Step-by-Step Procedure for Dialysis of Lyophilic and Lyophobic Sols
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.
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.
This ends our coverage on the topic “Dialysis of lyophilic and lyophobic sol”. We hope you enjoyed learning and were able to grasp the concepts. We hope after reading this article you will be able to solve problems based on the topic. If you are looking for solutions to NCERT Textbook problems based on this topic, then log on to Vedantu website or download Vedantu Learning App. By doing so, you will be able to access free PDFs of NCERT Solutions as well as Revision notes, Mock Tests and much more.
FAQs on Dialysis of Lyophilic and Lyophobic Sol: Complete Guide
1. What exactly is dialysis in the context of purifying colloidal solutions?
In chemistry, dialysis is a method used to purify colloidal solutions by separating the larger colloid particles from smaller dissolved impurities, known as crystalloids. This separation is achieved using a special filter called a semipermeable membrane, which allows the small impurities to pass through but retains the larger colloidal particles.
2. What is the main difference between a lyophilic and a lyophobic sol?
The primary difference lies in the interaction between the dispersed particles and the liquid they are mixed in (the dispersion medium).
- Lyophilic Sols: These are 'liquid-loving'. The particles have a strong affinity for the liquid, making them very stable and easy to prepare.
- Lyophobic Sols: These are 'liquid-hating'. The particles have little to no attraction for the liquid, which makes them unstable and difficult to prepare without a stabilising agent.
3. Why is dialysis effective for purifying colloids but not for true solutions?
Dialysis works because of the significant difference in particle size. In a colloidal solution, the colloid particles are much larger than the dissolved impurity ions. A semipermeable membrane has pores that are small enough to block the large colloid particles while allowing the tiny impurity ions to escape. In a true solution, both the solute and solvent particles are extremely small and can easily pass through the membrane's pores, making separation by this method impossible.
4. Can you provide some common examples of lyophilic and lyophobic sols?
Certainly! Common examples help clarify the difference:
- Lyophilic Sols: Starch mixed in water, gelatin, gum arabic, and protein solutions like egg albumin are excellent examples. They form easily.
- Lyophobic Sols: These typically include sols of inorganic substances like metals (e.g., gold sol, silver sol) or sparingly soluble salts (e.g., ferric hydroxide sol, arsenious sulfide sol).
5. How does a semipermeable membrane actually work during the dialysis of a sol?
A semipermeable membrane, like parchment paper or cellophane, functions as a highly selective filter. It contains microscopic pores of a specific size. When the impure sol is placed inside a bag made of this membrane and suspended in fresh water:
- The colloidal particles are too large to fit through the pores and remain inside the bag.
- The smaller impurity particles, such as ions from electrolytes, are small enough to pass through the pores and diffuse into the surrounding water, effectively washing them away from the sol.
6. What makes lyophilic sols reversible while lyophobic sols are irreversible?
This difference comes down to stability and the nature of their formation. Lyophilic sols are reversible because of the strong attraction between the particles and the liquid. If the liquid is evaporated, the solid residue can be easily turned back into a sol by simply adding the liquid again. In contrast, lyophobic sols are irreversible because they are inherently unstable. If the liquid is evaporated, the particles clump together permanently and cannot be easily redispersed by just adding the liquid back.
7. Is it possible to over-purify a sol by performing dialysis for too long?
Yes, performing dialysis for an extended period can destabilise the colloid. Lyophobic sols require a minimal amount of electrolyte to maintain the charge on their particles, which prevents them from clumping together. If dialysis is carried on for too long, it can remove almost all the electrolytes, causing the particles to neutralise, aggregate, and settle down. This process is called coagulation and it destroys the sol.
