In a titration, an indicator is a substance that is used to determine the endpoint. Organic substances (weak acids or weak bases) are commonly used as indicators in acid-base titrations. Each has its own pKa, pH range, and color change, and is employed in different types of titrations depending on the requirement. Quinonoid and Ostwald’s Theory are the two theories that have been presented to explain why acid-base indicators change color when pH changes.
What is bromothymol blue indicator?
Bromothymol blue, commonly known as bromothymol sulfonephthalein or BTB, is a dye that is used to determine pH. Bromothymol blue is a weak acid that can be in the form of an acid or a base depending on the pH of the solution. It is commonly employed in applications that require the measurement of chemicals at neutral pH (approximately 7.0).
Bromothymol blue is prepared by mixing elemental bromine with thymol blue in a glacial acetic acid solution. Depending on whether it is protonated or deprotonated, it may appear yellow or blue. It is usually sold in solid (powder, crystals, or chunks) form because the acid indicator is sodium salt.
Bromothymol blue has a pH range of 6.0 to 7.6 and a pKa of 7.1. It becomes yellow in an acidic medium, blue in basic conditions, and green in a neutral solution. Bromothymol blue is commonly used to determine the presence of carbonic acid in a liquid.
Physical properties of bromothymol blue:
Chemical formula
C27H28Br2O5S
Molecular Weight/ Molar Mass
624.38 g•mol−1
Density
1.25 g/cm3
Melting point
202 °C
Solubility
Sparingly soluble in water
Acidity (pKa)
7.0
pH range
6.0 to 7.6
Color in acid
Yellow
Color in base
Blue
FAQ (Frequently Asked Questions):
Bromothymol blue is the best indicator for which titration?
In chemistry, BTB is a suitable choice for titrations whose equivalence point is near-neutral pH. Generally, bromothymol blue indicator is used for strong acid-strong base titration.
Is bromothymol blue is a natural indicator?
The bromothymol blue is not a natural indicator; it is an organic compound that is synthesized in the laboratory.
Is bromothymol blue a weak acid or base?
Bromothymol blue acts as a weak acid. As a result, it may appear blue or yellow, depending on whether it is protonated or deprotonated.
What kind of indicator is bromothymol blue?
Bromothymol blue (BTB) is a pH indicator that is also known as bromothymol sulfone phthalein. It's most commonly employed in applications that require measuring substances with a pH that's close to neutral.
What is the pH range of the bromothymol blue indicator?
Bromothymol blue indicator has a working pH range of 6.0 to 7.6.
What is the color of the bromothymol blue indicator in an acidic solution?
In an acidic medium, the color of the bromothymol blue indicator is yellow.
What color is the bromothymol blue indicator in a basic solution?
In a basic medium, the color of the bromothymol blue indicator is blue.
How do you make a bromothymol blue indicator?
To make the bromothymol blue indicator, weigh 50 mg of bromothymol blue correctly and dissolve it in 100 ml of ethanol, containing 04.00 ml of 0.05N NaOH solution.
Is bromothymol blue a universal indicator?
It is not a universal indicator, but it is a portion of it. A universal indicator is a collection of indicators that display color changes in a solution and can be used to determine whether a solution is acidic or basic. Phenolphthalein, bromothymol blue, thymol blue, and methyl red, are the main component of universal indicator
References:
- Horobin R. W. and Kiernan J. A., 2002, 10th ed., CONN'S Biological Stains, A Handbook of Dyes, Stains
- INDIAN PHARMACOPOEIA 2018, VOL-I, 4.3(957-958)
- Wikipedia contributors. (2022, January 25). Bromothymol blue. In Wikipedia, The Free Encyclopedia.
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