K2Cr2O7+SnCl2+KOH=> K3[Cr(OH)6] + K2SnO3 + ...
1 | Cr₂O₇²⁻ + 7H₂O + 6e⁻ => 2[Cr(OH)₆]³⁻ + 2OH⁻
3 | Sn²⁺ + 6OH⁻ - 2e⁻ => SnO₃²⁻ + 3H₂O
Cr₂O₇²⁻ + 7H₂O + 3Sn²⁺ + 18OH⁻ = 2[Cr(OH)₆]³⁻ + 2OH⁻+3SnO₃²⁻+9H₂O
Отсюда:
K₂Cr₂O₇ + 3SnCl₂ + 2KOH => 2K₃[Cr(OH)₆] + 3K₂SnO₃ + 6KCl + 2H₂O