Determine prominent ion effect with a good example

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 12. Derive an expression for Ostwald’s dilution law. Answer: Ostwald’s dilution law: It relates the dissociation constant of the weak acid (K_a) 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 all know one weak acidic dissociates only to a highly short the total amount versus one, good is really brief. picture (1) becomes,

This is simply not entirely dissociated during the an enthusiastic aqueous service and therefore next equilibrium 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. pH = – log₁₀ [H₃O] (or) pH = – log₁₀ [H + ]

[OH – ] = 3 times ten 3 Yards. [pH + pOH = 1cuatro] pH = fourteen – pOH pH = fourteen – ( – journal https://www.datingranking.net/escort-directory/hampton [OH – ]) = fourteen + record [OH – ] = fourteen + diary (3 x ten -step three ) = 14 + log step three + log 10 -step 3 = 11 + 0.4771 pH =

Question 15. 50 ml of 0.05 M HNO₃ is added to 50 ml of 0.025 M KOH. Calculate the pH of the resultant solution. Solution. Number of moles of HNO₃ = 0.05 x 50 x = 2.5 x 10 -3 Number of moles of KOH = 0.025 x 50 x 10 -3 = 1.25 x 10 -3 Number of moles of HNO₃ after mixing = 2.5 x 10 -3 – 1.5 x 10 -3 = 1.25 x 10 -3

Question17

pH = – log [H + ] pH = – log (step one.twenty five x ten -2 ) = dos – 0.0969 = step one.9031

Question 16. The K_a value for HCN is 10 -9 . What is the pH of 0.4 M HCN solution? Answer: K_a =10 -9 c = O.4M pH = – log [H + ]

? pH = – log(2 x ten -5 ) = – journal 2 – diary (ten -5 ) = – 0.3010 + 5 pH = cuatro.699

Calculate the extent of hydrolysis and the pH of 0.1 M ammonium acetate Given that. K_a = K_b = 1.8 x 10 -5 Solution.

Question 18. Derive an expression for the hydrolysis constant and degree of hydrolysis of salt of strong acid and weak base. Answer: Let us consider the reactions between a strong acid, HCl, and a weak base, NH₄OH, to produce a salt, NH₄Cl, and water. HCl (aq) + NH₄OH (aq) \(\rightleftharpoons\) NH₄Cl (aq) + H₂O (I) NH₄CI(aq) > NH₄ + + Cl – (aq)