 6e 2Cr 3+ (q) + 7H 2 O(l) 3Zn(s) + Cr 2 O 2 7 (q) + 14H + (q) 3Zn 2+ (q) + 2Cr 3+ (q) + 7H 2 O(l) f CuO(s) + 2H + (q) + 2e Cu(s) + H 2 O(l) 5 NH 3 (q) + H 2 O(l) NO(g) + 5H + (q) + 5e 2 5CuO(s) + 2NH 3 (q) 5Cu(s) + 2NO(g) + 3H 2 O(l) Q11. Two hlf ells re set up. One ontins solution of mgnesium nitrte with strip of mgnesium s the eletrode. The other ontins led nitrte with strip of led s the eletrode. The solutions in the two hlf ells re onneted y piee of filter pper soked in potssium nitrte solution. When the eletrodes re onneted y wires to glvnometer, the mgnesium eletrode is shown to e negtively hrged. Sketh the glvni ell desried. Lel the positive nd negtive eletrodes. Mrk the diretion of the eletron flow. Write the hlf equtions for the retions tht our in eh hlf ell nd n eqution for the overll retion. Lel the node nd thode. d Indite the diretion in whih ions in the slt ridge migrte. A11. Mg(s) Mg 2+ (q) + 2e P 2+ (q) + 2e P(s) Overll: Mg(s) + P 2+ (q) Mg 2+ (q) + P(s) d led eletrode is the thode; mgnesium eletrode is the node Anions will migrte to the Mg 2+ (q)/mg(s) hlf ell, tions to the P 2+ (q)/p(s) hlf ell.

6 Worked solutions to textook questions 6 Q12. The overll eqution for the redox retion etween silver ions nd tin metl is: 2Ag(s) + Sn 2+ (q) Sketh suitle glvni ell to demonstrte tht there is flow of eletrons etween the retnts. Fully lel the ell. Write hlf equtions for the ell retions. Show the diretion of eletron flow. A12. Ag + (q) + e Ag(s) Sn(s) Sn 2+ (q) + 2e Q13. Refer to the eletrohemil series (Tle 16.2, pge 287) nd predit if the following retions will our spontneously. Silver metl is pled in opper nitrte solution. A strip of luminium is pled in sodium hloride solution. Mgnesium is dded to solution of iron(ii) nitrte. d The element zin is pled in tin(ii) solution. e A piee of tin is pled in silver nitrte solution. f Led nitrte solution is poured into eker ontining zin grnules. g Gold foil is dded to led nitrte solution. A13. For retions to our spontneously, the queous tion in the solution must e stronger oxidnt thn the tion of the metl dded. d e f g No No Yes Yes Yes Yes No

7 Worked solutions to textook questions 7 Q14. Solutions of zin nitrte, tin nitrte nd opper(ii) nitrte hve een prepred in lortory, ut hve indvertently een left unlelled. Nme two metls tht ould e used to identify eh solution. A14. Use iron nd led to test the solutions. The opper(ii) nitrte will ret with oth iron nd led. The tin nitrte will ret only with the iron. The zin nitrte will not ret with either of the metls. Q15. Eh of theses pirs of hlf ells omines to form glvni ell. i Ag + (q)/ag(s) nd Zn 2+ (q)/zn(s) ii Fe 2+ (q)/fe(s) nd P 2+ (q)/p(s) iii Ni 2+ (q)/ni(s) nd Cu 2+ (q)/cu(s) Drw digrm of eh glvni ell nd on your digrm show: the diretion of eletron flow in the externl iruit hlf eqution for the retion t eh eletrode full eqution for the overll retion in the glvni ell d whih eletrode is the node e whih eletrode is positive f whih wy negtive ions flow in the slt ridge A15. i Cthode (+): Ag + (q) + e Ag(s) Anode ( ): Zn(s) Zn 2+ (q) + 2e Overll: Zn(s) + 2Ag + (q) Zn 2+ (q) + 2Ag(s)

