Can Bang Phan Ung

8/8/2019 Can Bang Phan Ung

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NGUYN TN TI THPT LAIVUNG I NG THP

PHN A : PHN M UI. L do chn ch :

Trong ging dy v hc tp mn ha hc, vic vit ng v cn bng phng trnh ph

tr rt quan trng. Bi v ch vit v cn bng ng th vic tnh ton mi chnh xc v gian. Nhng hiu, nh v vn dng bi mt cch tt nht v hiu qu nht th khng p

n gin.Thc t cho thy, cch tt nht cc em c th hiu v vn dng kin thc hc

Nhng cng c mt vn t ra l qu nhiu bi tp nn cc em khng th no gii hch lm c nhng bi quen thuc v kh lng tng khi gp nhng bi tp mi mc d

nguyn nhn l do cc em khng nhn ra c dng ton, cha c ci nhn h thng v pgii cho cc dng bi tp ny. Nu chng ta c th h thng ha l thuyt v a ra cc phng php gii cho tng d

hc sinh d dng tip thu bi, hiu r bi hn v c bit, c kh nng vn dng kin gii cc bi tp lin quan.

T nhng thc t , ti quyt nh chn ch :Cc phng php cn bng phn nha kh

Tuy l mt phn nh trong mt th gii rng ln ca cc bi tp ha hc ni chung nhcng s p ng c phn no yu cu v cc dng bi tp trong chng trnh ha hc

II. Mc ch ca ch : Nhm gip hc sinh c ci nhn h thng v l thuyt v bi tp Ha hc trong dng

phn ng oxi ha kh trong chng trnh Ha hc ph thng, t khng nhng gip gii tt cc bi tp dng ny m cn to iu kin nng cao hiu qu ging dy trng

III. Nhim v ca ch : Nghin cu c s l lun v bi tp Ha hc. Tm tt l thuyt, phn loi v cc phng php cn bng phn ng oxi ha kh

IV. Khch th v i tng nghin cu : Khch th nghin cu: Qu trnh dy v hc Ha hc trng trung hc ph thng i tng nghin cu: Bi tp cn bng phn ng oxi ha kh

[email protected] Trang 1
mailto:[email protected]:[email protected]


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V. Phm vi nghin cu :Chng trnh Ha hc trung hc ph thng: Chng trnh ha hu c lp 10

VII. Gi thuyt khoa hc : Nu hiu r l thuyt, nm vng phng php gii bi tp cn bng phn ng ox

chng trnh Ha hc THPT s gip gio vin v hc sinh h thng ha v v hiu sutp ny, l bc khi du vng cho vic dy hc mn ha trng THPT

VIII. Phng tin v phng php nghin cu :1. Phng tin : Cc ti liu lin quan n l thuyt v bi tp Ha hc cn bng phn ng oxi ha kh Cc phng tin thng tin: Internet

2. Phng php : c ti liu, phn tch tng hp l thuyt v xut cc phng php gii a ra cc dng bi tp tiu biu minh ha v sau c bi tp tng t



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PHN B : XY DNG NI DUNG L THUYI. nh ngha phn ng oxi ha kh :

1. S oxi ha :

thun tin khi xem xt phn ng oxi ho - kh v tnh cht ca cc nguyn t, ngi nim s oxi ho (cn gi l mc oxi ho hay in tch ho tr). S oxi ho l in tch nguyn t c c nu gi thuyt rng cp e lin kt (do 2 nguyn t gp chung) chuyn pha nguyn t c m in ln hn.

2. Quy tc xc nh s oxi ha :

- Tng i s s oxi ho ca cc nguyn t trong phn t trung ho in bng 0.- Tng i s s oxi ho ca cc nguyn t trong mt ion phc tp bng in tch ca ioion HSO-4, s oxi ho ca H l +1, ca O l -2 ca S l +6.

1 + 6 + (-2. 4) = - 1.

- Trong n cht, s oxi ho ca cc nguyn t bng 0.

V d: Trong Cl2, s oxi ho ca Cl bng 0.

- Khi tham gia hp cht, s oxi ho ca mt s nguyn t c tr s khng i nh sau.+ Kim loi kim lun bng +1.

