SECTION II. INORGANIC CHEMISTRY
8.
Metallic elements and their compounds. Metals
8.5. Ferum
8.5.2. Iron Compounds ( III)
Ferum (III) oxide Fe 2 О 3 - the most stable natural spore of Iron, a brown powder, has atomic crystal lattices, does not dissolve in water. Ferum (III) oxide exhibits weak amphoteric properties (with a predominance of basic ones) - it easily reacts with acids:
Shows weak acidic properties of the alloy with alkalis and carbonates of alkali metal elements:
Sodium ferrite formed in an aqueous solution is completely decomposed by water (hydrolyzes):
Reducing agents reduce iron (III) oxide to iron:
Extraction of ferrum (III) oxide Ferum (III) oxide is obtained by thermal decomposition of ferum (III) hydroxide or ferrum (III) nitrate:
It is also obtained during the roasting of pyrite. FeS 2:
Ferrum (III) hydroxide Fe (OH) 3 1 - water-insoluble brown substance with weak amphoteric properties (with a predominance of basic ones):
Reactions with concentrated alkali solutions proceed only with prolonged heating. In this case, a stable hydroxocomplex is formed K 3 [Fe (OH) 6]:
Extraction of ferrum (III) hydroxide
Ferrum (III) hydroxide is obtained from water-soluble salts of Iron (III) by their interaction with alkalis:
Iron (III) salts, formed by strong acids, are readily soluble in water and can form crystalline hydrates: Fe (NO 3) 3 9H 2 O, Fe 2 (S O 4) 3 9H 2 O, FeCl 3 6H 2 O. Salts Fe 3+ hydrolyzed by cation:
Iron (III) compounds exhibit oxidizing properties, and therefore, when interacting with reducing agents Fe 3+ is converted to Fe 2+:
Qualitative ion reactions Fe 3+:
1. The reagent is potassium hexacyanoferrate (II) (yellow blood salt). A dark blue precipitate is formed - Prussian blue:
2. The reagent is potassium (or ammonium) thiocyanate. Blood-red ferrum (III) thiocyanate is formed:
Use of iron and iron compounds
Ferrous metallurgy (production of iron and its alloys) accounts for 90% of the world metallurgy. Ferrous metallurgy is the basis for the development of many industries: mechanical engineering takes a third of ferrous metal, construction (as a structural material, for the manufacture of reinforced concrete) - a quarter; a significant part is also used in transport.
Iron-based alloys (ferromagnetic) are used in electrical engineering in the production of transformers and electric motors.
Ferum (II) oxide FeO is one of the components of ceramics, a pigment for paints and heat-resistant enamel.
Ferum (III) oxide Fe 2 О 3 ocher is used as a mineral paint.
Magnetite Fe 3 O 4 used in the manufacture of hard drives, and ultrafine powder - as a toner in black and white laser printers.
Iron vitriol (iron (II) sulfate heptahydrate) FeS B 4 7H 2 O is used to combat plant pests, in the production of mineral paints, in construction.
Ferrum (III) chloride is used for water purification, as a mordant for dyeing fabrics, in radio engineering for etching printed circuit boards, in organic synthesis as a catalyst.
Aqueous solutions FeCl 2, FeCl 3, FeS B 4 is used as coagulants to purify water for industrial plants.
Ferrum (III) nitrate nonahidrate Fe (N О 3) 3 9H 2 B is used as a mordant in the process of dyeing fabrics.
1 As in the case of Fe 3 O 4, substances with the formula Fe (OH ) 3 does not exist. When you try to get it, you get Fe 2 O 3 n H 2 O or FeO (OH ) - ferrum (III) metahidroxide.
Qualitative reactions for iron (III)
Iron ions (III ) in solution can be determined using qualitative reactions. Let's carry out some of them. Take for the experiment a solution of ferric chloride ( III).
1. III) - reaction with alkali.
If the solution contains iron ions ( III ), iron hydroxide is formed ( III ) Fe (OH) 3. The base is insoluble in water and is brown in color. (Iron hydroxide ( II ) Fe (OH) 2. - also insoluble, but gray-green). A brown precipitate indicates the presence of iron ions in the initial solution ( III).
FeCl 3 + 3 NaOH = Fe (OH) 3 ↓ + 3 NaCl
2. A qualitative reaction to the iron ion ( III ) - reaction with yellow blood salt.
Yellow blood salt is potassium hexacyanoferrateK 4 [ Fe( CN) 6]. (To determine iron (II) use red blood saltK 3 [ Fe( CN) 6]). To a portion of the iron chloride solution, a solution of yellow blood salt. The blue Prussian blue precipitate * indicates the presence of ferric ions in the initial solution.
