What is the preparation method of potassium dichromate?

Generally, chromite is used, and the main component Feo·Cr2O3 is easily oxidized in alkaline media (such as sodium carbonate, etc.) to form chromium (VI) salt, which is soluble in water.

4feo·cr2o3+8na2co3+7o2 ==== 8na2cro4+2fe2o3+8co2

When the melt is leached with water, most of the iron remains in the residue in the form of Fe(OH)3. After filtration, the filtrate was adjusted to pH=7 8, and aluminum hydroxide and silicic acid were precipitated. The precipitate is filtered out, and the filtrate is acidified, and the chromate becomes sodium dichromate.

Potassium dichromate is prepared by metathesis reaction of sodium dichromate and potassium chloride.

Na2Cr2O7+2KCl === The solubility of potassium dichromate in K2Cr2O7+2NaCl is very small at room temperature, while at elevated temperature, its solubility increases greatly. Temperature has little effect on the solubility of sodium chloride. Therefore, after the solution is concentrated and cooled, a large amount of potassium dichromate crystals are precipitated, and the sodium chloride remains in the solution.

The main component of chromite is FeO·Cr2O3. Generally, chromite contains 40% Cr2O3, in addition to impurity iron, it also contains impurities such as silicon and aluminum. The method of preparing potassium dichromate from chromite is:

First, in an alkaline medium, chromium is oxidized to +6-valent chromate: 2FeO·Cr2O3+4Na2CO3+7nano3*****4Na2CRO4+Fe2O3+4CO2+7nano2. Sodium carbonate is used as the flux and sodium nitrate is used as the oxidant, which is mixed with chromite and then heated and melted to obtain chromate.

When the melt is leached with water, most of the iron remains in the residue in the form of iron hydroxide, which can be filtered out. The filtrate was adjusted to pH=7-8, and aluminum hydroxide and silicic acid were precipitated. Filter to remove the precipitate, and then acidify the filtrate to obtain dichromate

2cro4 2-+2h+====cr2o7 2-+h2o。Because the filtrate contains sodium nitrate, if it is too acidic during acidification, it can reduce +6 valence chromium to +3 valent chromium, so it is acidified with acetic acid, and the pH is kept at about 5. Then, potassium dichromate can be obtained by metathesis reaction Na2Cr2O7+2KC*****K2Cr2O7 +2NaCl.

Metathesis. Sodium dichromate (Na2Cr2O7·2H2O 100%)

Potassium chloride (KCL 100%)

Potassium dichromate method

The principle of potassium dichromate method is that in a strong acidic solution, a certain amount of potassium dichromate oxidizes the reducing substances in the water sample, and the excess potassium dichromate is tested with ferrous pyrine as an indicator, and ammonium ferrous sulfate solution is used for dripping. Based on the amount used, the oxygen consumed by the reducing substances in the water sample is calculated. ”

Accurately absorb the potassium dichromate standard solution in a 500ml Erlenmeyer flask, dilute it to about 110ml with water, and slowly add 30ml of concentrated sulfuric acid and shake well. After cooling, 3 drops of ferrous sulfate indicator solution were added (approximately, titrated with ammonium ferrous sulfate solution, and the color of the solution was from yellow to blue-green to reddish-brown as the end point.

For water samples with a chemical oxygen demand of less than 50 mg l, potassium dichromate standard solution should be used instead. Use ammonium ferrous sulfate standard solution when dripping back.

Precautions. 1) The maximum amount of mercury sulfate complexed chloride ions can reach 40ml, such as taking a water sample, that is, a water sample with a maximum concentration of 2000mg l chloride ions. If the chloride concentration is low, mercury sulfate can also be added less to maintain mercury sulfate

Chloride = 10:1 (ww). If a small amount of mercuric chloride precipitate occurs, it does not affect the determination.

2) The volume of water sample can be within the range, but the amount and concentration of reagents can be adjusted accordingly to obtain satisfactory results.

3) For water samples with a chemical oxygen demand of less than 50ml l, it should be a potassium dichromate standard solution. Use ammonium ferrous sulfate standard solution when dripping back.

Potassium dichromate is less oxidizing than potassium permanganate and weaker than chlorine, so it can be carried out in HCl media.

The reduction product of potassium dichromate is trivalent chromium ion, the color is green, relatively similar, so it can not use its own indicator, if it is titrated ferrous ions, sodium diphenylamine sulfonate needs to be used as an indicator.

The potassium dichromate standard solution is stable, so it does not need to be calibrated.

The potassium dichromate method is superior to the potassium permanganate method in that 1, potassium dichromate can be directly configured, and potassium permanganate needs to be calibrated every time; 2. The potassium dichromate method can be carried out directly in the HCl environment, while potassium permanganate must be carried out in sulfuric acid or phosphorus-sulfur mixed acid. The disadvantage is that redox indicators must be used.

The transformation is related to the pH of the solution of the aquebus, the shape of the chromate is a tetrahedral, and under acidic conditions, two disturbed n-chromate and two hydrogen ions condense to remove a molecule of water to form a dichromate, and the shape is that two regular tetrahedra share a vertex (that is, an oxygen atom).

cr2o7)2-

2(co3)2-h2o

2(cro4)2-

2(hco3)-

Potassium dichromate. It is difficult to undergo redox reaction with ammonium carbonate.

