Peptization is the process which involves the conversion of freshly prepared precipitate into a colloidal solution by adding any suitable electrolyte. The electrolyte added into the precipitate is called peptizing agent or the dispersion agent. For example, if freshly prepared ferric hydroxide is treated with the small quantity of FeCl 3 solution, a dark reddish brown colloidal solution Fe ( OH ) 3 is obtained. Here ferric chloride ( FeCl 3 ) is a peptizing agent.

The diagram given below represents a method for the preparation of colloids. With reference to the diagram answer the questions that follow : What is the nature of the sol obtained by this method ---lyophilic or lyophobic? Identify A in this diagram.

When current is passed through the electrodes an arc is produced forms vapours of metal electrodes which immediately condenses to form colloidal solution. By this method, colloidal solutions of many metals like copper, silver, gold, platinum can be prepared. The nature of this type of colloidal sol is lyophobic. A in the diagram represents the dispersion medium i.e., solvent and alkali.

Match List - I with List - II . List- I (Colloid Preparation Method) List- II (Chemical Reaction) ( a ) Hydrolysis ( i ) 2 AuCl 3 + 3 HCHO + 3 H 2 O → 2 Au ( sol ) + 3 HCOOH + 6 HCl ( b ) Reduction ( ii ) As 2 O 3 + 3 H 2 S → As 2 S 3 ( sol ) + 3 H 2 O ( c ) Oxidation ( iii ) SO 2 + 2 H 2 S → 3 S ( sol ) + 2 H 2 O ( d ) Double Decomposition ( iv ) FeCl 3 + 3 H 2 O → Fe ( OH ) 3 ( sol ) + 3 HCl Choose the most appropriate answer from the options given below :

( a ) - ( iv ) , ( b ) - ( i ) , ( c ) - ( iii ) , ( d ) - ( ii )

( a ) - ( i ) , ( b ) - ( iii ) , ( c ) - ( ii ) , ( d ) - ( iv )

( a ) - ( i ) , ( b ) - ( ii ) , ( c ) - ( iv ) , ( d ) - ( iii )

( a ) - ( iv ) , ( b ) - ( ii ) , ( c ) - ( iii ) , ( d ) - ( i )

Process of converting precipitate into colloidal solution

Process of converting a colloidal solution into precipitate

Process of converting soluble particles to form colloidal solution

Process of bringing colloidal molecule into solution

A colloidal solution of AgI is prepared by two different methods as shown below : What is the charge on AgI colloidal particles in the two test tubes (A) and (B) ?

In test tube (A), silver nitrate solution is added to the potassium iodide solution. The precipitated AgI adsorbs I - ions from the dispersion medium. When potassium iodide solution is added to silver nitrate solution in test tube (B), Ag + ions are adsorbed on the surface of AgI particles. Hence, test tube (A) has negative charge whereas test tube (B) has positive charge on the colloidal particles.

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Important Questions on Surface Chemistry

EASY

Chemistry>Physical Chemistry>Surface Chemistry>Preparation of Colloids

Define the following terms with suitable examples: Peptisation.

MEDIUM

Chemistry>Physical Chemistry>Surface Chemistry>Preparation of Colloids

Which method is used to prepare colloids?

${As}_{2} O_{3} + 3 H_{2} S \to {As}_{2} S_{3} (sol) + 3 H_{2} O$

MEDIUM

Chemistry>Physical Chemistry>Surface Chemistry>Preparation of Colloids

What happens when a freshly prepared precipitate of

Fe (OH)_{3}

is shaken with a small amount of

{FeCl}_{3}

solution?

MEDIUM

Chemistry>Physical Chemistry>Surface Chemistry>Preparation of Colloids

Draw a labelled diagram of the electrical dispersion method for preparation of colloidal solution.

EASY

Chemistry>Physical Chemistry>Surface Chemistry>Preparation of Colloids

Using Bredig's arc method, which of the following metallic sols cannot be prepared _______

MEDIUM

Chemistry>Physical Chemistry>Surface Chemistry>Preparation of Colloids

Define peptization.

MEDIUM

Chemistry>Physical Chemistry>Surface Chemistry>Preparation of Colloids

25 mL

of silver nitrate solution

(1 M)

is added dropwise to

25 mL

of potassium iodide

(1.05 M)

solution. The ion(s) present in very small quantity in the solution is/are

MEDIUM

Chemistry>Physical Chemistry>Surface Chemistry>Preparation of Colloids

The diagram given below represents a method for the preparation of colloids. With reference to the diagram answer the questions that follow :

Question Image

What is the nature of the sol obtained by this method ---lyophilic or lyophobic? Identify A in this diagram.

EASY

Chemistry>Physical Chemistry>Surface Chemistry>Preparation of Colloids

Match List - $I$ with List - $II .$

List- $I$ (Colloid Preparation Method)		List- $II$ (Chemical Reaction)
$(a)$	Hydrolysis	$(i)$	$2 {AuCl}_{3} + 3 HCHO + 3 H_{2} O \to 2 Au (sol) + 3 HCOOH + 6 HCl$
$(b)$	Reduction	$(ii)$	${As}_{2} O_{3} + 3 H_{2} S \to {As}_{2} S_{3} (sol) + 3 H_{2} O$
$(c)$	Oxidation	$(iii)$	${SO}_{2} + 2 H_{2} S \to 3 S (sol) + 2 H_{2} O$
$(d)$	Double Decomposition	$(iv)$	${FeCl}_{3} + 3 H_{2} O \to Fe (OH)_{3} (sol) + 3 HCl$