3 TO 4 +4 FeCl 3 = K Fe ) ↓ + 12 KCl
3. A qualitative reaction to the iron ion ( III ) - reaction with potassium thiocyanate.
First, we dilute the test solution - otherwise we will not see the expected color. In the presence of an iron ion (III) when potassium thiocyanate is added, a red substance is formed. This is iron thiocyanate (III). Rodanid from the Greek "rodeos" is red.
FeCl 3 + 3 KCNS= Fe( CNS) 3 + 3 KCl
Prussian blue was obtained by accident at the beginning of the 18th century in Berlin dyeing by master Diesbach. Disbach bought an unusual potash (potassium carbonate) from a merchant: the solution of this potash, when added with iron salts, turned out to be blue. When checking the potash, it turned out that it was calcined with bovine blood. The dye was found to be suitable for fabrics: bright, long-lasting and inexpensive. Soon the recipe for obtaining paint became known: potash was fused with dried animal blood and iron filings. Leaching of this alloy produced yellow blood salt. Prussian blue is now used to produce printing ink and tint polymers. .
Equipment: flasks, pipette.
Safety engineering ... Observe the rules for handling alkali solutions and solutions hexacyanoferrates. Avoid contact of hexacyanoferrate solutions with concentrated acids.
Experience setting - Elena Makhinenko, text- Ph.D. Pavel Bespalov.
FeCl 3 Mol. v. 162.21
FeCl 3 · 6H 2 O Mol. v. 270.30
PropertiesAnhydrous preparation - black-brown crystalline crusts or large lamellar crystals of the hexagonal system, garnet-red in transmitted light and green with a metallic sheen in reflected light. Pl. 2.898 g / cm 3. At 309 ° C, the drug melts into a mobile red liquid, boiling at 319 ° C with partial decomposition. However, already at 100 ° C, FeCl 3 noticeably volatilizes. In the air, it greedily attracts moisture and spreads. Let's very well dissolve in water (47.9% at 20 ° С, with significant heat release), we will well dissolve in ethyl alcohol, glycerin, diethyl ether and acetone, we will slightly dissolve in benzene. A solution of FeCl 3 in some organic solvents in the light is reduced to FeCl 2, while the solvent is oxidized or chlorinated, for example, FeCl 3 and ethyl alcohol form FeCl 2 and acetaldehyde.
Crystalline hydrate FeCl 3 · 6H 2 O - red-brown, moist to the touch, rather soft crystalline mass. Sometimes crystallizes from aqueous solutions in hemispherical aggregates of a radiant-crystalline structure. It spreads quickly in humid air. T. pl. 37 ° C; evaporates already at 100 ° C. Above 250 ° C decomposes into Fe 2 O 3, FeCl 3, Cl 2 and HCl. The drug is very soluble in water, soluble in ethyl alcohol, glycerin and diethyl ether.
Preparation of anhydrous FeCl 3
In a tube 4 made of refractory glass (Fig. 20) is placed 70 g of not too thin iron wire, dried at 110 ° C and cooled in a desiccator (it is even better to use Armco iron shavings). This tube is connected with a rubber stopper to a wide-mouth jar 5 with a capacity of 1 liter. The other end of the tube 4 is connected to a chlorine drying system, consisting of a wash bottle 1 with conc. H 2 SO 4 and tube 3 with P 2 O 5; flask 2 is a safety bottle in case of clogging of tube 4 with sublimated FeCl 3. air is displaced from the device with chlorine and tube 4 is heated with a burner flame, maintaining the flow of chlorine so that only rare gas bubbles pass through the absorption flask 8 with NaOH solution.
The resulting FeCl 3 sublimes into the jar 5. Immediately after the end of the reaction, jar 5 is disconnected and immediately closed with a previously prepared ground stopper.
Yield ~ 200 g (almost 100%). For final purification, FeCl 3 can be re-sublimated in a stream of chlorine, but even without this, the preparation is quite suitable for most purposes.
Preparation of crystalline hydrate FeCl 3 6H 2 O
First, a solution of FeCl 2 is obtained by dissolving metallic iron in hydrochloric acid, and then it is oxidized with chlorine:
Fe + 2HCl = FeCl 2 + H 2 b
2FeCl 2 + Cl 2 = 2FeCl 3
Work should be carried out under traction.
Into a 1 L conical flask containing 740 ml of 25% hydrochloric acid (analytical grade), add in small portions 120 g of pure iron shavings ( flammable - hydrogen!). When the stormy period of the reaction is over, the solution is heated to 80-90 ° C, filtered and the resulting FeCl 2 solution (about 700 ml) is chlorinated in the apparatus shown in Fig. 21.
