a) Reaction with potassium hexacyanoferrate (II) - potassium ferrocyanide K 4 (pharmacopoeial). Fe 3+ cations in an acidic environment react with potassium ferrocyanide to form a dark blue precipitate of “Prussian blue” - a complex compound of iron (III) hexacyanoferrate (II) Fe 4 3 X H 2 O with a variable number of water molecules. It has been shown that, depending on the precipitation conditions, the “Prussian blue” precipitate, like the “Turnboole blue” precipitate (see above), entrains other cations from the solution, so that its composition changes and can correspond to the formula KFe 3+:
Fe 3+ + K + + 4- →FeK↓
The reaction is specific. The reaction is interfered with by oxidizing agents that oxidize the reagent.
Executing the reaction. Add 2-3 drops of an iron (III) salt solution to a test tube, add 1-2 drops of an HCI solution and 2 drops of a K4 solution. The solution turns blue and a dark blue Prussian blue precipitate forms.
b) Reaction with thiocyanate ions (pharmacopoeial). Fe 3+ salts form red iron (III) thiocyanate. The reaction is carried out in an acidic environment. The composition of the resulting complex is not constant and, depending on the concentration of Fe 3+ and SCN ions, can range from 2+ to 3-. This reaction is sometimes used for the detection of iron in combination with reaction 1, with potassium hexacyanoferrate(II). First, by adding NH 4 SCN, a red iron thiocyanate complex is obtained, which is then converted to a blue precipitate of potassium iron (III) hexacyanoferrate (II) by the addition of potassium hexacyanoferrate (II):
Fe 3+ + 3SCN - →Fe(SCN) 3
The sensitivity of the reaction is 0.25 µg. The reaction is hindered by anions of oxygen acids (phosphoric, arsenic, etc.), fluorides that form compounds with Fe 3+ and NO 2, which gives SCN - the red compound NOSCN.
Executing the reaction. Add 3-4 drops of an iron (III) salt solution to a test tube and add 2-3 drops of a solution of ammonium thiocyanate NH4NCS or potassium thiocyanate KNCS. The solution turns blue.
c) Reaction with sodium sulfide (pharmacopoeial). Sodium sulfide precipitates a black precipitate Fe 2 S 3 from neutral and slightly alkaline solutions of iron (III) salts:
2Fe 3+ + 3S 2- → Fe 2 S 3 ↓
The Fe 2 S 3 precipitate is soluble in mineral acids.
Executing the reaction. Add 3-4 drops of a solution of iron (III) salt to a test tube and add 2-3 drops of a solution of ammonium sulfide or hydrogen sulfide water. A black precipitate of iron (III) sulfide is released.
d) Reaction with hydroxides. The precipitate of iron (III) hydroxide Fe(OH) 3, resulting from the interaction of Fe 3+ with hydroxide ions, is insoluble in alkali solutions and therefore, according to the acid-base classification, Fe 3+ is classified as a group of cations whose hydroxides are insoluble in alkalis. The Fe(OH) 3 precipitate is soluble in dilute acids; insoluble in a saturated solution of ammonium chloride (unlike the white precipitate Fe(OH) 2).
Executing the reaction. Add 3-4 drops of iron (III) salt solution to the test tube and add 3-4 drops of NaOH. A red-brown precipitate of iron (III) hydroxide Fe(OH) 3 precipitates.
e) Reaction with sulfosalicylic acid (pharmacopoeial). The Fe 3+ cation reacts in aqueous solutions with sulfosalicylic acid at pH ≈ 9-11.5 to form yellow complexes: Fe 3+ + L 2- → 3- ,
where L 2- is the designation of the sulfosalicylate anion formed from sulfosalicylic acid upon the abstraction of two protons presumably from groups
–COOH and –SO 3 H.
