Using English To Report

CHOLOID CHEMICALS

       I.            Purpose

The purpose of this practice is to study the properties of colloids.

    II.            Basic Theory

The colloid is a mixed form which lies between the solution and the crude mixture. Although microscopically colloid appears homogeneous, but colloids are classified into heterogeneous mixtures. The colloidal mixture is generally stable and can not be filtered. The size of the colloidal particles lies between 1nm - 100 nm. The colloidal system consists of being dispersed with a certain size in the diffusing medium. Substances that are dispensed are called the dissipated phase, while the medium used to dispensate is called the dispensing medium. The dispersed phase is discontinuous, while the dispensing medium is continuous. (Harvest, 1984)
In a homogeneous and stable mixture called a solution, a molecule, atom, or ion is dispersed in a second substance, in a somewhat similar fashion, the colloidal material may be dispersed or dispersed in a continuous medium, resulting in a colloidal dispersion or system Colloids, jams, mayonnaise, chinese inks, the like, colloid particles are referred to as dispersed and the continuous matter in the dispersed particles is called the diffusing agent or the medium of the dispersion. (Arsyad, 2001)

Properties - ifat owned colloidal system is as follows:

1.      Tyndall effect

The Tyndall effect is the effect of light scattering by colloidal particles. Colloidal particles will reflect and scatter the light that surrounds them so that the light will appear brighter. If this light is then caught on screen, the light on the screen looks blurry.

2.      Brownian motion

Brownian motion is irregular motion, random motion or zig - zag motion of colloidal particles. Brownian motion occurs due to irregular irregular colloidal particles and the medium of suspension. The collision caused the colloidal particles to vibrate with irregular atrah and short distances.

3.      Adsorption

Colloidal particles are able to absorb neutral molecules or ions on its surface. If the colloidal particles absorb charged ions, then the ions are attached to the surface, the colloidal particles become charged. Absorption that occurs only on the surface is called adsorption or absorption, while the absorption that occurs throughout the section is called adsorption.

4.      Coagulation

Koaguasi is a clumping of colloidal particles that occur due to damage to the stability of the colloidal system or due to the incorporation of different colloidal particles of charge to form larger particles of coagulation can occur due to the influence of heating, cooling, electrolyte addition, decay, mixing of different colloid charges, or because of electrophoresis.

5.      Electrophoresis

The movement of colloid particles to one electrode shows that the colloidal particles of electrically charged solid particles can be electrically charged due to ion absorption on the surface of colloidal particles.

6.      Colloid Protector

Protective colloid is a colloidal system that is added to other colloidal systems to obtain stable colloids.

7.      Dialysis

Dialysis is the process of screening colloidal particles from adsorbed ions so that the ions can be removed and the adsorbed substances free of unintended ions.
(Sutresna, 2007. 299-307).

 III.            Tools and Materials

Tool	Amount	Material	Amount
Chemical Glass 500 ml	2 pieces	Salt kitchen	10 gr
Centrifuge Tubes	2 pieces	HCL thick	Sufficiently
Funnel	2 pieces	Alum	1-2 gr
Filter paper	2 pieces	Milk	Sufficiently
Drop pipette	2 pieces	Aquadest	Sufficiently
Flashlight	1 pieces
Erlenmeyer	2 pieces
Measuring glass 20 ml	1 pieces
Measuring Glass 10 ml	1 piece
Centrifuge Tool	1        piece

 IV.            Ways Of Working

First set up all the equipment to be used, after all the tools are prepared, then prepared 10 grams of salt and dissolved with 10 mL of aquades. This mixture as a mixture (A). After which 100 mL of liquid milk is prepared, this mixture as a mixture (B). Then the mixture (A) and (B) illuminated with a flashlight, observed the course of the light.

The next experiment, taken 20 mL of mixture (A) and (B), then filtered each mixture separately using a regular filter paper. After that, the filtrate was obtained from each mixture.
The next experiment, prepared two centrifuge tubes. The first tube is filled with mixture (A) and the other tube is filled with the mixture (B) until the tube is filled as much as 7 mL. Then the two tubes are centrifuged for 15 minutes at a speed of 2000-3000 rpm. Then observed the changes that occurred.

The next experiment, measured pH on the mixture (A) and mixture (B). Then the pH of each mixture is decreased by 2 units by means of added concentrated HCl. Then observed the changes that occur if there is a change.

The last experiment, taken 20 mL of mixture (A) and (B), then placed on the beaker separately. Then add 1-2 grams of alum into the mixture and let stand for 20 minutes. Finally, observed changes that occur if there is a change.

