Determination Of Metal Ions By Control-potential Titration With Sodium Hydroxide Solution As Titrant

There are two different parts in this paper,the first part is about determination of mixed metal ions.Normally EDTA or EGTA is chosen to be the titrant in titration.The sodium hydroxide solution was chosen to be the titrant in this paper,and,Zn²⁺ and Al³⁺ were determined by control-potential titration method,with H⁺ selected electrode as work electrode.The job includes:(l)The determination of Zn²⁺ and Al³⁺ separately.with a good result that the errors were under 1%;(2)The determination of Zn²⁺ and Al³⁺ simultaneously,with a satisfying result,the errors of Al³⁺ were around 1% while the errors of Zn²⁺ were a little big correspondingly;(3)The determination of the content of Zn and Al in Zn-Al alloy;(4)It was disscued the elimination of the influence of HC1 in solution and the choice of potential points;(5)A try was made to calculate the concentration of Zn²⁺ and Al³⁺ according to the reaction of deposition.The result was disappointing because of the complicated species of Zn²⁺ and Al³⁺ in aqueous solution.But it was found that the n_NaOH/n_Zn(n_NaOH/n_Al) is a constant at the jump point.A method without knowing the concentration of titrant was devised to determin the concentration of Zn²⁺ and Al³⁺;(6)Had a try to determin the Zn²⁺ and Al³⁺ with alanine in the solution.It was found that the influence of alanine was so small because the reaction between alanine and Zn²⁺ was weak,and there was nearly no reaction between alanine and Al³⁺.The second part is the determination of the dissociation constant of amino acid in aqueous solution.Those below were included: (1)The calculation model of determination of the dissociation constant of amino acid was developed,and improved according to the experiment results;(2)The dissociation constant of five amino acid (Alane,Threonine,Serine,Proline and Hydroxyproline) was determined.and the results were closed to the literature value;(3)The importance of using hydrochloric acid was discussed;(4)The calculation model of determination of the stability constant of Zn-amino acid compound was developed.But the experiment got bad results,and the possible reasons were disscued.