hóa đại cương – vô cơ (tập 2): phần 2

Chticing 10<br /> <br /> PHAN AG OXY HOA KFICi VA DONG HIEN<br /> <br /> MVC TIED<br /> 1. Tim du'dc men tru'ang (khocing pH) cho mot phcin zing oxy hod khet nha can being<br /> phu'Ung trinh theo phuzing phdp<br /> phdn<br /> 2. Trinh bay each xdc dinh cac the-dien cu'c chudn E; y nghia va van dung crux E.<br /> 3. Thanh lap phudng trinh Nernst, va van dung phu'o'ng trinh do de xdc dinh<br /> chie'u hu'dng va md'c di) dal phdn ring oxy hod<br /> 4. Gidi thich cd the hoat crOng dia pin ndng di) (di ang dung do pH va gidi thich<br /> dien the mang to bao); ceia acquy; va aid srrt an mon him loci.<br /> 5. Xcic dinh va tinh dude lacing sdn pham trong pin dien phitn.<br /> Hieu du'o'c su' hinh theinh the dien hod va nang lu'o'ng lien ket trong te-bao<br /> <br /> 1. PHAN LANG OXY HOA KIIU'. KHAI QUAT VE PIN HIEN HOA<br /> 1.1. Khai niem chung<br /> Phan Ung oxy hod khit la phan ttng có su chuy6'n dich electron gifia cac<br /> chat phan ling, do do lam bie-n do7i s6 oxy hod cua cac nguyen to.<br /> Chat oxy hod (phan tit , nguyen tit, ion), vie't tat: chdt Ox, la chgt nhan<br /> electron va giam s6 oxy hod, no la chg bi<br /> Chat khU' (phan tit, nguyen tit, ion), viet tat: chgt Kh, la chgt cho electron<br /> va tang s6 oxy hod, no la chdt bi oxy hod.<br /> Theo do suy ra: su' khei la su nhan electron. Su' oxy hod la sit cho di electron.<br /> Rdt can<br /> hod, chat khit, su<br /> <br /> de khong nhdm ran cac thuat<br /> <br /> ch"dt oxy- hod., sit oxy<br /> <br /> Vi du, trong dung dich nude xay ra phan<br /> Fe(r) + CuNaq)<br /> <br /> FeNaq) + Cu(r)<br /> <br /> (10-1)<br /> 191<br /> <br /> Ion Cu' nhan electron (tit Fe) la chat ox, .s6 oxy hod dia no giarn tit +2<br /> clgn 0, no bi khit va goi la sit khii ion Cu' (bai Fe).<br /> Sat cho electron nen la chat kh, so oxy hod cUa no tang tit 0 den +2, no bi<br /> oxy hod va goi la su oxy hod sat (bai ion Cu').<br /> - Co the chia phan fing (10-1) thanh 2 nfia phan itng de) thay ro hdn ch'dt<br /> nhan electron va chat cho electron:<br /> Cu<br /> Cu" + 2e<br /> Fe' + 2e<br /> Fe<br /> Quy luat can bang cac nita phan itng gioeng nhu doi voi cac phan itng<br /> khac, nghia là s6 nguyen tit cua moi nguyen to va dien tich cua moi vg pinking<br /> trinh phai nhu nhau. Mac du cac nita phan itng duoc tach rieng, nhting std mat<br /> electron va nhan electron xay ra d6ng thai. So- electron mat bdi chdt bi oxy hoci<br /> luon tWing so- electron nkin du'oc bdi chdt bi khei.<br /> Phan itng oxy hod khit (vigt tat: phan itng ox-kh) c6 the nhin nhan tucing<br /> tit nhtt phan ling acid-base theo khai niem cUa. Bronsted-Lowry, bai vi ca<br /> 2 loci phan itng de'u lien quan dgn slat van chuygn mot hay nhie'u lieu<br /> phan mang dien tit chat cho den chat nhan: electron trong phan itng oxkh va proton trong phan ling trung hoa. Khi mot acid cho di 1 proton, no<br /> tra thanh 1 base lien hOp va c6 kha nang nhan 1 proton. Toeing tit, khi<br /> mot chat Kh cho electron, no tra thanh mat chat Ox va co the nhan<br /> electron ma hinh thfic co the goi la chat Ox lien hop. Tit d6, cac nits phan<br /> fing khi vigt d6c lap cling goi la cac cap oxy hoci khi' lien hop, chioc ky<br /> hieu va quy tiOc vigt: cap Ox/Kh.<br /> Vi du: O phan Ung (10-1) c6 2 cap Ox/Kh la Cu2 +/Cu va Fe/Fe.