QUY T®C L€M VI»†C TRONG PH’NG TH NGHI»†M H“A H»ŒC (Repaired)

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QUY TC LM VIC TRONG PHNG TH NGHIM HA HC I. An ton khi lm vic vi axit v kim1. An ton khi lm vic vi axit:-Phi lm vic trong t ht bt c khi no un nng axit hoc thc hin phn ng vi cc hi axit t do.-Khi pha long, lun phi cho axit vo nc tr phi c dng trc tip.-Gi axit khng bn vo da hoc mt bng cch eo khu trang, gng tay v knh bo v mt. Nu lm vng ln da, lp tc ra ngay bng mt lng nc ln.-Lun phi c k nhn ca chai ng v tnh cht ca chng.-Ly axit ng lng ghi trong ti liu, mi axit phi c mung hoc ng ht ring.. - Axit ri ra ngoi phi dn ngay, cc axit thi ng ni quy nh. 2. An ton khi lm vic vi kim-Kim c th lm chy da, mt gy hi nghim trng cho h h hp.-Mang gng tay cao su, khu trang khi lm vic vi dung dch kim m c.-Thao tc trong t ht, mang mt n chng c phng nga bi v hi kim.-Dung dch amoniac: l mt cht lng v kh amoniac rt n da, mang gng tay cao su, khu trang, thit b bo v h thng h hp. Hi amoniac d phn ng mnh vi cht oxi ho, halogen, axit mnh.-Kim loi Na, K, Li, Ca: phn ng cc mnh vi nc, m, CO2, halogen, axit mnh, dn xut clo ca hydrocacbon. To hi n mn khi chy. Cn mang dng c bo v da mt.-Canxioxit rt n da, phn ng cc mnh vi nc, cn bo v da mt, ng h hp do d nhim bi oxit.-Natri hiroxit v kali hiroxit: rt n da, ta nhit ln khi tan trong nc. Cc bin php an ton nh trn, cho tng vin hoc t bt vo nc ch khng c lm ngc li.- Ly kim ng lng ghi trong ti liu, mi loi kim phi c mung hoc ng ht ring.. - Kim ri ra ngoi phi dn ngay, cc kim thi ng ni quy nh. II. Quy tc lm vic vi ha cht th nghim1. Ho cht th nghim:Cc ho cht dng phn tch, lm th nghim, tin hnh phn ng, ... trong phng th nghim c gi l ha cht th nghim. Ho cht c th dng rn (Na, MgO, NaOH, KCl, (C6H5COOH) ...; lng (H2SO4, aceton, ethanol, chloroform, ...) hoc kh (Cl2 , NH3 , N2 , C2H2 ...) v mc tinh khit khc nhau:- Sch k thut (P): sch > 90%- Sch phn tch (PA): sch < 99%- Sch ha hc (PC): sch > 99%2. Cch s dng v bo qun ho cht:- Chai l ha cht phi c np. Trc khi m chai ha cht phi lau sch np, c chai, trnh bi bn lt vo lm hng ha cht ng trong chai.- Cc loi ha cht d b thay i ngoi nh sng cn phi c gi trong chai l mu vng hoc nu v bo qun vo ch ti.-Dng c dng ly ha cht phi tht sch v dng xong phi ra ngay, khng dng ln np y v dng c ly ha cht. - Khi lm vic vi cht d n, d chy khng c gn ni d bt la. Khi cn s dng cc ha cht d bc hi, c mi,... phi a vo t ht, ch y kn np sau khi ly ha cht xong.- Khng ht bng pipet khi ch cn t ha cht trong l, khng ngi hay nm th ha cht.-Khilmvicviaxithaybazmnh:Baogicngaxithaybazvonckhiphalong (khngcncvoaxithaybaz);Khnghtaxithaybazbngmingmphidngcc dngcringnhqubpcaosu,pipetmy.Trnghpbbngviaxithaybazrangayvi nc lnh ri bi ln vt bng NaHCO3 1% (trng hp bng axit) hoc CH3COOH 1% (nu bng baz). Nu b bn vo mt, di mnh vi nc lnh hoc NaCl 1%.Trnghpbhachtvominghayddy,nulaxitphiscmingvungnclnhc NaHCO3, nu l baz phi sc ming v ung nc lnh c CH3COOH 1%. MT S K NNG V THAO TC C BN V CHUN TRONG TH NGHIM THC HNH HA HC 1. Cch s dng Pipet: dng ly chnh xc th tch dung dch. Khi thao tc vi pipet trnh nm c tay vo pipet v nhit t tay s lm thay i th tch ca cht lng trong pipet. Khi ly dung dch bng pipet, tay cm u trn ca pipet bng ngn ci v ngn gia ca tay thun ri nhng u di ca pipet vo dung dch (gn y bnh). Tay kia cm qu bp cao su, bp li ri a vo u trn ca pipet ht dung dch vo pipet n khi dung dch trong pipet cao hn