Understanding Optical, Electrical, and Kinetic Behaviors in Colloids
The nature of the colloidal solution varies i.e. is not the same. These solutions fall into two distinct categories:
Dispersed Medium
Dispersed Phase
Despite the fact that colloidal dispersion is not the same in definition (nature), scattered fragments are not visible to the human eye. This is due to the small size of the particles in the solution.
The colour of colloidal dispersion is determined by the particles of the solution based on their size. The wavelength of the absorbent light will be longer if the particle size is greater.
Due to its size, colloidal particles can be easily transferred with traditional filter paper. However, these particles can be filtered using animal-like filters, cellophane, and ultrafilters filters.
A type of mixture consisting of particles whose size varies between 1 and 1000 nanometers is a colloidal solution. The particles are uniformly distributed in the colloidal solution. The particles do not settle down during this process. The properties and variability of colloids have been a well-known field since the primitive period. The best example to illustrate their familiarity with us is that we know that coagulation of milk results in the formation of curd from very early times.
In this article, we will study in detail-
The characteristics of colloids
The stability of colloids
The optical properties of colloids
The electrical properties of colloids
The kinetic properties of colloids
Properties of Colloidal Solution
Heterogeneity - colloidal solution is heterogeneous in nature as it consists of the dispersed phase and the dispersion medium.
The particles present in the colloidal solution are not visible and hence the solution appears homogeneous in nature.
The particles of colloidal solution can pass easily through filter paper but can be retained through animal membranes, ultrafilters, and cellophane.
Lyophilic sols in general and lyophobic sols in the absence of substantial concentrations are quite stable.
The colour of the colour solution depends on the size of the particle. The larger particle will absorb the light of a longer wavelength and shorter particles will absorb the light of a shorter wavelength.
Optical Properties of Colloids
Tyndall Effect
When a beam of light is passed through a colloidal solution kept in dark, the path of the beam gets illuminated with blue colour.
This phenomenon is known as the Tyndall effect and the path is known as the Tyndall cone.
The Tyndall effect is due to the scattering of light by colloidal particles.
Tyndall effect is not exhibited by a true solution. This is due to the particles in the solution are too small to scatter light.
Kinetic Properties of Colloids
Brownian Movement
The continuous zigzag movement of particles in the dispersion medium in a colloidal solution is called Brownian movement.
Brownian movement is due to the unequal bombardment of the moving molecules of dispersion medium on colloidal particles.
Brownian movement decreases with an increase in the size of the colloidal particles. So suspension does not exhibit the Brownian movement.
Electrical Properties of Colloids
The movement of colloidal particles towards a particular electrode under the influence of an electric field.
The colloidal particle with a positive charge moves towards the cathode under the influence of the electric field and the colloidal particle with a negative charge moves towards the anode.
Electrosmosis
The movement of dispersion medium under the influence of an electric field in a situation when the movement of the dispersed phase is prevented by a suitable membrane.
What are the Main Features of Colloidal Solutions?
The main features of colloidal solutions are as follows.
Heterogeneous Nature: Colloidal sols are biodiversity. They consist of two categories; dispersed phase and the dispersion medium.
Stable environment: Colloidal solutions are stable. Their particles are in motion and do not settle to the bottom of the container.
Filtering: Colloidal particles easily pass through standard filter sheets. However, they can be stored in special filters known as ultrafilters (leather paper).
Colligative Properties-
Due to the formation of associated molecules, the calculated values of the contrasting areas such as a moderate decrease in vapor pressure, height in boiling area, pressure in a cold environment, and osmotic pressure are less than expected.
With colloidal sol given the number of particles will be much smaller compared to the actual solution.
Disadvantages with colloids:
It is difficult to remove and clean.
They can cause significant losses in output or analysis, which later show more content
Targeted Drug Delivery: The liver and spleen take up liposome which is the best colloidal product. The colloidal system is therefore used in targeted drug delivery.
Nuclear Medicine: In nuclear medicine, colloidal particles containing radioactive isotopes are often used as diagnostic and therapeutic agents. Example: Colloidal Gold.
Advantages of Colloids
Colloidal particles allow the dispersion of insoluble materials such as metallic gold and fats. They can be used more easily and absorbed more easily.
Colloidal gold can be used in medicine to carry drugs and antibiotics
The paint industry uses colloids in the preparation of paints.
In milk, the colloidal suspension of fats prevents the milk from being thick and allows for easy absorption of nutrients.
Asphalt is emulsified in water used in the preparation of roads.
Soap solution is colloidal in nature which helps in removing dirt.
Food particles like butter, milk, and ice cream are colloidal in nature.
Did You Know?
Coagulation is a phenomenon involving the precipitation of a colloidal solution on the addition of an electrolyte.
Flocculation Value- The coagulating power of an electrolyte is expressed in terms of its flocculation value which is defined as the minimum concentration of an electrolyte required for the coagulation of a sol.
A smaller flocculation value shows the greater coagulating power of an electrolyte.
So coagulating power is inversely proportional to the flocculating value.