<br /> Phan itng Ox-Kh la tong dm 2 /lila phan itng, Wong fing vOi 2 cap Ox/Kh<br /> vigt day<br /> Kh i<br /> Oxl + nle<br /> Ox2 + n2e<br /> Kh2<br /> Va vi so electron cad. chdt Kh cho phai bang so- electron cila chat Ox<br /> nhan, nen phuong trinh tong quat cilia phan ling Ox-Kh c6 the vigt:<br /> (10-2)<br /> n2Kh1 + n10x2<br /> n20x1 + n1Kh2<br /> Vg mat hod hoc, to ngdm dinh can bang a phuong trinh (10-2) nghieng ve<br /> ben phai, vi the chat 0)c1 nhan electron tot lion (chat Ox manh hcin) so \Ted<br /> Ox2, va chat Kh2 cho electron tot bon (chat Kh manh hcin) so voi Khi.<br /> <br /> 192<br /> <br /> 1.2. S6 oxy hoa (S.0)<br /> - S6 oxy hod (con goi IA mite oxy hod, trang thdi oxy hod) IA din tich hinh<br /> thfic cua nguyen to trong don chat, ion hay hop chat khi quy uric cac cap<br /> electron dung chungl8ch hoAn than ve nguyen to c6 dO am din lon hon.<br /> Chit Srrang, S.0 cUa nguyen to c6 gid tri dai so khdc hod tri. S.0 c6 the là<br /> s6 am, s6 &tong hoac bang khong. Trdi lai, hod tri tinh theo s6 electron tham<br /> gia lien ke't nen chi c6 gia tri during.<br /> - S.0 dm mot nguyen to duoc xdc ctinh the() nhfing quy vac' sau:<br /> Quy tcic chung:<br /> 1/ Nguyen to trong don chat (Na, Cu, 02, N2, S); ,S.0 = 0.<br /> 2/ Nguy8n to trong ion don nguy8n tit: S.0 = di.8ntich ion.<br /> 3/ Tang dai s6 S.0 dia cac nguyen to trong phan tit = 0, con trong ion<br /> nhi6u nguyen tit = din tich ion.<br /> Quy tat cu the'cho cac nguyen tit hoac nh6m nguyen to trong Bang tuan hoan:<br /> 1/ Nhom IA: S.0 = +1 trong tat ca cac hop chat.<br /> 2/ Nh6m IIA: S.0 = +2 trong tat ca cac hdp chat.<br /> 3/ Hydro: S.0 = +1 trong cac hdp chat vdi phi kim<br /> S.0 = -1 trong cac hop chat V6i kim loaf va Bor<br /> 4/ Fluor: S.0 = -1 trong moi hdp chat<br /> 5/ Oxy: S.0 = -1 trong cac hop chat peroxyd<br /> S.0 = -2 trong tat ca cac hop chat khdc (tru vdi fluor)<br /> 6/ Nhom VIIA: S.0 = -1 trong cac hop chat vdi kim loaf, vol plii kim (trit<br /> vdi oxy) va vdi cac halogen khdc phia du6i. nhom.<br /> Lau 31:<br /> 1/ S.0 diking cao nhat cita cac nguy8n to trong cac nh6m chinhA bang s6<br /> this to cua nhom (trit 0 va F).<br /> 2/ S.0 dm thap nhat cua cac phi kim va mot s6 a kim bang s6 thi tit cita<br /> nhom frit 8.<br /> Vi du: ktu huSm.h.;c6 S.0 during cao nhgt là +6 (vi nguyen to S o nhom VI<br /> A) nhu trong hop chAl SF6 va c6 S.0 am thap nhat = 6 - 8= -2 nhu trong FeS.<br /> 3/ V6 nguyen vac, de xdc dinh so oxy hod can phai bie't cau tao phan tit vA.<br /> 'dO arh, di0 cua cac nguyen to. Di) am din c6 th8) suy ra gan thing tit vi tri cua<br /> 193<br /> <br /> nguyen to trong Bang tun hoan. C6n n6u kh8ng biet r5 cgu tao phan tit thi<br /> S.0 xdc dinh &toe tit cac nguyen tae da neu co the la S.O gia. Chang haa,,dat<br /> S.0 ciia lUu huynh la x, tim duoc S.0 cua no trong 52082- qua pinking trinh:<br /> x = +7. Day la s6 oxy hod gia, vi lttu huYnh o nhom VIA,<br /> (x.2) + (-2.8) = -2<br /> S.0 cao nhat cua no chi la +6 plul hop voi cong thlic eau tao:<br /> <br /> -o \<br /> <br /> -0\ ,0s,<br /> <br /> O'<br /> <br /> , s,<br /> „<br /> <br /> hoac<br /> <br /> 0 0<br /> <br /> 0 \ 0/ - 0 \ / 0-<br /> <br /> z%<br /> 0 00<br /> 0<br /> <br /> Hon ncia, con gap so oxy hod gia va le, nhti S trong Na2S406 cO S.0 = +2,5.<br /> Tuy nhien, S.0 that hay gia deu có gia tri nhU nhau trong can bang<br /> phuong trinh cua phan itng Ox-Kh.