Iron (III) chloride in the form of a brown solution can be prepared in the laboratory or at home. You will need heat-resistant non-metallic utensils and clean hot water (boiled or distilled). After dissolution and settling, a dark brown liquid is obtained. There are a number of features in the preparation of a ferric chloride solution that you should learn about before you start working with it.
Anhydrous ferric chloride produced by the chemical industry - FeCl3, - dark brown crystals with shades of red, purple, dark green. Molar mass - 162.21 g/mol. The substance melts at a temperature of 307.5 °C, at 500 °C it begins to decompose. A sample of anhydrous s alt dissolves in 100 g of water:
- 74.4g (0°C);
- 99g (25°C);
- 315g (50°C);
- 536g (100°C).
Anhydrous iron (III) chloride is a very hygroscopic substance that quickly attracts moisture from the environment. In air, it interacts with water, turning into yellow crystals of hexahydrate FeCl3 + 6Н2О.The mass fraction of anhydrous ferric chloride in the substance purchased in the distribution network reaches 95%. There is a small amount of ferric chloride FeCl2 and insoluble impurities. The trade name is Ferric Chloride. The substance is fire and explosion-proof, but its solution has a corrosive effect on metal objects.
Iron(III) chloride hexahydrate
In addition to anhydrous, the industry produces crystalline hydrate, in which the mass fraction of ferric chloride (III) is 60%. The substance is a yellow-brown crystalline mass or loose pieces of the same shade. An important distinguishing feature of ferrous and ferric ions is color. The oxidation state of Fe2+ is characterized by a greenish hue, the hexahydrate iron chloride hydrate is a bluish-green substance. In the oxidation state of Fe3+ ions become yellow to brown in color. For a qualitative determination, a solution of ferric chloride is treated with reagents:
- NaOH (a brown precipitate appears Fe(OH)3);
- K4[Fe(CN)6] (KFe precipitate [Fe(CN)6] in blue);
- KCNS, NaCNS (forms iron thiocyanate Fe(CNS)3 red).
How to dilute ferric chloride
Iron (III) chloride in the form of a brown or red solution can be found in the distribution network, prepared in the laboratory or at home. In the latter case, a heat-resistantnon-metallic utensils (glass, plastic, ceramic). Water for dissolving s alt can be taken from the tap. Safer - boiled or distilled. Water heated to 50-70 ° C is placed in a container, and then the substance is poured in small portions. The proportions of ferric chloride and water are 1:3. If you prepare a solution from crystalline hydrate, then less water will be required, because it is contained in crystalline hydrate (40% by weight). The substance is added to the solution little by little, each portion is about 5–10 g. It is not recommended to immediately pour the entire sample due to the rapid nature of the hydration reaction. Do not use metal utensils (spoons, spatulas). S alt must be completely dissolved in warm water, for which the crystals must be mixed well with the liquid. The process is accelerated by the addition of hydrochloric acid (1/10 of the mass of the crystals). After settling for several hours, a precipitate may appear on the bottom due to the presence in the sample and the formation of iron hydroxide during the reaction. Filter the finished dark brown solution and store in a tightly closed plastic container at moderate temperature and out of direct sunlight.
The use of ferric chloride in industry and public utilities. Domestic use
Iron s alts are used in many areas. Trivalent metal chloride is used for water treatment, metals and paint fixing. The substance is used in industrial organic synthesis (catalyst, oxidizing agent). The coagulating properties of the Fe3+ ion are especially appreciated in the treatment of municipal and industrial wastewater. Underthe action of ferric chloride, small insoluble particles of impurities stick together and precipitate. Also, there is a binding of a part of soluble contaminants, which are removed at the treatment plant. Crystal hydrate and anhydrous s alt FeCl3 are used in the etching process of metal printing plates. A substance is added to concrete to strengthen its strength.
Chemical phenomena during etching of boards. Security measures
A popular chemical for PCB etching is ferric chloride. A solution for these purposes is prepared from 0.150 kg of s alt and 0.200 liters of warm water. It contains ions Fe3+, Cl–, and during hydrolysis a brown compound is formed - ferric iron hydroxide. The process follows the scheme: FeCl3 + 3HOH↔ Fe(OH)3 + 3Cl– + 3H +. The disadvantage of this method is the contamination of the board with reaction by-products, which make further etching difficult. S alt itself is a non-volatile substance, but in the process of interaction with water it releases caustic fumes. Work must be carried out outdoors or in a well-ventilated room. Contact with the solution on the skin and mucous membranes leads to irritation and can cause dermatitis. Personal protective equipment (goggles, gloves) should be used. In case of contact with a caustic solution, wash the skin with plenty of water.