Reaction

log K^*

Ref.^†

Aqueous arsenic species

H₂AsO₃^- + 0.5 O_2(aq) = H₂AsO₄^-

30.53

1

AsO₄^3- + 2 H⁺ = H₂AsO₄^-

18.80

1

H₃AsO_4(aq) = H₂AsO₄^- + H⁺

-2.30

1

HAsO₄^2- + H⁺ = H₂AsO₄^-

6.99

1

H₃AsO_3(aq) = H₂AsO₃^- + H⁺

-9.17

1

HAsO₃^2- + H⁺ = H₂AsO₃^-

14.1

1

AsO₃^3- + 2 H⁺ = H₂AsO₃^-

29.1

1

AsS(OH)(SH)^- + 2 H₂O = H₂AsO₃^- + 2 HS^- + 2 H⁺

-27.19

1

As₃S₄(SH)₂^- + 9 H₂O = 3 H₂AsO₃^- + 6 HS^- + 8 H⁺

-99.78

1

Surface complexation

>FeO^- + H⁺ = >FeOH

8.93

2

>FeOH₂⁺ = >FeOH + H⁺

-7.29

2

>FeH₂AsO₃ + H₂O = >FeOH + H₃AsO_3(aq)

-5.41

2

>FeH₂AsO₄ + H₂O = >FeOH + AsO₄^3- + 3 H⁺

-29.31

2

>FeHAsO₄^- + H₂O = >FeOH + AsO₄^3- + 2 H⁺

-23.51

2

>FeOHAsO₄^3- = >FeOH + AsO₄^3-

-10.58

2

Arsenic solids

As_(s) + 1.5 H₂O + 0.75 O_2(aq) = H⁺ + H₂AsO₃^-

42.80

1

Arsenolite (As₂O₃) + 3 H₂O = 2 H₂AsO₃^- + 2 H⁺

-19.72

1

Claudetite (As₂O₃) + 3 H₂O = 2 H₂AsO₃^- + 2 H⁺

-19.75

1

As₂O_5(s) + 3 H₂O = 2 H⁺ + 2 H₂AsO₄^-

3.65

1

Realgar (AsS) + 2.5 H₂O + 0.25 O_2(aq) = H₂AsO₃^- + 2 H⁺ + HS^-

-7.8

1

Orpiment (As₂S₃) + 6 H₂O = 2 H₂AsO₃^- + 3 HS^- + 5 H⁺

-64.6

1

As₂S_3(am) + 6 H₂O = 2 H₂AsO₃^- + 3 HS^- + 5 H⁺

-63.2

1

Green rusts

Fe₂(OH)_5(s) + 5 H⁺ = Fe³⁺ + Fe²⁺ + 5 H₂O

12.2^‡

3

Fe₃(OH)_8(s) + 8 H⁺ = 2 Fe³⁺ + Fe²⁺ + 8 H₂O

19.3^‡

3

Fe₃(OH)_7(s) + 7 H⁺ = Fe³⁺ + 2 Fe²⁺ + 7 H₂O

15.0^‡

3

Fe₄(OH)₈Cl_(s) + 8 H⁺ = Fe³⁺ + 3 Fe²⁺ + Cl^- + 8 H₂O

28.47

3

Fe₆(OH)₁₂CO_3(s) + 13 H⁺ = 2 Fe³⁺ + 4 Fe²⁺ + HCO₃^- + 12 H₂O

29.11

3

Fe₆(OH)₁₂SO_4(s) + 12 H⁺ = 2 Fe³⁺ + 4 Fe²⁺ + SO₄^2- + 12 H₂O

30.55

3