The FeCl 2 solution from the pressure flask 1 is fed into the absorber 3 at a rate of 5 ml / min. The absorber is a column 100 cm high and 4 cm in diameter, filled with scraps of glass tubes 6–8 mm in diameter and 3 cm long. Chlorine is introduced into the column from below at a rate of 6 l / min. The gas is preliminarily sucked for flushing through a bottle 2 with water. Excess chlorine through the Tishchenko 4 bottle is taken away into the draft.
The chlorinated solution flows from the column through a siphon into the receiver 5. The process must be adjusted so that the oxidation is complete (the liquid sample should not give a blue precipitate with the K 3 Fe (CN) 6 solution).
The solution from receiver 5 is transferred into a porcelain dish and evaporated at 90-95 ° C exactly to pl. 1.659 (at 25 ° C). Failure to comply with this condition will lead to the fact that either the solution will not crystallize, or another, metastable crystalline hydrate will be released. The remaining solution is cooled to 4 ° C, stirring occasionally. The separated crystals are sucked off on a Buchner funnel and transferred to a jar with a ground stopper.
Yield 500 g (66% for iron). The resulting preparation usually corresponds to a reagent of analytical grade, but sometimes it is possible to obtain preparation x. h.
General information on the hydrolysis of iron (III) chloride
DEFINITION
Iron (III) chloride- a medium salt formed by a weak base - iron (III) hydroxide (Fe (OH) 3) and a strong acid - hydrochloric (hydrochloric) (HCl). Formula - FeCl 3.
It is a substance with a crystal structure of black-brown, dark red, violet or green, depending on the angle of the incident light. The molar mass is 162 g / mol.
Rice. 1. Chloride of iron (II). Appearance.
Iron (III) chloride hydrolysis
Hydrolyzed by cation. The nature of the environment is sour. The second and third stages are theoretically possible. The hydrolysis equation is as follows:
First stage:
FeCl 3 ↔ Fe 3+ + 3Cl - (salt dissociation);
Fe 3+ + HOH ↔ FeOH 2+ + H + (cation hydrolysis);
Fe 3+ + 3Cl - + HOH ↔ FeOH 2+ + 3Cl - + H + (ionic equation);
FeCl 3 + H 2 O ↔ Fe (OH) Cl 2 + HCl (molecular equation).
Second stage:
Fe (OH) Cl 2 ↔ FeOH 2+ + 2Cl - (salt dissociation);
FeOH 2+ + HOH ↔ Fe (OH) 2 + + H + (cation hydrolysis);
FeOH 2+ + 2Cl - + HOH ↔ Fe (OH) 2 + + 2Cl - + H + (ionic equation);
Fe (OH) Cl 2 + H 2 O ↔ Fe (OH) 2 Cl + HCl (molecular equation).
Third step:
Fe (OH) 2 Cl ↔ Fe (OH) 2 + + Cl - (salt dissociation);
Fe (OH) 2 + + HOH ↔ Fe (OH) 3 ↓ + H + (cation hydrolysis);
Fe (OH) 2 + + Cl - + HOH ↔ Fe (OH) 3 ↓ + Cl - + H + (ionic equation);
Fe (OH) 2 Cl + H 2 O ↔ Fe (OH) 3 ↓ + HCl (molecular equation).