8 Worked solutions to textook questions 8 ii iii Cthode (+): P 2+ (q) +2e P(s) Anode ( ): Fe(s) Fe 2+ (q) + 2e Overll: Fe(s) + P 2+ (q) Fe 2+ (q) + P(s) Q16. Cthode (+): Cu 2+ (q) + 2e Cu(s) Anode ( ): Ni(s) Ni 2+ (q) + 2e Overll: Ni(s) + Cu 2+ (q) Ni 2+ (q) + Cu(s) Use equtions to explin why the orrosion of iron is n eletrohemil proess. A16. 2Fe(s) + O 2 (q) + 2H 2 O(l) 2Fe 2+ (q) + 4OH (q) 4Fe(OH) 2 (s) + O 2 (q) + 2H 2 O(l) 4Fe(OH) 3 (s) Q17. Explin why iron orrosion ours more rpidly ner ostl environments. A17. Ner the ost, moisture in the ir ontins higher mount of dissolved slts (e.g. NCl(q)). Slts re good eletrolytes nd elerte the rusting proess. They do this

9 Worked solutions to textook questions 9 euse they filitte the prodution of ions t the oxidtion nd redution sites of orroding metl. Q18. A18. Q19. Whih of the following metls ould e used s srifiil node in order to prevent the orrosion of iron? mgnesium, zin, led, opper Explin your nswer in terms of the eletrohemil series of metls. mgnesium nd zin Only metls more retive (i.e. more esily oxidised) thn iron will t s srifiil nodes. These more retive metls will e oxidised in preferene to the iron. The iron will eome the thode (the site of redution) nd no oxidtion of the iron will tke ple. Underwter steel pillrs often orrode more rpidly just eneth the surfe of the wter thn ove. Suggest reson for this. A19. Redution of oxygen ours when there is plenty of moisture nd the oxygen onentrtion is high tht is, t or just ove the surfe of the wter. A thodi region forms here. The nodi region, then, is lose to the thode nd where the oxygen onentrtion is less tht is, just elow the surfe. Oxidtion, or orrosion, therefore ours more rpidly elow the surfe. Q20. Explin why it is ommon for mnufturers to ot steel nils with zin rther thn opper or tin. A20. As zin is more retive thn steel, it will e the node nd steel will e the thode. Oxidtion, nd so orrosion, of the nils will thus e prevented. Chpter review Q21. Define oxidtion nd redution in terms of: the trnsfer of oxygen the trnsfer of eletrons oxidtion numers A21. Oxidtion is the gin of oxygen toms; redution is the loss of oxygen toms. Oxidtion is the loss of eletrons; redution is the gin of eletrons. Oxidtion involves n inrese in oxidtion numer; redution de.rese in oxidtion numer

10 Worked solutions to textook questions 10 Q22. Identify the following hlf equtions s involving either oxidtion or redution: Mg(s) Mg 2+ (q) + 2e Fe(s) Fe 2+ (q) + 2e O 2 (q) + 2H 2 O(l) + 4e 4OH (q) d Cu 2+ (q) + 2e Cu(s) A22. d Q23. oxidtion oxidtion redution redution In these redox retions, whih speies hve een oxidised nd whih redued? Cu 2+ (q) + Mg(s) Cu(s) + Mg 2+ (q) Zn(s) + 2Ag 2+ (q) Zn 2+ (q) + 2Ag(s) PO(s) + CO(g) P(s) + CO 2 (g) d C(s) + HCl(q) CCl 2 (q) + H 2 (g) e P 2+ (q) + Fe(s) P(s) + Fe 2+ (q) A23. d e Q24. Mg(s) oxidised, Cu 2+ (q) redued Zn(s) oxidised, Ag + (q) redued CO(g) oxidised, PO(s) redued C(s) oxidised, H + (q) redued Fe(s) oxidised, P 2+ (q) redued Would elements from the following groups e more likely to e oxidised or redued when they tke prt in hemil retions with the other group? Give resons for your nswers. Group A: sodium, lium nd mgnesium. Group B: sulfur, oxygen nd hlorine. A24. Group A will e oxidised euse metls tend to lose eletrons to non-metls when they ret. Group B will e redued euse non-metls tend to gin eletrons when they ret. Q25. Stte whih of the retions elow re redox retions: i CO 2 (g) + C(s) 2CO(g) ii H 2 S(g) + Cl 2 (g) 2HCl(g) + S(s) iii 2H 2 O 2 (q) 2H 2 O(l) + O 2 (g) iv MnO 4 (q) + 8H + (q) + 5Fe 2+ (q) Mn 2+ (q) + 4H 2 O(l) + 5Fe 3+ (q) v Cd(s) + NiO 2 (s) + 2H 2 O(l) Cd(OH) 2 (s) + Ni(OH) 2 (s) vi 2Fe(OH) 2 (q) + H 2 O 2 (q) 2Fe(OH) 3 (q)