<br /> <br /> 1.3. Can bang phan itng oxy hoa khif<br /> Co nhieu phuong phap de can bang phan itng Ox-Kh, nhung thitang<br /> dtiOc sit dung la phuong phap s6 oxy hod, va quan trong hdn la phtiong phap<br /> nfia phan fing.<br /> 1.3.1. Phu'o'ng phcip so oxy hod<br /> <br /> Duoc thuc hien theo cac bit& sau:<br /> 1/ Viet cac chat dal' (chat phan Ung) va cac sari pham. Vi du:<br /> HC103 + P -> HC1 + H3PO4<br /> (di nhien chat dAu da biet, nhung san pham là gi thi phai dita vao cac<br /> phep phan tich hod hoc hoac can cit vao quy luat bien dOi cua cac nguyen to va<br /> hop chat).<br /> 2/ Xac dinh S.0 cua cac nguyen to trade va sau pilau ling. O vi du tren,<br /> tim thay:<br /> HC15+03 + P° ---> HC11- + H3P5+04<br /> 3/ Tim so electron ma 1 phan tit chat khii cho va s6 electron ma 1 phan<br /> tit chat oxy hoa nhan, tit do lap phuong trinh trao &di electron de tim he s6<br /> chinh cua chat khit va chat oxy hod. Ti6p vi du tren, thanh lap:<br /> 61P° - 5e ---> P5+<br /> <br /> *15+ + 6e —÷ C11cac he s6 chinh phai có mot boi s6 chung nhO What bieu thi tang<br /> s6 electron ma -chat khif cho bang tong so electron ma chat oxy hod nhan.<br /> Chu<br /> <br /> 194<br /> <br /> 4/ Oat he s6 chinh phis hdp vao cac chdt khit va chgt oxy hod ban ddu,<br /> kiem tra s6 nguyen tit ciia<br /> nguyen to d 2 ve pinking trinh de can bang<br /> chting nhung chua can chi]. Y den s6 nguyen tii H va 0 (nefu 2 nguyen 16 nay<br /> khong truc tiep là chgt khit hay chgt oxy hod). Tiep theo vi du tren, thu duoc:<br /> 5HC103 + 6 P = 51,-1C1 + 6 H3PO4<br /> 5/ Kiem tra s6 nguyen ti H 6 2 ve de tim s6 phan tit int& tham gia hoac<br /> tao thanh. Vdi vi du dang xet, can 9 phan tit H2 O tham gia phan ling. Vay:<br /> 5HC103 + 6P + 9H20 = 5HC1 + 6H3PO4<br /> 6/ Kiem tra lai s6 nguyen tit 0 d 2 v6 va tin rang thuc chgt phuong trinh<br /> da duoc can bang.<br /> Vdi 6 buoc tien hanh nhu tren, moi phan ling oxy hod khit viet diidi clang<br /> pinking trinh phan tii deu có the &toe can bang. Tuy nhien, nhieutrliang hop<br /> khOng can thiic hien du cac buoc va khi da quen thi chi can nlidm tinh tren<br /> mot phtiong trinh phan ling.<br /> 1.3.2. Phtto'ng phcip nita phdn zing<br /> <br /> - Pinking phap can bang nay quan trong va có nhieu loi ich, bai vi:<br /> + Noi chung, khong yeu cdu viec xac dinh S.0 ciia moi nguyen to.<br /> + Tdch qud trinh Ox-Kh thanh 2 niia phan ling se phan dnh ban chdt<br /> thuc xay rad 2 dien cue trong pin dien hoa (gioi. thieu 6 muc sau)<br /> + Lam chO viec can bang cac phan ling Ox-Kh de dang hdn khi chung<br /> xay ra trong moi truang acid hay base, dieu thuang gap trong cac pin.<br /> - Cac bade tien hanh<br /> . Noi chung, to bat ddu vdi "130 khung phan ling ion", trong do chi viet<br /> dang Ox va dang Kh, chua can chit Sr H2O, H+ hay 0H-1/ Chia 13O khung phan iing thanh 2 rata phan ling (nita nao la Kh, rata<br /> nao la Ox se ro rang cac buck tiep theo).<br /> 2/ Can bang cac nguyen tit va dien tich trong moi nita phan ling (electron<br /> cluoc them vao ben trdi cua niia phan ling Kh va vao ben phai cua nita phan<br /> ling Ox).<br /> 3/ Nhan moi niia phan ling vdi mot s6 nguyen, neu can thiet, d6 s6<br /> electron nhan 6 niia phan iing Kh bang s6 electron cho d.niia phan itng Ox.<br /> 4/ COng cac nita phan ling da can bang de thu dtioc phan ling tong (chd<br /> ghi kern ca trang thai chdt).<br /> 5/ Kiem tra lai s6 nguyen tii va dien tich phan iing tong.<br /> <br /> a<br /> <br /> a<br /> <br /> 195<br /> <br />