A common role of indicator is to detect the titration's endpoint. The color of an indicator changes when the acidity or oxidizing strength of a solution, or the concentration of a specific chemical species, exceeds the critical range of values.
Titration is the most popular quantitative and volumetric laboratory technique for determining an unknown concentration of an analyte in the presence of an indicator by comparing it to a known concentration of a solution.
A titrant is placed in a burette, and a pipette is used to introduce the titrant into the conical flask where the reaction takes place. A known concentration of titrant is added until the reaction is complete, i.e. the chemical equivalence point is reached.
| Table of Contents: |
Based on the chemical reaction that occurs between the titrant and the sample. Acid-base, redox, precipitation, and complexometric titration are four different types of titration.
What is an indicator in chemistry?
Compound that changes color when exposed to acidic or alkaline solutions is known as an indicator. Colored indicators are widely used to detect pH and can be added to the reaction mixture to determine the titration's endpoint or equivalence point.
An indicator has a specific pH range within which it transitions from acid to base. For example, litmus paper turns blue in a basic solution and turns red in an acidic solution. The range is 0 to 14, with 07 serving as the neutral point. A pH less than 07 indicates acidity, while a pH greater than 7 indicates alkalinity.
Types of the indicator:
Indicators are weak acids or bases (typically derived from plant pigments) that have distinct colors in both ionized and non-ionized states and are connected to the pH of the sample solution being analyzed. The two theories that explain the acid-base indicator are Ostwald's theory and the quinonoid theory.
In chemistry, there are three types of indicators: natural indicators, artificial indicators, and olfactory indicators, while artificial and natural indicators are the two most usually employed forms. Each has its own pKa, pH range, and produces a different color at different pH levels.
Role of the indicator:
We use an indicator in titration for the purpose to know whether the reaction (endpoint) is completed. When the color changes in the sample, you know the reaction is over. For example, the color of phenolphthalein changes from purple to pink, while the color of methyl orange changes from yellow to orange.“The basic function of an indicator is to signal a stoichiometric endpoint of the titration”
Examples of the indicator are a universal indicator, litmus paper, phenolphthalein, methyl orange, bromothymol blue, phenol red, methyl red, turmeric, onion, etc.
How do indicators work in titrations?
Indicators are both weak acids and bases, by reacting with H+ and OH-, pH indicators detect the presence of H+ and OH-. When an indicator is a weak acid that is colored and its corresponding base is a different color, deprotonation causes a color change.
On what basis is an indicator selected for a particular titration experiment?
The indicator is selected for particular titration based on the pH range of the reaction, whose falls within the pH change of the reaction.
For example, A phenolphthalein indicator is used to perform a strong acid–strong base titration. Because it changes color in the pH range of 8.3 to 10, in basic solutions, it will appear pink; In acidic solution, it would seem clear.
References:
- Wikipedia contributors. (2022, January 23). PH indicator. In Wikipedia, The Free Encyclopedia. Available Here
- Chemical Sensing Using Indicator Dyes: Wolfbeis, Otto F. Optical Fiber Sensing 1997, 4, 53-107.
- Modern reaction-based indicator systems. Dong-Gyu Cho and Jonathan L. Sessler Chem. Soc. Rev. 2009, 38, 1647-1662.
- ‘What Is the Function of an Indicator in a Titration?’ Reference.Com, 4 Aug. 2015, Available Here
You may also like this:
No comments:
Post a Comment