Dialysis of Lyophilic and Lyophobic Sol

Before discussing the experiment of purifying lyophilic and lyophobic sol, you need to have a basic idea about what are lyophilic and lyophobic sols. So, first we are discussing here lyophilic and lyophobic sols in brief. 

What are Lyophilic Sols?

Lyophilic means ‘liquid loving’. Those sols in which dispersed phase and dispersion medium (water) have strong attraction between them are called lyophilic sols. For example, colloidal solution formed by dissolving starch in water. In this colloidal solution dispersion medium is water and dispersed phase is starch. This sol can be prepared by heating water at 100 ℃ and dissolving starch in it. It is a stable sol and cannot be separated easily due to strong attraction between dispersed phase and dispersion medium. Egg albumin sol is another example of lyophilic sol. 

What are Lyophobic Sols?

Lyophobic means ‘Liquid hating’. Those sols in which dispersed phase and dispersion medium (water) have very less attraction or no interaction between them are called lyophobic sols. In these sols dispersed phase particles show very less or no affinity for dispersion medium. These are not stable sols and can be separated easily. If a small quantity of an electrolyte is added to these types of sols, then dispersed phase and dispersion medium are easily separated. To make them stable sols, we need to add stabilizers while preparing them. These are also known as hydrophobic sols. Example of a lyophobic sol is ferric hydroxide sol. It is prepared by hydrolysis of ferric chloride. In this boiling water is used. In this process hydrochloric acid is also produced which is removed from the sol as it makes the sol unstable. It is removed by dialysis of the ferric hydroxide sol (lyophobic sol). 

Dialysis of Lyophilic and Lyophobic sols 

Aim – To purify lyophilic and lyophobic sols by dialysis. 

Material Required – Parchment or cellophane paper, iron stand, trough, thread, test tubes, egg albumin sol, distilled water, silver nitrate and uranyl zinc acetate etc. 

Theory – Dialysis is done to remove that compound from the sol which makes it unstable. Thus, dialysis is a process which is performed to purify the lyophilic and lyophobic sols. In this process a parchment membrane is used from which colloidal particles of the sol cannot pass but the ions of the electrolyte can. Thus, impurities get separated. 

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Procedure – Follow the following steps while performing the experiment –

  • Wash all test tubes and trough with distilled water and dry them. 

  • Take a square sheet of 30 cm 30 cm of parchment or cellophane paper. 

  • Soak the square sheet of parchment paper in distilled water and give it a conical shape. 

  • Now pour the egg albumin colloidal sol in the cone made up of parchment or cellophane paper. 

  • Take the iron stand and place it at the suitable place and tie the thread on its side arm. 

  • Fill the trough with distilled water. 

  • Now tie the parchment paper cone filled with albumin with the thread and suspend it in the trough which contains distilled water. Apparatus set up is given below –

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  • After half an hour, check the water of the trough for the impurities or ions and change the water in the trough after every half an hour till it's free of ions or impurities. 

  • To check the presence of ions or impurities such as Na+ and Cl- in case of egg albumin sol, take water from the trough in two test tubes. 

  • Add uranyl zinc acetate in one test tube to check the presence of sodium ions. If it gives yellow precipitate with trough water, then it indicates presence of sodium ions.

  • Add silver nitrate in another test tube to check the presence of chloride ions. If it gives white precipitate with trough water, then it indicates the presence of chloride ions. 

  • Continue changing the trough water after every half an hour till you get an impurity free through water. 

  • Note the time required to purify colloidal dispersion. 

Result – Dialysis of egg albumin sol took ____ min. 

Precautions – During experiment following precautions must be taken –

  • Make sure that the parchment bag should be airtight. Airtight parchment or cellophane bags will prevent the entry of water into it. 

  • Keep the neck of the parchment cone or bag above the surface of water in the trough. 

  • During dialysis, change the trough water timely, almost after every half an hour. 

  • Keep changing the trough water timely till you get impurity free water. 

Viva Voice 

What is Lyophilic Sol?

Those colloidal solutions in which dispersed phase particles possess strong attraction for dispersion medium are called lyophilic sols. 

What is Lyophobic Sol?

Those colloidal solutions in which dispersed phase particles possess very less or no attraction for dispersion medium are called lyophobic sols. 

Give Examples of Lyophilic and Lyophobic Sols?

Example of Lyophilic Sols – Gum sol, starch sol, rubber, gelatin, egg albumin sol etc. 

Examples of Lyophobic Sols – Ferric hydroxide sol, aluminium hydroxide sol, arsenious sulfide sol etc. 

State Difference between Lyophilic and Lyophobic Sols.

S. No. 

Lyophilic Sol 

Lyophobic Sol 

1.

In these sols, the dispersion phase has strong affinity for dispersion medium. 

In these sols, the dispersion phase has very less or no affinity for the dispersion medium. 

2.

They are more stable. 

They are less stable.

3.

They are reversible.

They are irreversible. 

4.

Colloidal particles have no charge. 

Colloidal particles carry either positive or negative charge. 

5.

They need no stabilizers during preparation.

They need stabilizers during preparation. 

6.

They are solvent loving colloids. 

They are solvent hating colloids.

7.

They are highly viscous sols.

They possess the same viscosity as the solvent. 

8.

When water is taken as solvent, it is called hydrophilic sol. 

When water is taken as solvent, it is called hydrophobic solvent. 

9. 

Examples – Starch sol, egg albumin sol etc. 

Examples – Ferric hydroxide sol, aluminium hydroxide sol etc. 

Why do We Use Parchment Paper in the Experiment?

We use parchment paper in the experiment because colloidal particles cannot pass through it while ions can pass, so they get separated. 

Why do We Keep the Parchment Cone Airtight?

We keep the parchment cone airtight, so that it will prevent the entry of water into it. 

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