Bromothymol blue refers to laboratory chemicals. It is mainly used for titration of weak acids and alkalis. The color of the solution changes from yellow to intense blue. There are other uses for it.
Description
Bromothymol blue is an indicator of the acidity of the medium, which allows you to record changes in pH in the range of 6-7, 6. Other names for this compound are bromthymol blue, bromothymol sulfone phthalein, dibromothymol sulfophthalein ammonium s alt. According to the degree of chemical purity, it is produced with one qualification - NDA (pure for analysis).
Chemical formula of the compound: C₂₇H₂₈Br₂O₅S.
The substance belongs to the category of triphenylmethane dyes, which also includes brilliant green, magenta and phenolphthalein.
The structural formula of water-soluble bromothymol blue is shown in the figure below.
Chemical properties
The main properties of the compound, due to which its practical application is determined, are indicator. Depending on the environmental conditions and the concentrationsolutes bromthymol blue changes its color. The indicator does not interact with the components of the environment and does not affect the course of chemical processes. Reagents of this type allow you to determine the parameters of the working environment.
The compound has the following colorimetric characteristics:
- alkaline environment - intense blue color;
- neutral environment - grassy green;
- acid environment - yellow coloration.
Color change from yellow to blue occurs through different shades of green. To obtain the desired color, use 0.5% sodium hydroxide solution or 10% sodium carbonate solution (alkalinization), as well as 10% HCl solution (acidification).
In aqueous solution, bromthymol blue acts as a weak acid. The acid dissociation constant for this chemical indicator is 7.1.
Physical properties
Bromothymol blue is a crystalline powder in appearance, the color of which can be from yellow-brown to black (most often pinkish-purple). The powder has a faint smell of acetic acid.
The main physical characteristics of this compound are:
- molar mass – 624.39 g/mol;
- aggregate state - solid;
- density - 1250 kg/m3;
- mass fraction of the residue after calcination - no more than 1%;
- melting point - 202 °C;
- shareactive substance in powder - not less than 95% by weight.
The solubility of bromthymol blue in water is moderate, in ethyl alcohol it is good (with the formation of a brown color), in acetone it is good.
Application
The main field of application of this compound is the determination of the concentration of hydrogen ions by the colorimetric method. Bromothymol blue can also be used for:
- indication of respiratory activity or photosynthesis (when carbon dioxide is released, it turns yellow, when it is absorbed, the solution turns green);
- controlling the production of the enzyme asparaginase, which catalyzes the breakdown of the aspartic amino acid (the blue color of the solution indicates an increase in enzyme activity);
- application as one of the components of the nutrient medium in bacteriology to control the development of culture;
- visualization of cell walls or nuclei when examined under a microscope;
- in gynecology - detection of premature rupture of membranes (amniotic fluid has pH=7.2, so the indicator solution becomes blue).
Its properties as an indicator are most widely used in industries such as:
- chemical;
- metallurgical;
- textile;
- food;
- agriculture.
Working solutions
In analytical chemistry, there are 2 mainhow to make bromthymol blue:
- 0, 04% solution - 0.04 g of dry matter is diluted in 0.64 milliliters of 0.1-N NaOH solution, then diluted with 100 ml of cooled boiled water;
- 1% solution - a reagent taken in an amount of 0.1 g is diluted in 100 ml of 20% ethanol.
The alcohol solution is environmentally stable and can be stored for a long period of time.
Safety measures
Bromothymol blue is flammable and can also form explosive dust. Fires are extinguished with water spray, foam, carbon dioxide, or dry extinguishing powder. When burning, carbon monoxide and carbon dioxide, sulfur oxide and hydrogen bromide are released.
It may cause an allergic reaction and permanent staining if it comes into contact with the skin. Upon contact, flush skin with water. Avoid contact with eyes and respiratory tract, as this leads to irritation of the mucous membranes. If you feel worse, you should consult a doctor. When working with the substance, it is necessary to use personal protective equipment: goggles, overalls, gloves made of nitrile rubber. It is recommended to periodically apply protective creams and ointments to your hands.
Store this chemical in a dry place in closed containers. The room must have local and general ventilation.
