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Environmental fate & pathways

Hydrolysis

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Reference
Endpoint:
hydrolysis
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:

Sédy et al. pointed out that in the most studies to high concentrations of tin were used and so polytin complexes were formed. Further Sédy et al. show that there is a different in the species formed in a solution with and without halogeninde.

The values measured under standard conditions (25°C, 1bar)

 

Chemical equilibrium

-log^{m}K°

I (mol L^{-})

Remark

Sn^{2+} + H_{2}O <=> SnOH^{+} + H^{+}

3.8 +/- 0.2

0.1, 0.5, 1.0

Inorganic tin hydrolysis

Sn^{2+} + 2H_{2}O 

<=>

Sn(OH)^{0}_{2} + 2H^{+}

7.8 +/- 0.2

0.1, 0.5, 1.0

Inorganic tin hydrolysis

Sn^{2+} +3H_{2}O 

<=>

SnOH^{-}_{3} + 3H^{+}

-17.5 +/- 0.2

0.1, 0.5, 1.0

Inorganic tin hydrolysis

Sn(OH)_{2}(s)óSn^{2+} + OH^{-}

25.80

0_{corr}

Precipitation Reactions

SnO(s) + H_{2}O  

<=>

Sn^{2+} + OH^{-}

26.24

0_{corr}

Precipitation Reactions

 

The ion interaction coefficients are:

%epsilon

Value (L mol^{-1}

Sn^{2+}, NO_{3}^{-}

0.4 +/- 0.1

SnOH^{+}, NO_{3}^{-}

0.2 +/- 0.1

Sn(OH)_{2}, NO_{3}^{-}

0.3 +/- 0.1

H^{+}, NO_{3}^{-}

0.07 +/- 0.01

 

 

Distribution of various species of tin (II) as a function of pH

 

Sn^{2+} / %

Sn(OH)^{+} / %

Sn(OH)_{2} / %

Sn(OH)_{3}^{-} / %

4.0

30

40

30

0

4.5

7

34

59

0

5.0

2

11

87

0

5.5

0

4

96

0

6.0

0

2

98

0

6.5

0

1

99

0

7.0

0

0

100

0

7.5

0

0

99

1

8.0

0

0

98

2

8.5

0

0

95

5

9.0

0

0

80

20

9.5

0

0

50

50

10.0

0

0

30

70

 

Distribution of various species of tin (II) as a function of pH in present of 10^{-2} mol L^{-} [Cl^{-}]

 

Sn^{2+} / %

SnCl^{+} / %

SnCl_{2} / %

Sn(OH)^{+} / %

Sn(OH)_{2} / %

Sn(OH)_{3}^{-} / %

4.0

27

10

1

35

27

0

4.5

8

3

0

29

60

0

5.0

0

0

0

15

85

0

5.5

0

0

0

5

95

0

6.0

0

0

0

3

97

0

6.5

0

0

0

1

99

0

7.0

0

0

0

0

100

0

7.5

0

0

0

0

99

1

8.0

0

0

0

0

98

2

8.5

0

0

0

0

95

5

9.0

0

0

0

0

80

20

9.5

0

0

0

0

50

50

10.0

0

0

0

0

30

30

 

recovery of data: 95%

Martyak reports for the hydrolysis reaction of stannos sulfate a free energy of %DELTA G = -7.37 kcal/mol and a equilibrium constant of ~1.8 x 10^5.

Validity criteria fulfilled:
yes
Conclusions:
Tin(II) can be hydrolysed into SnOH^{+}, Sn(OH)_{2} and Sn(OH)^{-}_{3}. In The pH frame according the guideline most of the Sn(II) exists as
Sn(OH)_{2}. The equilibrium constant for the dissioziation logK = 7.8 +/- 0.2 (@20°C).
Martyak reports for the hydrolysis reaction of stannos sulfate a free energy of %DELTA G = -7.37 kcal/mol and a equilibrium constant of ~1.8 x 10^5.

So the stannous sulfate ist not stable in water. Under alkaline conditions (pH>8 ) changes immediately oxidation state 2 to 4.

Description of key information

There are no proprietary studies investigating the hydrolysis of the substance in aqueous media. The substance of interest is an inorganic element.

Typically salts (ionic bonding) are electrovalent substance. Electrovalent substances are made up of ions in the solid state. The oppositely charged ions are held together by strong electrostatic (coulombic) force of attraction. Due to these forces the ions cannot move. When these substances are dissolved in water, the ions free themselves from this binding. Thus the break up of an electrovalent compound into free mobile ions when dissolved in water or when melted, is called electrolytic dissociation. In the liquid state the ions become free and mobile. But the oppositely charged ions always remain in close proximity of each other.

SnSO4(s) ---> Sn2+(aq) + SO42- (aq). This is a 100% dissociation.

In addition this dissociation behaviour is depended from the solubulity of the substance and environmental conditions. Tin(II) can be hydrolysed into SnOH+, Sn(OH)2 and Sn(OH)3-, based on the conditions. At environmental relevant pH-values the Sn(OH)2 species is the predominant one (Séby, 2001). Consequently it is not technically possible to perform testing to measure simple dissociation events so testing is waived.

Key value for chemical safety assessment

Additional information

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