For the indicator thymol blue, the value of pH is 2.0 when half of the indicator is present in t

step 1 Answer for Part A, add pH is equal to 2. pH is changing gradually with added N -A -O -H. No cert

For the indicator thymol blue, the value of pH is 2.0 when...

For the indicator thymol blue, the value of $\mathrm{pH}$ is $2.0 \mathrm{when}$ half of the indicator is present in the unionized form. The percentage of the indicator in the unionized form in a solution of $4.0$ $\times 10^{-3} \mathrm{M}$ hydrogen ion concentration is (a) $40 \%$ (b) $28.6 \%$ (c) $71.4 \%$ (d) $60 \%$

For the indicator thymol blue, the value of $\mathrm{pH}$ is $2.0 \mathrm{when}$ half of the indicator is present in the unionized form. The percentage of the indicator in the unionized form in a solution of $4.0$ $\times 10^{-3} \mathrm{M}$ hydrogen ion concentration is
(a) $40 \%$
(b) $28.6 \%$
(c) $71.4 \%$
(d) $60 \%$

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Key Concepts

Acid?Base Indicator Equilibrium

An acid?base indicator exists in two forms—a unionized (acid) form and an ionized (base) form—each displaying a different color. The equilibrium between these forms changes with pH, which forms the basis of the color change observed during acid-base titrations.

pKa

The pKa is the negative logarithm of the acid dissociation constant (Ka) and represents the pH at which the indicator is 50% unionized and 50% ionized. This key value is critical in determining the pH range over which the indicator changes color.

Henderson?Hasselbalch Equation

The Henderson?Hasselbalch equation, given by pH = pKa + log([ionized form]/[unionized form]), provides a convenient way to relate the pH of a solution to the ratio of the indicator’s ionized and unionized forms. It is essential for quantifying the color change of the indicator by calculating the percentage distribution of these forms.

pH and Hydrogen Ion Concentration

pH is defined as the negative logarithm of the hydrogen ion concentration. This relationship is fundamental in determining the acidity of a solution, which in turn influences the equilibrium position of acid-base reactions, such as the dissociation of an indicator.

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