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EXP3-chm171L - CHM171L A11 Physical Chemistry Laboratory 2...

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CHM171L / A11 Physical Chemistry Laboratory 2 3 rd Quarter S.Y. 2010-2011 TRANSFRERENCE NUMBER Austria, Maynard 1 , Co, Argenia B. 2 1 Professor, CHM171L/A31, School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology; 2 Student, CHM171L /A31 , School of Chemical Engineering, Chemistry and Biotechnology, Mapua Institute of Technology ABSTRACT The Experiment aims to determine the transport numbers of hydrogen and nitrate ions and to relate the transport number with ionic size and mobility. Transference number of an ion is actually the fraction of the total current that is carried by that ion during electrolysis. Different ions carry different fractions of the current because different ions move at different speeds under the same potential gradient. In general, a cation and an anion differ in the amount of current they can carry during electrolysis. In the experiment, copper plates were used and had been individually subjected to a cathode and anode. It was discerned that at an electrolytic solution, cations and anions both contribute to charge transport in an electric field. The transport numbers are related to the ionic mobilities and ionic conductivities and are thus a function of the migration velocity of the respective counter-ions. Furthermore, the transference number is affected by the atomic weights of the ions. Hydrogen ion, having the smaller atomic weight, has the higher transference number compared to the nitrate ion. The difference between the values of the transference number of these compounds is big. This difference is because of the transport speed of ions. Hydrogen ion, which is much lighter compared to nitrate ion, is much faster. It is clearly observed that ions with smaller atomic weights can move faster. Nitrite ions have a smaller value of the transference number because it is bonded to oxygen that affects the movement of ions. INTRODUCTION The fraction of the total current carried in a solution by a given ion. Ions may carry drastically different portions of the total current if their mobilities are different. E.g., in a solution of sodium chloride, less than half of the current is carried by the positively charged sodium cations and more than half is carried by the negatively charged chloride anions because the chloride ions are able to move faster (they have a larger ionic mobility). The transport numbers of the anion and the cation adds up to unity. As a matter of fact, the case when the ions move equally and the transport number of both ions is equal to 0.5 is a rarity. The Hittorf method is an experimental technique for the determination of the transport numbers. Also called "transference number." For the simplest case of a solution of a single salt of univalent ions, the transport numbers are defined as the mobility of the ion divided by the sum of mobilities of the two ions. If there are more than one solutes present (e.g., an acidified sodium chloride solution or a mixture of sodium chloride and potassium bromide), every ion will have its own transport number with the sum of them being unity. In these cases, the concentrations of the ions must also be taken into
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  • Spring '11
  • Calderon
  • Ion, Physical Chemistry Laboratory, A11 Physical Chemistry, 03│Transference Number│ Group, Experiment 03│Transference Number│

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