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Cations are grouped on the basis of their solubility product (K_sp).

When ionic product is greater than solubility product.

When high current is passed through water it under goes partial dissociation.

H₂O ⇌ H⁺ + OH^-

Applying law of mass action,

K = \(\frac{[H^+][OH^-]}{[H_2O]}\); 

K[H₂O] = [H⁺][OH^-]

But k[H₂O] = K_w

∴ K_w = [H⁺][OH^-]

Where, K_w is ionic product of water.

Value of K_w at 25°C:

It is found that at 25°C [H⁺] = [OH^–] = 10^-7 mol/dm³

∴ K_w = [H⁺][OH^–] = 10^-7 × 10^-7 = 10^-14 (mol/dm³)²

At 25°C the value of K_w is 10^-14(tmol/dm³)²

pH = pK_in ± 1.

As the value of equilibrium constant increases with increase in temperature so, the reaction is endothermic in nature. 

Group reagent: HCl → H⁺ + Cl^– ; H₂S ⇌ 2H⁺ + S^2-

Radicals: Cu²⁺, Bi²⁺, Sn²⁺

Here HCl is a strong electrolyte under goes complete dissociation where as H₂S is a weak electrolyte under goes partial dissociation and attains equilibrium between it’s ions and molecules.

In this solution, because of common ion (H⁺) effect supression of degree of dissociation of H₂S takes place. As a result [S^2-] decreases. Hence the metal radical forms it’s respective sulphides [CuS, SnS, BiS] whose solubility product is less than ionic product. Hence forms precipitate.

Group reagent: NH₄Cl → NH₄⁺ + Cl^– ; NH₄OH ⇌ NH₄⁺ + OH^–

H₂S ⇌ 2H⁺ + S^2- ; H⁺ + OH^– → H₂O

Radicals: Zn²⁺, Mn²⁺

Here, NH₄Cl is a strong electrolyte undergoes complete dissociation, where as NH₄OH^– and H₂S are weak electrolytes undergoes partial dissociation and attains equilibrium between their ions and molecules. Along with common ion (NH₄⁺) effect, the H⁺ and OH^- ion combines to form water molecules.

At the same time the metals forms their respective sulphides [ZnS, MnS] Whose solubility product is less than ionic product. Hence, forms precipitate.

Group reagent: NH₄OH ⇌ NH₄⁺ + OH^– ; NH₄Cl ⇌ NH₄⁺ + Cl^–

Radicals: Al³⁺, Cr³⁺, Fe³⁺

Here NH₄Cl is a strong electrolyte under goes complete dissociation where as NH₄OH is a weak electrolyte under goes partial dissociation and attains equilibrium between it’s ions and molecules. In this solution because of common ion (NH₄⁺) effect supression of degree of dissociation of NH₄OH takes place. As a result [OH^–] decreases. Hence the metal radical forms it’s respective hydroxides [Al(OH)₃, Cr(OH)₃, Fe(OH)₃]. Whose solubility product is less than ionic product. Hence forms precipitate.

The increase in temperature favours forward reaction because the reaction is endothermic.

Solubility of AgCI decreases due to common ion effect.

Group reagent: Dil. HCl → H⁺ + Cl^–

Redicals present: Pb²⁺, Hg²⁺, Cd²⁺

The group reagent HCl is a strong electrolyte under goes complete dissociation. The metal radicals forms it’s respective chlorides [PbCl₂, HgCl₂, CdCl₂]. Whose solubility product is less than ionic product. Hence, forms precipitate.

\(\because\) K = \(\frac{K_f}{K_b}\)

In exothermic reaction, with the increase in temperature, equilibrium constant for backward reaction (K_b) increases much more than K_f. Thus, equilibrium constant (K) decreases with increase in temperature for an exothermic reaction.

(i) Large value of equilibrium constant (>10³) shows that forward reaction is favoured, i.e., concentration of products is much larger than that of the reactants at equilibrium. 

(ii) Intermediate value of K(10^-3 to 10³) shows that the concentration of the reactants and products are comparable, 

(iii) Low value of K(<10^-3)shows that backward reaction- is favoured, i.e, concentration of reactants is much larger than that of the products.

It is the ratio of number of ions or molecules produced to the total number of molecules.

Solubility will decrease because it is an exothermic process.

Pressure has no effect. Decrease of temperature will shift the equilibrium in the backward direction.

Strong electrolytes can dissociate into ions completely in aqueous solution whereas weak electrolytes do not dissociate into ions completely and there exist an equilibrium between ioins and unionized molecules, called Ionic Equilibrium.

K_sp = [Ag⁺][Cl^-]

1.8 x 10^-10 = [Ag⁺]0.01

[Ag⁺] = \(\frac{1.8\times 10^{-10}}{0.01}\) = 180 x 10^-10

= 1.8 x 10^-8 mol/dm³

Equilibrium will shift in the forward direction, i.e., more of ice will melt.

AgCl ionizes completely in the solution as AgCl ----> Ag+ +Cl^— 

One mole of AgCl in the solution gives 1 mole of Ag⁺ ions and 1 mole of Cl^—ions.

Now as the solubility of AgCl= 1.06*10^—5 moles per litre. 

Therefore [Ag+]=1.06*10^—5 moles per litre and [Cl^--] = 1.06*10^—5 moles per litre. 

Ksp for AgCl=[Ag+] [Cl^--]=1.06*10^—5 *1.06*10^—5 =1.1*10^—10

To an ionic equilibrium, AB ---->  A+ +B+,a salt containing a common ion ( AC or BD is added, the equilibrium shifts in the backward direction. This is called common ion effect. On passing hydrogen chloride gas through a saturated solution o sodium chloride, the concentration of chloride ions will be increased. This increases the ionic product of NaCl and the solid salt will be precipitated.

Supression in degree of dissociation of a weak electrolyte by addition of a common ion is called common ion effect. 

Example:- CH₃COOH and CH₃COONa

Shift in equilibrium on adding a substance that provides more of an ionic species already present in the dissociation equilibrium.

(i) HCl. It helps in digestion of food. Sometimes stomach produces too much acid and this causes pain and irritation. To neutralize the acidity antacids such as magnesium hydroxide are taken. 

(ii) When acidic gases present in the air dissolve in the rain water, such that the pH of the rain water falls below 5.6, it is called acid rain. When it flows into the rivers, it lowers the pH of river water; hence the survival of the aquatic life becomes difficult. When such water is absorbed by the soil, the soil becomes acidic and unfertile. The acidity is neutralized by adding slaked lime (Calcium Hydroxide). 

(iii) Honey bee or ant injects methanoic acid (formic acid) into our body causing pain and irritation. Use of mild base like baking soda on the stung area gives relief as it neutralizes the acid. 

(iv) Leaves of nettle plants contain methanoic acid causing pain and irritation. Rubbing with the leaf of dock plant (which also grows nearby) gives relief as it contains mild base and neutralizes the acid.

(a) If both assertion and reason are true, and reason is the true explanation of the assertion.

Soap is sodium salt of higher fatty acids (RCOONa). On adding common salt, Na⁺ ion concentration increased. Hence, the equilibrium RCOONa (s) ----- RCOO- ⁺ Na ⁺ shifts in the backward dirction, i,e, soap precipitates out.