If the pH is somewhere between these two limits, the colour is orange. Methylene red is useful when it comes to testing the pH changes in acidic solutions. The hydrocarbon chains or rings are typically aryl groups, which are derived from aromatic compounds.
Acid Red 2. It has a molar mass of Its simple chemical formula can be written as C 15 H 15 N 3 O 2. Together with murexide , methyl red is being investigated for its potential for the sonochemical destruction of chlorinated hydrocarbon pollutants. Sonochemistry is a relatively new field of research that focuses on the chemical reactions that occur with the application of powerful ultrasonic waves, specifically ones with frequencies between 20 kHz and 10 MHz.
Structurally, the chemical composition and molecular relationships of the elements in methyl red can be illustrated as:. Methyl red can be prepared through the diazotisation of anthranilic acid, which is followed by a chemical reaction with dimethylaniline.
The series of chemical processes is illustrated below:. Azo dyes have important commercial value as dyes for textiles, leather products, and some food products. Something went wrong. Try again? Cited by. Download options Please wait Article type Paper. Download Citation. Request permissions. They are usually weak acids or bases, which when dissolved in water dissociate slightly and form ions.
The equilibrium solution has the colour A. In contrast, the pKin for methyl red 5. In general, for titrations of strong acids with strong bases and vice versa , any indicator with a pK in between about 4.
For the titration of a weak acid, however, the pH at the equivalence point is greater than 7. Conversely, for the titration of a weak base, where the pH at the equivalence point is less than 7.
In the titration of a weak acid with a strong base, which indicator would be the best choice? The correct answer is C. In the titration of a weak acid with a strong base, the conjugate base of the weak acid will make the pH at the equivalence point greater than 7. Therefore, you would want an indicator to change in that pH range. Both methyl orange and bromocresol green change color in an acidic pH range, while phenolphtalein changes in a basic pH.
The existence of many different indicators with different colors and pKin values also provides a convenient way to estimate the pH of a solution without using an expensive electronic pH meter and a fragile pH electrode. Acid—base indicators are compounds that change color at a particular pH.
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