+ Kim loi kim th lun bng +2.

+ Oxi ( tr trong peoxit bng - 1) lun bng - 2.

+ Hiro ( tr trong hirua kim loi bng - 1) lun bng - 2.

+ Al thng bng +3.

Ch : Du ca s oxi ho t trc gi tr, cn du ca ion t sau gi tr.V d:

3. nh ngha phn ng oxi ha kh :



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- Phn ng oxi ho - kh l phn ng trong c s trao i e gia cc nguyn t hoc iocht tham gia phn ng, do lm thay i s oxi ho ca chng.

V d:

- Cht nhng e gi l cht kh (hay cht b oxi ho).

Cht thu e gi l cht oxi ho (hay cht b kh).

- Qu trnh kt hp e vo cht oxi ho c gi l s kh cht oxi ho

Qu trnh tch e khi cht kh c gi l s oxi ho cht kh:

4. Cc phng trnh phn ng oxi ha kh thng gp :

vit c cc phn ng oxi ha kh th chng ta cn bit mt s cht oxi ha v mts cht kh thng gp. Cht oxi ha sau khi b kh th to thnh cht kh lin hp (cng); cng nh cht kh sau khi b oxi ha th to thnh cht kh lin hp (cht kh t phi bit cc cht kh v cht oxi ha tng ng th mi vit c phn ng oxi ha kh

Cc cht oxi ha thng gp :

- Cc hp cht ca mangan: KMnO4, K 2MnO4, MnO2 (MnO4-, MnO42-, MnO2)+7 +6 +4

- KMnO4, K 2MnO4, MnO2 trong mi trng axit (H) thng b kh thnh mui Mn2+Th d:

+7 +2 +2 +32 KMnO4 + 10 FeSO4 + 8 H2SO4 2 MnSO4 + 5 Fe2(SO4)3 + K 2SO4 + 8 H2OKali pemanganat St (II) sunfat Mangan (II) sunfat St (III) sunfatThuc tm(Cht oxi ha) (Cht kh)- KMnO4 trong mi trng trung tnh (H2O) thng b kh thnh mangan ioxit (MnO2)Th du:

+7 +4 +4 +62KMnO4 + 4K 2SO3 + H2O MnO2 + K 2SO4 + KOHKali pemanganat Kali sunfit Man ganioxit Kali sunfat



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(Cht oxi ha) (Cht kh)- KMnO4 trong mi trng baz (OH-) thng b kh to K 2MnO4 Th d:

+7 +4 +6 +42 KMnO4 + K 2SO3 + 2 KOH 2 K 2MnO4 + K 2SO4 + H2OKali pemanganat Kali sunfit Kali manganat Kali sunfat (Cht oxi h(Cht kh)- Hp cht ca crom: K 2Cr 2O7; K 2CrO4 (Cr 2O72-; CrO42-)K 2Cr 2O7 (Kali icromat; Kali bicromat), K 2CrO4 (Kali cromat) trong mi trng axit (H+) thng bkh thnh mui crom (III) (Cr 3+)Th d:

+6 +2 +3 +3K 2Cr 2O7 + 6FeSO4 + 7H2SO4 Cr 2(SO4)3 + 3Fe2(SO4)3 + K 2SO4 + 7H2O

Kali icromat St (II) sunfat Crom (III) sunfat St (III) sunfat(Cht oxi ha) (Cht kh)Trong mi trng trung tnh, mui cromat (CrO42-) thng b kh to crom (III) hiroxit (Cr(O3)

Th d:+6 -2 +3 0

2KCrO4 + 3(NH4)2S + 2H2O 2Cr(OH)3 + 3S + 6NH3 + 4KOHKali cromat Amoni sunfua Crom (III) hiroxit Lu hunh (Cht ox

(Cht kh)- Axit nitric (HNO3 ), mui nitrat trong mi trng axit (NO3-/H + )

