Preparation of Colloidal Solutions

Preparation of a Sulphur Sol. Prepare a saturated solution of sulphur in ethanol in a test tube. Take 2-3 g of sulphur and 10 ml of ethanol for this purpose. The solution will become saturated after vigorous shaking during 15 min. Filter off the undissolved sulphur, measure off 5 ml of the solution, and carefully pour it dropwise into 20 ml of distilled water. Pour part of the colloidal solution into two test tubes in equal portions. Add 1 ml of water to the first tube and 1 ml of a barium chloride solution to the second one, and heat both tubes. What happens How does the electrolyte affect the stability of the solution Define a gel and a sol. 

Preparation of an Iron(in) Hydroxide Sol. Heat 85 ml of distilled water in a conical flask up to boiling. Without removing the flask from the gauze, remove the burner and add 15 ml of a 0.1 N iron(III) chloride solution dropwise to the flask. Again boil the solution for several minutes. What occurs How can the change in the colour of the solution be explained Cool the solution and keep it for subsequent experiments. 

Preparation of Manganese(IV) Oxide Sol. Add a 2% hydrogen peroxide solution to 5 ml of a potassium permanganate solution containing 14 g of salt per litre of solution until the violet colour disappears. Write the equation of the reaction. To determine the end of the reaction, proceed as follows add a few drops of a saturated sodium chloride solution to a small sample and heat it. If a violet colour is noticeable, add more hydrogen peroxide solution to the main solution. 

Subject the solution obtained to dialysis and treat the washing water first with phenolphthalein and then with methyl orange. Pour the solution into a number of test tubes and add to them 1 N solutions of salts of mono-, di-, and trivalent cations, respectively. What is observed Explain the occurring processes. 

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Problem 1 Explain the terms colloidal state and colloidal solution. Describe various methods used in the preparation of colloidal solutions. Also mention the different methods used for the purification of colloidal solutions. (Meerut 2002 Agra 2005, 2003, 2001 Kanpur 2005, 2000)... 

Nanoparticles are very suitable as SERS substrates as was demonstrated in previous section. However, for 2,4,6-TNT a strong base was needed to increase the intensity. The method for the preparation of colloidal solutions was optimized to have the maximum SERS effect on TNT vibrational signatures. The concentration of the reducing agent, the addition rate of the reducing agent, and the stirring rate were also evaluated in the previous context. 

Principally purification and characterization methods of monometallic nanoparticles are directly applied to those of bimetallic nanoparticles. Purification of metal nanoparticles dispersed in solution is not so easy. So, in classical colloid chemistry, contamination is carefully avoided. For example, people used pure water, distilled three times, and glass vessels, cleaned by steam, for preparation of colloidal dispersions. In addition, the reagents which could not byproduce contaminates were used for the preparation. Recently, however, various kinds of reagents were used for the reaction and protection. Thus, the special purification is often required especially when the nanoparticles are prepared by chemical methods. 

Taramasso et al. (5) had originally reported two methods for the hydrothermal synthesis of TS-1. The first method (mixed alkoxide method) involves the preparation of a solution of mixed alkoxides of titanium and silica (preferably ethoxides) followed by hydrolysis with alkali-free solution of tetrapropylammonium hydroxide (TPAOH), distillation of the alcohol and crystallization of the resulting gel at 448 K. In the second method (dissolved or hydrolyzed titanium method) a soluble tetrapropylammonium peroxo-titanate species was prepared initially and then colloidal SiC>2 (Ludox AS-40) was added. This entire operation had to be carried out at 278 K. The TS-1 samples obtained by these two synthesis routes differed, particularly because of the presence of impurities such as Al3+ usually present in colloidal silica (33). 

Fig. 9.4.25 Optical absorption spectra of copper colloid prepared by the gas flow-solution trap method as a function of lime development. The numbers in the figure are the time after the preparation of Lhe sample. The spectrum of sodium eihoxidc in ethanol (authentic sample) is also shown in the same figure, marked by b. The insertion is the expansion of the region of the isosbestic point. The deviation from the isosbestic point at 10 h after the preparation of colloids is shown by a in the insert. (From Ref. 26.)...

When warmed with neutral organic substances selenium frequently passes into colloidal solution and remains in this condition even after solidification of the solvent. Even when the solid suspension in anthracene or phthalic acid is melted the selenium does not pass into the grey crystalline condition although the points of fusion of these solvents are higher than the transformation temperature. The higher the temperature reached in the preparation of these solutions and the slower the cooling the smaller are the selenium particles.7... 

Tire electrical method, commonly applied to the preparation of colloidal metals, can also be extended to selenium. When an electric discharge is made to pass under pure water between a platinum anode and a cathode prepared by fusing a small piece of selenium on to platinum foil, colloidal selenium is slowly formed.6 When a dilute solution of selenious anhydride is electrolysed using platinum electrodes, a colloidal solution of selenium and a black cathodic deposit of selenium... 

P roblem 3 How will you prepare the colloidal solutions of the following Arsenic sulphide, ferric hydroxide, gold, sulphur, silicic acid, carbon, iodine, mastic. (Meerut 2000)... 

The applications of colloid solutions are not restricted to paints and clay. They are also to be found in inks, mineral suspensions, pulp and paper making, pharmaceuticals, cosmetic preparations, photographic films, foams, soaps, micelles, polymer solutions and in many biological systems, for example within the cell. Many food products can be considered colloidal systems. For example, milk is an interesting mixture containing over 100 proteins, mainly large casein and whey proteins [6,7]. 

A therapeutic preparation of colloidal silver is known as collargol. Crede s ointment also contains this form of silver, and is employed in the treatment of certain types of septic infection. An astringent antiseptic is prepared by the action of an alkaline tannin solution on aqueous solutions of silver salts.11... 

Fig. 3.6. UV-vis spectra recorded from the as-prepared gold colloidal solution (curve l),the gold colloidal solution after capping with a-CD threaded ODT molecules (curve 2), the chloroform solution after phase transfer of the gold nanoparticles (curve 3), and the aqueous gold colloidal solution after phase transfer of the gold nanoparticles into chloroform (curve 4). The inset is a picture of test tubes containing...

Preparation of Colloidal CdS. Colloidal CdS samples were prepared by precipitation from an aqueous surfactant solution. Aqueous sodium sulfide was slowly added to a stirred solution of cadmium chloride plus surfactant, which produced a clear, yellow-orange colloidal sample of cadmium sulfide. The particle sizes of the colloids were on the order of 250-300 A in radius. There was no observable change in the particle radius upon addition of MV to the CdS colloids. Furthermore, in the absence of surfactant CdS rapidly precipitates from solution. 

The synthesis of mesoporous silica films typically begins with the preparation of precursor solutions. These solutions contain a silica source (typically an alkoxide, although chloride and colloidal precursors can be used), a surfactant molecule used to template the mesostructure, an acid or base catalyst, and solvents. The nanoscale structure is then formed by a cooperative self-assembly of monomeric or partially... 

The preparation of colloidal gold is generally accomplished by reduction of chloroauric acid (HAUCI4) solution with sodium citrate [19-23], which is known to be influenced by several factors such as temperature and reactant concentrations [22]. Alternatively, other reducing agents can be used such as tetrakis(hydroxymethyl)phosphonium chloride (THPC) [24], borohydride [20,25] and toluene [26]. 

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