What are colorimetric tubes?
are the main instrument used for visual colorimetric analysis in chemical experiments and can be used to roughly measure the concentration of a solution. When comparing the color, the colorimetric tube containing the solution to be measured and a colorimetric tube containing the standard solution are placed in front of a white paper with the same degree of illumination for comparison, and the color difference is observed with the naked eye. The appearance of the colorimetric tube is similar to the ordinary test tube, but more than the test tube with a precise scale and a rubber or glass stopper, and the wall are thinner than the ordinary test tube, the common specifications are 10ml, 25ml, 50ml three.
Application of colorimetric tubes
Colorimetric detector tubes
What is chromaticity?
is the color of the water. Chroma refers to the degree of dissolved substances or colloidal substances in the water presented as yellow-like or even yellow-brown. The chromaticity of water is divided into two kinds of surface color and true color. Surface color refers to the color of the water without removing the suspended matter, including the color produced by the dissolved substances and insoluble suspended substances. The true color is the color of the water after the removal of suspended matter, produced only by dissolved colored substances. Clean or very low turbidity of the water, the true color, and table color are similar; the coloring is very dark, more suspended matter industrial wastewater, and domestic sewage two differences. Water quality physical and chemical tests usually only determine the true color.
Clean natural water, in the water layer shallow for colorless transparency, deep when the light blue or light green. Natural water often presents different colors in the decomposition of organic matter in the water and contains inorganic substances caused the most common is the color of organic complexes produced by the decomposition of natural organic matter. For example, plant organic matter dissolved in water, the water will be pale yellow or even brownish yellow; water containing high iron compounds is yellow; hydrogen sulfide in water is oxidized to precipitate sulfur, which can make the water light blue; some swamp water, because the plant contains tannic acid and gallic acid and iron into iron salts and black; the presence of a large number of algae in the water will be different colors due to the type of algae, such as chlorella to make the water is green, diatoms were brownish green, methanogamous algae were brownish green. Diatoms are brownish green, methanogens are dark brown, and blue-green algae are emerald; water polluted by industrial wastewater, the color of the industrial wastewater can be presented. If the water has a color, it signifies that the water is contaminated. Colored water affects human psychology and makes the drinker feel unpleasant. Chromaticity is one of the main pollution indicators, some countries' water quality standards, require chromaticity between 5 and 20 degrees.
B. Colorimetric determination
The colorimetric methods include the platinum-cobalt standard colorimetric method, the chromium-cobalt colorimetric method, and the dilution multiplier method.
a. Platinum - cobalt standard colorimetric method This method uses potassium chloroplatinate and cobalt chloride to form a standard Israel with a similar yellow hue to natural water, and water samples for visual colorimetric determination. The color of 1L of water containing 1mg of platinum [in the form of (PtC16)2-] and 0.5mg of cobalt is specified as a unit of color, i.e. 1 degree.
Preparation of platinum-cobalt standard solution: Weigh 1.2468 potassium chloroplatinate (K2PtC16, equivalent to 500mg platinum) and 1.000g dried cobalt chloride (COC12-6H2O, equivalent to 250mg cobalt), dissolve in 100m1 pure water, add 100m1 HCl, and fix the volume with pure water to 1000ml, the color of the standard solution is 500 degrees. Then prepare standard Israel, take the appropriate volume of the solution in a set of 50ml colorless stoppered colorimetric tubes, add pure water to the scale, shake well, and prepare standard Israel with the chromaticity of 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50 degrees. Take 50ml of water sample in the colorimetric tube and compare the water sample with standard Israel to determine the color of the water sample. If the color of the water sample is too high, you can draw a small number of water samples, add pure water dilution after colorimetric, and multiply the results by the dilution times.
The minimum detection chromaticity of this method is 5 degrees, and the measurement range is 5 to 50 degrees. If the water sample does not agree with the hue of standard Israel, that is, heterochromatic, can be described in writing.
b. Chromium - cobalt colorimetric method weighing potassium dichromate (K2Cr2O7) 0.0437g and cobalt sulfate (CoSO4-7H2O) 1.000g dissolved in a small amount of pure water, add 0.5 ml H2SO4, mixed with pure water volume to 500ml, this standard solution color is also 500 degrees. Determination of water samples, except for diluted standard Israel with dilute hydrochloric acid (1 + 1000) instead of pure water, the rest is the same as the platinum and cobalt colorimetric method. The method of the minimum detection of chromaticity and measurement range and the same method.
c. When the dilution multiplier method is used to determine industrial wastewater or water from water sources contaminated by industrial wastewater, the dilution multiplier method is generally used when the color cannot be determined by the platinum-cobalt or chromium-cobalt colorimetric method due to the complexity of the hue.