+5 +4- HNO3 m c thng b kh to kh mu nu nit ioxit NO2. Cc cht kh thng b HNO3 oxi ha l: Cc kim loi, cc oxit kim loi c s oxi ha trung gian (FeO,Fe3O4), mt s phi kim (C, S, P), mt s hp cht ca phi kim c s oxi ha thp nhthay trung gian (H2S, SO2, SO32-, HI), mt s hp cht ca kim loi trong kim loic s oxi ha trung gian (Fe2+, Fe(OH)2 Th d:

0 +5 +3 +4Fe + 6 HNO3 (, nng) Fe(NO3)3 + 3 NO2 + 3 H2OSt Axit nitric St (III) nitrat Nit ioxit



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(Cht kh) (Cht oxi ha) (Kh c mi hc, mu nu)- HNO3 long thng b kh thnh NO (kh nit oxit). Cc cht kh thng gp l: cc oxit kim loi hay hp cht kim loi c s oxi ha trung gian (FeO, Fe(OH)2, Fe3O4, Fe2+), mt s pkim (S, C, P), mt s hp cht ca phi kim trong phi kim c s oxi ho thp nht c s

trung gian (NO2-, SO32-

).Th d:0 +5 +3 +2

Fe + 4HNO3(l) Fe(NO3)3 + NO + 2H2OBt st Axit nitric (long) St (III) nitrat Nit oxit

(Cht kh) (Cht oxi ha) (Kh khng c, khng khng c mu)- Mui nitrat trong mi trng axit (NO3-/H+) ging nh HNO3 long, nn n oxi ha c cloi to mui, NO3- b kh to kh NO, ng thi c s to nc (H2O)Th d:

0 +5 +2 +23Cu + 2NO3- + 8H+ 3Cu2+ + 2NO + 4H2Ong Mui nitrat trong mi trng axit Mui ng (II)(Cht kh) (Cht oxi ha) (Dung dch c mu xanh lam)

Kh NO khng mu thot ra kt hp vi O2 (ca khng kh) to kh NO2 c mu nu - Axit sunfuric m c nng, H 2 SO4 (, nng); Kh sunfur (SO2 )

+6 +4- H2SO4 (, nng) thng b kh to kh SO2. Cc cht kh thng tc dng viH2SO4(, nng) l: cc kim loi, cc hp cht ca kim loi s oxi ha trung gian (nh F3O4mt s phi kim (nh C, S, P), mt s hp cht ca phi kim (nh HI, HBr, H2S)Th d:

0 +6 +2 +4Cu + 2H2SO4(, nng) CuSO4 + SO2 + 2H2O

ng Axit sunfuric (c, nng) ng (II) sunfat Kh sunfur (Cht kh) (Cht oxi ha)Cc kim loi mnh nh Mg, Al, Zn khng nhng kh H2SO4 m c, nng thnhSO2 m cn thnh S, H2S. H2SO4 m c nhng nu long bt th s b kh to luhunh (S) hay hp cht ca lu hunh c s oxi ha thp hn (H2S). Nguyn nhnca tnh cht trn l do kim loi mnh nn d cho in t ( H2SO4 nhn nhiu in



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t) v do H2SO4 t m c nn n khng oxi ha tip S, H2S.- Kh sunfur (SO2) oxi ha c cc cht kh mnh nh cc hp cht ca phi kim c thp (nh H2S, CO), mt s phi kim (nh H2, C), cc kim loi mnh (nh Na, K, Ca, Ba, MSO2 l cht oxi ha th n thng b kh to S.

+4 -2 0SO2 + H2S S + H2OKh sunfur Kh hiro sunfua Lu hunh(Cht oxi ha) (Cht kh)Kh mi hc Kh c mi trng thi Cht rn, mu vng nhtKhc vi HNO3, dung dch H2SO4 long l a xit thng thng (tc nhn oxi ha l H+), cdch H2SO4 m c, nng mi l axit c tnh oxi ha mnh (tc nhn oxi ha l SO42dung dch HNO3 k c m c ln long u l axit c tnh o xi ha mnh (tc nhn NO3-Th d:0 +6 +2 0Fe + H2SO4(l) FeSO4 + H2

