Colloids - IPSE FPMIPA UPI Assignment

 Colloids 

Colloid is a mixture of heterogeneous substances between two or more substance in which particles of colloidal-size substance is uniformly dispersed in another substance. Colloidal size range between 1-100 nm. For example: Mayonnaise and paint. Mayonnaise is a homogeneous mixture in water and oil and paint is a homogenous mixture of solids and liquid.

Sometimes the dispersed substance alone is called the colloid. Because the size of dispersed phase may be difficult to measure and because colloids have the appearance of solutions, this table summarizes the properties of solutions, colloids, and suspensions to differentiate them.

Property		System
	Solution	Colloid	Suspension
Particle type	Ions, atoms, small molecules	Large molecules or particle	Large particles or aggregates
Particle size	0,1 – 1 nm	1 – 1000 nm	1000 nm and larger
Effect of light	No scattering	Exhibit Tyndall effect	Exhibit Tyndall effect
Effect of gravity	Stable, does not separate	Stable, does not separate	Unstable, sediment forms
Filtration	Particles not retained on filter	Particles not retained on filter	Particles retained on filter
Uniformity	Homogenous	Heterogeneous	Heterogeneous
Example	Salt and sugar solution	Milk, fog, mayonnaise	Wheat flour in water, muddy water, Italian salad dressing

 

Colloidal system is a form of mixtures whose state lies between the solution and the suspension (rough mix). The colloidal systems have distinctive properties that are different from the nature of a solution or suspension. Colloidal state is not the characteristic of certain substances for all substances, whether solid, liquid, or gas, can be created in a state of colloid. Colloidal system is closely relative to life and our daily lives. Body fluids, such as blood is a colloidal system. Paints, different types of drugs, cosmetics, agricultural land is also colloidal system.

Colloid is a mixed system ‘’metastable’’ (as if it seems stable, but it will separated after a certain time). Colloid is different from solution because solution is stable. In the colloid solutions generally, there are two substances as follows:

-          Dispersed Substance: Dissolved substance in a colloidal system

-          Dispersing agents: Solvent substance in a colloidal system

The dispersed-phase particles have a diameter between approximately 1 and 1000 nano meters. Such particles are normally easily visible in an optical microscope. Although, at the smaller size range (r<250 nm), an ultra microscope or an electron microscope may be required. Homogenous mixtures with a dispersed phase in this size range may be called colloidal aerosols, colloidal emulsions, colloidal foams, colloidal dispersion, or hydrosols.

 

B.    Types of Colloids

Based on Dispersed phase and Dispersing agents, colloid can be classified as follows:

Phase of Dispersion	The Medium of Dispersion	Colloid Type	Examples
Solid	Solid	Solid Sol	Gemstone, Alloys, Pearls
Gas	Gas	It’s not colloid because the gases immiscible homogeneously	Helium and Xenon are known to be immiscible under certain condition
Liquid	Solid	Gel	Cheese, Jelly, Jams,
Gas	Solid	Solid Foam	Pumice stone
Solid	Liquid	Sol	Gum, Cell fluids
Liquid	Liquid	Emulsion	Milk
Gas	Liquid	Foam	Whipped cream
Solid	Gas	Solid Aerosol	Smoke, dust
Liquid	Gas	Liquid Aerosol	Fog, mist, Cloud, Sprays

 

Aerosol: Aerosol which has dispersion agents in the form of gas. Aerosol which has dispersed phase in form of liquid called liquid aerosol (example: fog and clouds) while having dispersed phase in form of solid called solid aerosols (example: smoke and dust in the air).

Sol: Colloidal system of solid particles dispersed in a liquid. Example: The river water, paints, and ink.

Emulsion: Colloidal system of liquid dispersed in another liquid substance but the two liquid are not mutually dissolve. Example: coconut milk, milk, mayonnaise, and fish oils.

Foam: Colloidal system of gas dispersed in a liquid. Example: on the processing of metal ore, fire extinguishers, some types of cosmetics, and others. There is also a solid foam which is a gas dispersed in a solid. Example: Styrofoam, pumice stone, sponges, marshmallow.

Gel: Colloidal system of rigid or semi-solid and half liquid. Example: gelatin and glue.

Based on the nature of interaction between the dispersed phase and the dispersion medium, colloids can be classified as:

-          Hydrophilic colloids: These are water-loving colloids. The colloid particles are attracted toward water. They are also called reversible sols.

-          Hydrophobic colloids: These are opposite in nature to hydrophilic colloids. The colloid particles are repelled by water. They are also called irreversible sols.

