KMnhas to be acidified first, otherwise brown ppt of Mn is formed instead of 2 H2O + MnO4- + 3 e- i?? Mn+ 4 In addition to that, the reaction solution has to be warmed to about 70 as the reaction rate is very slow. MATERIALS AND APPARATUS beaker measuring cylinder. Safety spectacles beaker conical flask pipette ,25 burette ,50, and stand wash bottle white file electrical heater sulphuric acid Potassium permanganate KMn solution Mixture solution PROCEDURE 1. 25. 00of the mixture solution was transferred into a 250conical flask using a pipette rinsed by distilled water and the mixture solution 2.
The burette rinsed by distilled water and NaOH is filled with NaOH 3. Titrate the mixture solution with 0. 1M NaOH solotuion using phenolphthalein as indicactor 4. Until the solution turns pink, result is recorded in table 1 5. About 25. 00of 1M sulphuric acid (using measuring cylinder) is added to the conical flask . 6. The mixture is then heated by electrical heater to at least 70. 7. The heated mixture is then titrated with 0. 02M Potassium permanganate KMn until a permanent pink colour is observed 8. Record the result in Table2 RESULT Table 1 Titration result of mixture solution against NaOH Trial 1 2 3 Final burette reading 15.
4 27. 3 39. 0 12. 8 Initial burette Reading 3. 1 15. 4 27. 3 1. 0 Volume of NaOH Added 12. 3 11. 9 11. 7 11. 8 Mean Volume of NaOH added ( 11. 7+11. 8+11. 9) /3 =11. 8 Table 2 Titration result of mixture solution against KMn Trial 1 2 3 Final burette reading 35. 0 26. 4 45. 5 40. 6 Initial burette Reading 16. 3 7. 1 26. 4 21. 4 Volume of NaOH Added 18. 7 19. 3 19. 1 19. 2 Mean Volume of NaOH added ( 19. 3+19. 1+19. 2) /3 =19. 2 CALCUALTION Equation involved in the reaction between NaOH and mixture solution: + +Na(aq) Mole ratio of NaOH:=2:1 = =11. 8/1000—0. 1/2 =5. 9xmol Molarity of = 5. 9X/(25/1000) =2. 36 x M + 2 Mn+ 16 2+8+10
Mole ratio of : Mn=5:2 = =5—19. 2/1000—0. 02/2 =9. 6—10^-4 mol Mole of sodium ethane-1,2-dioate = 9. 6x-5. 9—1 l = 3. 7 x mol Molarity of sodium ethane-1,2-dioate in mixture = 3. 7 x/(25/1000) =1. 48xM DISCUSSIONS CHOICE OF INDICATORS Phenolphthalein is used as indicator in the reaction between Sodium hydroxide and ethane-1, 2-dioic acid because the reaction involves a weak acid titrated against a strong alkali. REASON FOR HEATING THE MIXTURE SOLUTION The rate reaction between and Mn is very slow as there is repulsion between anion. REASON FOR HEATING MIXTURE SOLUTION IN THE CONICAL FLASK INSTEAD OF MN IN THE BURETTE.
Aqueous solution of Potassium permanganate KMn is unstable and can easily be decomposed. The decomposition is accelerated by heat. If it is put in the conical flask and heated, it will easily oxidize water to oxygen and the amount of KMn is therefore decreased. 4Mn 4Mn +3 In addition, if hot Potassium permanganate solution is added to the burette, it may cause expansion of burette, causing inaccurate measurement. END POINT The end-point is not very permanent because if the Mn ion is in large excess, the following reaction occur: 2 Mn+3+ 2 +4 DECOPOSITION OF POTASSIUM PERMANGANATE.
Potassium permanganate is easily decomposed and the decomposition is speed up by light, heat, acids, base, reducing agent in air such as hydrogen sulphide gas, , , and even by the end-product Therefore, it should be stored in brown bottle and should be standardized before use. ABSORPTION OF WATER BY SODIUM HYDROXIDE sodium hydroxide absorb water from air. The volume of solution increase, and hence cause a decrease in concentration, causing inaccurate calculation.
CONCLUSION The concentration of sodium ethane-1,2-dioate is 1. 48xM while ethane-1, 2-dioic acids is 2. 36 x M REFERFERNCE Wikipedia ?? ?? ?? ?? Chan ting hin 6b 11 ? 1.