When congo red is added to an acid it?
Asked by: Quincy Kunze
Congo red was formerly used to dye cotton but has been superseded by dyes more resistant to light and to washing. It is still used in histology to stain tissues for microscopic examination, and to serve as an acid-base indicator, since it turns red in the presence of alkalies and blue when exposed to acids.
Is Congo Red acidic?
Congo red is an acid-base indicator dye. In free solution the colour and absorption characteristics of Congo red depend not only on the pH but are also governed by the nature of the solvent environment.
Why is Congo red an acidic substance?
Due to a color change from blue to red at pH 3.0–5.2, Congo red can be used as a pH indicator. ... This property gives Congo red a metachromatic property as a dye, both in strongly acidic solutions and with strongly acidophilic tissue.
What does it mean when Congo red paper turns blue?
The Congo Red test paper is used to test narrow-range acidic solutions. Congo Red Test Paper is used in acid washes for metal plating where pH values are very low (pH 1.0-3.0). The Congo Red indicator remains blue below pH 3.0, then gradually turns to a brilliant red above pH 5.2.
How do you dissolve Congo red?
Place directly into Working Congo red solution for 1 hour. Dissolve the hematoxylin in water, heat to boiling, boil for 5 minutes. Remove from heat, add sodium iodate, wait 10 minutes to ripen. Add the remainder of the chemicals in the order given, dissolving each one before adding the next.
Kongo red .. the indicator
How do you make a 1% Congo Red solution?
Congo Red powder dye solution (for staining acc. to the Highman method): 1% solution of Congo Red powder dye: • Dissolve 0.5 g of Congo Red dye in 50 ml of distilled/demi water. Add 50 mL of 100% ethanol. Filter before use.
What is the use of congo red?
What color is Thymolphthalein in acid solutions?
Thymolphthalein is an acid-base indicator that changes color from colorless to blue. Below a pH of 9.3-10.5, it s colorless. Above this range, it is blue.
Is Congo red toxic to humans?
Congo Red is an azo dye, it is toxic to many organisms and is a suspected carcinogen and mutagen.
Is pH a chemistry?
In chemistry, pH (/piːˈeɪtʃ/, historically denoting "potential of hydrogen" or "power of hydrogen") is a scale used to specify the acidity or basicity of an aqueous solution. ... More precisely, pH is the negative of the base 10 logarithm of the activity of the H+ ion.
What disease processes can Congo red identify?
Staining with Congo red (CR) is a qualitative method used for the identification of amyloids in vitro and in tissue sections. However, the drawbacks and artefacts obtained when using this dye can be found both in vitro and in vivo .
How Congo red are formed?
Congo Red is synthesised by coupling bis-diazotised benzidine with two molecules of napthionic acid. The blue dye so obtained is converted into its red disodium salt during its salting out with sodium chloride (Fig. 4.2).
What is the pH range of Congo red?
"Congo red" is not the name of a famous African explorer, but a dye that dates to 1883. It was synthesized by P. Böttiger as a textile dye, but it subsequently became more important as a pH indicator. It colors aqueous solutions blue below pH 3.0 and becomes red above pH 5.0.
What type of stain is Congo red?
Congo red is still the standard stain used in most histopathology laboratories to identify amyloid material in tissues. The identification of Congophilic amyloid material is challenging because of multiple interfering factors.
What is the pH of phenol red?
Phenol red, also known as phenolsulfonphthalein, is a pH indicator dye that exhibits a gradual transition from yellow to red over a pH range of 6.2 to 8.2 (Figure 2). Above 8.2 the dye turns a bright fuchsia color.
What color is Nigrosin?
In staining dyes, nigrosin (CI 50415, Solvent black 5) is a mixture of black synthetic dyes made by heating a mixture of nitrobenzene, aniline, and hydrochloric acid in the presence of copper or iron.
Why is it called Congo red?
"Congo" red was introduced in Berlin in 1885 as the first of the economically lucrative direct textile dyes. ... Conclusions: The Congo red stain was named "Congo" for marketing purposes by a German textile dyestuff company in 1885, reflecting geopolitical current events of that time.
Is used as a red paper dye?
Cochineal extract can dye paper a lovely red color.
How does Congo red stain work?
Congo red demonstrates the accumulation of amyloid. With light microscopy it stains a pink or light red colour and shows green birefringence with polarized light. With rhodamine or Texas fluorescence the deposits show enhanced red fluorescence.
What is the pH color scale?
The pH scale runs from 0 to 14, with each number assigned a different color. At the bottom of the scale sits red, which represents the most acidic, and a dark blue at its opposite end represents 14 and alkalinity. In the middle zone, the pH scale becomes neutral. Milk has a pH of 6 and a neutral off-white color.
What Colour is methyl red in acidic solution?
Methyl red (2-(N,N-dimethyl-4-aminophenyl) azobenzenecarboxylic acid), also called C.I. Acid Red 2, is an indicator dye that turns red in acidic solutions. It is an azo dye, and is a dark red crystalline powder.
Could you use Congo red for positive staining?
Congo red cannot be used for direct staining since it is an acid stain (negatively charged) and the goal of a direct stain is to use a basic stains (positively charged) to stain the bacterium itself since a negative charge and positive charge are attracted to each other, negative and negative charge repel each other ...
What is a Congo red indicator?
Congo Red is the sodium salt of benzidinediazo-bis-1-naphthylamine-4-sulfonic acid; a diazo dye that is red in alkaline solution and blue in acid solution and used especially as an indicator and as a biological stain. NCI Thesaurus (NCIt) Congo Red is an indicator dye that is blue-violet at pH 3.0 and red at pH 5.0.
What does Congo red bind to?
The fact that Congo red binds to native, partially folded conformations and amyloid fibrils of several proteins shows that it must be used with caution as a diagnostic test for the presence of amyloid fibrils in vitro.
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