0 +6 +3 +42Fe + 6H2SO4(, nng) Fe2(SO4)3 + 3SO2 + 6H2O

0 +5 +3 +2

Fe + 4HNO3(l) Fe(NO3)3 + NO + 2H2O0 +5 +3 +4

Fe + 6HNO3(, nng) Fe(NO3)3 + 3NO2 + 3H2OBa kim loi Al, Fe, Cr khng b ha tan trong dung dch H2SO4 m c ngui(cng nh trong dung dch HNO3 m c ngui) (b th ng ha, tr)- Ion H + Ion H+ca axit thng thng oxi ha c cc kim loi ng trc H trong dyth in ha. Ion H+ b kh to kh H2, cn kim loi b kh to mui tng ng (ion kim lo

K Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H Cu Ag Hg Pt AuTh d:

Zn + 2HCl ZnCl2 + H2 0 +1 +2 0Zn + 2H+ Zn2+ + H2

(Cht kh) (Cht oxi ha) (Cht oxi ha) (Cht kh)



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NGUYN TN TI THPT LAIVUNG I NG THPII. Cn bng phn ng oxi ha kh :

a. Nguyn tc khi cn bng :

Tng s e m cht kh cho phi bng tng s e m cht oxi ho nhn v s nguyn t

nguyn t c bo ton.b. Cc bc tin hnh cn bng phn ng :

1) Vit phng trnh phn ng, nu cha bit sn phm th phi da vo iu kin chsuy lun.

2) Xc nh s oxi ho ca cc nguyn t c s oxi ho thay i. i vi nhng nguynoxi ho khng thay i th khng cn quan tm.

3) Vit cc phng trnh e (cho - nhn e).

4) Cn bng s e cho v nhn.

5) a h s tm c t phng trnh e vo phng trnh phn ng.6) Cn bng phn khng tham gia qu trnh oxi ho - kh.

V dCho ming Al vo dung dch axit HNO3 long thy bay ra cht kh khng mu, kkhng chy, nh hn khng kh, vit phng trnh phn ng v cn bng.

Gii: Theo u bi, kh bay ra l N2.

Phng trnh phn ng (bc 1):

Bc 5:

Bc 6: Ngoi 6 HNO3 tham gia qu trnh oxi ho - kh cn 3.10 = 30 NO3 to thnh mui nitr(10 l(NO3)3).

Vy tng s phn t HNO3 l 36 v to thnh 182O.

Phng trnh cui cng:



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Dng ion:

Ch : i vi nhng phn ng to nhiu sn phm trong nguyn t nhikhc nhau, ta c th vit gp hoc vit ring tng phn ng i vi tng sn phm, s phn ng ring vi h s t l theo iu kin u bi. Cui cng cng gp cc phn

V d: Cn bng phn ng:

Gii

Cc phn ng ring ( cn bng theo nguyn tc trn):

c t l mol trn, ta nhn phng trnh (1) vi 9 ri cng 2 phng trnh li:



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PHN C : CC PHNG PHP CN BNG C THI. Cc phng php cn bng phn ng oxi ha kh:

1. Phng php i s :

- Nguyn tc: S nguyn t ca mi nguyn t hai v phi bng nhau.- Cc bc cn bng:Thc hin cc bc sau:+ Vit phng trnh phn ng xy ra vi y tc cht, sn phm (nu u bi yu cu bsu phn ng ri mi cn bng).+ t cc h s bng cc ch a, b, c, d, ng trc cc cht trong phn ng.+ Lp h phng trnh ton hc lin h gia cc h s ny vi nguyn tc s nguyn t ca tnguyn t bn tc cht v bn sn phm bng nhau. Nu phn ng dng ion th cn t thm m phng trnh ton na l in tch bn tc cht v bn sn phm bng nhau.+ Gii h phng trnh ton. Thng s phng trnh ton lp c t hn mt phng trnh so vn s. Tuy nhin ta c th chn bt c mt h s no bng 1. Do c s phng trnh ton bs n s, nn s gii c. Sau , nu cn, ta nhn tt c nghim s tm c vi cng mt s thhp cc h s u l s nguyn.

