Key Methods and Applications of Colloidal Coagulation
Define Coagulation in Chemistry?
In general, we can define coagulation in chemistry as it is one of the various properties exhibited by the colloidal solutions. Where, a colloid is a heterogeneous mixture of one single substance of very fine particles (a dispersed phase) dispersed into another substance (a dispersion medium).
Few substances such as metals, and their sulfides, etc. cannot simply be mixed with the dispersion medium to produce a colloidal solution. Some special methods are used to develop their colloidal solutions. Solutions of this type are known as lyophobic solutions. This kind of colloidal solution carries some charge on them always. The charge present on the colloidal solutions indicates their stability. By any chance, if we can remove the charge present on the solution, the particles get closer to each other and accumulate to produce precipitate and aggregates under the gravity action. The accumulation and settling down of the particle process is further referred to as precipitation or coagulation.
Coagulation Techniques
Since the process of coagulation can be carried out in a few ways, such coagulation techniques are defined below in a brief manner. Let us look at it.
1. By Electrophoresis
The colloidal particles are compelled to move towards the oppositely charged particles in this method, and later they are discharged and collected at the bottom.
2. By Mixing Two Oppositely Charged Solutions
In this type of coagulation technique, an equal amount of oppositely charged particles are mixed, and they precipitate by canceling out their charges.
The below representation shows the coagulation technique by mixing two oppositely charged solutions.
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3. By Boiling
Whenever we boil a solution, the molecules of the dispersion medium start colliding with each other and with the surface, and resultantly this disturbs the adsorption layer. This reduces the charge on the solution because of which the particles settle down.
4. By Persistent Dialysis
Under the persistent dialysis parts, the electrolytes are removed completely, and the solution loses its stability and coagulates ultimately.
The below representation shows the coagulation by persistent dialysis.
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Coagulation of Lyophilic Solutions
The lyophilic solution's stability depends on the below two factors.
Charge
Solvation
When these two factors are removed, then only the lyophilic solutions can be coagulated. And, it can be done either by adding an electrolyte or a suitable solvent.
Coagulation Process
The coagulation process in chemistry can be explained by taking an example of drinking water treatment, which is provided in a brief way below.
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Solids are removed by the sedimentation (settling) process, followed by filtration. The small particles are not removed by sedimentation efficiently because they settle very slowly, and they may also pass through filters. If they clumped together (coagulated), it would be easier to remove to form larger particles. But they don't because they repel each other (like two north poles of a magnet) due to the reason they have a negative charge.
We add a chemical in coagulation, such as alum, produces positive charges to neutralize the negative charges on the particles. Then, the respective particles can stick together, forming larger particles that are removed more easily.
The coagulation process includes the addition of chemicals (for example, alum), and then, a rapid mixing occurs to dissolve the chemical and distribute it throughout the water evenly.
Coagulation Tests
Clotting prevents excessive bleeding when anyone cuts themselves. But the blood moving through our vessels should not clot. If any such clots form, they can travel through our bloodstream to the lungs, brain, and heart. This may cause a heart attack, stroke, or even death.
Coagulation tests measure our blood's clotting ability, and how long it takes to get a clot. Testing can help the doctor to assess our risk of excessive bleeding or clot developing (thrombosis) somewhere in our blood vessels.
Coagulation tests are the same as most blood tests. There is a minimal chance of side effects and risks. A professional medical representative will collect a blood sample and send it to a laboratory for tests and analysis.
Types of Coagulation Tests
There are various types of coagulation tests. A few of them are explained below.
Complete Blood Count (CBC)
The doctor may suggest a complete blood count (CBC) as part of our routine physical. This test result can alert our doctor if we have a low platelet count or anemia, which can interfere with our ability to clot.
Factor V Assay
This test measures the V Factor, a substance that is involved in clotting. An abnormally low level can be indicative of primary fibrinolysis (a breakdown of clots), liver disease, or disseminated intravascular coagulation (DIC).
Fibrinogen Level
Fibrinogen is a protein made by the human liver. This test measures how much fibrinogen is present in our blood. The abnormal results may result in a sign of hemorrhage or excessive bleeding, fibrinolysis, or placental abruption, which is a placenta separation from the uterine wall.
Other names for this test include hypofibrinogenemia test and factor I.
FAQs on Coagulation of Colloidal Solutions Explained
1. What is the coagulation of a colloidal solution as per the CBSE Class 12 syllabus?
In chemistry, coagulation (or flocculation) is the process where the dispersed particles in a colloid aggregate or clump together to form larger particles, which then settle down as a precipitate. This destabilises the colloidal system. The stability of a colloid is primarily due to the like charges on its particles, which cause them to repel each other. Coagulation occurs when this charge is neutralised.
2. What are the common methods used to cause coagulation in colloids?
Coagulation can be induced through several methods designed to destabilise the colloidal solution. The most common methods are:
- By adding an electrolyte: When an electrolyte is added, the colloidal particles take up the oppositely charged ions, neutralising their charge and leading to aggregation.
