Abstract: This paper suggests a method for the determination of the ionic hydration num- bers, The method is based on the selectivity of the ion exchange membrane for ion to pass through.Only one kind of ions—anions or cations is allowed to get across the membrane, when an ion exchange membrane is used as an electrolysis membrane.
Three factors causing the volume change of solution in electrode compartment are counted here: (1) the transference of water which are carried by transferring ions, (2)the transference of ions, (3) the electrode reaction. By means of the measured volume change of solution in the anode or cathode compartment, minus the volume change caused by the latter two factors, the transferring volume of water can be obtained, then the transferring mole numbers of water can be calculated. The transferring mole numbers of ions can be calculated from the neasurement of quantities of electricity. The transferring mole numbers of water were divided by the transferring mole numbers of ions, that is the ionic hydration number.
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