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
-
25.00of the mixture solution was transferred into a 250conical flask using a pipette rinsed by distilled water and the mixture solution
- The burette rinsed by distilled water and NaOH is filled with NaOH
- Titrate the mixture solution with 0.1M NaOH solotuion using phenolphthalein as indicactor
- Until the solution turns pink, result is recorded in table 1
-
About 25.00of 1M sulphuric acid (using measuring cylinder) is added to the conical flask .
-
The mixture is then heated by electrical heater to at least 70.
-
The heated mixture is then titrated with 0.02M Potassium permanganate KMn until a permanent pink colour is observed
- Record the result in Table2
RESULT
Table 1
Table 2
CALCUALTION
Equation involved in the reaction between NaOH and mixture solution:
+ +Na(aq)
Mole ratio of NaOH:=2:1
=
=11.8/1000x0.1/2
=5.9xmol
Molarity of = 5.9X/(25/1000)
=2.36 x M
+ 2 Mn+ 16 2+8+10
Mole ratio of : Mn=5:2
=
=5x19.2/1000x0.02/2
=9.6x10^-4 mol
Mole of sodium ethane-1,2-dioate = 9.6x-5.9x1 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 acid’s is 2.36 x M
REFERFERNCE
Wikipedia