Acid-Base Indicators quiz #1 Flashcards
Acid-Base Indicators quiz #1
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Which acid-base indicator is yellow in a solution with a pH of 9.8?
Thymol blue is yellow in a solution with a pH of 9.8, as its color transitions from yellow to blue in the pH range of 8.0 to 9.2. At pH 9.8, it has already transitioned to blue, but just before this, in the range near 9.2, it is yellow. Therefore, thymol blue is the indicator that is yellow close to pH 9.8. What is the difference between the endpoint and the equivalence point in a titration?
The equivalence point is when the amount of acid equals the amount of base, while the endpoint is just after this, when the indicator changes color. Why does an acid-base indicator change color during a titration?
An indicator changes color because its weak acid or base form is converted to its conjugate form, which has a different color. What is the ideal relationship between the pKa of an indicator and the pH at the equivalence point?
The ideal indicator has a pKa value close to the pH at the equivalence point for accurate detection of the endpoint. How does the color of an indicator relate to the concentrations of its weak acid and conjugate base forms?
The color depends on which form is predominant; the weak acid form shows one color, and the conjugate base form shows another. What is the typical pH range over which an acid-base indicator changes color?
An indicator usually changes color within one pH unit above and below its pKa value. What color does methyl orange start as, and what color does it transition to during titration?
Methyl orange starts as red and transitions to yellow as the pH increases from 3.3 to 4.5. How does the color of a solution at the intermediate form of an indicator relate to its weak acid and conjugate base concentrations?
At the intermediate form, the concentrations of weak acid and conjugate base are equal, resulting in a mixed or averaged color. What happens to the color of an indicator when the pH is one unit below its pKa?
When pH is one unit below the pKa, the indicator is mostly in its weak acid form and shows the color associated with that form. Why does thymol blue have two distinct pH transition ranges?
Thymol blue has two transition ranges because it has more than one site where it can act as an acid or base, leading to multiple color changes.