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Chem 14.1 report

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Wendell Cruz

on 8 May 2013

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Transcript of Chem 14.1 report

Colloids Experiment # 5 Experiment # 5 focuses on different kinds of colloids and is divided into 3 parts. Introduction Part I.
Preparation of Colloids Part II.
Alexander's Patriotic Tube Part III.
Properties of Colloids QUESTIONS Colloids are mixtures which properties are neither homogeneous nor heterogeneous. Their properties are somewhere in between. They have particles bigger than that of a solution and smaller than that of a suspension.
It is composed of a dispersed phase (particles) and a dispersing phase (medium).
A sol is dispersion of solid in liquid while emulsion is dispersion of liquid in liquid. And an aerosol is a dispersion of liquid or solid in gas. Foams are dispersion of gas in liquid or solid.
The higher the charge of the ions in the colloid, the higher its coagulatory effect.
Tyndall effect results from scattering of light by dispersed particles in the colloid.
Dispersion is concerned with reduction of size of particles while condensation includes forming of colloidal particles out of small particles. Conclusion Part I. Preparation of Colloids. involved the preparation of a sol (dispersion of solid in liquid) and emulsion (dispersion of liquid in liquid).

Part II. Alexander's Patriotic Tube. shows the preparation of a gel which is a sol where the particles are arranged loosely with a definite structure.

Part III. Properties of Colloids. shows different solutions exhibiting properties of colloids such as Tyndall Effect and precipitation. A. Sol
a. Preparation of Fe(OH)3 sol
Add 1M FeCl3 drop by drop into boiling 50 mL H2O until change in color is observed.
Cool and reserve for next procedures. b. Preparation of Sulfur sol
1.Add a pinch of sulfur powder in 50 mL of H2O and stir.
2. Dissolve a pinch of sulfur powder in 5 mL hot alcohol. Alcohol should be prepared hot in a water bath because it is flammable. Pour solution b2 into 50 mL water.

B1 is not a sol because the sulfur powder did not dissolve in water. On the other hand, B2 is a sol because it dissolves in alcohol-water solution. B. Emulsion
Add dropwise with shaking 1.0 mL of oil to 10 mL H2O.

Oil was observed to form a layer on top of the water.

Let it stand for 10-20 mins. Add 5 mL concentrated soap solution and shake.

After shaking, it was observed that oil and water mixed. Dissolve a pinch of agar in 15 mL boiling H2O.
Add 2 drops 1 M NaOH, few drops of phenolphthalein to color it pink, and 1 mL 1 M (K4[Fe(CN)6])
Pour immediately into a test tube and allow the agar to cool and set into gel.
Pour 1 mL of 0.1 M FeCl3 on top of the gel.
Cork the test tube and let it stand for any hour. There were 4 observed layers.

Topmost layer: Fe(OH)3 in yellow-orange liquid form

2nd layer: blue layer formed from FeCl3 +K4[Fe(CN)6]KCL + Fe4[Fe(CN)6]3

3rd layer: Layer is colored in between yellow and white.
Layer of HCl formed from the reaction.

4th layer: Pink layer from original solution; basic due to NaOH A. Tyndall Effect
Put Fe(OH)3 from IA-a, Sulfur sol from IA-b2, 1 M CuSO4, dilute evaporated milk, boiled starch solution, unboiled starch solution, soap solution in separate test tubes
Place it against a beam of light coming from a small hole.
Observe the path of light from right angle to the source of light.
Compare the results using distilled water as the negative reference. Fe(OH)3 Orange,exhibits Tyndall effect
Sulfur sol Cloudy white, exhibits Tyndall effect
1 M CuSO4 Blue, no Tyndall effect
dilute evaporated milk Cloudy white, exhibits Tyndall effect
boiled starch solution Cloudy white, exhibits Tyndall effect
unboiled starch solution Cloudy white(particles at bottom), no Tyndall effect
soap solution Cloudy, exhibits Tyndall effect B. Precipitation
In 3 separate 10 mL test tubes, place 2 mL Fe(OH)3 sol. (from IA-a)
To the first, second, and third test tubes, add 10 drops 1 M NaNO3, 10 drops 1 M Na2SO4, and 10 drops 1 M Na3PO4, respectively.

1 M NaNO3 - least amount of precipitate
1 M Na2SO4 - moderate amount
1 M Na3PO4 - greatest amount 1. Why is sulfur not soluble in water? What kind of colloidal dispersion is a sol?

Sulfur is nonpolar and water is polar. Only like dissolves like. In the same way, nonpolar substances can only be dissolved in nonpolar substances as well. A sol is composed of small solid particles dispersed in liquid.

2. How would you account for the observation in IA b2?

Sulfur, being nonpolar, was partly dissolved in the hot alcohol because the alcohol was partly non-polar. Adding water to the solution dissolves the alcohol. 3. What is the role of soap solution in the oil emulsion prepared in IB?

Soap acted as the emulsifier. Its nonpolar end mixed with oil because it is hydrophobic. Its hydrophilic polar end mixed with water.

4. There were 4 observed layers.

Topmost layer: Fe(OH)3 in yellow-orange liquid form

2nd layer: blue layer formed from FeCl3 +K4[Fe(CN)6]KCL + Fe4[Fe(CN)6]3

3rd layer: Layer is colored in between yellow and white.
Layer of HCl formed from the reaction.

4th layer: Pink layer from original solution; basic due to NaOH

5. What causes Tyndall effect?
The dispersed particles in the colloid scatters light and produces the Tyndall effect. http://www.ehow.com/info_8646487_methods-used-form-colloids.html

http://sciencesquad.questacon.edu.au/activities/oil_water.html References Chem 14.1 Module Chem 14.1
Group # 5

Cruz, Wendell
Renti Cruz, Abraham What's a colloid? Colloids are mixtures which properties are neither homogeneous nor heterogeneous.
They have particles bigger than that of a solution and smaller than that of a suspension.
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