 

A hydrocolloid is defined as a colloid system wherein the colloid particles are hydrophilic polymers dispersed in water. A hydrocolloid has colloid particles spread throughout water and depending on the quantity of water available that can take place in different states, e.g., gel or sol (liquid). Hydrocolloid can be either irreversible (single-state) or reversible. For example, agar, a reversible hydrocolloid of seaweed extract, can exist in a gel and solid state and alternate between states with the addition or elimination of heat.

Many hydrocolloid are derived from natural source. For example, agar-agar and carrageenan are extracted from seaweed, gelatin is produced by hydrolysis of proteins of mammalian and fish origins and pectin or extracted from citrus peel and apple pomace.

 

C.   Characteristics of Colloids

 

1.      Tyndall Effect

Tyndall Effect is the scattering of light by the colloidal solution, in which the course of events in the light of colloids can be seen as the colloidal particles can scatter light in all directions. This is because the size of the colloid molecules are quite large. Tyndall effect was discovered by John Tyndall (1820-1893), an English physicist. Therefore, the nature of the so-called Tyndall.

By the time, the true solution is irradiated with light, then the solution will not scatter light, while on the colloidal system, the light will be scattered. It happens because the colloidal particles are relatively large I order to scatter the light. Instead, the true solution, the particles are relatively small so the scattering occur only a few and very difficult to observe.

 

2.      Brownian Motion

Brownian motion is the movement of colloidal particles in the dispersing medium continuously because of the collision between particles of matter are dispersed and dispersing agents. If colloidal is observed under the microscope, then we will see that the particles will move to form a zigzag. Therefore the particles size is small enough, then the collision tend to be unbalanced. So there is a resultant collision that causes a change in direction of motion of particles which resulting in a zigzag motion or Brown Motion. The smaller size of colloid particles, the faster the Brown Motion that occurs. On the other hand, the bigger size of colloid particle, the slower the Brown motion that occurs. Due to continuous active motion, the colloidal particles do not separate if it is ignored.

Brown motion is also affected by temperature. The higher temperature of the colloidal system, the greater the kinetic energy that has particles dispersing medium. As a result, the Brownian motion of the particles dispersed phase is more quickly. Vice versa, the lower the temperature of the colloidal system, the slower that Brownian motion that occurs.

 

3.      Colloidal Adsorption

Colloidal adsorption is absorption or ion on colloid surface. The nature of adsorption is used in the process:

-          Bleaching cane sugar

-          Diarrhea medicine

-          The water purification

Example: Colloid between diarrhea and fluid in the gut that absorbs germs that cause diarrhea. And colloidal Fe(OH)₃ will absorb ion H⁺ until becomes positive charge. If there are the same charges, then colloidal Fe(OH)₃ will repel each other so colloidal particles will not gather each other. Colloids As₂S₃ will absorb ion OH^- in solution until it becomes negative charge. And will repel each other then colloids As₂S₃ will not gather.

4.      Colloid charge and Electrophoresis

Colloidal charge is determined by the charge ions adsorbed colloid surface. Electrophoresis is the movement of colloidal particles due to the influence of an electric field. Because the colloidal particles have a charge, it can move in an electric field. If the colloidal inserted into a direct current through the electrode, the positively charged colloid will move towards the negative electrode and upon arriving at the negative electrode will occur and colloid charge neutralization will clot (coagulation).

Example: Factory chimneys fitted with a metal place that is electrically charged with the purpose to agglomerate the dust.

 

5.      Colloidal Coagulation

Colloidal coagulation is colloidal clotting due to oppositely charged electrolytes. For example is dirt on the water is coagulated by alum so the water becomes clear.

Factors that cause coagulation:

-          Changes in temperature

-          Stirring

-          Adding ion with a large payload colloidal

-          Mixing positive and negative colloid

Colloids will undergo coagulation by:

a.      Mechanics

Mechanically performed by heating, cooling, or stirring rapidly

b.      Chemistry

With the addition of electrolyte (acid, base, or salt)

Example:

Milk and sour syrup will clot

Mud and alum will clot

      By mixing the two kinds of colloids of the positive charge. For example, Fe(OH)₃ are positively charged will clot when mixed As₂S₃ negatively charged.

 

 

6.      Liofil and Liofob colloidal

 

a.      Colloidal Liofil

Liofil colloid is a colloid which adsorbs the liquid, thus forming a sheath around the colloid. Example: Gelatin.

b.      Colloidal Liofob

Liofob colloid is colloidal fluid that does not adsorb water. In order for the charge of colloidal stable, liquid dispersant should be free from electrolyte by means of dialysis, the purification of the electrolyte dispersing medium.

 

7.      Emulation

Emulation is a colloidal fluid in a liquid medium. In order for a stable colloidal solution into colloid usually added emulsifiers, stabilizers which are substances that stable colloid. For example, milk is an emulsion of fat in water with casein as an emulsifier.

