How to check for CO3 ions and for the presence of trivalent chromium ions?

It is a test of carbonate ions (CO3

2-), right? The detection of carbonate ions cannot be done with only one reagent, but also by a combination of tests.

1) Add CaCl2 solution to the solution first, which can generate white precipitate;

2) Filter to obtain white precipitate, add hydrochloric acid, dissolve and produce gas that can make the clarified lime water turbid;

Combining (1) and (2) can determine the presence of carbonate ions in the solution.

If CaCl2 and hydrochloric acid are used to make a simple judgment, the following situations cannot be ruled out:

The solution contains Na2SO4 and NaHCO3

The addition of HCl releases gas to make the lime water turbid, and at the same time, it cannot fade the potassium permanganate solution (exclude SO3(2-) ions).

Take a small amount of sample, add dilute hydrochloric acid dropwise to it, and bubbles are generated, and the gas is passed into the clarified lime water, and the clarified lime water becomes turbid.

Acid is added, gas is generated, and there is a white precipitate when lime water is introduced.

With the addition of HCl, the generated gas is passed into the clarified lime water, resulting in a white precipitate.

CO32 can react with BaCl2 solution to form a white BaCO3 precipitate, which is dissolved in nitric acid (or hydrochloric acid) to form a colorless and odorless CO2 gas that can make the clarified lime water turbid.

Add hydrochloric acid. The raw gas can make the clarified lime water turbid.

Add barium chloride again.

A white precipitate is generated.

1. Add barium chloride solution, and add hydrochloric acid to the filtered precipitate. If the white precipitate dissolves, it proves that the solution contains carbonate ions.

2. Add dilute nitric acid, and then use barium ions or calcium ions to test whether carbon dioxide is generated.

3. Hydrochloric acid can be added first, and the bending gas produced is passed into the magenta solution, if it does not fade, it is then passed into the clear lime water, if it becomes turbid, then add calcium chloride solution to the original solution, if there is a white precipitate, it can prove that there are carbonate ions in the solution.

4. Add barium chloride first to produce white precipitate, and then add hydrochloric acid to produce a colorless and odorless gas that can make the clarified lime water turbid, which can prove that it is carbonate.

To see if there are any interfering ions, the simplest is that the trivalent chromium ions are green.

Or use the substitution method 2Cr3+ +Zn = 2Cr2+(blue) +Zn2+

- A slightly better way ———

Trivalent chromium ions can be oxidized to chromate by hydrogen peroxide under alkaline conditions

cr3+ +4oh- == [cr(oh)4]-

2[cr(oh)4]- 3h2o2 + 2oh- == 2cro42- +8h2o

After acidification with sulfuric acid. Make pH = 2 3, chromate becomes dichromate:

2cro42- +h+ == cr2o72- +h2o

Dichromate reacts with hydrogen peroxide to produce blue perchromatic acid

cr2o72- +4h2ho +2h+ == 2h2cro6

Because perchromic acid is easily decomposed into chromic acid and oxygen, it is extracted with pentanol and has a blue-purple color in the organic phase.

This identification method is not interfered with by manganese ions, nickel ions, ferrous ions, iron ions, aluminum ions, etc.

- Quantitative determination of ———

Make sure there are no interfering ions.

Remove 2 ml of the reagent to be measured with a pipette and place it in a 250 ml beaker.

Add 50 ml of distilled water and adjust the pH to 10 with 10% NaOH solution (the color will change at this point).

Add 30% H2O2 to the above solution and cook for 30 for 40 minutes (completely remove the excess of 30% H2O2).

After cooling, adjust the volume of the solution to 100ml with distilled water.

The solution is made acidic with 35% hydrochloric acid (the color changes from yellow to orange).

Add 1 g of KI to the above solution and calibrate it with Na2S2O3 5H2O until the color of the solution changes to light yellow.

Add 1% starch solution to continue calibration (preferably until the cyan color of the solution disappears).

cr（3+）vol%= v(na2s2o3•5h2o) x x f (

Make a small amount of homemade- solution Add 3% H2O2 Water bath to heat After cooling, add 3 5 drops of ether , then add 6M nitric acid Shake The ether layer is observed to be dark blue.

Test SO4(2-): add BACL2 or BA(NO3)2 to the solution, and then add dilute nitric acid, if the precipitation is produced and insoluble, it means that there are sulfate ions.

Test Cl(-) Add AGNO3 to the solution, and then add dilute nitric acid, if the precipitation is produced and does not dissolve, it means that there are chloride ions.

Test CO3(2-):1) Add acid (HCl, H2SO4 can be, but not carbonic acid) to the solution, if bubbles are generated, and the gas can make the clear lime water turbid, the solution contains carbonate ions.

2) Add Ca(OH)2 to the solution, if a white precipitate is produced, it means that there are carbonate ions in the solution.

SO4 ion test.

HCL is added first to exclude. so3co3ag

Plasma interference.

Add BaCl2 or Ba(NO3)2 to the solution

If precipitation occurs.

Indicates the presence of sulfate ions.

Cl ionic.

Inspection. Add agno3 to the solution, and then add dilute nitric acid, if the precipitation is produced and does not dissolve, it means that there are chloride ions.

Test CO3 (2-): 1) Add acid (HCl, H2SO4 can be, but not carbonic acid) to the solution, if bubbles are produced, and the gas can make the clear lime water turbid, but not make the magenta fade.

2) Add CaCl2 to the solution, if a white precipitate is produced, it means that there are carbonate ions in the solution.

Hello! A colorimetric detection analysis method for cobalt ions, characterized by the following steps:

a. Using 8-hydroxyquinoline and 7,7,8,8-tetracyanoquinone dimethane, acetonitrile as a solvent, a green charge transfer complex was prepared as a detection reagent;

b. Prepare a buffered aqueous solution with a concentration of 2-hydroxyethyl-1-piperazinylethanesulfonic acid and sodium hydroxide solution; The cobalt salt was dissolved with a buffered aqueous solution to prepare the solution to be tested, and the concentration of cobalt ions was;

c. Mix the detection reagent with the same volume of the test solution containing cobalt ions, and the mixed solution will soon turn from green to orange-yellow.

And, of course, atomic absorption, emission spectroscopy, etc.

Positive solution of hexabeliium stone. However, it should be reminded that this method is to be carried out in an acid environment, and both iron ions and nitrite can interfere with the reaction.

There is another method below: add an equal amount of pan reagent (1-(2-pyridine azo)-2-naphthol), the solution is red, and then add concentrated hydrochloric acid, the color immediately turns green due to the oxidation of CO2+ in the air. Cobalt ions are present.

However, this method requires that the amount of cobalt ions be constant, and spectroscopy is recommended for trace or trace analysis.

First, check that CO3- bubbles are produced when excessive dilute nitric acid is added.

Equation: CO3-+2H+==H2O+CO2 in the test of SO42-, add excess BaNo3 to generate a precipitate that does not match the dissolution in dilute nitric acid.

Equation: SO42-+BA+==BASO4

Finally, chloride ions are tested, silver nitrate is added to generate a precipitate that is not dissolved in acid.

Equation: cl-+ag-==agcl