Example 1-2 for your own practice) As2S3 (s)+HNO3 (aq)>H3AsO(aq)+H2SO(aq)+NO(g) Answer As2S3 +NO3>H;AsO+SO2+NO (ionic form) NO:+4H*+3e=NO+2H,O ① As2S+6H+20H20 =2H3As04+3S0+40H++28e ② or:As2S3+20H20=2H3As04+3S0￥+34H+28e ctions ①×28+②×3： 28NO3+3As2S,+4H20+10H =6H,As04+9SO2+28NO 3As2S3+28HN03+4H2O =6H3AsO4+9H2S04+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 1-2 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 N O H AsO SO N O 2 2 3 + 3 → 3 4 + 4 + ： − − (ionic form)two half reactions
Example 2-1 Cl,(g)+NaOH-A NaCl+NaCIO, 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 Cl+CIO3 ionic form Cl2(g)+2e=2C1 ① Two half-reactions Cl2(g)+120Hf=2C1O3+6H20+10e②@ ①X5+②，we get 6C12(g)+120H=10C1+2C103+6H,0 or be simplified as 3C12g)+60H=5C1+CI03+3H,O
Example 2-1 3 Δ Cl2 (g) + NaOH ⎯→NaCl+ NaClO Anwser： Two half-reactions ①×5+②, we get or be simplified as ： 3Cl2（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 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. Cl2 (g) + OH- = Cl- + ClO3 - ionic form
molecular equation: 3C1,(g)+6NaOH=5NaCl+NaClO,+3H2O Example 2-2:for your own practice Cr(OH)(s)+Br2 (I)+KOH->K2CrO+KBr Anwser:Cr(OH)(s)+Br,(1)>CrO+Br Ionic form Br2 )+2e=2Br ① 2 half-reactions CrOH)(s)+80H =CrO+30H+4H2O+3e Cr(OH)(s)+50H CrO+4H,O+3e ② ①X3+②X2,we get 2CrOH),(s)+3Br1+100H Molecular equation: =2CrO+6Br+8H,O 2Cr(OHS+3B5①+10KOH =2K,CrO+6KBr+8H,O
Example 2-2： 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： Cr(OH)(s) Br2 (l) CrO2 4 Br Ionic form 3 + → + − − molecular equation： 3Cl2（g）+ 6NaOH = 5NaCl + NaClO3 + 3H2O
Example 3: (nutral media) Ca3(PO4)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+4H+①） ② Two half-reactions 2Ca3(P04)2+6Si02+10H20+20e =6CaSi03+P4+200H ①×5t②：equation in molecular form: 2Ca3(P04)2+6Si02+5C=6CaSi03+P4+5C02
Example 3： 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 H2Oat 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 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. Summary