Steps for Creating a Gold Plating Solution
Gold Electroplating is a method of depositing a thin layer of gold onto the surface of another metal. Gold plating solutions are the chemical component needed for gold electroplating to take place.
Gold plating uses an alkaline gold plating solution to deposit gold onto a metal substrate by electrolysis. Traditionally, such a solution is prepared using extremely poisonous cyanide compounds which are reasonably restricted because they are poisonous and must be dispensed in a very restrictive manner. We will be using publicly available chemicals, which are not as toxic as the cyanide compounds but can still be poisonous.
Gold plating solutions should not be done unsupervised as some components can be extremely poisonous. This blog will give instructions to make an alkaline gold plating solution that can deposit gold by electrolysis.
Below are the steps to be followed to make a gold plating solution;
Prepare your Nitric Acid:
If you already have nitric acid at a concentration of 50% or above, you can skip this step. Otherwise, here is how to make yours.
Gold can either be dissolved using aqua regia or royal water, which is nitric acid, combined with hydrochloric acid at a ratio of 1:3. Hydrochloric acid is commercially available as muriatic acid. Since nitric acid is restricted, it must be prepared using available chemicals.
There are quite a few ways to make nitric acid under laboratory conditions. We will be showing two ways.
One way of preparing nitric acid is by catalyzing a reaction of sodium nitrate with sulphuric acid and distilling the mixture to reduce acid to a concentration higher than 90%. At this concentration level, nitric acid becomes highly corrosive and will produce fumes of toxic nitrogen dioxide gas.
Another way which less dangerous is concentrating very dilute nitric acid that is commercially available for the public. You can use fractional distillation to concentrate nitric acid from 30% to 50% concentration.
Making the Gold Chloride
Gold chloride can be made by dissolving gold in aqua regia. These two components’ reaction produces toxic fumes, so the process is conducted under a fume hood or outdoors. Gold will dissolve in around 20 minutes at room temperature. The reaction will be a solution of dissolved gold, copper compounds, and solid crystals of silver salts. Filtration will separate the liquid from the solids. Gold will then be precipitated out of the solution by adding a sodium metabisulfite solution. The final step will be the separation of the solid gold to be dissolved again in aqua regia. The acid needs to be evaporated at 120°C to obtain the red gold chloride crystals.
Making the Gold Plating Solution
For this final step, a strongly alkaline solution of gold chloride and potassium ferrocyanide is needed. The solution and the electric current will allow gold to be deposited over the surface of another metal. This solution contains gold cyanide ions, which are extremely poisonous. Under no circumstances can the solution be mixed with acids, as it will release hydrogen cyanide gas. Which is so toxic, words are insufficient.
Making gold plating solution is no business of a novice, please exercise caution.