What is the Ka of thymol blue?
Table of Contents
What is the Ka of thymol blue?
Acid-Base Indicators
| Indicator | pH Range | pKa |
|---|---|---|
| Phenol red | 6.4 to 8.0 | 7.9 |
| Thymol blue | 8.0 to 9.6 | 8.9 |
| Phenolphthalein | 8.0 to 10.0 | 9.4 |
| Alizarin yellow R | 10.0 to 12.0 | 11.2 |
What pH does thymol blue change?
8.0 to 9.6
Some indicators change colour more than once over the pH range. For example, thymol blue changes from red to yellow in the pH range of 1.2 to 2.8, then from yellow to blue in the pH range of 8.0 to 9.6.
How do you convert pKa to Ka?
To create a more manageable number, chemists define the pKa value as the negative logarithm of the Ka value: pKa = -log Ka. If you already know the pKa value for an acid and you need the Ka value, you find it by taking the antilog.
Is thymol blue a weak acid?
Thymol blue is another weak acid that is used as an indicator. The fully protonated species (abbreviated H2Thy) is red, the monoprotonated species (HThy-) is yellow, and the fully deprotonated species (Thy2-) is blue.
What is the Ka of bromophenol blue?
6×10−5
Bromophenol blue is an acidic indicator with Ka value of 6×10−5. .
Is pKa and Ka the same?
Ka is the acid dissociation constant. pKa is simply the -log of this constant.
What is the pKa of an indicator?
Consequently, the pKa of an indicator corresponds to the pH of the solution at the inflection point in a plot of absorbance as a function Page 2 of pH as shown in Figure 1. Note, however, that it is critical that the absorbance at each wavelength corresponds to the absorbance of only HIn at λ1 and only In- at λ2.
At which K value of acid can use thymol blue indicator?
For the titration of a weak acid, however, the pH at the equivalence point is greater than 7.0, so an indicator such as phenolphthalein or thymol blue, with pKin > 7.0, should be used.
Why is thymol blue used as an indicator?
Thymol blue (thymolsulfonephthalein) is a brownish-green or reddish-brown crystalline powder that is used as a pH indicator. It is insoluble in water but soluble in alcohol and dilute alkali solutions. It transitions from red to yellow at pH 1.2–2.8 and from yellow to blue at pH 8.0–9.6.
Is pKa the same as ka?
Similar to pH, the value of Ka can also be represented as pKa. pKa = -log Ka. The larger the pKa, the weaker the acid. pKa is a constant for each conjugate acid and its conjugate base pair.
Is Bromothymol blue and bromophenol blue the same?
As a pH indicator, bromothymol blue, for example, would be useful between from about pH 6.0 to pH 7.6….
| Indicator | Bromophenol blue |
|---|---|
| Low pH color | yellow |
| Transition pH range | 3.0–4.6 |
| High pH color | purple |
What is the pH of bromophenol blue?
pH 4.6
It changes from yellow at pH 3.0 to blue at pH 4.6; this reaction is reversible. Bromophenol blue is structurally related to phenolphthalein (a popular indicator)….Acid–base indicator.
| Bromophenol blue (pH indicator) | ||
|---|---|---|
| below pH 3.5 | above pH 4.6 | |
| 3.5 | ⇌ | 4.6 |
How are Ka and pKa related?
Relationship between Ka, pKa and acid strength: The smaller the value of Ka, the larger the value of pKa, the weaker the acid. If the pH of a solution of a weak acid and the pKa are known, the ratio of the concentration of the conjugate base to the concentration of the acid may be calculated.