The coagulation of colloids can be achieved by various methods-
By electrophoresis
By mixing two opposite sols
By persistent dialysis.
Conclusion
We have covered all the major aspects of Properties of Colloids that students can use for learning and understanding the concepts.
FAQs on Essential Properties of Colloids Explained
1. What are the essential properties that distinguish a colloid from a true solution and a suspension?
Colloids are distinguished by a unique combination of properties. The key differentiators are:
- Particle Size: Colloidal particles have a diameter between 1 to 1000 nanometers, making them larger than particles in a true solution (<1 nm) but smaller than those in a suspension (>1000 nm).
- Stability: Colloids are quite stable and do not settle down under gravity, unlike suspensions. This stability is due to Brownian movement and electrical charge on the particles.
- Filterability: They can pass through ordinary filter paper but are retained by ultra-fine membranes (ultrafilters).
- Optical Property: Colloids exhibit the Tyndall effect (scattering of light), which is not observed in true solutions.
2. What is the Tyndall effect and why is it considered a defining characteristic of colloids?
The Tyndall effect is the phenomenon where a beam of light passing through a colloid is scattered by the dispersed particles, making the path of the light visible. It is a defining characteristic because the particle size in colloids (1-1000 nm) is large enough to scatter light, a property not seen in true solutions where particles are too small. This effect provides a simple and definitive visual test to differentiate a colloid from a true solution.
3. How does Brownian movement contribute to the stability of a colloidal solution?
Brownian movement is the continuous, random, zig-zag motion of colloidal particles. This motion is caused by the constant, unbalanced bombardment of the colloidal particles by the much smaller and faster-moving molecules of the dispersion medium. The significance of this movement is that it acts as a constant stirring mechanism, which effectively counters the force of gravity. This prevents the particles from settling down, thereby imparting stability to the colloidal system.
4. What are the key electrical properties of colloids and what is their importance?
The primary electrical properties stem from the charge on colloidal particles and are crucial for their stability. They include:
- Charge on Particles: All particles in a colloid carry a like charge (e.g., all positive or all negative), causing them to repel each other and preventing aggregation.
- Zeta Potential: This is the potential difference at the boundary between the fixed layer and the diffuse layer of ions surrounding a colloidal particle. A higher zeta potential indicates greater stability as it signifies stronger repulsion between particles.
- Electrophoresis: This is the movement of charged colloidal particles towards the oppositely charged electrode under an applied electric field. It serves as proof of the charge on particles and has practical applications like industrial smoke precipitation.
5. If every colloidal particle is charged, how is the colloidal solution as a whole electrically neutral?
This is a key concept. While all the dispersed particles in a sol carry a like charge, the dispersion medium contains an equal amount of opposite charge in the form of counter-ions. These counter-ions are attracted to the charged particles, forming what is known as an electrical double layer. This arrangement ensures that the net charge of the entire system (dispersed particles plus dispersion medium) is zero, making the colloidal solution electrically neutral as a whole.
6. How does the Hardy-Schulze rule explain the coagulation of colloids?
The Hardy-Schulze rule explains how adding an electrolyte causes the coagulation (or precipitation) of colloidal particles. It states two main principles:
- The ion responsible for coagulation is the one carrying a charge opposite to that of the colloidal particles (the counter-ion).
- The coagulating power of an ion increases drastically with an increase in its valency (charge). For example, to coagulate a negative sol like As₂S₃, the effectiveness of positive ions follows the order: Al³⁺ > Mg²⁺ > Na⁺.
7. What is the fundamental difference between lyophilic and lyophobic colloids in their properties?
The fundamental difference lies in the interaction between the dispersed phase and the dispersion medium:
- Lyophilic ('solvent-loving') colloids (e.g., starch, gelatin in water) have a strong affinity between the two phases. They are highly stable, easy to form (by simple mixing), and are reversible.
- Lyophobic ('solvent-hating') colloids (e.g., gold sol, sulphur sol) have very little affinity between the phases. They are inherently unstable, require special methods for preparation, and are irreversible. Their stability depends primarily on the charge of the particles.
8. Why are colligative properties (like osmotic pressure) of very small magnitude in colloids compared to true solutions?
Colligative properties depend solely on the number of solute particles in a solution, not on their size or mass. Colloidal particles, being large aggregates or macromolecules, are far fewer in number for a given mass compared to the number of ions or small molecules in a true solution of the same concentration. Because there are significantly fewer particles in a colloid, the observed values for colligative properties like osmotic pressure, elevation in boiling point, and depression in freezing point are very small and often difficult to measure accurately.
9. What are some examples of different types of colloids from daily life?
Colloids are very common in our daily lives. They are classified based on the state of the dispersed phase and dispersion medium:
- Sol (Solid in Liquid): Paints, cell fluids, muddy water.
- Gel (Liquid in Solid): Cheese, butter, jellies.
- Emulsion (Liquid in Liquid): Milk, hair cream, mayonnaise.
- Foam (Gas in Liquid): Whipped cream, soap lather.
- Aerosol (Solid/Liquid in Gas): Smoke (solid in gas), and fog, mist, or clouds (liquid in gas).