    V.            Observation Results

Treatment	Mixed (A)	Mixed (B)
Illumination with a flashlight	Flashlight is translucent, colorless and there are no particles.	Flashlight is not translucent (light not straight) "Brown motion".
Filtering	Nothing changes, the solution remains colorless.	Changes occur, the initial white to white fade.
Centrifugation	Nothing changes, the solution remains colorless.	There was a change, which was initially pale white and liquid to a turbid white color and there was a lump on it "Coagulation"
The addition of concentrated HCl	An initial pH change of 6 turns to 4 after adding 1 drop of concentrated HCl. But the solution did not change.	There was a pH change that initially 5, changed to 3 after added 3 drops of concentrated HCl. The solution also changed into two phases above the form of sediment and below a solution. "Coagulation"
The addition of alum	There is no change, it's just that there is a dissolved alum that is not soluble because the solution through saturated.	Changes occurred, after adding 2g of alum. The solution becomes two phases, the particles separated by the precipitate above and the solution below. "Electrophoresis"

 VI.            Discussion

In this paraktikum discuss about colloidal system. The colloid is a mixed form which lies between the solution and the crude mixture. Although microscopically colloid appears homogeneous, but colloids are classified into heterogeneous mixtures.

Common properties that distinguish colloidal systems from true solutions and rough dispersions include:

1.      The amount of particles

Colloidal particles have a diameter between 1-100nM, can not be seen with a microscope. The coarse dispersion particle is larger than 100nM.

2.      Filtering

Rough dispersions can be filtered with ordinary filter paper, while colloid solutions can not be filtered with ordinary filter paper, but by ultra filters, such as fine ceramics.

3.      Diffusion

Due to the large amount of colloids and coarse dispersions, these substances are difficult to diffuse. So different from the true solution that is easy to diffuse.

4.      Fine

Colloid solutions are usually cloudy and scatter about the solution. These symptoms are also called Tyndall Effects. If a beam is passed in a true solution, all rays will be transmitted. Whereas when a beam is passed in a colloidal solution, some rays are scattered and partially transmitted.

5.      Surface Area

Colloidal particles have a very large surface area when compared to particles of the true solution with the same mass. On this basis the colloid solution has a large adsorption power.

6.      Electricity

Colloidal particles have an electrical charge due to the imaging of ions in solution.

The properties of colloids are as follows:

1.      Colligative nature

Colligative properties are the increase in boiling point, decrease in freezing point, decrease of vapor pressure, and osmotic pressure. This property depends on the number of colloidal particles, not on the type. Colligative properties are useful for calculating the number of moles or concentrations of colloidal particles. This trait provides benefits to the organism.

2.      Optical properties

The size of the colloidal particles is rather large, then the light passing through it will be reflected. The direction of the reflection is irregular because the particles are scattered randomly so that the reflection of light is scattered in all directions.

3.      Kinetic properties

As free particles in the medium, colloidal particles always move in all directions. His movements are always straight and will break when collided with other particles. The movement was called Brownian movement.

4.      Adsorption

On the surface of colloidal particles, there is a Van Der Waals force to the surrounding molecules or ions. The attachment of other substances to the colloidal surface is called adsorption. A colloid generally only adsorbs positive ions or negative ions only. The adsorbed ions can form one or two layers.

5.      Electrical Properties

The colloidal particles that have adsorbed the ion will be electrically charged according to the ion charge they absorb. The colloid charge can be determined by dipping the electrode. The positively charged will be attracted to the negative electrode, while the negatively charged are attracted to the positive electrode.

6.      Coagulation

Colloid if left within a certain time will be affected by the force of gravity, so that the particles down slowly to the bottom of the vessel. This event is called coagulation (clumping).

Before doing the experiment, we made salt and milk solution. 10 grams of salt dissolved in 100 ml of water and produce a colorless solution. While milk is white. In the first experiment, the use of salt and milk was detected. At the time the salt solution is given a flashlight then the light can penetrate the salt solution and light is passed on. While in milk, when given radiation from a flashlight then the light does not penetrate the milk.

This happens because the salt water is not a colloidal system so that the flashlight can be continued while the milk is a colloidal system. This is in accordance with the nature of colloids that When a beam is passed in a true solution, all rays will be passed on. Whereas when a beam is passed in a colloidal solution, some rays are scattered and partially transmitted. Milk is a colloidal system consisting of a dispersed phase and a liquid dispersing phase which is usually called an emulsion. In this process, there is a colloidal nature of the tyndall effect.
The Tyndall effect is the effect that occurs when a solution is exposed to light. When the true solution is irradiated with light, the solution will not scatter light, whereas in the colloidal system light will be dissipated. It happens because the colloidal particles have relatively large particles to be able to scatter the rays. In contrast, in the true solution, the particles are relatively small so that the scattering occurs only slightly and is very difficult to observe.

