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Experiment 5: COLLOIDS
Transcript of Experiment 5: COLLOIDS
Table 1. Results obtained from the preparation of Sol
Table 2. Results obtained from observing Tyndall effect on different mixtures
Table 3. Results obtained from observing the amount of precipitate present when 3 different precipitants was mixed with Fe(OH)3 sol
Definition of Terms
I. Preparation of Colloids
Sulfur did not mix with water (Figure 2) since sulfur is non polar and water is polar. Dissolution only happens between like substances resulting to the immiscibility of sulfur and water in the mixture. On the other hand, sulfur in hot alcohol and water (Figure 3) was partly dissolved due to alcohol being partly non polar resulting to a sol solution.
Oil is immiscible in water because oil is non polar while water is polar. When soap solution was added to the mixture (shown in Figure 4), it sank to the bottom of the tube dragging the oil with it. The soap solution served as an emulsifier between oil and water since its molecules have both properties of non polar and polar molecules. An emulsifier is capable of dispersing one liquid into another immiscible liquid.
II. Tyndall Effect
Summarized in Table 2 are the proofs of the existence/or nonexistence of Tyndall effect in the various systems tested.
The CuSO4 solution showed a negative result on the appearance of Tyndall effect because it did not scatter light due to its particles being less than 1 nm, appearing as a clear blue solution. Unboiled starch solution also did not show Tyndall effect because no scattering of light was observed when the said effect was being observed for this system. Distilled water served as the negative reference.
All other systems (except CuSO4 solution, unboiled starch solution and distilled water) were positive in exhibiting Tyndall effect.
3. What is the role of shampoo solution in the oil emulsion prepared in procedure IB?
Originally, oil and water will not mix because water is polar and oil is non polar. The soap solution in the oil emulsion served as the emulsifier between water and oil. It is the reason why oil and water seemed to be “bonded” when oil, together with soap solution, mixed with water.
1. Why is sulfur not soluble in water? What kind of colloidal dispersion is sol?
Sulfur was not soluble in water because it is non polar while the latter is polar. Hence, based on the “
like dissolves like
” rule, sulfur cannot be dissolved in water.
A sol is a kind of colloidal dispersion wherein the mixture is composed of solid particles dispersed in liquid.
5. What causes Tyndall effect?
Tyndall effect is the scattering of light due to the presence of colloidal particles which are able to maintain a homogeneous appearance yet are large enough to be able to scatter light. The dispersed particles in the colloid scatter light and produce Tyndall effect.
I. Preparation of Colloids
a. Preparation of Fe(OH)3 sol
A 50 mL water was heated to boiling. When the solution started to boil, 20 drops of freshly prepared 1 M FeCl3 were added. After the solution was heated continuously for 2 to 3 minutes, it was allowed to cool and was reserved for use in subsequent procedures.
b. Preparation of sulfur sol
1. A pinch of sulfur powder was placed in 50 mL of water and was stirred.
2. A pinch of sulfur powder was dissolved in 5 mL hot alcohol. Since alcohol is flammable, the hot alcohol was prepared in a water bath. The solution is poured with stirring into a new beaker with 50 mL water and was observed. The obtained mixture was compared with the mixture in b1.
To 10 mL water in test tube, 1.0 mL of oil was added dropwise with shaking and was observed. It was left to stand for 3 to 5 minutes and was observed again after. 2 mL concentrated soap solution was added to the mixture and was shook after. What happened by doing the procedures were noted.
II. Patriotic tube
One to two spatulafuls of agar was dissolved in 15 mL of boiling water and 2 drops of 1 M NaOH, a few drops of phenol red to color it red, and 1 mL 1 M potassium ferrocyanide (K4[Fe(CN)6]) were added. The mixture was poured immediately into a test tube and the agar was allowed to cool and set into gel. On top of the gel, 1 mL of 0.1 M FeCl3 was poured. The tube was corked and left to stand for an hour. Results were then observed and described.
III. Properties of Colloids
A. Tyndall Effect
Fe(OH)3 sol that was prepared in IA-a was placed in a test tube and viewed using a beam of light coming through a small hole. The path of light was observed by viewing it at right angle to the source of light. The same procedure was repeated for the following systems: sulfur sol (prepared in IA-b2), copper sulfate solution (0.1 M solution), dilute evaporated milk (10 mL milk in 40 mL water), boiled starch solution (1 g starch in 100 mL water), unboiled starch solution and, shampoo solution (1 mL shampoo in 5 mL water). The results that were obtained were then compared using distilled water as the negative reference.