11 Worked solutions to textook questions 11 A25. If the ove re redox retions, stte: i whih speies hs een oxidised ii whih speies hs een redued All re redox retions i C oxidised, CO 2 redued ii Cl 2 redued, H 2 S oxidised iii H 2 O 2 oxidised nd redued iv Fe 2+ oxidised, MnO 4 redued v Cd oxidised, NiO 2 redued vi Fe(OH) 2 oxidised, H 2 O 2 redued Q26. Assign oxidtion numers to the underlined speies in eh of the following: V V 2+ V 2 O 5 d MnO 4 e Mn 2+ 2 f Cr 2 O 7 g Cr 3+ h F 2 O i CrO 4 j O 2 A d +7 e f +6 g +3 h +2 i +7 j 0 Q27. Assign oxidtion sttes for nitrogen in eh of the following: HNO 3 NO 3 NO 2 d N 2 O 4 e HNO 2 f NO g N 2 O h N 2 i N 2 H 4 j NH 3

12 Worked solutions to textook questions 12 k NH 4 + l LiN 3 A d +4 e +3 f +2 g +1 h 0 i 2 j 3 k 3 l 3 Q28. Photosynthesis is well-known redox retion: 6H 2 O(l) + 6CO 2 (g) C 6 H 12 O 6 (s) + 6O 2 (g) Whih element is oxidised nd whih is redued? A28. Cron in ron dioxide is redued, oxygen in wter is oxidised. Q29. When zin rets with solution of hydrohlori id, hydrogen gs is produed. Wht hs een oxidised in this retion? Write hlf eqution for the oxidtion retion. Wht hs een redued in this retion? d Write hlf eqution for the redution retion. e Identify the oxidnt. f Identify the redutnt. g Write lned full eqution for this retion. A29. zin Zn(s) Zn 2+ (q) + 2e H + (q) d 2H + (q) + 2e H 2 (g) e Zn(s) f H + (q) g Zn(s) + 2HCl(q) ZnCl 2 (q) + H 2 (g) Q30. Refer to the eletrohemil series (Tle 16.2, pge 287) nd predit whether the following mixtures would result in spontneous retions. If so, write overll ioni equtions. Zin metl is dded to solution of silver nitrte. Copper metl is pled in n luminium hloride solution. Tin sulfte is pled in opper ontiner.

13 Worked solutions to textook questions 13 d e f g h i j A30. Mgnesium metl is dded to solution of led nitrte. Silver metl is dded to nikel hloride solution. Solutions of potssium hloride nd opper hloride re mixed. Iodine is mixed with luminium. Chlorine gs is mixed with mgnesium. Potssium nitrte solution is dded to silver metl. Elementl led is pled in solution of silver nitrte. Zn(s) + 2Ag + (q) Zn 2+ (q) + 2Ag(s) no retion no retion d Mg(s) + P 2+ (q) Mg 2+ (q) + P(s) e no retion f no retion g Al(s) + I 2 AlI 3 (s) h Mg(s) + Cl 2 (g) MgCl 2 (s) i no retion j P(s) + 2Ag + (q) P 2+ (q) + 2Ag(s) Q31. You re given three olourless solutions (A, B nd C) known to e sodium nitrte, silver nitrte nd led nitrte ut not neessrily in this order. You lso hve some piees of mgnesium rion nd opper wire. Desrie how you ould identify eh of the solutions using only the hemils supplied. A31. Ple 10 ml of eh solution into len test-tue. Add smll piee of mgnesium rion to eh solution. The mgnesium should e oted y displed metl in the silver nitrte nd led nitrte solutions, ut not in the sodium nitrte. The led oting will e lk. Over time, the silver oting will hnge from lk to silver s more metl is deposited. To onfirm the identity of the silver nitrte solution, tke fresh smple nd dd smll piee of opper. Copper will disple silver from the solution, giving silver deposit nd lue solution. Copper will not disple led from the solution. Q32. An unknown metl is pled in solutions of luminium nitrte nd iron sulfte. After period of time, the metl is found to hve reted with the iron solution, ut not the luminium solution. Suggest the nme of the unknown metl. A32. zin Q33. If piee of zin metl is dded to the following solutions, will retion e expeted? If so, write the eqution for the retion. AlCl 3 AgNO 3 SnCl 2 d CuSO 4