Th d :

Cu + NO3-+ H+ Cu2+ + NO + H2O

aCu +bNO3-+ cH+ dCu2+ + eNO + fH2O

Cu : a = d (1) N : b = e (2)O : 3b = e + f (3)H : c = 2f (4)

in tch : -b + c = +2d (5) Chn e = 1(2) b =1 (3) f = 2

(4) c = 4

(5) d = 3/2 (1) a = 3/2

Nhn tt c nghim tm c vi 2 a = 3 b = 2 c = 8 d = 3 e = 2 f = 4



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3Cu + 2NO3-+ 8H+ 3 Cu2+ + 2NO + 4H2O

2. Phng php cn bng electron :

- Nguyn tc: Da vo s bo ton electron ngha l tng s electron ca cht kh cho ph

s electron cht oxi ha nhn.- Cc bc cn bng :

+ Vit phng trnh phn ng xy ra vi y tc cht, sn phm (nu u bi yu cu b sung phng, ri mi cn bng).+ Tnh s oxi ha ca nguyn t c s oxi ha thay i. Nhn din cht oxi ha, cht kh.+ Vit phn ng cho, phn ng nhn in t (Phn ng oxi ha, phn ng kh). Ch cn vit

nguyn t ca nguyn t c s oxi ha thay i, vi s oxi ha c bn trn. Thm h s thchhp s nguyn t ca nguyn t c s oxi ha thay i hai bn bng nhau.+ Cn bng s in t cho, nhn. S in t cho ca cht kh bng s in t nhn ca cht oxi h(Hay s oxi ha tng ca cht kh bng s oxi ha gim ca cht oxi ha) bng cch them h s thchp.+ Phi hp cc phn ng cho, nhn in t; cc h s cn bng tm c; v phn ng lc u sung h s thch hp vo phn ng lc u.

+ Cui cng cn bng cc nguyn t cn li (nu c) nh phn ng trao i.

- Lu : Khi vit cc qu trnh oxi ho v qu trnh kh ca tng nguyn t, cn theo ng ch s qnguyn t .+ V d:Fe + H2SO4 c nng Fe2(SO4)3 + SO2 + H2O

Fe0 Fe+3

+ 3e1 x 2 Fe0 2Fe+3 + 6e3 x S+6 + 2e S+4 2 Fe + 6 H2SO4 Fe2(SO4)3 + 3SO2 + 6H20

- Cc th d: Cn bng cc phn ng sau y theo phng php cn bng in t.+Th d 1



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+7 +2 +2 +3KMnO4 + FeSO4 + H2SO4 MnSO4 + Fe2(SO4)3 + K 2SO4 + H

Cht oxi ha Cht kh+7 +2

2 Mn + 5e- Mn (phn ng kh)

+2 +3

5 2Fe - 2e- 2Fe (Phn ng oxi ha)

(+4) (+6)2KMnO4 + 10FeSO4 + H2SO4 2MnSO4 + 5Fe2(SO4)3 + K 2SO4 + H

Th d 2 :-1 +6 +1 +3CH3-CH2-OH + K 2Cr 2O7 + H2SO4 CH3 -CHO + Cr 2(SO4)3 + K 2SO4 + H

Cht kh Cht oxi ha -1 +1

3 C - 2e- C (Phn ng oxi ha)

+6 +3

2Cr + 6e- 2Cr (Phn ng kh)

(+12) (+6)3CH3-CH2-OH + K 2Cr 2O7 + H2SO4 3CH3-CHO + Cr 2(SO4)3 + K 2SO4 + H2O

3CH3-CH

2-OH + K

2Cr

2O

7 + 4H

2SO

43CH

3-CHO + Cr

2(SO

4)3 + K

2SO

4 + 7H

2O

3. Phng php cn bng ion electron :

- Phm vi p dng: i vi cc qu trnh xy ra trong dung dch, c s tham gia ca mi(H2O, dung dch axit hoc baz tham gia).

