
Cresol Red (CAS 1733-12-6) is a high - quality chemical compound that offers excellent value for its price. It has a molecular formula of C₂₁H₁₈O₅S. The compound typically appears as a dark red or brown powder. It is sparingly soluble in water but more soluble in ethanol and other organic solvents.
The melting point of Cresol Red is around 295 - 300 °C. Its pH range for color change is from 7.2 (yellow) to 8.8 (red). This property makes it a useful pH indicator in various laboratory and industrial applications.
One of the primary uses of Cresol Red is as a pH indicator in titration experiments. In acid - base titrations, it helps chemists determine the endpoint of the reaction accurately. For example, in a titration of a weak base with a strong acid, Cresol Red can signal when the pH of the solution reaches the appropriate range by changing color.
It is also used in microbiology. In culture media, Cresol Red can indicate changes in pH due to the metabolic activities of microorganisms. If the microorganisms produce acidic or basic by - products, the color of the medium containing Cresol Red will change, allowing researchers to monitor the growth and metabolic status of the cultures.
In the field of environmental science, Cresol Red can be used to measure the pH of natural water bodies such as lakes, rivers, and groundwater. By adding a small amount of Cresol Red to a water sample, scientists can quickly assess whether the water is acidic, neutral, or basic.
When using Cresol Red as a pH indicator in titration, first, prepare a stock solution. Dissolve an appropriate amount of Cresol Red in ethanol or a suitable solvent according to the experimental requirements. Then, add a few drops of the indicator solution to the sample solution before starting the titration.
During the titration process, slowly add the titrant while continuously swirling the sample. Observe the color change of the solution. When the color changes from the initial color (yellow in acidic solutions) to the final color (red in basic solutions), the endpoint of the titration is reached.
For microbiological applications, add Cresol Red to the culture medium during its preparation. Make sure it is evenly distributed in the medium. After inoculating the microorganisms, incubate the culture. Monitor the color change of the medium over time to study the metabolic processes of the microorganisms.
Case 1: Laboratory Titration Experiment
In a chemistry laboratory, a student was tasked with determining the concentration of a sodium hydroxide solution. They used Cresol Red as the pH indicator. By carefully adding a hydrochloric acid solution to the sodium hydroxide sample, the student observed the color change from red (basic) to yellow (acidic). Using the volume of hydrochloric acid added at the endpoint and the known concentration of hydrochloric acid, the student was able to accurately calculate the concentration of the sodium hydroxide solution.
Case 2: Microbiological Research
A research team was studying the growth of lactic acid bacteria in a dairy - based culture medium. They added Cresol Red to the medium. As the lactic acid bacteria grew and produced lactic acid, the pH of the medium decreased. The color of the medium changed from red to yellow, indicating the acid production. This allowed the researchers to track the growth kinetics and metabolic activity of the lactic acid bacteria.
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