The most stable complex is yellow in color, containing iron (III) and sulfosalicylic acid anions in a molar ratio of iron (III): sulfosalicylate anions equal to 1:3, i.e. There are three sulfosalicylate ligands per iron atom. This complex dominates in ammonia solution. The exact structure of the complexes in solution is unknown. The sensitivity of the reaction is 5-10 µg.
Executing the reaction. Add ~5 drops of an iron (III) salt solution to a test tube, add ~10 drops of a sulfosalicylic acid solution and ~0.5 ml of a concentrated ammonia solution. The solution takes on a yellow color.
Analytical reactions of magnesium (II) cations.
a) Reaction with alkalis. Alkali solutions release from solutions of magnesium salts a white gelatinous precipitate of magnesium hydroxide Mg(OH) 2, easily soluble in acids and solutions of ammonium salts:
Mg(OH) 2 ↓+ 2HCI→MgCI 2 + 2H 2 O
Mg(OH) 2 ↓+ 2NH 4 CI→ MgCI 2 + 2NH 4 OH
Executing the reaction. To 1-2 drops of a solution containing magnesium ions, add 2-3 drops of 1M NaOH. A white gelatinous precipitate forms. Divide the resulting sediment into 2 test tubes. Add 3-4 drops of HCl to the first test tube, the precipitate dissolves. Add 3-4 drops of NH 4 Cl to the 2nd test tube, the precipitate also dissolves.
b) Reaction with potassium hypoiodite. When iodine reacts with alkali, potassium hypoiodite KIO is formed; in this case, the equilibrium in the solution shifts to the right and it becomes discolored:
I 2 + 2OH - ↔I - + IO - + H 2 O
When a magnesium salt is added, Mg 2+ ions form a Mg(OH) 2 precipitate with OH ions, which causes the equilibrium to shift to the left. The iodine released during this process is adsorbed by the Mg(OH) 2 precipitate and colors it red-brown.
Executing the reaction. Lugol's solution is decolorized by adding KOH solution drop by drop. A solution of magnesium salt is added to the resulting colorless solution. An amorphous precipitate, colored red-brown, immediately stands out.
c) Reaction with sodium hydrogen phosphate (pharmacopoeial). Sodium hydrogen phosphate forms a white crystalline precipitate with magnesium ions in the presence of NH 3 at pH ~ 9:
At pH> 10, Mg(OH) 2 and Mg 3 (PO 4) 2 can be formed. It is recommended to add NH 3 to the acidic test solution until pH ~9. Due to the formation of NH 4 C1, the pH of the solution is maintained constant. The precipitate dissolves in strong acids and acetic acid:
MgNH 4 PO 4 ↓+ 3HCI→ H 3 PO 4 + MgCI 2 + NH 4 CI
MgNH 4 PO 4 ↓+ 2CH 3 COOH →Mg(CH 3 COO) 2 + NH 4 H 2 PO 4
The detection limit of magnesium is 10 mcg. Ions that form poorly soluble phosphates interfere; NH 4 + , K(I) and Na(I) do not interfere.
Executing the reaction. To 1-2 drops of a solution containing magnesium ions, add 2-3 drops of 2 M HCl, 1 drop of Na 2 HPO 4 solution, and while stirring, add 2 M NH 3 drop by drop until the smell of ammonia appears (pH ~ 9). A white crystalline precipitate forms.
d) Reaction with 8-hydroxyquinoline (luminescent reaction). 8-Hydroxyquinoline forms hydroxyquinolinate with magnesium ions at pH 9 - 12, which fluoresces green:
The detection limit for magnesium is 0.025 mcg. The intensity of the glow increases when the wet spot is treated with magnesium oxyquinolinate and NH 3 solution. A1(III), Zn(II) interfere.