14 Worked solutions to textook questions 14 A33. d Q34. no Zn(s) + AgNO 3 (q) Zn(NO 3 ) 2 (q) + Ag(s) Zn(s) + SnCl 2 (q) ZnCl 2 (q) + Sn(s) Zn(s) + CuSO 4 (q) ZnSO 4 (q) + Cu(s) List the following in order of inresing reduing strength: Mg, I, Ag, F, Ni, Sn, Li, Cu A34. F, Ag, I, Cu, Sn, Ni, Mg, Li Q35. The Ostwld proess for the mnufture of nitri id requires three stges: 4NH 3 (g) + 5O 2 (g) 4NO(g) + 6H 2 O(l) 2NO(g) + O 2 (g) 2NO 2 (g) 3NO 2 (g) + H 2 O(l) 2HNO 3 (q) + NO(g) Whih of the stges involves redox retions? Whih elements re undergoing oxidtion nd whih re redued? Identify the oxidnts nd redutnts. A35. ll Nitrogen in NH 3 is oxidised in stge 1. Nitrogen in NO is oxidised in stge 2. Some nitrogen in NO 2 is oxidised nd some is redued in stge 3. Oxygen is redued in stges 1 nd 2. Oxidnts: oxygen nd nitrogen. Redutnt: nitrogen. Q36. A glvni ell is onstruted from n iron nil pled in eker ontining solution of iron(ii) sulfte onneted to nother eker ontining piee of zin in solution of zin sulfte. A slt ridge onnets the two hlf ells. Sketh this ell. Use the eletrohemil series of metls to predit the diretion of eletron flow. At whih eletrode will oxidtion e ourring? d Write hlf eqution for the oxidtion retion. e At whih eletrode will redution e ourring? f Write hlf eqution for the redution retion. g Lel the node nd thode. h Why is slt ridge needed for this ell to work?

15 Worked solutions to textook questions 15 A36. from the zin to the iron node (zin) d Zn(s) Zn 2+ (q) + 2e e thode (iron) f Fe 2+ (q) + 2e Fe(s) h A slt ridge is needed to omplete the iruit nd to mintin eletril neutrlity in the hlf ells. Q37. An iron nil eomes oted when pled in solution of opper(ii) sulfte. Use the eletrohemil series to write full eqution for the oxidtion/redution retion involved. A37. Fe(s) Fe 2+ (q) + 2e Cu 2+ (q) + 2e Cu(s) Fe(s) + Cu 2+ (q) Fe 2+ (q) + Cu(s) Q38. A glvni ell is set up y omining hlf ell ontining zin rod in solution of zin nitrte with hlf ell ontining metl X in solution of X nitrte. The zin eletrode is found to e the negtive eletrode. Would you expet metl X to e more or less retive thn zin? Explin your resoning. A38. Sine the zin eletrode is the negtive eletrode, eletrons must e relesed there. Therefore, zin metl must e oxidised. Metl X must e less retive thn zin. Q39. Two glvni ells re onstruted from different hlf ells. Cell A: strip of nikel in nikel hloride solution onneted to opper rod in opper sulfte solution. Cell B: strip of silver in silver nitrte solution onneted to opper rod in opper sulfte solution.