Because (NH4)2CO3 is very unstable, and K2Cr2O7 oxidation NH4+ can not be carried out at room temperature, so there is no need to think about it.

Erjian Qiaolou obviously does not understand K2Cr2O7, which only exists under strong acid conditions, and under neutral conditions, it is mostly chaotic (CRO4)2-, and only (CRO4)2-, (NH4)2CO3 solution is alkaline, and (CR2O7)2- naturally cannot exist and is converted into (CR4)2-

The transformation is related to the pH of the solution, and the shape of the chromate is a tetrahedron, and under acidic conditions, two chromate and two hydrogen ions are condensed, and a molecule of water is removed to form a dichromate, which is shaped like two tetrahedra sharing a vertex (that is, oxygen atoms).

Macroscopically, potassium dichromate is only soluble in water and has no obvious reaction.

But there is an equilibrium Cr2O7 (2-)H2O in the water

2cro4^(2-)

2h (+, where the equal sign should be replaced with a reversible sign.)

Therefore, by adding alkali solution to the heavy potassium oak chromate solution, the transformation of potassium dichromate to potassium perchromate (K2CRO4) can be realized, and the color next to the hood changes from orange to yellow.

The potassium dichromate method is a commonly used method for determining chemical oxygen demand (COD), which is based on the principle of reacting organic matter with the oxidant potassium dichromate to determine COD. The specific steps are as follows:

Take a certain amount of water sample of plex fiber, add a known amount of sulfuric acid and potassium chromate solution (potassium dichromate), and shake well.

Under high temperature conditions, potassium dichromate infiltration will oxidize with organic matter in water and reduce to chromium ions.

At the same time as the reduction reaction, the chromium ions react with the ferric ions to form a red ferrochrome complex.

Based on the concentration of unreduced potassium dichromate remaining after the reaction, the concentration of COD can be calculated.

The effect of adding various reagents:

Sulfuric acid: used to reduce the pH value of water samples and promote oxidation reactions.

Potassium dichromate: It is an oxidizing agent, which can oxidize the organic matter in the water sample and reduce it to chromium ions.

Iron salts: used to generate chromium-iron complexes, forming a red product.

The factors that affect the accuracy of the determination include the color, turbidity, pH value, etc. of the water sample, which may affect the reaction rate of the reagent and the stability of the Chai bending product, thereby affecting the accuracy of COD determination. In addition, adding too much reagent may prevent some organic matter in the water sample from being oxidized, which will also affect the determination of COD. Therefore, proper handling and dilution of samples are required when performing COD assays to ensure the accuracy of the assay results.

Because potassium dichromate has a reference substance, the standard solution of potassium dichromate can be used to directly prepare the standard solution.

After dissolving, the volume is fixed to a certain volume; The other is the calibration method, that is, the ballast is first rented to prepare the approximate required concentration, and then the reference substance or standard solution is used for calibration.

Chromium that enters the body is deposited in human tissues and is metabolized and removed slowly. After chromium enters the bloodstream, it mainly binds to ferroglobulin, albumin, and -globulin in the plasma mouth. Hexavalent chromium may also penetrate the red blood cell membrane, and within 15 minutes, 50% of hexavalent chromium can enter the cell, and after entering the red blood cell, it binds to hemoglobin.

The metabolites of chromium are excreted mainly from the kidneys and in small amounts through the feces.

Hello, potassium dichromate is an important chemical raw material, which can be used to prepare metal chromium, dyes, catalysts, etc. The following describes a method for preparing potassium dichromate in Zhouqing: Materials:

Chromium trichloride, potassium hydroxide, water. Steps:1

Dissolve chromium trichloride in water to give a dark green solution. 2.Potassium hydroxide is dissolved in water to obtain a colorless and transparent solution.

3.Slowly add the potassium hydroxide solution to the chromium trichloride solution and stir it when it is sold. 4.

Add just the right amount of potassium hydroxide to give the solution a red color. 5.Continue stirring and heat until boiling.

6.Boil for 5-10 minutes until the solution turns dark red. 7.

The solution was cooled to a trace temperature in the chamber and filtered to obtain potassium dichromate. Notes:1

Pay attention to safety when handling and avoid contact** and inhalation of gases. 2.Add the potassium hydroxide solution slowly to avoid a violent reaction.

3.Keep stirring during the preparation process to avoid uneven solution. 4.

The filtered potassium dichromate should be dried to avoid moisture absorption.

Molar concentration (1 6 k2Cr2O7 = sensitive, 1 6 potassium dichromate phase bridge talk on the amount of molecular mass multiplication, York, dissolved in water, diluted to a concentration of 1000 ml. 1 6 The relative molecular weight of potassium dichromate is also called the equivalent of potassium dichromate.

1 6 in 1 6k2cr2o7 = In order to be in line with international standards, the molarity concentration was uniformly used and the equivalent concentration was abolished.

Molecular formula: K2Cr2O7, molecular weight, melting point: 398 C, boiling point: 500 C.