Two mL of the Fe(OH)3 sol prepared in IA-a was placed in three separate 10 mL test tubes. To the first test tube, 10 drops of 1 M NaNO3 were added, to the second test tube, 10 drops of 1 M Na2SO4 were added, and to the third test tube, 10 drops of 1 M Na3PO4 were added. The amounts of precipitation in each case were compared.
a type of mixture whose properties are between heterogeneous mixtures and homogeneous solutions
has particles between 1 to 1000 nanometers
has two phases:
dispersed phase - substance being dispersed
dispersing phase - medium
Dispersion of solid in liquid
Dispersion of liquid in liquid
Dispersion of liquid or solid in gas
Dispersion of gas in liquid or solid
the scattering of light as light beam passes through a colloidal dispersion
This experiment specifically aimed to:
(a) compare condensation from dispersion method of colloidal dispersion;
(b) identify the different types of colloids; and
(c) observe the different properties of colloids.
I. Preparation of Colloids
II. Tyndall Effect
Figure 1. Fe(OH)3 sol
Figure 2. Sulfur in water
Figure 3. Sulfur in hot alcohol and water
Figure 4. Oil (in water and soap solution)
Figure 7. Results obtained after different precipitants (from left to right: 1 M Na3PO4, 1 M Na2SO4, 1 M NaNO3) were added to 2 mL of Fe(OH)3 sol
The experiment showed that in terms of the formation of precipitate when three precipitants were added to Fe(OH)3 sol, this result was obtained: NaNO3 < Na2SO4 < Na3PO4.
This can be explained by the Hardy Schulze Law which states that the greater is the valency of the oppositely charged ion of the electrolyte being added, the faster is the coagulation. Coagulation is a process which involves coming together of colloidal particles so as to change into large sized particles which ultimately settle as a precipitate or float on the surface.
The charges of the anions of the precipitants, in this case, NO3-, SO42- and PO43- affected the amount of precipitate produced. Hence, for the coagulation of negatively charged ions, trivalent anions (PO43-) are far more effective than divalent anions (SO42-) which in turn are more effective than monovalent anions (NO3-). The more negative the anion is, the higher is its tendency to form precipitate when mixed with Fe(OH)3 sol.
2. How would you account for the observation in procedure IA-b2?
Sulfur was partly dissolved in hot alcohol and water. This is because the molecules of alcohol exhibit both polar and non polar properties. Thus, the partial non polar property of alcohol reacted with non polar sulfur to dissolve it. The solution of alcohol and sulfur was then mixed with water to form the sol.
4. Give an explanation for the results obtained in procedure II. What ions/compounds are responsible for the different colors observed in the Alexander’s patriotic tube?
Four layers were observed in Alexander’s patriotic tube (shown in Figure 6): the topmost layer which is in liquid form was the Fe(OH)3, the second layer which appeared to be dark blue in color was formed from
4FeCl3 + 4K4[Fe(CN)6] → 12KCl + Fe4[Fe(CN)6]3
The third layer which was yellow is the acidic layer. It is an HCl layer formed from the reaction. The last layer is the pink gel. The pink color is due to the NaOH which is basic, the phenol red acted as the pH indicator.
The layers were arranged based on the density of ions/compounds present in each layer.
is a mixture whose properties are found between homogeneous solution and
. It is composed of two phases namely the
dispersed phase (particles)
dispersing phase (medium)
scattering of light
by dispersed particles in a colloids.
There are two types of colloidal dispersions:
or solvent-loving and
is the reduction of size of particles while
includes forming of colloidal (or bigger) particles out of smaller particles.
For future conduction of the same experiment, the following things are being recommended:
(1) Perform precisely the indicated instructions in order to obtain accurate results,
(2) Make use of accurate measurements when using different reagents, chemicals, etc.,
(3) Strict use of different spatulas and pipets for the different reagents to avoid contamination and impurities in mixtures,
(4) Provide enough number of apparatus needed for the experiment to avoid wasting time in cleaning the needed apparatus for another set up in the experiment,
(5) Strictly enforce laboratory rules with regards to handling laboratory apparatus and reagents in order to avoid breakage of the apparatus or contamination of the reagent/s,
(6) Research on the nature of the substances used beforehand in order to know how to dispose of the substances after the experiments
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