In: Chemistry
How to balance redox reactions in acid?
a. Br2 + NO2^- ---> Br^- + NO3^-
b. H2O2 + Cr^+3 ---> Cr2O7^-2 + H2O
c. Cr2O7^-2 + CH3OH ---> Cr+3 + CH3COOH
d. NO2^- + I^- --> N2 + I2
I believe a. is NO2^-1 + H2O + 2Br2 --> 2Br^- + NO3^- + 2H+ but
am very confused about the rest
a. split:
Br2 = Br-
NO2- = NO3-
balance Br
Br2 = 2Br-
NO2- = NO3-
balance O
Br2 = 2Br-
H2O + NO2- = NO3-
balance H
Br2 = 2Br-
H2O + NO2- = NO3- + 2H+
balance e-
2e- + Br2 = 2Br-
H2O + NO2- = NO3- + 2H+ +2e-
add
2e- + Br2 + H2O + NO2- = NO3- + 2H+ +2e- + 2Br-
Br2 + H2O + NO2- = NO3- + 2H+ +2Br-
b.
H2O2 = H2O
Cr+3 = Cr2O7-2
--
H2O2 = H2O + H2O
7H2O + 2Cr+3 = Cr2O7-2
--
2e- + 2H+ + H2O2 = 2H2O
7H2O + 2Cr+3 = Cr2O7-2 + 14H+ + 6e-
--
6e- + 6H+ + 3H2O2 =6H2O
7H2O + 2Cr+3 = Cr2O7-2 + 14H+ + 6e-
--
6e- + 6H+ + 3H2O2 + 7H2O + 2Cr+3 = Cr2O7-2 + 14H+ + 6e- + 6H2O
--
3H2O2 + 7H2O + 2Cr+3 = Cr2O7-2 + 8H+ +6H2O
c.
CrO7-2 + CH3OH = Cr+3 + CH3COO-
CH3OH = CH3COO-
Cr2O7-2 = 2Cr+3
--
H2O + CH3OH = CH3COO-
Cr2O7-2 = 2Cr+3 + 7H2O
--
H2O + CH3OH = CH3COO- + 3H+
14H+ + Cr2O7-2 = 2Cr+3 + 7H2O
--
H2O + CH3OH = CH3COO- + 3H+ + 2e-
6e- + 14H+ + Cr2O7-2 = 2Cr+3 + 7H2O
--
3H2O + 3CH3OH = 3CH3COO- + 9H+ + 6e-
6e- + 14H+ + Cr2O7-2 = 2Cr+3 + 7H2O
--
6e- + 14H+ + Cr2O7-2 + 3H2O + 3CH3OH = 3CH3COO- + 9H+ + 6e- + 2Cr+3 + 7H2O
sikmplify
14H+ + Cr2O7-2 + 3CH3OH = 3CH3COOH + 6H+ 2Cr+3 + 4H2O
--
8H+ + Cr2O7-2 + 3CH3OH = 3CH3COOH + 2Cr+3 + 4H2O
d.
NO2- = N2
I- = I2
--
2NO2- = N2 + 4H2O
2I- = I2 + 2e-
--
6e- + 8H+ + 2NO2- = N2 + 4H2O
2I- = I2 + 2e-
---
6e- + 8H+ + 2NO2- = N2 + 4H2O
6I- = 3I2 + 6e-
add
6I- + 6e- + 8H+ + 2NO2- = N2 + 4H2O + 3I2 + 6e-
6I- + 8H+ + 2NO2- = N2 + 4H2O + 3I2