vch mc 2-3 cm. Dng ngn taytrbtnhanhutrncapipetlichtlngkhngchykhipipet.Dngtaykhngthun nng bnh ng dung dch ln, iu chnh nh ngn tay tr cht lng chy t t ra khi pipet cho n khi mt cong pha di ca cht lng trng vi vch ca pipet th dng ngn tay tr bt cht u trn ca pipet l v chuyn pipet c cha mt th tch chnh xc cht lngsang bnh chun . Khi lydungdch v khi cho cht lng chykhi pipet cn gi chopipet v tr thng ng.Khi cht lng chy xong cn chm nh pipet vo phn bnh khng c dung dch (hnh 3) nhng tuyt i khng thi git dung dch cn li trong pipet (nu thnh pipet c ch thch l loi TD). Khi c th tch trn pipet ch ly 02 ch s c ngha sau du phy. 2. Cch s dng Buret: Khi lm vic vi buret cn kim tra cu kha buret c m bo kn v trn, nu cn th bi kha vi mt lp mng vaselin tng kn v trn. Kp buret vo gi buret v tr thng ng. Trc mi ln chun cn trng buret bng chnh dung dch s ng trong buret v phi dung dch vo buret ti vch 0 pha trn v ch lm y c phn cui v c kha buret. Khi c th tch buret, mt phi v tr ngangmt cong pha di dung dch trong sut hoc phn trn mt li vi dung dch khng mu v ch ly 01 ch s c ngha sau du phy. Khi tin hnh chun phi cho dung dch chy khi buret t t tt c cht lng chy ra ht khi buret v sau 30 giy k t khi kha dung dch mi c kt qa. Cui qu trnh chun phi nh tng git dung dch v lm vi ln ly gi tr trung bnh. Php chun c coi l kt thc khihiu th tch gia cc ln chun song song khng qu 0,1 ml. (a)npdungdch vo buret (b)Kimtraxemc cnbtkhkha van khng (c)rauburet bng nc ct (d) lm sch v kh burettrckhi chun 3. Cch ly dung dch chun :(ch dng nc ct trng, khng c dng dung dch cn ly trngbnhnn).sdngpipetlydungdchchunhocdungdchphntchvobnhnn (hnh 12). (a) trng pipetbng chnhdungdch cn ly (b)lauphangoi pipetbnggiy thm (c)pipetthng ngvnghing bnhnndung dch chy vo (d)Tiancct xungquangbnh nnmbott c th tch chnh xc dungdchly cphnngvi cht chun Hnh 3. Cc thao tc ly dung dch vo bnh nn bng pipet 4. pha dung dch chun t cht gc, ngi ta cn mt lng xc nh ph hp cht gc trn cn phn tch c chnh xc 0,0001 hoc 0,00001g, ho tan nh lng lng cn trong bnh nh mc c dung tch thch hp ri pha long bng nc ct hoc dung mi thch hp ti vch mc. Th d: pha dung dch chun NaOH 0,0500 M (M = 40), trc tin cn tnh khi lng NaOH cn thit pha ch c 250 ml dung dch NaOH nng 0,0500M theo cng thc:m= 0,2500,0540 = 0,50 gam. Cn 0,50 gam NaOH c tinh khit phn tch trong cc cn trn cn phn tch, chuyn cht rn qua phuvobnhnhmc250,0ml.Trngcccn3lnbngncctvobnhnhmc.Thm khong 150ml nc ct na v lc k cho tan ht sau thm nc ct n vch mc, lc k trn u, ta c dung dch chun NaOH 0,0500M. 5. Cch tin hnh chun : -Tay khng thun cm kha van (hnh 13a) -Tay thun cm bnh nn (hnh 13b) -Chun vi tc nhanh trc im tng ng mt vi ml - u buret chm vo bnh nn (hnh 13c) -Tiancctxungquanhdungdchcachtchunnucbmtrnthnhcabnhnns c i xung (hnh 13d) -Khi gn n im tng ng chun vi tc chm -Du hiu kt thc chun l khi dung dch va chuyn t mu A sang mu B (a)(b)(c)(d) Hnh 4.Cc thao tc trong qu trnh chun Phn 2. Mt s bi th nghim thc hnh mn ha hc Bi 1.CHUN AXIT BAZI. Cc bc tin hnh th nghim 1. Cch pha dung dch chun t cht gc,ngi ta cnmt lng xc nh ph hp cht gc trn cn phn tch c chnh xc 0,0001 hoc 0,00001g, ho tan nh lng lng cn trong bnh nh mc c dung tch thch hp ri pha long bng nc ct hoc dung mi thch hp ti vch mc. Th d: pha dung dch chun NaOH 0,0500 M (M = 40), trc tin cn tnh khi lng NaOH cn thit pha ch c 250 ml dung dch NaOH nng 0,0500M theo cng thc:m= 0,2500,0540 = 0,50 gam. Cn 0,50 gam NaOH c