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A gradient of red cabbage extract pH indicator from acidic solution on the left to basic on the right. Red cabbage contains an anthocyanin-based dye that can be used as a pH indicator. It is red, pink, or magenta in acids (pH < 7), purple in neutral solutions (pH ≈7), and ranges from blue to green to yellow in alkaline solutions (pH > 7). [7]
In and of themselves, pH indicators are usually weak acids or weak bases. The general reaction scheme of acidic pH indicators in aqueous solutions can be formulated as: HInd (aq) + H 2 O (l) ⇌ H 3 O + (aq) + Ind − (aq) where, "HInd" is the acidic form and "Ind −" is the conjugate base of the indicator. Vice versa for basic pH indicators ...
Experiment Observation Inference Substance in water + 3 mL Benedict's solution, then boil for few minutes and allow to cool. Red, green, or yellow precipitate is obtained Reducing sugar, such as glucose, is present Substance in water + 3 mL Benedict's solution, then boil for few minutes and allow to cool. Solution remains clear or is a little blue
Anthocyanins may be used as pH indicators because their color changes with pH; they are red or pink in acidic solutions (pH < 7), purple in neutral solutions (pH ≈ 7), greenish-yellow in alkaline solutions (pH > 7), and colorless in very alkaline solutions, where the pigment is completely reduced.
Titration indicator table [11] Indicator name Indicator colour Transition interval (pH range) Color after high pH conditions Methyl Orange Orange/red 3.1 - 4.4 Yellow Methyl Red Red 4.4 - 6.3 Yellow Congo Red Blue 3.0 - 5.2 Red Phenolphthalein Colourless 8.3 - 10.0 Pink Thymolphthalein Colourless 9.3 - 10.5 Blue Bromophenol Blue Yellow 3.0 - 4.6
Phenol red exists as a red crystal that is stable in air. Its solubility is 0.77 grams per liter (g/L) in water and 2.9 g/L in ethanol. [1] It is a weak acid with pK a = 8.00 at 20 °C (68 °F). A solution of phenol red is used as a pH indicator, often in cell culture.
Bromothymol blue (also known as bromothymol sulfone phthalein and BTB) is a pH indicator. It is mostly used in applications that require measuring substances that would have a relatively neutral pH (near 7). A common use is for measuring the presence of carbonic acid in a liquid. It is typically sold in solid form as the sodium salt of the acid ...
The indicator is used in photosynthesis and respiration experiments to find out whether carbon dioxide is being liberated. [1] It is also used to test the carbon dioxide content during gaseous exchange of organisms. When the carbon dioxide content is higher than 0.04%, the initial red colour changes to yellow as the pH becomes more acidic.