Copper color changes

During the oxidation process, leaf color changes from green to copper and a pleasant characteristic aroma develops. In most instances, the proper termination point is deterrnined by the skill of the process supervisor (tea maker) on whose judgment the value of the final product is highly dependent. However, some attempts to control a suitable end point by instmmental techniques have been made. The fermentation step is terrninated by firing (drying). 

Special consideration should be paid to metal complexes such as azomethine pigments (Sec. 2.10). At high temperatures, the yellow copper complex with the chemical constitution 10, incorporated in PVC, will exchange its chelated copper atoms with the metal atoms present in the application medium. Stabilizers containing barium/cadmium or lead produce yellow shades, while dibutyl tin thiogly-colate or other tin compounds produce a brilliant medium red. Color change is slow at low temperatures, but at 160°C the effect is rapid [108],... 

Sulfur can be analyzed by x-ray, GC and GC/MS techniques. Alpha-octacy-closulfur is dissolved in benzene, toluene, or chloroform and analyzed for sulfur by GC using a flame photometric detector or by GC/MS. The characteristic mass ions for its identification are multiples of 32 (i.e. 32, 64, 128, and 256). Sulfur may be identified by mixing a little powder with copper, silver, or mercury at room temperature and identifying the metal sulfide from color change and various instrumental methods. 

Some crystal substances, such as copper sulfate, have water locked into them. This is known as "water of crystallization, and may affect their color. If blue copper sulfate is heated to drive the water away, a whitish powder is formed - "anhydrous (waterless) copper sulfate. This can be used to test for water. When a liquid such as( pure alcohol is poured onto the powder, there is no color change. But if any water has been added to the alcohol, the copper sulfate powder will turn blue again. This is because it has taken some water from the alcohol-water mixture tp re-form the blue crystals. 

Ultramarines are zeolites, though lattice paths are restricted by 0.4 nm diameter channels. The sodium ions can be exchanged for other metal ions (e.g., silver, potassium, lithium, copper). Although this produces marked color change, none of the products have commercial value. 

The copper (I) and silver salts of tetrarodomercuric (II) add, H2[HgI, exhibit color changes with variations in temperature which are reversible in nature. 

Analytical Reagents. Various chelators give specific color changes on combining with different metal salts, such as vanadium, iron, cobalt, nickel, copper, and palladium salts and thus identify the corresponding metal ions [74], Other chelators, such as C.I. Mordant Black 11 (Eriochrome Black T) (2 see Section 3.11.1), are employed as indicators for complexometric titrations. 

Thin films of Pcs have shown to undergo reversible electrochromic changes depending upon their oxidation state [169,250,251], An example of ions detection by a Pc in aqueous solution has also been recently reported. In such a system, the RuPc 32 (Fig. 31a) experiences a dramatic color change due to the Cu(II)-promoted, one-electron oxidation of the macrocycle, thus providing a useful tool for the selective and highly sensitive colorimetric detection of copper(II) ions in neat aqueous solutions (Fig. 31b) [252],... 

In the first experiment with the copper-ammonia complex, you added ammonia to change the color and, later, equal strength HC1 to change it back to blue. Did you require more, less, or an equal number of drops from each to accomplish the color change On the basis of stoichiometry, what was your expectation ... 

Procedure Dissolve 43 grams of crystallized cupric chloride in 100 cc. of water, and filter the solution into a 500-cc. flask. Rinse the filter with 10 cc. of water. Add 100 cc. of 12 N HC1 and then 25 grams of fine copper ribbon. Note the color changes which take place. Suspend a short-stemmed funnel in the neck of the flask to prevent the loss of acid and to exclude air. Heat the mixture with a low flame until it just reaches the boiling point. Then reduce the flame to the smallest possible size and keep the solution just below the boiling point until the color... 

An induction period of 10 to 20 minutes is required before the reaction begins. The induction period is complete when the copper in the 2-liter 3-neck flask looses its sheen and becomes bronze colored and then chocolate colored (watch for these color changes closely). When the chocolate color appears, add the remainder of the contents in the dropping funnel over a period of 20 minutes while constantly stirring of the reaction mixture. After the addition of the contents in the dropping funnel, keep the reaction temperature at 160 Celsius for 20 minutes. After this 20 minutes, remove the heat source and allow the reaction mixture to cool to room temperature. 

The mordanting process had a profound effect on the shade and depth of shade of the natural-dyed wool and silk. This result was expected because the metal ions used in mordanting complex with the dye on the fiber (9). Copper, chromium, and iron mordants gave the greatest color changes. The morphology and chemical structure of the protein fiber also affect the nature of the interaction between the dye... 

Brazilin-dyed wool and silk underwent less darkening and shade change on burial than alizarin-dyed fabrics, and they became darker and more nearly like the shade of the mordanted-dyed samples. The mordanted-brazilin-dyed samples showed much less darkening and in most cases showed less color change than unmordanted-dyed samples on burial. Copper-mordanted wool and silk underwent the smallest degree of color change due to burial. 

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