- Cc nguyn tc:



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Nu phn ng c axit tham gia: v no tha O phi thm H+ to H2O v ngc li.Nu phn ng c baz tham gia: v no tha O phi thm H2O to ra OH-

- Cc bc cn bng :

+ Vit phng trnh phn ng vi y tc cht, sn phm (nu cha c phn ng sn).+ Tnh s oxi ha ca cc nguyn t c s oxi ha thay i. Nhn din cht oxi ha, cht kh.+ Vit di dng ion cht no phn ly c thnh ion trong dung dch. (Cht no khng phn ly

thnh ion nh cht khng tan, cht kh, cht khng in ly, th nguyn dng phn t hay nguyn tTuy nhin ch gi li nhng ion hay phn t no cha nguyn t c s oxi ha thay i (ion hay pht no cha nguyn t c s oxi ha khng thay i th b i).+ Vit cc phn ng cho, phn ng nhn in t (chnh l cc phn ng oxi ha, phn ng kh). V

nguyn c dng ion hay phn t, vi s oxi ha bn trn. Thm h s thch hp s nguyn t cnguyn t c s oxi ha thay i hai bn bng nhau.+ Cn bng s in t cho, nhn. S in t cho ca cht kh phi bng s in t nhn ca cht o

ha (Hay s oxi ha tng ca cht kh phi bngs oxi ha gim ca cht oxi ha) bng cch nhn h s thch hp. Xong ri cng v vi v cc phng cho, phn ng nhn in t.+ Cn bng in tch. in tch hai bn phi bng nhau. Nu khng bng nhau th thm vo ion H

hoc ion OH- ty theo phn ng c thc hin trong mi trng axit hoc baz. Tng qut thm Hvo bn no c axit (tc cht hoc sn phm); Thm OH- vo bn no c baz. Thm H2O pha ngli cn bng s nguyn t H (cng l cn bng s nguyn t O).+ Phi hp h s ca phn ng ion va c cn bng xong vi phn ng

lc u b sung h s thch hp vo phn ng lc u (Chuyn phn ng dng ion tr li thnh d phn t).

+ Cn bng cc nguyn t cn li, nu c, nh phn ng trao i.

- Cc th d: Cn bng cc phn ng sau y theo phng php cn bng ion - electronTh d 1:

+7 +2 +2 +3KMnO4 + FeSO4 + H2SO4 MnSO4 + Fe2(SO4)3 + K 2SO4 + H2O

Cht oxi ha Cht kh7 +2



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2 MnO4- + 5e- Mn2+ (Phn ng kh )

+2 +3

5 2Fe2+ - 2e- 2Fe3+ (Phn ng oxi ha )

(+4) (+6)

2MnO4- + 10Fe2+ 2Mn2+ + 10Fe3+

in tch :2(-1) + 10(+2) 2(+2) + 10(+3)+18 +34

+ 16H+ + 8H2O

2KMnO4 + 10Fe2(SO4)3 + 8H2SO4 2MnSO4 + 5Fe2(SO4)3 + K 2SO4 + 8H2OTh d 2 :

+7 +4 +6 +6

KMnO4 + K 2SO3 + KOH K 2MnO4 + K 2SO4 + H2O

Cht oxi ha Cht kh

MnO4- + SO32- MnO42- + SO42-

+7 +6

2 MnO4- + e- MnO42- (Phn ng kh )

+4 +6

SO32- - 2e- SO42- (Phn ng oxi ha )

2MnO4- + SO32- 2MnO42- + SO 2-

in tch : 2(-1) + 1(-2) 2(-2) + 1(-2)



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- 4 - 6

2MnO4- + SO32- + 2OH- 2MnO42- + SO42 + H2O

2KMnO4 + K 2SO4 + 2KOH 2K 2MnO4 + K 2SO4 + H2O

II. Cc dng phn ng oxi ha kh phc tp :

1. Phn ng oxi ha kh c h s bng ch :

- Nguyn tc: Cn xc nh ng s tng gim s oxi ho ca cc nguyn t- V d:Fe3O4 + HNO3 Fe(NO3)3 + NxOy + H20

(5x 2y) x 3Fe+8/3 3Fe3 + e

1 x x N+5 + (5x 2y)e xN+2y/x (5x-2y) Fe3O4+ (46x-18y) HNO3 (15x-6y) Fe(NO3)3+ NxOy+(23x-9y) H2O

2. Phn ng c cht ha hc l t hp ca hai cht kh :

- Nguyn tc :

Cch 1 : Vit mi phng trnh biu din s thay i s oxi ho, ch s rng buc hca phn ng v rng buc h s trong cng phn t.