Executing a reaction. A drop of a solution containing magnesium ions and a drop of an ethanol solution of the reagent are applied to the filter paper. The resulting magnesium hydroxyquinolinate is treated with a drop of 10% ammonia solution. When viewing a wet spot under ultraviolet light, a green glow is observed.
e) Reaction with quinalisarin (1,2,5,8-tetraoxyanthraquinone)(I). Quinalizarin (1,2,5,8-tetraoxyanthraquinone)(I) with magnesium ions forms a slightly soluble blue compound in an alkaline solution, which is assigned structure (II):
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It is assumed that quinalizarin varnish is an adsorption compound of magnesium hydroxide with a reagent. The formation of chelates of variable composition is very likely.
The detection limit of magnesium is 5 mcg. Detection is not interfered with by alkaline earth metal ions; in the presence of a sufficiently large amount of alkali, aluminum ions do not interfere.
The ammonium ion interferes with the detection of the magnesium ion because it interferes with the formation of magnesium hydroxide. The reagent solution in an alkaline medium is purple, so a control experiment is necessary.
Executing the reaction. To 1 - 2 drops of a solution containing magnesium ions, add 1 drop of quinalizarin solution and 2 drops of 30% NaOH solution. A blue precipitate forms. To conduct a control experiment, add one drop of quinalizarin solution and 2 drops of 30% NaOH solution to 1 - 2 drops of water. The solution turns purple.
4. Test control 1
Qualitative reactions to iron (III)
Iron ions (III ) in solution can be determined using qualitative reactions. Let's go through some of them. Let us take a solution of ferric chloride for the experiment ( III).
1. III) – reaction with alkali.
If there are iron ions in the solution ( III ), iron hydroxide is formed ( III ) Fe(OH) 3 . The base is insoluble in water and brown in color. (Iron hydroxide ( II ) Fe(OH) 2 . – also insoluble, but gray-green in color). A brown precipitate indicates the presence of iron ions in the original solution ( III).
FeCl 3 + 3 NaOH = Fe(OH) 3 ↓+ 3 NaCl
2. Qualitative reaction to 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 ]). Add a solution of yellow blood salt to a portion of ferric chloride solution. A blue precipitate of Prussian blue* indicates the presence of ferric ions in the original solution.
3 TO 4 +4 FeCl 3 = K Fe ) ↓ + 12 KCl
3. Qualitative reaction to 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 iron ion (III) when potassium thiocyanate is added, a red substance is formed. This is iron thiocyanate (III). Rodanide from the Greek "rodeos" - 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 by the dyeing master Diesbach. Disbach bought an unusual potash (potassium carbonate) from a merchant: a solution of this potash when added with iron salts turned out blue. When testing the potash, it turned out that it was calcined with ox blood. The paint turned out to be suitable for fabrics: bright, durable and inexpensive. Soon the recipe for making paint became known: potash was fused with dried animal blood and iron filings. By leaching such an alloy, yellow blood salt was obtained. Prussian blue is now used to produce printing ink and tint polymers. .
Equipment: flasks, pipette.
Safety precautions . Follow the rules for handling alkalis and solutions hexacyanoferrates. Avoid contact of hexacyanoferrate solutions with concentrated acids.
Setting up the experiment – Elena Makhinenko, text– Ph.D. Pavel Bespalov.
The method is based on the determination of the wine-red color characteristic of complexes formed by ferric ions and thiocyanate ions. These complexes are unstable, so a large excess of thiocyanate ions is required to suppress the dissociation of the complex. The process of interaction of ferric iron ions with thiocyanate ions proceeds according to equation (1):
|
Fe 3+ + 6 NH 4 CNS = 6NH 4 + + 3- |
It must be taken into account that in addition to 3-, other, less intensely colored complexes can be formed, therefore the concentration of ammonium thiocyanate should be the same in the analyzed and standard solutions. Determination is interfered with by strong oxidizing agents (potassium permanganate, ammonium persulfate, hydrogen peroxide, etc.) that oxidize the thiocyanate anion, as well as substances that reduce iron (III) to iron (II). The best medium is nitric acid, and a low acidity of the solution is sufficient to prevent hydrolysis of the iron salt (1-2 ml of concentrated nitric acid per 50 ml of solution).