16 Worked solutions to textook questions 16 When slt ridge is dded to omplete the iruit, it is found tht the opper eletrode is the positive eletrode in ell A ut is the negtive eletrode in ell B. Sketh nd fully lel eh ell. Write hlf equtions nd full eqution for eh ell retion. Explin why the polrity of the opper eletrode differs in the two ells. A39. Q40. Cell A: Ni(s) Ni 2+ (q) + 2e ; Cu 2+ (q) + 2e Cu(s) Overll: Ni(s) + Cu 2+ (q) Ni 2+ (q) + Cu(s) Cell B: Ag + (q) + e Ag(s); Cu(s) Cu 2+ (q) + 2e Overll: Cu(s) + 2Ag + (q) Cu 2+ (q) + 2Ag(s) The polrity of the opper eletrode depends on its retivity reltive to the retivity of the other metl to whih it is onneted. Copper is weker redutnt thn nikel, so the opper eletrode is positive in ell A. However, opper is stronger redutnt thn silver, so opper is the negtive eletrode in ell B. Drw digrm of glvni ell with eletrodes of silver nd nikel, nd solutions of their solule ions. Lel the node nd thode. Identify the positive nd negtive eletrodes. Write the eqution for the oxidtion nd redution retions. d Write the overll eqution. e Drw n rrow to indite the diretion of eletron flow. f Whih eletrode will lose mss?

17 Worked solutions to textook questions 17 A40.,, e d f Q41. Redution: Cthode (+): Ag + (q) + e Ag(s) Oxidtion: Anode ( ): Ni(s) Ni 2+ (q) + 2e Overll: Ni(s) + 2Ag + (q) Ni 2+ (q) + 2Ag(s) the Ni eletrode Blne these hlf equtions: Ag(s) Cu(s) Cu 2+ (q) Zn(s) Zn 2+ (q) d H + (q) H 2 (g) A41. Ag + (q) + e Ag(s) Cu(s) Cu 2+ (q) + 2e Zn(s) Zn 2+ (q) + 2e d 2H + (q) + 2e H 2 (g) Q42. Write hlf equtions for the following retions: the redution of NO 3 to HNO 2 the redution of VO 2+ to V 3+ the oxidtion of NO to NO 3 d the oxidtion of Cl 2 to HOCl 2 e the oxidtion of S to SO 4 A42. NO 3 (q) + 3H + (q) + 2e HNO 2 (q) + H 2 O(l) VO 2+ (q) + 2H + (q) + e V 3+ (q) + H 2 O(l) NO(q) + 2H 2 O(l) NO 3 (q) + 4H + (q) + 3e d Cl 2 (q) + 2H 2 O(l) 2HOCl(q) + 2H + (q) + 2e e S(s) + 4H 2 O(l) SO 2 4 (q) + 8H + (q) + 6e

