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How And Why Nitric Acid Is Used
How And Why Nitric Acid Is Used For Etching
Etching is a process in which textures or graphics are bitten (etched) into metal by using various mordants or etchants (e.g. acids). It involves multiple steps in which a metal plate is first covered with an acid-resistant coating (ground). Texture or design is then pressed into the ground that exposes the metal in these areas. Metal plate is then submerged in an acid solution until the desired degree of etching is achieved. Common etchants include nitric acid, ferric chloride, hydrochloric acid, and copper sulfate. Nitric acid is widely used for etching copper and brass. It is also used for etching steel and stainless steel. Metals used for jewelry, like silver, can also be etched with nitric acid to get results better than other etchants. Nitric acid for etching commonly comes as concentrated 67-70% strength that is extremely harmful and its handling requires safety gear. One common recipe for a nitric acid solution for etching is 3 parts water to 1 part concentrated nitric acid. Solutions having varying (5, 8, or 10 water to 1 nitric acid) strengths of nitric acid can also be used depending upon the type of metal and level of etching. In all cases, it's extremely important to add nitric acid slowly to the water rather than the other way around. This is because mixing nitric and water releases intense heat that can sometimes lead to boiling of solution. This requires protective clothing (goggles, rubber gloves, apron, etc.) and reasonable care during mixing.
How And Why Nitric Acid Is Used For Cleaning Stainless Steel
Stainless steels are highly resistant to corrosion, however, they can undergo surface damage under long-term harsh environments without routine cleaning and maintenance. Moreover, the cleanliness of stainless steel is essential for applications like foods, chemicals, and pharmaceuticals. Routine cleaning of stainless steel can be simply done using soap or a mild detergent in warm water. Any soft cloth or fine nylon sponge can be used followed by a rinse and drying with a soft cloth. Heavier staining like heat discoloration, corrosion, and rust stains require cleaning with an acid solution. Nitric acid is the only mineral acid that is safe for cleaning stainless steel. A commonly used solution for this purpose constitutes 1 part of concentrated nitric acid added to 9 parts water. This is a weak solution of nitric acid known as 10% solution and may be obtained from most chemists. Rubber gloves and safety goggles should be used when working with nitric acid and its solutions. Glass containers are most suitable for mixing and storing nitric acid solutions. Stainless steel cleaning with nitric acid often requires thorough washing with plenty of water and the spent acid should be drained with thorough flushing.
How And Why Nitric Acid Is Used For Cleaning Glassware
Clean laboratory glassware forms the basis of successful chemical analysis. Contaminated or dirty glassware can lead to inaccurate results and loss of valuable time. Cleaning glassware is tricky, just because something looks clean it is not necessarily clean. A simple way to confirm the cleanliness of glassware is by performing a surface wetting test. In this test, distilled water is used to wet the surface of the glass. Water will uniformly wet the clean surface but will form beads on the walls of dirty glassware. This test by itself should not, however, be used as the sole criterion for clean glass. The best time to clean glassware is just after use. One usual practice is to start with the gentlest method which is to scrape off any residue and use brushes with normal soaps or detergents. If basic cleaning doesn’t get the job done, a next step could be to soak in a gentle solvent with heating or mild agitation. Occasionally, more aggressive cleaning methods may be necessary when laboratory glassware is contaminated with chemicals or stains. For this purpose, along with organic solvents and bases, acids and their diluted solutions are also used. Nitric acid is one of the commonly used acids that is used in varying concentrations for cleaning glassware. For example, new glassware is soaked in a 1-2% solution of nitric acid for several hours before conducting sensitive chemical tests. Likewise, acid baths, a suitable container that holds up to several liters of acid, often use 10% nitric acid solution (1 part of concentrated nitric acid added to 9 parts water) to clean glassware. In some cases, 1 part of concentrated nitric acid is mixed with 3 parts of concentrated hydrochloric acid to form aqua regia. It is an aqueous-based acidic oxidizing solution for cleaning glassware contaminated with strong organic compounds and metal particles. Aqua regia and similar solutions are hazardous and should be used while wearing personal protective gear.
How And Why Nitric Acid Is Used For Silver Refining And Purifying
Silver has long been valued for its white metallic luster, its ability to be readily worked, and its corrosion resistance. Silver refining by using acid is a simple process requiring almost no investment in time, equipment, or supplies. It can be done by almost anybody. The most common refining method uses 67-70% nitric acid to dissolve silver, which is precipitated as silver chloride by the addition of un-iodized table salt. Nitric acid, along with dissolved silver and other base metals, is separated from gold or other metals. The sludge of contaminants settled at the bottom and is separated by pouring the contents into another container. Silver salt is turned back into silver by adding silver precipitant crystals and nitric acid is poured off. Purified silver is washed with water and dried afterward. This process, however, requires the use of concentrated nitric acid that produces corrosive fumes. A 4-5% nitric acid solution formed by adding 3 to 4 parts of distilled water and 1 part of concentrated nitric acid can also be used for the purification of silver. When done properly, this procedure enables silver recovery of up to 99.95%. The refining and purifying procedures, however, must be done out-of-doors with protective clothing (goggles, rubber gloves, apron, etc.) and reasonable care must be taken while draining spent acid.