If white light is passed to a colloidal dispersion system where the dispersed phase particles are so small that visible light will be dissipated more by their colloidal particles. The occurrence of Tyndall effect on colloids is influenced by the optical properties and kinetic properties possessed by colloids. Colloidal Optical Properties: The size of the colloid particle is larger than the true solution so that the light passing through it will be reflected. The direction of this reflection is irregular because the colloid particles are scattered randomly so that the reflection of light is scattered in all directions. Colloidal Kinetic Character: The nature of colloid particles that always moves in all directions. The movement of these colloidal particles is always straight and will break if it collides with other particles. The presence of optical and kinetic properties in the colloids causes colloid to experience Tyndall effect. A beam of light passed on a colloidal system will show light scattering in all directions. This light scattering is caused because randomly scattered colloidal particles will reflect the light passing through it. The intensity of light scattering is influenced by particle size and concentration of colloidal particles. The intensity of the scattered light increases with increasing particle concentration and particle size. This can be further investigated using an ultra microscope. The observations of the Tyndall effect undertaken under an ultra-microscope give rise to very small spots that emit light. Thus, the particles that emit these rays are very small or even invisible, but what is visible is the reflection of light from the particles of light will not be visible. This is because colloidal particles are in an ultra-microscopic state. It can be concluded that the Tyndall effect occurs because the colloidal particles will scatter the light it receives in all directions. This does not occur in true solutions, because the particles are so small that they do not change the direction of light. The light passed on the true solution will be continued.

The Tyndall effect is one of the many colloidal traits. To be able to experience a tyndall effect a colloidal particle must have a size large enough that is about 1 - 100 nm. To be able to have a tyndall effect colloid solution should be homogeneous. In the next experiment, screening was done on 20 ml of salt and milk solution. From the filtering results obtained in salt solution did not happen any change whereas in milk after screening the white color is more faded.

The next experiment is to make a centrifuge on salt and milk. After the centrifuge process on the salt solution did not happen anything. After the milk solution is inserted into a centrifuge tube at a rate of 2000rpm for 15 minutes, a clear solution and colloidal deposits are placed at the bottom of the test tube. Centrifugal is a centrifugation rotary motion that causes the particles in the solution to collide with each other the same relatively short. The centrifuge principle is separating particles based on their specific gravity.

Conducted this centrifuge in order to speed up coagulation. As we have seen before, this centrifuge uses a centrifugal force which causes a large artificial gravity force to separate and draw the sediment to the bottom of the tube. The centrifuge principle is to separate particles based on their specific gravity.

The next experiment was the addition of HCl to salt and milk solution. Previously, using the universal indicator obtained pH salt solution is 6. After the addition of HCl as much as one drop then the pH of the salt solution drops to 4. After addition of HCl, the salt solution does not change anything.

While in milk, the previous pH is five. After the addition of three drops of concentrated HCl solution the pH turned into three. In addition, white deposits are formed in milk. After the addition of HCl to milk then formed precipitate. This is because the milk emulsion will break (break) in the presence of H + ions from HCl. The decrease in pH is due to the HCl being a strong acid so that when the concentration of hydrogen ions in a large solution, then the solution is acidic with a pH less than 7. the solution becomes more clear than the mother liquor. This fluid pH is due to some free particles in the medium. Colloidal particles always move in all directions. In accordance with the theory that states the occurrence of Brownian motion. In addition, the solution also has a large adsorption capacity, ie the ability to absorb the surrounding ions. In the experiment of milk plus HCl this happens the nature of colloid is coagulation.

Coagulation is the process of agglomerating colloidal particles. This coagulation process occurs due to unstable colloidal system. The colloidal system is stable when the colloid is positively charged or negatively charged. If the charge on the colloidal system is disarmed by neutralizing its charge, the colloid becomes unstable and then coagulates (clumps). Coagulation by neutralizing colloid charge can be done in this experiment which is addition of electrolyte.
If on a charged colloid is added electrolyte, the colloid will be coagulated. For example as in the practicum that has been done above if the milk when added HCl, then the milk will clot.
In the next experiment as much as 20 mL of salt and milk solution was added with one gram of alum. After sterilization for 20 minutes there is no change in salt solution while in the milk formed two phases, namely the white sediment phase and the cloudy white solution phase.
In the process of milk purification with alum this happens the nature of colloid that is coagulation and absorption. As mentioned earlier, the coagulation process occurs due to the unstable system of colloids; Which is due to the addition of electrolyte to the colloidal system. While absorption is the process when the colloidal surface includes other substances. River water or cloudy well water may contain mud (clay soles), dyestuffs, detergents, pesticides, and others.
The colloidal system is stable when the colloid is positively charged or negatively charged. If the charge on the colloidal system is disarmed by neutralizing the charge, the colloid becomes unstable and then coagulates (clumps).

In addition to alum, the solution becomes slightly clearer and precipitated at the base of the beaker. Tawas has the ability to bind dirt in a liquid because alum will form aluminum hydroxide which will release positive Al3 + ions in water. This positive ion will neutralize the colloid negative ions in the solution so that the absorption of Al3 + ions leads to the coagulation (clumping) of colloidal particles to settle. Reactions:

Al2 (SO4) 3 + 6H2O → Al (OH) 3 + 3H2SO4

VII.          Conclusion

Based on the work that has been done, proved that salt solution is not a form of colloid while milk is a form of colloid. This is because, at the time of experiments on salt solution there are no properties of colloids whereas in milk there are changes that is the properties of colloids that prove that milk is colloidal. In a radiation experiment with a flashlight the colloidal properties of the tyndall effect occur. In the process of centrifuge and the addition of concentrated HCl occurs the nature of colloid in the form of coagulation. In the experiment of addition of alum occurs the nature of colloid in the form of coagulation and absorption.

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