Silver plating process is widely used in electronics, military industry, musical instruments and jewelry industries. The content of silver in the plating solution has a great influence on the quality of the coating. The commonly used silver content determination methods have serious environmental pollution. Potassium. The surrounding environment of some laboratories does not allow the emission of harmful gases, making silver analysis impossible. This article uses the drying gravimetric method to determine the silver content, and the accuracy is close to the gravimetric method. The method is simple and does not pollute the environment. 01 Method summary Use potassium persulfate to destroy cyanide, use sodium chloride to precipitate silver into silver chloride, and measure the silver content by drying gravimetric method after filtration. 02 Instruments and Reagents Analytical balance (one in ten thousand); oven; dryer; potassium persulfate (solid); sodium chloride (solid); absolute ethanol. 03 Analysis Method Use a pipette to draw 5 mL of plating solution into a 300 mL beaker, add about 20 mL of water, and add 2 to 3 g of potassium persulfate. Cover the watch glass and heat it to a boil. After holding on the electric furnace for a few minutes, the solution turned into a turbid yellowish color. Add about 50mL of water, add 2-3g of sodium chloride, the solution will turn to milky white, and then heat to a slight boiling point. The solution is kept warm for about 10 minutes with the waste heat of the electric furnace, and the silver chloride precipitate is flocculated at the bottom of the cup. Take two medium-speed qualitative filter papers and place them on both sides of the analytical balance, and use the trimming method to make the two filter papers the same quality. Two pieces of filter paper overlap, fold it and place it on the funnel to filter while it is hot. Wash with hot water, wash until the filtrate turns from slightly acidic to near-neutral (extensive test paper), and finally wash once with absolute ethanol. Carefully separate the two filter papers, dry them in an oven at 105°C for 30 minutes, and cool them to room temperature in a desiccator. Weigh with an analytical balance, put the filter paper with sediment on the carrier tray, and put the blank filter paper on the weight tray. Weigh the sediment mass. 04Calculation  In the formula: m is the mass of precipitation, g 0.1753 is MAg/MAgCl. 05 Notes 1) Ammonium persulfate should not be used to destroy cyanide, because the presence of a large amount of NH4+ ions affects the precipitation of silver chloride, making the result low. 2) After potassium persulfate destroys cyanide, the solution should be weakly acidic. If the silver plating solution contains too much alkaline substances such as cyanide, and it still cannot be acidic after boiling, add 1g potassium persulfate and heat again to complete the cyanide breaking reaction. 3) The cyanide breaking and precipitation reaction can be heated to a slight boiling point and the watch glass is covered, otherwise gas such as HCl will overflow and pollute the air. The effect of using a temperature-regulating electric stove is better. |
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