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Determination of Ksp of copper(II) iodine by emf measurement

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Introduction

Date of experiment: 19/05/2011 Name: Cheung Lap Kwan (6) Po Leung Kuk Ngan Po Ling College 2010-2011 Form 6 Chemistry Laboratory Report Title: Determination of Ksp of copper(II) iodate by e.m.f. measurement Introduction: Copper(II) iodate(V) ionizes weakly in water: Cu(IO3)2 + aq Cu2+(aq) + 2IO3-(aq) For a saturated solution of copper(II) iodate(V), concentration of IO3- ions doubles that of the Cu2+ (aq) ions, and Ksp of Cu(IO3)2(s) can be calculated by determining the concentration of Cu2+(aq) ion of a saturated Cu(IO3)2(aq). The e.m.f. of a galvanic cell consisting of a Zn(s)/Zn2+(aq) half-cell and another half-cell containing a copper strip in contact with a saturated solution of Cu(IO3)2(aq) is measured by a commercial DMM. Concentration of Cu2+(aq) is determined with reference to the EO values of the Zn(s)/Zn2+(aq) and the Cu(s)/Cu2+(aq) couples as well as the Nernst equation for a metal/metal ion half-cell: where n is the number of electrons transferred in the reduction process. ...read more.

Middle

+ Zn(s)Zn2+(aq) + Cu(s) Procedures: 1. 50 drops of 1M ZnSO4(aq) were placed into a well of the well-plate; 2. 25 drops of 0.3M KIO3(aq) were placed into an empty well next to the well containing the 1M ZnSO4(aq), by using a clean Jumbo pipette; 3. The plastic pipette used in step(2) was cleaned. By using the same plastic pipette, 25 drops of 0.15M CuSO4(aq) were added and stirred well with a micro-stirrer or toothpick. 5 minutes were waited to attain equilibrium; 4. The two wells were connected by a strip of filter paper moistened with saturated KNO3(aq); 5. A clean homemade copper wire electrode and a clean zinc plate electrode were placed into the well containing the pale blue suspension and the well containing the 1M ZnSO4(aq) respectively; 6. The prepared galvanic cell was connected to a DMM. The steady voltage developed was recorded. ...read more.

Conclusion

Obviously, the literature value was much larger than the experimental value. The discrepancy came from several reasons: 1 The experimental temperature was 26?, which was different from the expected room temperature 25?. As temperature is the main factor of Ksp, the discrepancy of Ksp was caused by the difference of temperature; 2 The low quality of copper and zinc electrode may affected the e.m.f. taken from the DMM, so the Ksp result was also affected; 3 The concentration of solutions prepared may be different with the expected value. The e.m.f. given out may not equal to the theoretical values, so the Ksp obtained may be different. Conclusion: By the e.m.f. method, the solubility product of copper(II) iodate(V) at room temperature and pressure was determined. Ksp for = 1.34 � 10-10 mol3dm-9 Reference: [1] : Solubility Product Constants, Faculty of Chemistry and Technology, University of Split http://www.ktf-split.hr/periodni/en/abc/kpt.html --End of the Report-- ?? ?? ?? ?? Page 1 of 4 ...read more.

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