Reagents
Ammonium rhodanide (NH4CNS), 10% solution;
Nitric acid, concentrated;
Basic standard solution. To prepare the basic standard solution, 0.8634 g of ferric ammonium alum is dissolved in a small volume of distilled water. If the solution turns out to be opaque, then add a few drops of concentrated nitric acid and adjust the volume to 1 liter. The solution contains 0.1 mg of iron per 1 ml;
Working standard solution. The working standard solution is prepared by diluting the stock standard solution 10 times. The solution contains 0.01 mg of iron per 1 ml.
Progress
Add 1 and 5 ml of the working standard solution, as well as 1; 2.5 and 5 ml of the main standard solution of iron and adjust the volume to the mark with distilled water, obtaining solutions with a concentration of 0.1; 0.5; 1.0; 2.5; and 5.0 µg/l, respectively. The prepared solutions and 100 ml of the test sample are poured into 150 ml conical flasks, 5 ml of concentrated HNO 3 and 10 ml of a 10% NH 4 CNS solution are added to each flask. The solutions are thoroughly mixed and after 3 minutes they are photometered at a wavelength of λ = 450 nm, using cuvettes with an optical layer thickness of 5 mm, relative to distilled water to which the same reagents have been added. The mass concentration of iron is found using a calibrated graph. A calibration graph is constructed, plotting the mass concentration of iron in µg/dm3 on the abscissa axis and the corresponding optical density values on the ordinate axis.
Determination of chromium content using diphenylcarbazide
Principle of the method
The method is based on the interaction of chromates and dichromates in an acidic environment with diphenylcarbazide to form a red-violet colored compound in which chromium is contained in the reduced form of Cr(III), and diphenylcarbazide is oxidized to diphenylcarbazone. The detection limit is 0.02 mg/l. The range of measured amounts of chromium in the sample is from 1 μg to 50 μg.
When analyzing water, only Cr(vi) is determined in one sample, and in the other, the total content of Cr(iii) and Cr(vi), in which Cr(III) is oxidized to Cr(VI). Ammonium persulfate is used as an oxidizing agent. The oxidation process proceeds according to equation (2):
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2Сr 3+ + 3S 2 O 8 2- + 7H 2 O Сr 2 O 7 2- + 6SO 4 2- + 14Н + |
The difference in results is used to determine the Cr 3+ content.
Reagents
Double-distilled water (used for the preparation of all reagents);
Sulfuric acid, 1:1;
Concentrated phosphoric acid;
Diphenylcarbazide (C 13 H 14 ON 4), 0.5% solution in acetone (use freshly prepared);
Sodium hydroxide solution, 10% and 25%;
Basic standard solution of potassium bichromate K 2 Cr 2 O 7 .
The main standard solution is prepared by dissolving 2.8285 g of the reagent, dried at 150°C, in double-distilled water and adjusting the volume to 1 l (1 ml of solution contains 1 mgCr(VI);
Working standard solution 2. Prepare by diluting 4 ml of working standard solution 1 to 100 ml with bidistilled water (1 ml of the resulting solution contains 2 μg of Cr(VI)).
Building a calibration graph
0 is taken into 100 ml volumetric flasks; 0.5; 1.0; 2.0; 3.0; 5.0; 8.0; 10.0 ml of working standard solution 2, bring the volume of solutions to 50-60 ml, adjust the pH to 8 with an alkali solution, monitoring using universal indicator paper. Add 1 ml of H 2 SO 4 (1:1) and 0.3 ml of H 3 PO 4 and adjust the volume to 100 ml. The resulting solutions have a concentration of Cr(VI) 0; 10; 20; 40; 60; 100; 160; 200 µg/l. Add 2 ml of 0.5% diphenylcarbazide solution to each flask and mix well. The resulting solutions after 10-15 minutes. photometered at a wavelength of λ=540 nm, using cuvettes with an optical layer thickness of 30 mm, relative to distilled water to which the same reagents are added.
