Reaction mass of disodium hexatitanium tridecaoxide and disodium trititanium heptaoxide

Dissociation constant

Link to relevant study record(s)

Reference

Endpoint:

dissociation constant

Remarks:

Solublity in acid

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1 hour contact time

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Justification for type of information:

It is not considered possible to perform standard dissociation constant methods in view of the initial reported water solublity < 1 mg/l.
In addition, the substance will dissociate and hydrolyse resulting in an irreversible process to form stable poorly soluble salts (oxide) of titananium and water soluble salts of sodium. A speciflc method was devised to measure formation of water soluble salts.

Qualifier:

no guideline followed

Principles of method if other than guideline:

The substance was mixed in distilled water and in molar HCl. After mixing for one hour at room temperature, the liquids were filtered and washed to leave a clear filtrate and residual solid on the filters. The filtrates were dried to determine if any soluble fractions and the solids formed from solution were weighed to give an approximate quantitative result.

GLP compliance:

no

Dissociating properties:

yes

Remarks on result:

not determinable because of methodological limitations

Remarks:

The presence of soluble fractions implies dissociation, but pKa not determined.

As expected, both mixtures remained cloudy with a large amount of undissolved material, but when filtering and then evaporating the filtrate, some solid residues crystallised out of solution. The amount of solid formed was significantly higher in the acid-treated mixture, but some solids formed even with distilled water at pH10.

 

100 mg of sodium titanate mixed in 100 ml of distilled water or 1M HCl at 20 C resulted in 20 mg and 30 mg of solid crystallising from filtrate respectively; the acid treatment clearly led to a higher yield, suggesting more dissociation. However, even the 20 mg formed with distilled water implied some degradation.

 

In terms of Na solubility, loading at 1000 mg/l resulted in ca 120 mg Na (300 mg NaCl) when mixed in acid and ca 80 mg Na (200 mg NaCl) in deionised water. It is assumed that a trace of Ti will have passed through filters, but with reported Ti solubility < 1 mg/l, this will be negligible.

 

Further work is needed to identify the solid residues on the filter and crystallising from the filtrate. It is also considered important to work on environmentally relevant concentrations to determine if the rate of dissociation / hydrolysis is faster and/or more complete.

 

The proposed reaction scheme is:

 

Na₂O₃Ti + 2HCl dissociates and leads to 2NaCl + TiO₃H₂ and in turn 'hydrolyses' to TiO₂ + H₂O + 2NaCl

 

Theoretical yield of NaCl from 0.1 g sodium titanate (0.0007 moles) with excess 0.1 mole hydrochloric acid is ca 80 mg

Conclusions:

This experiment indicates that there is formation of soluble salts from mixing in excess acid or mixing in dilute forms in distilled water.

Soluble salts will form through dissociation of inorganic ions and in this case, the process is made irreversible through the formation of the stable titanium oxide

This experiment indicates that there is formation of soluble salts from mixing in excess acid or mixing in dilute forms in distilled water.

In terms of Na solubility, loading at 1000 mg/l resulted in ca 120 mg Na (300 mg NaCl) when mixed in acid and ca 120 mg Na (200 mg NaOH) in deionised water. It is assumed that a trace of Ti will have passed through filters, but with reported Ti solubility < 1 mg/l, this will be negligible.

Description of key information

The proposed reaction scheme is:

Na2O3Ti + 2HCl goes to 2NaCl + TiO3H2 which in turn hydrolyses to TiO2  + H2O + 2NaCl

Theoretical yield of NaCl from 0.1 g sodium titanate (0.0007 moles) with excess 0.1 mole hydrochloric acid is ca 80 mg

It is also noted from analysis (XRD) that the material tested contains a significant level of TiO2, therefore reducing apparent yield.

This experiment indicates that there is formation of soluble salts from mixing in excess acid or mixing in dilute forms in distilled water.

Soluble salts will form through dissociation of inorganic ions and in this case, the process is made irreversible through the formation of the stable titanium oxide