SilDHHtflllOlilBiiDIOJIIIfllBIIlGHieOHIiOHHOCIilJilCiCBlUIIlPHOllHOG HE PHAT T f t i TU M\ HO UOC S i i TRING HOC PUfi TU iG {MM HOANG THI THUY HUONG* Trong day hpc mdn Woa''''/jocd phd''''ttidng, bai tap h[.]
SilDHHtflllOlilBiiDIOJIIIfllBIIlGHieOHIiOHHOCIilJilCiCBlUIIlPHOllHOG HE PHAT T f t i TU M\ HO UOC S i i TRING HOC PUfi TUiG {MM H O A N G THI THUY HUONG* T rong day hpc mdn Woa'/jocd phd'ttidng, bai tap hoa hpc (BTHH) Id mpt nhiing cdng cu rat hihj ich de phat trie'n tu eho hpc sinh (HS) Khi HS giai BTHH se giiip cdc em eung CO vung ehdc li ttiuylt, phdt trien dU(3C tu linh hogt va dc sang tao; tii dd, cd kha ndng tu dpc lap, nhanh nhay, linh hogt hpc tap cung nhu cupc sd'ng Co sdli thuyet Khi giai cac BTHH cd nhimg bdl toan cd the giai theo phuang phdp kinh dien dua tren cac phuang trinh phan iimg, nhung ed nhung bdi toan nlu chi dua theo phuang trinh phan iing hda hpc thi khdng the tim kit qua hode cd t h i tim kit qua nhung rat phiire tgp Liic dd, nlu sii dung eac phuang phap nhu: phuang phap bao toan electron, phuang phap bao toan khdi lupng, phuang phap bao todn didn tich, thi vigc giai cac BTHH trd nen d l dang Rat nhilu BTHH chi cd t h i giai dupc su dung phuong phap bao todn dign tieh (djnh ludt bao toan didn tieh) Bdi tap (BT) sd dung djnh ludt bao toan dign tieh dua tren eo sd li ttiuylt: Dung dich iudn tmng hoi vediin hay long dien tich cua cic on dung djch bing khdng Nlu ki hidu td'ng so mol dien tich duong dung djch la n^^^ vd td'ng so mol didn tich dm dung djch Id /? thi ta ed: n^^^ = n^^ Mpt so BT SIX dung dmh luat bao toan dien tfch de giai S r / ; Mdt hdn hpp gom 0,25 mol FeS,; 0,35 mol CUjS va xmol S Cho toan bp hon hop ti'dn tan hit tiong dung djch HNG, dgc, ndng Sau cac phan irng hoan toan, ttiu dupe dung djch ehi cd hai chat tan Tinh gia trj cua x Phan tich:^d\ bai toan nay, nhiing HS cd tuduy tmng binh se ttiay ddy la bai toan khd va cac em thudng giai ttieo phuang phap kinh dien bdng each viet phuang tiinh phan iimg d dang phdn td: 2FeS, + 3OHNO3 _ ^ HjS0, + 14H,0(1) Fej(S0J3 -H 30NOJ + CUjS + 12HNO3 _ ! L ^ CuSO, + Cu(N03)2 + 10NO, + 6HjO(2) 58 Tap chi Gido due so 302 S + 6HNO3 _ ^ HjSO, -I- 6N0j + 2HjO (3) Sau v i ^ 6uoc phuang tiinh phan ting, HS ggp khd khdn bdi dung djch cd tdi bd'n chit tan ma theo gia ttiilt thi dung djch ehi cd hai chat tan Nhu vdy, nlu HS khdng ndm vumg kiln \h\sc se khdng giai dupc bdi todn Vdi nhi/ng HS cd kha nang suy ludn tot, ndm viing kiln thiie se cho rang Cu(N03)2 tao d phan umg (2) se tac dung trd Igi vdi HjSO^ cua phan umg (1) vd (3) ditao HNO3 va HNO3 lgi tham gia vao trude cac phan iing eho de'n hit va dung djeh thu dupe vdn cd hal chat tan la Fe2(SO,)3 va CuSO, Tuy nhidn, khdng the giai kit qua bai toan theo phuang trinh phan umg d dang phdn tu Vdi HS ed hpe lire kha, gidi, cac em cd the giai ttieo phuang trinh Ion nit gpn: FeS;+l4H*+l5NO;—^ Fe' + I5N02 + 2SOJ- +7H2O So mol: 0.2s 0,25 0,5 Cu;S+12H*+ lONO; — ^ 2Cu-' + S0;- +I0NO 0J5 0.70 0,35 S + 4H* + 6NO; -^-> SO;- +6NO; + 2H20 Oln ddy, nlu HS khdng nam viing djnh ludt bao toan dign tich thi se khdng tim dupc dap so ciia bai toan Vol HS su dung tot djnh ludt bao todn illdn tieh (td'ng dign tich mdt dung djch bang khdng), eac em se tim mdi lien he giira so' mol Fe^Cu^SO^ddla: 0,25 X + 0,7 x = (0,5 + 0,35 + x) x => x = 0,225 mol Thdng qua bai toan da phat trie'n eho HS tu kinh nghjgm, tu phdn tich va tu sang tao BT2: Hon hop X gom: CuO, Fe203, Ag^O vd FeO.Ol khd hoa hoan toan m gam hdn hop X d n 8,96 lit CO (dkte) Mudn tdc dung hit m gam hdn hpp dd,cln V lit dung djch HCI 1M Tinh V Phin tich: Khi gap bai toan nay, vdi nhiing HS cd ldi tu kinh nghigm, cac em ttiudng vilt cac phuang ti'inh phan ting xay ra, ddt d'n so cho so mol cac oxit va tinh the tich HCI dua ttieo ttie tieh * TnfJigTIPT ViM)^ Bai hfc Vinh • Nghf ta — (ki2-1/2013) CO Tuy nhidn, each giai ttiuijng ddi va HS cung d l gap b l tde va nham lln Vdi HS ed loi tu linh hoat, sang tao bilt su dung djnh ludt bao toan didn tieh, cac em se nhdn ttily duac: phan img cila oxit vdi HCI la su ttiay ttie Ct cho 0^' =>«,., =2n„, Ma: «„, =«,.„ =0,4 mol => />,., =0,8 mol => «„„ = «,/ =0-8^01 => i.«„ = o.8(lit) BT3: Dung djch X chtia cdc ton: HCO^; Ba^*; Na*; Ct; tong so mol Na' vd Ct Id 0,15 moL Chia X ttianh hai phan bdng nhau, eho phln phan ting viii mgt lupng du dung djch NaOH, kit ttiuc phan iing ttiay cd 9,85 gam kit tua xuat hien Cho dung djch NaHSO, tdl du vao phln 2, sinh 1,68 lit CO^ (dkte) Tinh tong khdi lupng mudi dung djch X Phin tich: Vdi nhi/ng HS cd tu tot vd ndm vihig thuylt dign li se giai nhu sau: Phin tieh: Vdi nhifng HS cd tu td't vd ndm viing thuylt didn li sd giai nhu sau: 1,68 |1.X + NaHSO,:",.,, =22,4° j?^ = 0,075 w HCO - + H S O co,t+so^ + H2O 0,075 0,075 ãô(.-(X) = 2x0,075 = 0,15 moL i X + NaOH: «,«„, = ^ = o,05mo/ < 0,075 Ba^' hit, CO ^ edn du H C O ' + O H ' - ^ C O j + Hp 0,075-» 0,075 Ba^* + C O ^ - » B a C 0,05