- By electrophoresis: When an electric current is passed, charged colloidal particles move towards the oppositely charged electrode, get discharged, and precipitate.
- By mixing two oppositely charged sols: When a positively charged sol (like ferric hydroxide sol) is mixed with a negatively charged sol (like arsenious sulphide sol), their charges are mutually neutralised, causing coagulation.
- By persistent dialysis: Prolonged dialysis can remove almost all traces of the electrolyte that stabilises the colloid, making it unstable and causing it to coagulate.
- By boiling: When a sol is boiled, the adsorbed layer of ions is disturbed due to increased collisions, which reduces the charge on the particles and leads to coagulation.
3. Can you provide some real-life examples of coagulation?
Coagulation is a common phenomenon with many practical applications and natural occurrences. Some key examples include:
- Formation of deltas: River water contains negatively charged colloidal particles of clay and sand. When river water meets salty seawater (which is rich in electrolytes like NaCl and MgCl₂), the charges are neutralised, causing the clay to coagulate and settle, forming a delta.
- Water purification: In water treatment plants, alum (potassium aluminium sulphate) is added to raw water. The Al³⁺ ions from the alum neutralise the charge on suspended impurities, causing them to coagulate and settle down, making the water clear.
- Stopping bleeding: Blood is a colloid. Applying a solution of ferric chloride or alum (styptic pencil) to a cut causes the coagulation of blood, which helps in forming a clot and stopping the bleeding.
- Rubber plating: Latex is a negatively charged colloidal solution of rubber particles. Articles are coated with rubber by placing them as the anode in a latex bath; the negatively charged rubber particles migrate to the anode, get deposited, and coagulate to form a layer.
4. What is the Hardy-Schulze rule and how does it explain the effectiveness of electrolytes in coagulation?
The Hardy-Schulze rule provides two key principles for the coagulation of colloids by adding electrolytes. It states that:
- The ion responsible for causing coagulation is the one carrying a charge opposite to that of the colloidal particles. This ion is called the coagulating ion or flocculating ion.
- The greater the valency (charge) of the coagulating ion, the greater its power to cause coagulation.
For example, to coagulate a negatively charged sol like arsenious sulphide (As₂S₃), the coagulating power of cations would be in the order: Al³⁺ > Ba²⁺ > Na⁺. Similarly, for a positively charged sol like ferric hydroxide (Fe(OH)₃), the coagulating power of anions would be: [Fe(CN)₆]⁴⁻ > PO₄³⁻ > SO₄²⁻ > Cl⁻. A higher valency means the ion can neutralise the colloidal charge more effectively, making it a better coagulating agent.
5. What is the difference between coagulation and peptization?
Coagulation and peptization are opposite processes. Coagulation is the process of converting a colloidal solution into a precipitate by aggregating the dispersed particles. In contrast, peptization is the process of converting a freshly prepared precipitate back into a colloidal solution by shaking it with a dispersion medium in the presence of a small amount of a suitable electrolyte, known as a peptizing agent. Essentially, coagulation brings particles together to settle, while peptization breaks down a precipitate into colloidal particles.
6. How do protective colloids prevent coagulation?
Protective colloids, which are typically lyophilic (solvent-loving) colloids, prevent the coagulation of lyophobic (solvent-hating) colloids. They achieve this by forming a thin protective layer around the lyophobic particles. This layer physically prevents the lyophobic particles from coming close enough to aggregate when an electrolyte is added. Furthermore, the stabilising properties of the lyophilic colloid (like hydration) are imparted to the lyophobic particles, increasing their overall stability. A common example is adding gelatin (a lyophilic colloid) to a gold sol (a lyophobic colloid) to protect it from coagulation by NaCl.
7. What is meant by the coagulation value or flocculation value?
The coagulation value (or flocculation value) is a quantitative measure of the coagulating power of an electrolyte. It is defined as the minimum concentration of an electrolyte, in millimoles per litre, that is required to cause the coagulation of a given colloidal solution in two hours. A smaller coagulation value indicates a higher coagulating power because less of the electrolyte is needed to cause precipitation. For example, if electrolyte 'A' has a coagulation value of 0.5 and electrolyte 'B' has a value of 50, then 'A' is 100 times more effective as a coagulating agent than 'B'.
8. Why is it important to understand coagulation in industrial processes like tanning and sewage disposal?
Understanding coagulation is crucial for several industrial applications:
- Tanning of Leather: Animal hides are colloidal in nature and consist of positively charged particles. During tanning, the hide is soaked in tannin, which contains negatively charged colloidal particles. This leads to mutual coagulation, resulting in the hardening of leather.
- Sewage Disposal: Sewage water contains colloidal particles of dirt, mud, and other waste materials carrying a charge. When passed through electrified plates, the charged particles are coagulated at the oppositely charged electrodes. The coagulated matter can then be separated and used as manure.
These examples show how coagulation is used to separate and solidify materials from a dispersed state, which is vital for manufacturing and environmental management.