 

8.      Colloidal stability

 

Many colloid to be maintained in colloidal form to use. Example: ice cream, ink, paint. For that use, other colloids which can form a layer around the colloid. Another colloid is called a protective colloid. Example: gelatin on sol Fe(OH)₃. For the colloidal form of emulsions can be used emulsifier is a substance that could be interested in a second liquid to form an emulsion Example: detergent as an emulsifier of emulsions of oil and water.

 

9.      Purification Colloid

 

To purify colloids of eliminating ions destabilize colloids, dialysis can be done the way.Colloid be purified put into a bag made of semi-permeable membranes are membranes that can only be bypassed ion particles and cannot be bypassed colloid molecules.

 

Example: parchment paper, selopan, or collodion.

 

Colloid bag inserted into a vessel containing water, the ions in the colloid will be out of pocket, and out of the vessel and colloidal left in the bag. Dialysis will be brought forward if in a vessel supplied electric current is called electro dialysis.

 

The process of separation of dirt result of metabolism from the blood by the kidneys, including dialysis. So, if someone is suffering from kidney failure, the person must undergo a "dialysis" machine dialisator hospital. Colloids can also be purified with ultra filter.

 

 

D.   The Making of Colloidal Systems

 

A.    Condensation

Making the colloidal system by means of condensation done by agglomeration of very small particles. Clumping of particles can be done in the following way:

1.       Precipitation Reaction

Making the colloidal system in this manner is done by mixing the electrolyte solution so as to produce precipitate. Example: AgNO₃ + NaCl -> AgCl (s) + NaNO₃

2.       Reaction Hydrolysis

The hydrolysis reaction is the reaction of a substance with water. Colloidal systems can be prepared by reaction of a substance with water. Example: AlCl₃ + H₂O -> Al (OH)₃ (s) + HCl.

3.      Redox Reactions

Making colloid can be formed as a result of redox reactions. Example: the solution of gold.

Reaction: AuCl₃ + HCOH -> Au + HCl + HCOOH

 

4.      Shift Reaction

Example: sol preparation As₂S₃ by bubbling H2S into aqueous H₃AsO₃ at a certain temperature. Reaction: 2 H₃AsO₃ + 3 H₂S -> 6 H₂O + As2S₃

 

5.       Solvent Substitution Reactions

Example: the manufacture of calcium acetate gel by adding 96% alcohol to a solution of calcium acetate saturated.

B.     Dispersion

Making the colloidal system by dispersion carried out with far too great a suspension of particles into the colloidal particles, breaking coarse particles into a colloid.

1.      Mechanical

The particle size of the suspension is reduced by means of grinding solids, with a large grain smoothing and then stirred in the dispersing medium. Example: Wadding alum milled, mixed into water to form a colloid with polluted water.

-          Make ink by smoothing carbon colloid mill and then dispersed in water.

-          Make a sulfur sol by smoothing sulfur and sugar (1: 1) on a colloid mill, then dissolved in water, the sugar will dissolve and the sulfur into sol.

 

2. Peptizing

Making colloids by way peptizing is the manufacture of colloids by adding a type of ion, so the sediment particles will be broken. Example: sol Fe(OH)₃ by adding FeCl₃. For example, sol NiS by adding H₂S, rubber peptized by gasoline, gelatin peptized by water, and precipitated Al(OH)₃ peptized by AlCl₃.

 

3. Bredia / Bredig

Making colloid by means of the arc Bredia / Bredig done by dipping a metal wire (electrode) that electricity into the water, so that the metal wire to form colloidal particles of dust in the water.

 

4. Ultrasonic

Namely the destruction of large grains with ultrasonic frequency (> 20,000 Hz)

 

E.     Colloidal Particle Shape

1. Circle: For example: virus, silica.

2. Stem. For example: viruses

3. The dish: For example: globulin in the blood.

4. Fiber: For example: cellulose.

 

F.     Use of Colloidal Systems

1. Drugs: ointment, cream, fish oil.

2. Food: ice cream, jelly, and gelatin.

3. Cosmetics: hair cream, skin spray, body lotion.

4. Industry: ink, paint.

 

 

Soap / detergent is a substance the molecules of which consist of hydrophobic and hydrophilic groups at the same time.

 

Water Purification

1. The river water containing silt plus alum -> clear water.

2. Clear water plus chlorine -> clear water free of germs.

3. Clear water germ-free filtered -> clean water.

 

G.   References

 

Hasannudin. 2012. Jenis-jenis Koloid. http://kimiadasar.com/jenis-jenis-koloid/. 28 November 2016.

Law, Jimmy. 2016. Colloids. http://chem.libretexts.org/Core/Physical_and_Theoritical_Chemistry/Phyical_Properties_of_Matter/Solutions_and_ Mixtures/Colloid. 1 December 2016

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