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 areas of its application.
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 bromothymolblow, bromothymol sulfulfon phthalein, dibromthymol sulfulfophthalein ammonium salt. According to the degree of chemical purity, it is produced in one qualification - PSA (pure for analysis).
Chemical formula of the compound: C₂₇H₂₈Br₂O₅S.
The substance belongs to the category of triphenylmethane dyes, which also includes brilliant green, fuchsin 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 what the environmental conditions are and the concentration of dissolved substances, bromothymol blue changes color. The indicator does not interact with the components of the medium and does not affect the course of chemical processes. Reagents of this type can determine the parameters of the working environment.
The compound has the following colorimetric characteristics:
- alkaline environment - intense blue color;
- neutral environment - grassy green color;
- acidic medium - yellow color.
The color change from yellow to blue occurs through various shades of green. To obtain the desired color, use a 0.5% sodium hydroxide solution or 10% sodium carbonate solution (alkalization), as well as a 10% HCl solution (acidification).
In an aqueous solution, bromothymol 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 tan 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;
- state of aggregation - solid;
- density - 1250 kg / m 3 ;
- mass fraction of the residue after calcination - not more than 1%;
- melting point - 202 ° C;
- the proportion of active substance in the powder is not less than 95% by weight.
The solubility of bromothymol blue in water is moderate, in ethanol - good (with the formation of a brown color), in acetone - 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 the following purposes:
- 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 asparaginase enzyme that catalyzes the splitting of the aspartic amino acid (the blue color of the solution indicates an increase in enzyme activity);
- use as one of the components of a nutrient medium in bacteriology to control the development of culture;
- visualization of cell walls or nuclei when examined under a microscope;
- in gynecology - the detection of premature rupture of the membranes (amniotic fluid has a pH of 7.2, so the indicator solution acquires a blue color).
Most widely, its properties as an indicator are used in such industries as:
- chemical;
- metallurgical;
- textile;
- food;
- Agriculture.
Working solutions
In analytical chemistry, 2 main methods of preparing bromothymol blue are used:
- 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 - the reagent, taken in an amount of 0.1 g, diluted in 100 ml of 20% ethyl alcohol.
The alcohol solution is resistant to environmental influences and can be stored for a long period of time.
Security measures
Bromothymol blue is a combustible substance, and is also able to form explosive dust. Ignite the fire by spraying it with water, foam, carbon dioxide or dry powder for fire fighting. When burning, carbon monoxide and carbon dioxide, sulfur oxide and hydrogen bromide are released.
If it gets on the skin, it can cause an allergic reaction and persistent staining. Upon contact, rinse skin with water. Avoid contact with eyes and respiratory tract, as this leads to irritation of the mucous membranes. If you feel worse, you must consult a doctor. When working with the substance, personal protective equipment must be used: glasses, protective clothing, gloves made of nitrile rubber. It is recommended that you periodically apply protective creams and ointments to your hands.
Keep this chemical reagent in a dry place in closed containers. The room must have local and general ventilation.