Content DefinitionCr(VI)
Place a volume of sample in a 100 ml volumetric flask such that it contains from 0.005 to 0.1 mg of chromium, adjust the pH to 8 with an acid or alkali solution, monitoring using universal indicator paper. Add 1 ml of H 2 SO 4 (1:1) and 0.3 ml of H 3 PO 4, bring the volume to 100 ml and mix. Add 2 ml of 0.5% diphenylcarbazide solution to each flask and mix again. The resulting solutions after 10-15 minutes. photometered as indicated above.
Material from Wikipedia - the free encyclopedia
| Iron(III) thiocyanate | |
| Are common | |
|---|---|
| Systematic Name |
Iron(III) thiocyanate |
| Traditional names | iron thiocyanate; thiocyanate iron |
| Chem. formula | Fe(SCN) 3 |
| Physical properties | |
| State | red crystals with a greenish tint |
| Molar mass | 230.09 g/mol |
| Data are based on standard conditions (25 °C, 100 kPa) unless otherwise stated. | |
Iron(III) thiocyanate- an inorganic compound, a salt of iron metal and hydrothiocyanate acid with the formula Fe(SCN) 3, dissolves in water, forms a crystalline hydrate - red crystals.
Receipt
- Exchange reactions:
- Neutralization of a solution of hydrothiocyanate acid with freshly precipitated iron(III) hydroxide:
Physical properties
Iron(III) thiocyanate forms crystalline hydrate Fe(SCN) 3 3H 2 O - paramagnetic red hygroscopic crystals, soluble in water, ethanol, ether, sparingly soluble in carbon disulfide, benzene, chloroform, toluene.
Aqueous solutions contain Fe 6H 2 O dimers.
Chemical properties
- With thiocyanates of other metals it forms coordination compounds hexathiocyanatoferrates(III), for example Li 3 n H 2 O, Na 3 12H 2 O, K 3 4H 2 O, Cs 3 2H 2 O, (NH 4) 3 4H 2 O.
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Literature
- Chemical Encyclopedia / Editorial Board: Knunyants I.L. and others. - M.: Soviet Encyclopedia, 1990. - T. 2. - 671 p. - ISBN 5-82270-035-5.
- Ripan R., Ceteanu I. Inorganic chemistry. Chemistry of metals. - M.: Mir, 1972. - T. 2. - 871 p.
| This is a draft article about inorganic matter. You can help the project by adding to it. |
Excerpt characterizing iron(III) thiocyanate
- To the future life? – Prince Andrei repeated, but Pierre did not give him time to answer and took this repetition as a denial, especially since he knew Prince Andrei’s previous atheistic beliefs.– You say that you cannot see the kingdom of goodness and truth on earth. And I have not seen him and he cannot be seen if we look at our life as the end of everything. On earth, precisely on this earth (Pierre pointed in the field), there is no truth - everything is lies and evil; but in the world, in the whole world, there is a kingdom of truth, and we are now children of the earth, and forever children of the whole world. Don't I feel in my soul that I am part of this huge, harmonious whole. Don’t I feel that I am in this huge countless number of beings in which the Divinity is manifested - the highest power, as you like - that I constitute one link, one step from lower beings to higher ones. If I see, clearly see this staircase that leads from a plant to a person, then why should I assume that this staircase breaks with me, and does not lead further and further. I feel that not only can I not disappear, just as nothing disappears in the world, but that I will always be and always have been. I feel that besides me there are spirits living above me and that there is truth in this world.
“Yes, this is Herder’s teaching,” said Prince Andrei, “but that, my soul, is not what convinces me, but life and death, that’s what convinces me.” What is convincing is that you see a being dear to you, who is connected with you, before whom you were guilty and hoped to justify yourself (Prince Andrei’s voice trembled and turned away) and suddenly this being suffers, is tormented and ceases to be... Why? It cannot be that there is no answer! And I believe that he is... That’s what convinces, that’s what convinced me,” said Prince Andrei.
