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Volumetric analysis

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Introduction

EXPERIMENT 2(A) - VOLUMETRIC ANALYSIS Introduction :- Volumetric analysis is any method of quantitative chemical analysis in which the amount of a substance is determined by measuring the volume .The standard solution(titrant) is chemically reacted with a solution of unknown concentration(analyte) in order to determine the concentration of the unknown. The end-point of the titration is noted by observing the change of colour of an indicator. The titrant (potassium permanganate) was standardized against primary standard (sodium oxalate).In this experiment ,we did the direct titration and back titration. The standardization equation in the ionic form: 5 C2O42- + 2MnO4- + 16 H+ 10 CO2 + 2 Mn2+ + 8 H20 This solution can determined the quantity of nitrite ions in back titration because we can get the molarity exactly. The back titration equations : 5 NO2- + 2MnO4 + 6 H+ 5 NO3- + 2Mn2+ + 3 H2O 2 MnO4- + 10 Fe 2+ + 16 H+ 10 Fe3+ + 2Mn2+ + 8H20 The second set of titration experiments we used a Sodium thiosulfate pentahydrate (Na2S2O3.5H20) To standardized against iodine. The reactions equation :- l03- + 5 l- +6H+ 3l2 + 3H20 2 S2032- + l2 S4062- + 2 l - The standardized sodium thiosulfate solution: (To determine the amount of chlorine in "Chlorox" 0Cl- + 2l- + 2 H + l2 + Cl- +H20 Objective 2(A) ...read more.

Middle

Initial reading(ml) Final reading(ml) Volume(ml) 1. 4.85 14.10 9.25 2. 14.10 23.30 9.20 3. 23.30 32.70 9.40 Average volume =(9.25+9.20+9.40) / 3 = 9.28 ml Observation : Purple colour change Pink pale colour The molarity of the potassium permanganate solution : 5 C2O42- + 2MnO4- + 16 H+ 10 CO2 + 2 Mn2+ + 8 H20 aA(aq) + bB(aq) Products MAVA = a MBVB b n(sodium oxalate) = 0.2998 g / 123.99 gmol-1 = 2.4179x10-3 mol Molarity of sodium oxalate = 2.4179x10-3 mol 0.1L =0.024179 M MAVA = a MBVB b 0.024179 M x 25 = 5 MB X 9.28 2 MB = M potassium permanganate = 0.02605 M The potassium permanganate solution now becomes the '' standard solution'' after it has been standardized against sodium oxalate. This solution was used to determine the quantity of nitrite ions in a Back titration in the first part. Volume of potassium permanganate = 10mL(excess) added to the nitrite solution under acid conditions. Because there is an excess ,the excess was titrated against iron(ll) ammonium sulfate solution. 5 NO2- + 2MnO4 + 6 H+ 5 NO3- + 2Mn2+ + 3 H2O 2 MnO4- + 10 Fe 2+ + 16 H+ 10 Fe3+ + 2Mn2+ + 8H20 Molarity of standard iron (ll) ...read more.

Conclusion

4. Titration which use potassium permanganate does not need any indicator because it indicate itself.In a direct titration,the titrant is added to analyte until end point is observed whereas in a back titration, a known excess of a standard reagent is added to the analyte. The end point is when the solution change color to pale pink. 5.From the first titration, the molarity of potassium permanganate is determined and in the second titration it react as standard solution then can determined the molarity of nitrite solution. 6.Note that for the HCl, use must be made of ultrapure HCl. Normal (reagent grade) 0.1 M HCl can have a significant amount of iodide (~100-300 mM) in it, which can easily be avoided by using triple distilled ultrapure HCl. 7.It is of great importance to calibrate the 5 cm3 and 3 cm3 pipettes with distilled water and to note their precise volumes. The volumes should remain fixed for the duration of the cruise. They are important for establishing the dilution factor to be used for further work on the samples. The standardization of the acid, of course, takes account of the volumes. 8.There should no excess of chlorine in the hypochlorite solution. CONCLUSION: FOR (A) Molarity of potassium permanganate = 0.02605 M Molarity of nitrite solution = 1.53875 M FOR (B) The average molarity of the thiosulfate solution =3. ...read more.

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