How And Why Nitric Acid Is Used For Inductively Coupled Plasma Mass Spectrometry (ICP-MS)
Inductively coupled plasma mass spectrometry (ICP-MS) is an elemental analysis technology. It can detect a majority of the elements in the periodic table in trace (milligram to nanogram) quantities. ICP-MS uses an inductively coupled plasma to ionize the sample forming detectable atomic and small polyatomic ions. It is used in a variety of industries such as environmental monitoring, geochemical analysis, metallurgy, pharmaceutical analysis, and clinical research. Samples for the ICP-MS study are relatively simple to prepare. Biological samples are usually diluted or thermally digested before analysis. Depending on the sample type, usually, 5 mL of reagent is added to a test tube along with 10–500 microliters of sample. This mixture is then vortexed until mixed well and then loaded for analysis. Common diluents used in the ICP-MS study are dilute acid (e.g. nitric acid, hydrochloric acid) or alkali (e.g. ammonium hydroxide) solutions. Among acids, nitric acid (1% to 5%) is preferred for metal dissolution and stabilization of ICP-MS analysis. This is because all nitrate salts are soluble in water. Using sulfuric acid or hydrochloric acid will produce sulfate or chloride salts. Some metal sulfates and chlorides are not very soluble in water limiting their application in sample preparation. ICP-MS analysis requires high purity nitric acid for sensitive determination of elements in trace concentration. The presence of impurities in nitric acid will strongly influence the trace analysis. Therefore, the selection of a suitable grade is essential for reliable results.
How And Why Nitric Acid Is Used For Gold Recovery
Gold is a valuable metal with sources that are not only limited but also rarely pure. Either as freshly mined ore or in jewelry in refined form, gold often contains contaminants, unwanted minerals, and other metals. Gold rings, chains, and necklaces are often blends of gold with a percentage of silver and copper. While various procedures can purify gold, today nitric acid combined with hydrochloric acid is a convenient method for gold recovery. This combination produces aqua regia, a corrosive reagent that is used in gold refining processes. It is made by mixing nitric acid and hydrochloric acid in 1:3 ratios. Gold refining with aqua regia involves steps such as dissolving, filtration, and retrieval of gold from the substances bonded to it. Aqua regia refinement can also be used to recover 99.95% pure gold from smelted gold. Smelt gold, even though purer than the original ore, contains impurities such as silver, copper, and platinum. One has to be very careful when handling the various substances involved in the stages of the gold refining and retrieval process. Parting, a commercial-scale method, is also used for separating silver and gold. It is performed to dissolve metallic silver from gold alloys of less than 30% gold by boiling with 30-40% nitric acid solution. Nitric acid is not able to (fully) extract silver and other impurities from an alloy with a content of gold greater than 30%. It only reacts with silver and impurities resulting in pure gold (very close to 99.5% pure) upon completion of the process.
How And Why Nitric Acid Is Used For Gold Testing
Gold testing is essential to avoid buying gold that is hallmarked, but not authentic. A few scientific methods can precisely determine karat gold purity. These include destructive (fire assay) and non-destructive (X-ray fluorescence) methods. But costly equipment and special procedures make it difficult to use them in routine gold testing. Acid test, a simpler and cheaper method, can be conveniently used for determining gold purity in jewelry. Gold testing by using nitric acid is relatively nondestructive to jewelry and offers quick results. Nitric acid is freely available and testing usually takes a few minutes. First, a gold-colored item is rubbed on a black stone leaving visible marks. The mark is tested by applying nitric acid, which dissolves the mark of any item that is not gold. If the mark remains, it is tested by applying aqua regia, a mixture of concentrated nitric acid and hydrochloric acid in 1:3 ratios. Aqua regia is used to test higher karat purity through the process of comparison and elimination. If the mark is removed, then this test dissolves the gold, proving the item to be genuine gold. The purer the gold (e.g. 24k), the stronger the acid required to dissolve it. Gold testing can be routinely done by using an acid testing kit. Such gold testing incorporates the use of acids, so paying close attention to personal safety and safety gear (rubber gloves, safety goggles, apron) is a must. Nitric acid gold testing, though reasonably accurate at authenticating gold, poses some limitations. First, it only tests the surface layers, and, secondly, the test is limited in accuracy to rough karat counts such as 10k, 14k, 18k, etc. The acid is pre-made to test for a certain karat and one has to watch out for false positives.