Effective pH Indicator: Methyl Red is highly reliable for acid-base titrations, clearly indicating pH changes through distinct color transitions.
Precise Titration Endpoint Detection: Its sharp color change allows for accurate identification of the titration endpoint, enhancing analytical precision.
Good Solubility in Organic Solvents: Though nearly insoluble in water, Methyl Red dissolves easily in ethanol, chloroform, and acetic acid, offering flexibility in various lab environments.
Stable Physical Properties: Available as a lustrous purple crystal or reddish-brown powder, Methyl Red maintains stable form and quality for consistent laboratory use.
Methyl Red typically appears as shiny purple crystals or a reddish-brown powder. While it is nearly insoluble in water, it dissolves readily in ethanol, chloroform, and acetic acid. Its primary application is in acid-base titrations, where it serves as a pH indicator, signaling the titration endpoint by changing color.
Methyl Red Chemical Properties
| Melting point | 179-182 °C (lit.) |
| Boiling point | 412.44°C (rough estimate) |
| Density | 0.839 g/mL at 25 °C |
| Bulk density | 300-500kg/m3 |
| Vapor density | 9.3 (vs air) |
| Refractive index | 1.5930 (estimate) |
| Fp | 11 °C |
| Storage temp. | Store at +5°C to +30°C. |
| Solubility | ethanol: soluble1mg/mL |
| Form | Solid |
| Pka | 4.95(at 25℃) |
| Colour Index | 13020 |
| Color | Reddish-violet |
| PH Range | 4.4(red)-6.3(yellow) |
| Odor | Odorless |
| Water Solubility | Practically insoluble in water. Soluble in alcohol, acetic acidSoluble in ethanol. Insoluble in water. |
| λmax | 410nm, 530nm, 427nm, 519nm |
| ε(extinction coefficient) | ≥10000 at 282-288nm in methanol ≥20000 at 509-519nm in methanol ≥7000 at 329-335nm in methanol |
| Merck | 14,6119 |
| BRN | 750102 |
| Stability | Stable. Incompatible with strong oxidizing agents. |
| Major Application | Waveguides, LED sensors, photoresists, liquid crystals, sol-gel matrix, optical sensors, paints, toys, detection of thiols, food freshness sensors, dental product, saliva sampling method, detecting lactic acid, carbohydrates |
| InChIKey | CEQFOVLGLXCDCX-MSUUIHNZSA-N |
| CAS DataBase Reference | 493-52-7 |
| NIST Chemistry Reference | Benzoic acid, 2-[[4-(dimethylamino)phenyl]azo]-(493-52-7) |
| IARC | 3 (Vol. 8, Sup 7) 1987 |
| EPA Substance Registry System | Methyl red (493-52-7) |
Methyl red is used as an indicator in a 0.1% alcoholic solution, showing a red color at pH 4.4 and turning yellow at pH 6.2. It is suitable for titrating ammonia and weak organic bases, such as alkaloids, but not ideal for most organic acids, with the exception of oxalic and picric acids. Due to its tendency to be easily reduced and lose color, observations should be made quickly. Methyl red is increasingly being replaced by sulfonphthalein indicators like bromcresol green, which are more stable and offer a more distinct color transition.
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