Question 11. Answer: Common ion Effect: When a salt of a weak acid is added to the acid itself, the dissociation of the weak acid is suppressed further. Acetic acid is a weak acid. CH3COOH (aq) \(\rightleftharpoons\) H + (aq)+ CH3COO – (aq)
However, the added salt, sodium acetate, completely dissociates to produce Na + and CH3COO ion. CH3COONa (aq) > Na + (aq) + CH3COO (aq) Hence, the overall concentration ofCH3COO is increased, and the acid dissociation equilibrium is disturbed.
We know from Le chatelier’s principle that when stress is applied to a system at equilibrium, the system adjusts itself to nullify the effect produced by that stress. So, in order to maintain the equilibrium, the excess CH3COO – ions combine with H ions to produce much more unionized CH3COOH i.e.,
the equilibrium will shift towards the left. In other words, the dissociation of CH3COOH is suppressed. Thus, the dissociation of a weak acid (CH3COOH) is suppressed in the presence of a salt (CH3COONa) containing an ion common to the weak electrolyte. It is called the common ion effect.
Question 1dos. Derive an expression for Ostwald’s dilution law. Answer: Ostwald’s dilution law: It relates the dissociation constant of the weak acid (Ka) with its degree of dissociation (?) and the concentration (c). Considering a weak acid, acetic acid. The dissociation of acetic acid can be represented as, CH3COOH \(\rightleftharpoons\) CH3COO – + H + The dissociation constant of acetic acid is,
We know you to definitely weakened acidic dissociates simply to an incredibly quick extent compared to the one, a is really so quick. formula (1) becomes,
It is not completely dissociated into the an aqueous service and therefore the following harmony is present
Question 13. Define pH. Answer: pH of a solution is defined as the negative logarithm of base ten of the molar concentration of the hydronium ions present in the solution. Continue reading