With the visual colorimetric method, the water sample is diluted with high-purity water, while comparing with high-purity water, the intensity of the color of the water sample is expressed by the dilution times when the color is just invisible, and the color of the water sample is observed and described in words such as red, orange, yellow, green, cyan, blue and violet. The combination of dilution times the value and textual description to express the results.
Measurement first observes the color of the water sample and describes it in words. Then according to the size of the color, take a certain volume of water samples, high purity water as a control, the water samples with high purity water diluted exponentially, until just invisible water samples of color, record the dilution times the value at this time.
a. Whether using a platinum-cobalt colorimetric method or chromium-cobalt colorimetric method, can only determine the yellow tone of the water sample. Clean water samples can be directly sampled for determination, turbid water samples should be centrifuged to separate the suspended matter or left to clarify for a few hours, absorbing the upper layer of clarified water samples test. It is not recommended to filter with filter paper, because the filter paper can adsorb some of the colored substances, and the chromaticity is reduced. If the particles contained in the water sample are too fine, the method of centrifugation is not easy to remove the suspended material, you can only determine the surface color of the water sample, as indicated in the report.
b. The platinum-cobalt standard colorimetric method is easy to operate, stable in color, and can be used for a long time if standard Israel is preserved properly. However, potassium chloroplatinate is relatively expensive, and it is not economical to use in large quantities. The chromium-cobalt colorimetric method uses potassium dichromate and cobalt sulfate as the standard, the reagents are cheap and easy to obtain, and the precision and accuracy are the same as the platinum-cobalt colorimetric method, but the preservation time of standard Israel is shorter.
c. The dilution multiplier method can also refer to the determination and calculation of the smell threshold to do the determination of any dilution multiplier.
d. PH has a greater impact on the chromaticity, the pH of the water sample should be measured at the same time as the chromaticity. pH should also be reported at the same time as chromaticity.
C. Wastewater decolorization technology
a. Adsorption decolorization
Adsorption decolorization technology relies on the adsorption of adsorbent to remove the color. Usually used adsorbents include renewable adsorbents such as activated carbon, and ion exchange fibers and non-renewable adsorbents such as various natural minerals (bentonite, diatomaceous earth), industrial wastes (cinder, fly ash), and natural wastes (charcoal, sawdust). At present, the adsorbent used for adsorption decolorization mainly relies on physical adsorption, but ion exchange fibers, modified bentonite, etc. also have a chemical adsorption effect.
b. Flocculation decolorization
Coagulation decolorization is decolorization by using flocculants to flocculate the color-forming substances in wastewater and precipitate them.
Flocculation decolorization technology, with low investment cost, small equipment area and large treatment capacity, is a commonly adopted decolorization technology.
Inorganic coagulants include metal salts and inorganic polymer flocculants. The widely used metal salts are aluminum salt and iron salt; inorganic polymer flocculant is a new type of water treatment agent developed on the basis of the traditional metal salt flocculant, which has the advantages of strong adaptability, non-toxic, and can multiply the efficiency and relatively inexpensive, etc. It has been rapidly developed and widely used.
Organic polymer flocculant, polyacrylamide (PAM) is the most used, it has non-ionic, cationic and anionic type.
c. Oxidation decolorization
Oxidative decolorization includes chemical oxidation, photocatalytic oxidation and ultrasonic oxidation. Although the specific processes are different, the decolorization mechanism is the same. Chemical oxidation is the more mature method currently studied. The oxidizing agent generally uses a Fenton reagent (Fe2+-H2O2), ozone, chlorine, sodium hypochlorite, etc. The chemical oxidation decolorization method refers to the oxidation of chlorine, ClO2, O3, H2O2, HClO4, and hypochlorite, etc., which makes the color-emitting groups in wastewater break or change their chemical structure under certain conditions, so as to achieve the purpose of wastewater decolorization.
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