“Well, yes, well,” said Pierre, “isn’t that what I’m saying!”
- No. I’m only saying that it’s not arguments that convince you of the need for a future life, but when you walk in life hand in hand with a person, and suddenly this person disappears out there into nowhere, and you yourself stop in front of this abyss and look into it. And, I looked...
- Well then! Do you know what is there and that there is someone? There is a future life there. Someone is God.
Prince Andrei did not answer. The carriage and horses had long been taken to the other side and had already been laid down, and the sun had already disappeared halfway, and the evening frost covered the puddles near the ferry with stars, and Pierre and Andrey, to the surprise of the footmen, coachmen and carriers, were still standing on the ferry and talking.
– If there is God and there is a future life, then there is truth, there is virtue; and man's highest happiness consists in striving to achieve them. We must live, we must love, we must believe, said Pierre, that we do not live now only on this piece of land, but have lived and will live forever there in everything (he pointed to the sky). Prince Andrey stood with his elbows on the railing of the ferry and, listening to Pierre, without taking his eyes off, looked at the red reflection of the sun on the blue flood. Pierre fell silent. It was completely silent. The ferry had landed long ago, and only the waves of the current hit the bottom of the ferry with a faint sound. It seemed to Prince Andrei that this rinsing of the waves was saying to Pierre’s words: “true, believe it.”
Prince Andrei sighed and with a radiant, childish, tender gaze looked into Pierre’s flushed, enthusiastic, but increasingly timid face in front of his superior friend.
- Yes, if only it were so! - he said. “However, let’s go sit down,” added Prince Andrei, and as he got off the ferry, he looked at the sky that Pierre pointed out to him, and for the first time, after Austerlitz, he saw that high, eternal sky that he had seen lying on the Field of Austerlitz, and something that had long fallen asleep, something that was best in him, suddenly woke up joyfully and youthfully in his soul. This feeling disappeared as soon as Prince Andrei returned to the usual conditions of life, but he knew that this feeling, which he did not know how to develop, lived in him. The meeting with Pierre was for Prince Andrei the era from which, although in appearance the same, but in the inner world, his new life began.
It was already dark when Prince Andrei and Pierre arrived at the main entrance of the Lysogorsk house. While they were approaching, Prince Andrey with a smile drew Pierre's attention to the commotion that had occurred at the back porch. A bent old woman with a knapsack on her back and a short man in a black robe with long hair, seeing the carriage driving in, rushed to run back through the gate. Two women ran out after them, and all four, looking back at the stroller, ran into the back porch in fear.
“These are the Machines of God,” said Prince Andrei. “They took us for their father.” And this is the only thing in which she does not obey him: he orders these wanderers to be driven away, and she accepts them.
- What are God's people? asked Pierre.
Prince Andrei did not have time to answer him. The servants came out to meet him, and he asked about where the old prince was and whether they were expecting him soon.
The old prince was still in the city, and they were waiting for him every minute.
Prince Andrei led Pierre to his half, which was always waiting for him in perfect order in his father’s house, and he himself went to the nursery.
“Let’s go to my sister,” said Prince Andrei, returning to Pierre; - I haven’t seen her yet, she is now hiding and sitting with her God’s people. Serves her right, she will be embarrassed, and you will see God's people. C "est curieux, ma parole. [This is curious, honestly.]
– Qu"est ce que c"est que [What are] God's people? - asked Pierre
- But you'll see.
Princess Marya was really embarrassed and turned red in spots when they came to her. In her cozy room with lamps in front of icon cases, on the sofa, at the samovar, sat next to her a young boy with a long nose and long hair, and in a monastic robe.
On a chair nearby sat a wrinkled, thin old woman with a meek expression on her childish face.
“Andre, pourquoi ne pas m"avoir prevenu? [Andrei, why didn’t you warn me?],” she said with meek reproach, standing in front of her wanderers, like a hen in front of her chickens.