Given three acid-base indicators-methyl orange (end point at pH 4 ), bromthymol blue (end point

step 1 Okay, so we're being asked to choose the proper indicator here. Okay? So let's take a look at th

Given three acid-base indicators-methyl orange (end point at...

Given three acid-base indicators-methyl orange (end point at $\mathrm{pH} 4$ ), bromthymol blue (end point at $\mathrm{pH} 7$ ), and phenolphthalein (end point at $\mathrm{pH}$ 9)-which would you select for the following acid-base titrations? (a) perchloric acid with an aqueous solution of ammonia (b) nitrous acid with lithium hydroxide (c) hydrobromic acid with strontium hydroxide (d) sodium fluoride with nitric acid

Given three acid-base indicators-methyl orange (end point at $\mathrm{pH} 4$ ), bromthymol blue (end point at $\mathrm{pH} 7$ ), and phenolphthalein (end point at $\mathrm{pH}$ 9)-which would you select for the following acid-base titrations?
(a) perchloric acid with an aqueous solution of ammonia
(b) nitrous acid with lithium hydroxide
(c) hydrobromic acid with strontium hydroxide
(d) sodium fluoride with nitric acid

Key Concepts

Acid-Base Titration

Acid-base titration is an analytical method used to determine the concentration of an acid or a base by gradually adding a titrant of known concentration until the reaction reaches completion. In this process, the point at which stoichiometrically equivalent amounts of the acid and base have reacted is called the equivalence point, which is crucial for accurate measurements.

Equivalence Point

The equivalence point is the stage in a titration at which the amount of titrant added is chemically equivalent to the quantity of the analyte in the sample. The pH of the solution at the equivalence point depends on the strengths of the acid and base involved, and it often dictates the choice of the indicator, as the indicator must change color near this critical pH value.

Acid-Base Indicators

Acid-base indicators are substances that change color within a specific pH range, signaling the endpoint of a titration. They are weak acids or bases that exhibit different colors in their protonated and deprotonated forms. The proper indicator must have a transition range that encompasses the pH of the equivalence point to ensure an accurate determination of the titration endpoint.

Indicator Selection Based on pH Range

The selection of an appropriate indicator for a titration involves matching the indicator's color change (transition) pH range with the pH at the equivalence point of the reaction. For titrations involving weak acids or bases, the equivalence point pH may be significantly shifted from neutral, requiring the use of indicators with transition ranges suited to these conditions. This ensures that the color change occurs at or very near the true equivalence point.

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