tinh khit phn tch trong cc cn trn cn phn tch, chuyn cht rn qua phuvobnhnhmc250,0ml.Trngcccn3lnbngncctvobnhnhmc.Thm khong 150ml nc ct na v lc k cho tan ht sau thm nc ct n vch mc, lc k trn u, ta c dung dch chun NaOH 0,0500M. Vic pha NaOH gp nhiu kh khn nh sau: 1/ NaOH dng rn l cht cc k d ht m, do lng NaOH thc t ko ng bng lng NaOH bn em cn m ln t nc. 2/ Trong qu trnh bo qun NaOH trong bnh, nng NaOH cng b gim theo thi gian. Do trong khng kh ca chng ta c kh CO2, l mt acid yu khi tan trong nc ---> tc dng vi NaOH to NaHCO3 v Na2CO3 gy gim nng ca cht chun NaOH. V vy, khi pha dung dch NaOH, ta phi lm tht nhanh v y kn bnh cha trnh CO2 tc dng vi NaOH gy gim nng NaOH. 2. Cch chun : Ly dung dch chun NaOH vo buret. Ly dung dch HCl cn xc nh nng vo bnh tam gic sch (dng pipet). Thm vo 1 - 2 git cht ch th, th d phenolphtalein. Thm t t dung dch chun vo bnh (va thm va lc trn) n khi dung dch cht ch th chuyn mu t khng mu sang mu hng nhtbn trong khong 30 giy th kt thc. c th tch dung dch chun tiu tn. Tin hnh chun t 2 n 3 ln, ghi cc kt qu v tnh gi tr trung bnh. II. Mt s lu th nghim thc hin thnh cng Pha dung dch chun cn thn Ccthaotcsdngpipetvburetphithnhtho,nnsdngtrckhichunchnhthc (nu kha buret b kt cn nh 1 -2 git glyxerol) Khi cht ch th nhum mu hng, cn lc k, nu mu hng bin mt th thm cn thn tng git nh dung dch chun ng thi lc bnh n khi mu hng khng bin mt trong 30 giy th kt thc. Bi 2. XC NH HM LNG AXIT AXETYLSALIXYLICTRONG ASPIRIN BNG PHNG PHP CHUN AXIT BAZ I. C s l thuyt Aspirin (axit axetylsalixylic) l mt axit hu c c cha c este hu c. N c s dng rng ri trong y hc nh mt loi thuc gim au v nh mt loi thuc gim st. N thng c iu ch bng phn ng ca axit salixylic vi anhydrit axetic theo phn ng sau: axit Salixylic anhydrit axeticaxit axetyl salixylic axit axetic MtlngaxitaxetylsalixyliccthcxcnhbischunvimtbazmnhnhNatri hiroxit CH3COO-C6H4COOH(aq)+ OH-(aq) CH3COOC6H4COO-(aq)+ H2O(l) Khi x l vi mt dung dch natri hidroxit, aspirin b thy phn v hai axit sinh ra cng c trung ha ngay. CH3COOC6H4COOH + 2NaOH CH3COO Na + HOC6H4COONa + H2O NudngmtlngddungdchNaOHtrongphnngny,thlngNaOHdcxcnh bngphpchunvidungdchaxit.Tuynhin,iucnthitlaxitdngchunphi khng tc dng vi natri axetat v natri salicylat (c hai cht ny u cha nhng anion baz). C th trnh iu ny bng cch chn cht ch th l phenol (khong chuyn mu pH t 6,8 n 8,4) hoc phenolphatalein (khong chuyn mu pH t 8,3 n 10,0). Tuy nhin, axit axetylsalixylic cng l mt este nn d dng b thy phn khi chun vi mt baz mnh, do trong mi trng kim n b phn hy dn n sai st trong s phn tch. Nh vy, khi p dng phng php chun th tt c axit c mt trong dung dch s thy phn hon ton trong NaOH d. Mt mol axit trong aspirin phn ng va vi mt mol NaOH, mt mol este trong aspirin phn ng va vi mt mol NaOH. Nh vy s mol NaOH phn ng s gp i s mol aspirin, sau lng NaOH tha s c chun vi dung dch axit chun. Trong th nghim ny, axit acetylsalicylic s c chun b, tng lng acid c mt s c xc nh bng cch s dng mt phng php chun li. II.Cc bc tin hnh th nghim 1. Cn cc vin aspirin c lng khong 0,5 g. Ghi li s vin v khi lng. Ha tan cc vin aspirin cn c vo 15 ml etanol trong mt bnh tam gic 250 ml. 2. Thm 20 mL dung dch NaOH 0.50 mol.L-1. 3. tng tc phn ng thy phn, un nng cc mu trong mt cc nc khong 15 pht.4.Lm lnhmu n nhit phngv cn thn ttc vomt bnh nhmc 250mL. Ra bnh phn ng vi ln vi nc, thm phn ra vo bnh nh mc. Lm long dung dch n vch mc v lc k hn hp.Ly 25 mL