Cch 2 : Nu mt phn t c nhiu nguyn t thay i s oxi ho c th xt chuyn nh b phn t, ng thi ch s rng buc v sau.Luyn tp: Cn bng phn ng sau :FeS2 + O2 Fe2O3 + SO2

Fe+2 Fe+3 + 1e2S-1 2S+4 + 2.5e

4 x FeS2 - 11e Fe+3 + 2S+4

11 x 2O0 + 4e 2O2-



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4 FeS2 + 11 O2 2 Fe2O3 + 8 SO23. Phn ng c nguyn t tng hoc gim s oxi ha nhiu nc :

Nguyn tc :

Cch 1 :Vit mi phng trnh thay i s oxi ho, t n s cho tng nc tng, gim Cch 2 :Tch ra thnh hai hay nhiu phng trnh ng vi tng nc s oxi ha tng hay V d: Cn bng phn ng sau: Al + HNO3 Al(NO3)3 + NO + N2O + H2OCch 1:

(3x + 8y) Al0 - 3e Al+3

3 x N+5 + 3e N+5 3 y 2 N+5 + 8e 2N+1

(3x+8y) Al + (12x+30y) HNO3 (3x+8y) Al(NO3)3+ 3x NO + 3y NO2+(6x+15y) H2O

Cch 2:Tch thnh 2 phng trnh :

a x Al + 4HNO3 Al(NO3)3 + NO + 2H2O b x 8Al + 30 HNO3 8Al(NO3)3 + 3N2O + 15H2O

(a+8b)Al + (4a+30b) HNO3 (a+8b) Al(NO3)3 + a NO + 3b N2O+(2a+15b) H2O

4. Phn ng khng xc nh r mi trng :

- Nguyn tc: C th cn bng nguyn t bng phng php i s hoc qua trung gian phng tgn. Nu do gom nhiu phn ng vo, cn phn tch xc nh giai on no l oxi h

V d:



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Al + H2O + NaOH NaAlO2 + H2Al + H20 Al(OH)3 + H2

2 x Al0 Al+3 + 3e

3 x 2H+ + 2e H2

2Al + 6H20 2Al(OH)3 + H2 (1)2Al(OH)3 + 2NaOH 2NaAlO2 + 4H20 (2)

Tng hp 2 phng trnh trn:

2Al + 2NaOH + 2H2O 2NaAlO2 + 3H2

III. Cc bi tp b sung :

1. Bi tp 1 :

Cn bng cc phn ng oxi ha kh sau y theo phng php cn bng electron:

1) C12H22O11 + MnO4- + H+ CO2 + Mn2+ + H2O

2) CnH2n + 1CHO + KMnO4 + H2SO4 CH3COOH + CO2 +

MnSO4 + K 2SO4 + H2O (n CH 3 COOH : n CO 2 = 1 : 1)

3) Ca3(PO4)2 + SiO2 + C P4 + CO + CaSiO3

4) MxOy + H2SO4(, nng ) M2(SO4)n + SO2 + H2O

5) NaCrO2 + Br 2 + NaOH Na2CrO4 + NaBr + H2O

6) Zn + HNO3 Zn(NO3)2 + xNO2 + yNO + H2O

2. Bi tp 2 :

Cn bng cc phn ng sau y theo phng php cn bng ion electron1) KMnO4 + KNO2 + H2SO4 MnSO4 + KNO3 + K 2SO4 + H2O



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2) Zn + HNO3 Zn(NO3)2 + NO2 + NO + H2O

(T l th tch:: V NO2 : V NO = 1 : 3)

