Example 2 for your own practice) As2S3 (s)+HNO3 (aq)->H3AsO(aq)+H2SO(aq)+NO(g) Answer:As2S3 +NO>HAsO+SO2+NO (ionic form) NO:+4H*+3e=NO+2H,O ① As2S+6I+20H,0 half =2H3As04+3S0￥+40H++28e ② or:As,S,+20H,O=2H,AsO+3S0+34H*+28e reactions ①×28+②X3: 28NO3+3As2S3+4H2O+10H =6H3As04+9S02+28NO 3As2S3+28HN03+4H2O =6H3AsO4+9H,S04+28NO
As S (s) HNO (aq) H AsO (aq) H SO (aq) NO(g) 2 3 + 3 3 4 + 2 4 + ①×28+②×3: ② ① Example 2 for your own practice) 6H AsO 9H SO 28NO 3As S 28HNO 4H O 3 4 2 4 2 3 3 2 + + + + 6H AsO 9SO 28NO 28NO 3As S 4H O 10H 2 3 4 4 3 2 3 2 + + + + + + + or As S + 20H O 2H AsO +3SO +34H + 28e 2 ： 2 3 2 3 4 4 + + + + + + + 2H AsO 3SO 40H 28e As S 6H 20H O 2 3 4 4 2 3 2 NO3 + 4H + 3e NO+ 2H2 O + Answer As S NO H AsO SO NO 2 2 3 + 3 3 4 + 4 + ： (ionic form)two half reactions
Example 3 Cl2(g+NaOH->NaCl+NaCIO (basic media) Anwser: Disproportionaton reaction Basic medium: When the left side has excess n oxygen atoms,add n H2O at the left side,and add 2n OH-at the right side. When the left side lacks n oxygen atoms,add 2n OH-at the left side,and add n H2O at the right side. Cl2 (g)+OH=CI+CIO3 ionic form Cl2(g)+2e=2C1 ① Two half-reactions Cl2(g)+120H=2C1O3+6H20+10e② ①X5+②，we get 6C12(g)+12OH=10C1+2C103+6H20 or be simplified as 3C12 (g)+60H =5C1+CIO3 +3H2O molecular 3C12 (g)+6NaOH=5NaCl+NaClO3 +3H2O equation:
Example 3 3 Δ Cl2 (g) + NaOH NaCl+ NaClO Anwser： Two half-reactions ①×5+②, we get or be simplified as ： 3Cl 2（g）+ 6OH 5Cl + ClO3 + 3H2O 6Cl2 (g) +12OH 10Cl +2ClO3 + 6H2O ① Cl (g) 12OH 2ClO 6H O 10e ② Cl (g) 2e 2Cl 2 3 2 2 + + + + Disproportionaton reaction Basic medium： When the left side has excess n oxygen atoms，add n H2O at the left side, and add 2n OH- at the right side. When the left side lacks n oxygen atoms，add 2n OH- at the left side, and add n H2O at the right side. Cl2 (g) + OH- = Cl- + ClO3 - ionic form molecular equation： 3Cl 2（g）+ 6NaOH 5NaCl + NaClO3 + 3H2O (basic media)
Example 4 for your own practice Cr(OH):(s)+Br2(I)+KOH->K2CrO+KBr Anwser: CrOH)(s)+Br 1)>CrO+Br Ionie form Br2 (1)+2e=2Br ① 2 half-reactions Cr(OH)(s)+8OH=CrO+30H+4H2O+3e Cr(OH),(s)+50H=Cro+4H2O+3e ② ①X3+②X2,we get 2CrOH)(s)+3Br1)+100H Molecular equation: =2CrO+6Br+8H2O 2CrOH)s)+3Br1+10KOH =2K,CrO+6KBr+8H,O
Example 4 for your own practice Cr(OH) (s) Br (l) KOH K CrO KBr 3 2 2 4 + + + ①×3+②×2, we get Molecular equation： ( )( ) () ( )( ) () 2K CrO 6KBr 8H O 2Cr OH s 3Br l 10KOH 2CrO 6Br 8H O 2Cr OH s 3Br l 10OH 2 4 2 3 2 2 2 4 3 2 + + + + + + + + ① ② 2 half-reactions () ( )( ) Cr(OH)(s) 5OH CrO 4H O 3e Cr OH s 8OH CrO 3OH 4H O 3e Br l 2e 2Br 2 2 3 4 2 2 3 4 2 + + + + + + + + Anwser： ( )( ) () CrO Br Ionic form Cr OH s Br l 2 3 2 4 + +
Example 5:(nutral media) Cas(PO)2+C+SiO2>CaSiO3+P4+CO2 Neutral medium: When the left side lacks n oxygen atoms,add n H2O at the left side,and add 2n H+at the right side. When the left side has excess n oxygen atoms,add n H2O at the left side,and add 2n OH-at the right side. Answer: C+2H20=C02+4e+4H① Two half-reactions 2Ca3(P042+6Si02+10H20+20e ② =6CaSi03+P4+200H ①×5+②：equation in molecular form: 2Ca3P04)2+6Si02+5C=6CaSi03+P4+5C02
Example 5： ①×5+②: ① ② Two half-reactions equation in molecular form： (nutral media) Ca3 (PO4 )2 + C + SiO2 CaSiO3 + P4 + CO2 Answer: C + 2H2O = CO2 + 4H+ +4eCa3 (PO4 )2 + SiO2+ 10H2O + 20e- = 6CaSiO3 + P4 2 6 + 20OH- 2 Ca3 (PO4 )2 + 6SiO2+ 5C = 6CaSiO3 + P4 + 5CO2 Neutral medium： When the left side lacks n oxygen atoms，add n H2O at the left side, and add 2n H+ at the right side. When the left side has excess n oxygen atoms，add n H2O at the left side, and add 2n OH- at the right side
Summary Acidic medium: When the left side has excess n oxygen atoms,add 2n H+at the left side,and add n H2O at the right side. When the left side lacks n oxygen atoms,add n H2O at the left side,and add 2n H+at the right side. Basic medium: When the left side has excess n oxygen atoms,add n H2O at the left side,and add 2n OH-at the right side. When the left side lacks n oxygen atoms,add 2n OH at the left side and add n H2O at the right side. Neutral medium: When the left side has excess n oxygen atoms,add n H2O at the left side,and add 2n OH-at the right side. When the left side lacks n oxygen atoms,add n H2O at the left side,and add 2n H at the right side
Acidic medium： When the left side has excess n oxygen atoms，add 2n H+ at the left side, and add n H2O at the right side. When the left side lacks n oxygen atoms，add n H2O at the left side, and add 2n H+ at the right side. Basic medium： When the left side has excess n oxygen atoms，add n H2Oat the left side, and add 2n OH- at the right side. When the left side lacks n oxygen atoms，add 2n OH- at the left side, and add n H2O at the right side. Neutral medium： When the left side has excess n oxygen atoms，add n H2Oat the left side, and add 2n OH- at the right side. When the left side lacks n oxygen atoms，add n H2O at the left side, and add 2n H+ at the right side. Summary