2. (a) The thermodynamic acid dissociation constant (Ka) for a weakly dissociated acid can be determined using the Debye

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2 A The Thermodynamic Acid Dissociation Constant Ka For A Weakly Dissociated Acid Can Be Determined Using The Debye 1 (688.35 KiB) Viewed 54 times

2. (a) The thermodynamic acid dissociation constant (Ka) for a weakly dissociated acid can be determined using the Debye-Huckle theory. Justify why the Debye Huckle theory can be applied to weak acids when calculating their mean activity constants. For full marks, valid conditions for applying the Debye Huckle limiting law should be included in the answer. If suitable for the discussion include images and graphs (do not copy and paste) as well as equations. [5 marks] (b) Consider a weak acid (HA), which dissociates according to: HA(I) <H+(aq) + A-(aq) (2.1) The acid dissociaton constant is given by: [H+(aq)][A-(aq)] Ka Y [HA(1}] = (2.2) ,where the mean activity constant (y+) can be obtained using the Debye-Huckle theory: logy+ = -A[2_z_IVI (2.3) = - ,where / corresponds to ionic strength, zi formal charges and A is an environmentally dependent constant. Using this information show that: log Ko = logKa + B2.2.1 VI (2.4) (5 marks] =