3) Zn + KNO3 + KOH K 2ZnO2 + NH3 + H2O

4) Cr 2O72- + Fe2+ + H+ Cr 3+ + Fe3+ + H2O

5) Mg + NO3- + H+ Mg2+ + NH4+ + H2O

3. Bi tp 3 :Cn bng cc phn ng sau y theo phng php i s:

1. Al + NO2- + OH- + H2O AlO2- + NH3

2. FeS2 + H2SO4(, nng ) Fe2(SO4)3 + SO 2 + H2O

3. FeO + H2SO4(, nng ) Fe2(SO4)3 + SO2 + H2Od. MxOy + HNO3 M(NO3)n + NO + H2O

e. NO2- + MnO4-+ H+ NO3- + Mn2+ + H2O

f. FexOy + CO FemOn + CO2

4.Bi tp 4 :Cho m gam bt kim loi km ha tan ht trong dung dch HNO3, thu c 13,44 lt hn

hp ba kh l NO2, NO v N2O. Dn lng kh trn qua dung dch xt d, c 11,2 lt hn hpra. Cho lng kh ny trn vi khng kh d (coi khng kh ch gm oxi v nit) phhon ton, sau cho hp th lng kh mu nu thu c vo dung dch KOH d, thu D. Dung dch D lm mt mu va 100 ml dung dch KMnO4 0,4M trong mi trng HTh tch cc kh o ktc. Cc phn ng xy ra hon ton.a. Vit phn ng gia km vi dung dch HNO3 c hin din 3 kh trong phn ngtheo d kin trn.

b. Tnh m.(Zn = 65)S: 31 Zn + 80 HNO3 31 Zn(NO3)2 + 2 NO2 + 4 NO + 6 N2O + 40 H2Om = 100,75 gam

5. Bi tp 5 :



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A l mt kim loi. Ha tan hon ton 1,43 gam A bng dung dch H2SO4 c d 20% so vthu c mt kh c mi hc, mt cht khng tan c mu vng nht (c khi lng 0dung dch B (c cha mui sunfat ca A). Cho hp th lng kh mi hc trn vo 100 Ca(OH)2 0,03M, thu c 0,24 gam kt ta mu trng.

a. Xc nh kim loi A. Cho bit dung dch H2SO4 em dng khng c phn ng vicht rn mu vng. b. Tnh th tch dung dch Ba(OH)2 0,1M cn dng va khi cho tc dng vilng dung dch B trn th thu c:- Lng kt ta cc i- Lng kt ta cc tiu.c. Tnh khi lng kt ta ln nht v nh nht thu c cu (b).

Cc phn ng xy ra hon ton.(Na = 23; Mg = 24; Al = 27; K = 39; Ca = 40; Cr = 52; Mn = 55; Fe = 56; Cu = 64; Zn 108; Ba = 137; Hg = 200; Pb = 207; S = 32; O = 16; H = 1)

S: Zn; 284ml; 504ml; 8,7952g; 6,6172g

6. Bi tp 6 :Cho m gam kali kim loi vo 100 ml dung dch HCl 0,1M. Sau cn thm tip 10 ml du0,2M thu c dung dch c pH = 7.

a. Tnh m. b. Tnh th tch kh hiro thot ra trong th nghim trn 27,30C; 83,6 cmHg.c. Xc nh nng mol/lt ca dung dch c pH = 7 trn.Cc phn ng xy ra hon ton. Coi th tch dung dch khng thay i trong qu trnh phn ng. (K = 39)S: m = 0,468g; 134,4ml; KCl 0,091M; KBr 0,018M

7. Bi tp 7 :Hn hp cht rn X gm bt km v mui st (III) sunfat. Cho 200 ml nc vo mt bgam hn hp X. Dng a thy tinh khuy u phn ng xy ra hon ton. Thu tan gm 3,36 gam mt kim loi v dung dch Y c ha tan hn hp mui. Cho dung dchvo dung dch Y, sau khi phn ng xong, lc ly kt ta em nung ngoi khng kh cho lng khng i th thu c 11,2 gam mt cht rn.a. Vit cc phn ng xy ra.



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b. Tnh m.c. Tnh nng mol ca cht tan ca dung dch Y. Coi th tch dung dch Y bngth tch nc dng.(Zn = 65; Fe = 56; S = 32; O = 16)

S: m = 50,4g; ZnSO4 0,8M; FeSO4 0,7M

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Can Bang Phan Ung

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