18 Worked solutions to textook questions 18 Q43. Blne the following equtions y seprting them into two hlf equtions, lning eh hlf eqution seprtely, nd dding them together to form the omplete redox eqution. I (q) + ClO (q) I 3 (q) + Cl (q) Br (q) + MnO 4 (q) Br 2 (l) + Mn 2+ (q) CH 3 OH(q) + Cr 2 O 2 7 (q) CH 2 O(l) + Cr 3+ (q) d Mn 2+ (q) + BiO 3 (q) Bi 3+ (q) + MnO 4 (q) A43. 3I (q) I 3 (q) + 2e ClO (q) + 2H + (q) + e Cl (q) + H 2 O(l) 3I (q) + 2ClO (q) + 4H + (q) I 3 (q) + 2Cl (q) + 2H 2 O(l) 2Br (q) Br 2 (l) + 2e MnO 4 (q) + 8H + (q) + 5e Mn 2+ (q) + 4H 2 O(l) 5Br (q) + 2MnO 4 (q) + 16H + (q) 5Br 2 (l) + 2Mn 2+ (q) + 8H 2 O(l) CH 3 OH(q) CH 2 O(l) + 2H + (q) + 2e Cr 2 O 2 7 (q) + 14H + (q) + 6e 2Cr 3+ (q) + 7H 2 O(l) 3CH 3 OH(q) + Cr 2 O 2+ 7 (q) + 8H + (q) 3CH 2 O(l) + 2Cr 3+ (q) + 7H 2 O(l) d BiO 3 (q) + 6H + (q) + 2e Bi 3+ (q) + 3H 2 O(l) Mn 2+ (q) + 4H 2 O(l) MnO 4 (q) + 8H + (q) + 5e 2Mn 2+ (q) + 5BiO 3 (q) + 14H + (q) 5Bi 3+ (q) + 2MnO 4 (q) + 7H 2 O(l) Q44. Explin the term thodi protetion of iron. A44. Cthodi protetion involves protetion of metl, usully iron, y mking it the thode of ell. The metl n either e joined to more retive metl, suh s zin, or e onneted to the negtive terminl of DC power soure. Q45. Why is it not neessry to protet strutures mde of opper from orrosion? A45. Copper is not very retive metl nd so is not esily oxidised. Q46. The insides of food ns re proteted from orrosion y oting of tin. Explin why: tin lyer protets the n from orrosion zin would e unsuitle for oting the inside of food n the ontents of ns tht re dented my e dngerous to use A46. Tin is not very retive nd so does not orrode redily. It protets the steel lyer under it from orroding y preventing its ontt with wter nd oxygen. Zin is too retive to e used inside food ns. It would e oxidised esily y the ontents of the n nd so ontminte the food.

19 Worked solutions to textook questions 19 Q47. If n is dented, the tin lyer my e rked, exposing the steel underneth to the ontents of the n. The steel forms n node nd the tin, whih is less retive, forms the thode. The steel rpidly orrodes nd ontmintes the food. Rust tht forms my flke off, leving hole in the n. The iron in glvnised iron nils is proteted from orrosion y oting of zin. Explin why oting of tin insted of zin would not e pproprite protetion for iron nils. A47. Any oting on nil is likely to rk when the nil is used. If the oting is tin, the tin will form thode to the more retive iron. The iron will e oxidised, tht is, orrode rpidly. Zin, however, eing more retive thn iron, will e the node nd iron will e the thode. Oxidtion, nd so orrosion, of the iron nil will e prevented. Q48. Steel grden furniture rusts muh more redily ner the seside thn inlnd. Explin why. A48. Ner the seside, moisture in the ir ontins higher mount of dissolved slts (e.g. NCl(q)). Slts re good eletrolytes nd elerte the rusting proess. They do this euse they filitte the prodution of ions t the oxidtion nd redution sites of rusting metl. Q49. In erlier times, oxidtion ws defined s the ddition of oxygen. Show tht this definition is onsistent with the definitions of oxidtion used in Chpter 16. Why do you think this definition, lthough still useful in some situtions, hs een repled? A49. Q50. Given the high eletronegtivity of oxygen, the retion of nother element (fluorine exepted) with oxygen lwys results in the omplete or prtil trnsfer of eletrons from the other element to the oxygen. This mens the other element either loses one or more eletrons or undergoes n inrese in oxidtion numer s it gins oxygen ll re definitions of oxidtion. This definition hs een extended/repled euse it exludes mny retions tht re similr to the retion of n element with oxygen. The mteril ommonly used in slt ridge is potssium nitrte. Why is this suitle mteril for this purpose? Your lortory prtner nnot find ny potssium nitrte nd suggests using nother ioni ompound, lium ronte, in its ple. How would you respond?

20 Worked solutions to textook questions 20 A50. Q51. It is solule in wter. Neither the nitrte ion nor the potssium ion will tke prt in the redox retions within the hlf ells nd neither will form preipitte with ny other ions in solution. (All potssium slts nd ll nitrtes re solule in wter.) Clium ronte hs n extremely low soluility in wter nd so will not provide ions in solution tht n migrte from the slt ridge. The iruit will not e omplete. Construt onept mp tht shows lerly the links etween the following terms: oxidnt, redutnt, eletrons, oxidtion numer, oxidtion, redution node, thode, oxidtion, redution, eletrons, ions, externl iruit, internl iruit, slt ridge, positive, negtive A51. Individul students responses required.