AP Chem equations and reactions summary

Question

Balance the following redox reaction under acidic conditions.

MnO4^-1 + SO3^-2 --> Mn^+2 + SO4^-2

Answer 1

Balance the following redox reaction under acidic conditions.

MnO4^-1 + SO3^-2 --> Mn^+2 + SO4^-2

separate into two halves

balance O with H2O

balance H with H+

balance charge with electrons

equalize electrons in the two half reactions if necessary

add the reactions together and cancel species that are on both sides.

MnO4- → Mn2+

MnO4- → Mn2++4H2O

8H+ +MnO4- → Mn2++4H2O

charge=7+ charge=2+

5e-+8H+ +MnO4- → Mn2++4H2O

SO32- → SO42-

H2O+SO32- → SO42-

H2O+SO32- → SO42-+2H+

charge=2- charge=0

H2O+SO32- → SO42-+2H++2e-

equalize electrons

2(5e-+8H+ +MnO4- → Mn2++4H2O)

5(H2O+SO32- → SO42-+2H++2e-)

10e-+16H+ +2MnO4- → 2Mn2++8H2O

5H2O+5SO32- → 5SO42-+10H++10e-

cancel the e-, cancel the H2O to show excess (3 excess H2O on the right, 5H2O on the left cancelled) cancel H+ to show excess (16H+ on the left, 10H+ on the right, 6 excess H+ on the left)

6H⁺ +2MnO₄^-+5SO₃^2- → 2Mn²⁺+8H₂O+5SO₄^2-

charge=6-2-10=-6 charge=4-10=-6

balanced in elements and charge in acidic conditions