Experiments with silver

Silver nitrate solution is often used to determine hydrochloric acid or chlorides. Since silver nitrate is not easy to obtain, we can obtain a small amount by dissolving a piece of an old silver object (a silver coin, a piece of a spoon, jewelry, or chain). Silver objects, however, are not made of pure metal, but of alloys, which often contain copper as a second component. It gives the metal greater hardness, and at a high content, it promotes stretching. To obtain pure silver nitrate, both metals must be separated.

Silver nitrate solution is often used to determine hydrochloric acid or chlorides

First, let's dissolve the metal in pure nitric acid diluted with water in a 1:1 ratio. This produces a large amount of nitrogen oxides. (The experiment should be carried out only under draft or in the open air. Do not inhale gases!) If the reaction slows down, slightly heat the solution to completely dissolve. Due to the presence of copper, the solution will turn blue-green. Dilute the finished solution with a threefold amount of distilled water and filter it into a beaker.

In the meantime, we will prepare a strong solution of sodium chloride in distilled water and add it to the nitric acid solution of the metal until no flakes of precipitate form. Next, for 10 minutes, we will heat the liquid in a water bath, while a very thin precipitate will enlarge and large flakes will fall out. These flakes are composed of silver chloride with a solubility of 1,5 mg per liter of water. After filtering, separate the precipitate from the copper-containing solution and rinse it many times with warm water. The last wash water should not give a blue coloration when interacting with ammonia!

Now let's reduce the silver chloride to pure metallic silver. Place the sediment, along with twice the amount (by weight) of the pieces of zinc or aluminum, in a beaker and add dilute (10%) hydrochloric acid. Zinc or aluminum will dissolve with the evolution of hydrogen, and at the same time silver chloride is reduced to silver - a gray metal powder. We filter this powder and dissolve (outdoors or under a draft) in pure nitric acid. The latter should in no case contain hydrochloric acid, otherwise silver chloride will form again. Dilute the solution with distilled water and evaporate, resulting in solid silver nitrate. You can save and nitric acid solution and use it as a reagent. For all detection reactions, highly diluted solutions are used, but only distilled water should be used for dilution, since tap water contains traces of chlorides and gives turbidity with the silver nitrate solution.

Solid silver nitrate and its concentrated solutions are highly corrosive; therefore, salt used to be called a hellish stone. Strong solutions leave black spots on the skin that are very difficult to remove, they result from the reduction of salt to finely dispersed silver.

To detect silver in any metal product, we cut off a small amount of metal in an inconspicuous place and dissolve it in pure nitric acid (without admixture of hydrochloric acid). If a precipitate forms or the solution becomes cloudy, then either the nitric acid was contaminated, or the sample contained tin, antimony, or bismuth.

As with copper identification, detection is interfered with by the simultaneous presence of certain metals in the sample. If, for example, the sample contains lead, mercury, aluminum or zinc, then the precipitate of silver chloride does not completely dissolve in ammonia. The analyst must then conduct a chemical separation.

When hydrogen sulfide water is added, black silver sulfide precipitates from silver salt solutions. It also forms if silver is in an atmosphere containing traces of sulfur compounds. This happens, for example, in the air of industrial areas or in the kitchen, where a gas stove is on. Silver objects become brown or black over time. It can be removed with dilute acids, ammonia, or a commercially available silver cleaner.