Examples of problem solving
EXAMPLE 1
| Exercise | A solution of iron (III) chloride was added to a solution of sodium hydroxide weighing 150 g (ω = 10%), resulting in a brown precipitate - iron (III) hydroxide. Determine its mass. |
| Solution | Let us write the reaction equation for the interaction of sodium hydroxide and iron (III) chloride: 3NaOH + FeCl 3 = Fe (OH) 3 ↓ + 3NaCl. Calculate the mass of the sodium hydroxide solute in the solution: ω = m solute / m solution × 100%; m solute = m solution × ω / 100%; m solute (NaOH) = m solution (NaOH) × ω (NaOH) / 100%; m solute (NaOH) = 150 × 10/100% = 15g. Let's find the amount of sodium hydroxide substance (molar mass - 40 g / mol): υ (NaOH) = m solute (NaOH) / M (NaOH) = 15/40 = 0.375 mol. According to the reaction equation υ (Fe (OH) 3) = 3 × υ (NaOH) = 3 × 0.375 = 1.125 mol. Then we calculate the mass of the precipitate of iron (III) hydroxide (molar mass - 107 g / mol): m (Fe (OH) 3) = υ (Fe (OH) 3) × M (Fe (OH) 3) = 1.125 × 107 = 120.375g. |
| Answer | The mass of iron (III) hydroxide is 120.375 g. |
EXAMPLE 2
| Exercise | Calculate the mass fractions of each of the elements that make up iron (III) chloride. |
| Solution | The mass fraction of an element is calculated as follows: ω (X) = n × Ar (X) / Mr × 100%, those. the ratio of the relative atomic mass, taking into account the number of atoms that make up a substance, to the molecular weight of this substance, expressed as a percentage. The molecular weight of iron (III) chloride is 162. Let's calculate the mass fractions of elements: iron : ω (Fe) = n × Ar (Fe) / Mr (FeCl 3) × 100%; ω (Fe) = 1 × 56/162 × 100% = 34.27%. chlorine: ω (Cl) = n × Ar (Cl) / Mr (FeCl 3) × 100%; ω (Cl) = 3 × 35.5 / 162 × 100% = 65.73%. To check the correctness of the calculation, by adding the obtained mass fractions, we should get 100%: ω (Fe) + ω (Cl) = 34.27 +65.73 = 100%. |
| Answer | The mass fraction of iron is 34.27%, the mass fraction of chlorine is 65.73. |
Iron (III) chloride solution can be prepared in the laboratory or at home. You will need heat resistant non-metallic cookware and clean hot or distilled). After dissolving and settling, a dark brown liquid is obtained. There are a number of features of the preparation of a solution of ferric chloride, which should be learned about before starting to work with it.
Ferric chloride
Anhydrous ferric chloride produced by the chemical industry - FeCl 3 - crystals of dark brown color with shades of red, purple, dark green. The molar mass is 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 salt dissolves in 100 g of water:
- 74.4 g (0 ° C);
- 99 g (25 ° C);
- 315 g (50 ° C);
- 536 g (100 ° C).
Anhydrous (III) - a very hygroscopic substance, quickly attracts moisture from environment... In air, interacts with water, turning into yellow crystals of hexahydrate FeCl 3 + 6H 2 O. The mass fraction of anhydrous ferric chloride in the substance purchased in the trade network reaches 95%. There is a small amount of ferric chloride FeCl 2 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 lumps of the same shade. An important distinguishing feature of ferrous and ferric ions is their color. The oxidation state of Fe 2+ is characterized by greenish tint, ferric chloride hexahydrate is a bluish-green substance. In the Fe 3+ oxidation state, the ions acquire a color ranging from yellow to brown. For a qualitative determination, reagents act on a solution of ferric chloride:
- NaOH (a brown precipitate Fe (OH) 3 appears);
- K 4 (a blue KFe precipitate appears);
- KCNS, NaCNS (red iron thiocyanate Fe (CNS) 3 is formed).
How to dilute ferric chloride
Iron (III) chloride in the form of a brown or red solution can be found on the market, prepared in the laboratory or at home. In the latter case, you will definitely need heat-resistant non-metallic dishes (glass, plastic, ceramic). Water for dissolving salt 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% of the mass). The substance is added to the solution little by little, each portion is about 5-10 g. It is not recommended to pour the entire sample at once due to the violent nature of the hydration reaction. Do not use metal utensils (spoons, spatulas). The salt must completely dissolve in warm water, for which the crystals must be well mixed with the liquid. The process is accelerated by the addition of hydrochloric acid (1/10 of the mass of crystals). After settling for several hours, a sediment may appear on the bottom due to the presence of iron hydroxide in the sample and the formation of iron hydroxide during the reaction. The dark brown solution should be filtered and stored in a tightly closed plastic container at moderate temperatures and out of direct sunlight.
The use of ferric chloride in industry and municipal services. Household use
Iron salts have many uses. Trivalent metal chloride is used to treat water, metals, and paint curing. The substance is used in industrial organic synthesis (catalyst, oxidizing agent). The coagulating properties of the Fe 3+ ion in the treatment of municipal and industrial effluents are especially appreciated. Under the 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. Crystalline hydrate and anhydrous FeCl 3 salt are used in etching processes for metal printing plates. A substance is added to concrete to strengthen its strength.
Chemical phenomena during etching of boards. Security measures
Popular Chemical substance for etching printed circuit boards - ferric chloride. A solution for these purposes is prepared from 0.150 kg of salt and 0.200 liters of warm water. It contains ions Fe 3+, Cl -, and hydrolysis forms a brown compound - ferric hydroxide. The process goes according to the scheme: FeCl 3 + 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. Salt itself is a non-volatile substance, but in the process of interaction with water, it releases corrosive vapors. Work must be done 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 caustic solution, rinse the skin with plenty of water.
