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Related Concept Videos

Indicators02:39

Indicators

Certain organic substances change color in dilute solution when the hydronium ion concentration reaches a particular value. For example, phenolphthalein is a colorless substance in any aqueous solution with a hydronium ion concentration greater than 5.0 × 10−9 M (pH < 8.3). In more basic solutions where the hydronium ion concentration is less than 5.0 × 10−9 M (pH > 8.3), it is red or pink. Substances such as phenolphthalein, which can be used to determine the pH of a solution, are called...
Titration of Polyprotic Base with a Strong Acid01:18

Titration of Polyprotic Base with a Strong Acid

The titration of a polyprotic base such as sodium carbonate with a strong acid such as hydrochloric acid results in two equivalence points on the titration curve. At the first equivalence point, the carbonate ions in the base are completely converted to bicarbonate ions. The second equivalence point corresponds to the complete conversion of bicarbonate ions to carbonic acid, which dissociates into carbon dioxide and water. The region before the first equivalence point corresponds to the...
Titration of a Weak Acid with a Weak Base01:08

Titration of a Weak Acid with a Weak Base

Weak acids and bases do not undergo dissociation completely, and titrations between these two are rarely studied. When such studies are performed, say, for the titration of a weak acid with a weak base, the titration curve plots the change in pH as a function of the volume of base added. Take the titration of acetic acid with ammonia, for instance. During the titration, these two species form ammonium acetate and water, but the pH change is slow and gradual.
As a result, there is no simple...
Titration of a Weak Acid with a Strong Base01:30

Titration of a Weak Acid with a Strong Base

In titrating a weak acid with a strong base, different calculation methods are applied at various stages. Initially, the pH of a weak acid like acetic acid is calculated using its dissociation constant (Ka) and an ICE table. Upon addition of a strong base such as sodium hydroxide, a buffer forms, and its pH is determined using the Henderson-Hasselbalch equation. As more base is added and the titration reaches the halfway point, the pH becomes equal to the pKa of the acid, indicating equal...
Precipitation Titration: Endpoint Detection Methods01:19

Precipitation Titration: Endpoint Detection Methods

In argentometric precipitation titrations, endpoints can be detected visually by the Mohr, Volhard, and Fajans methods. In the Mohr method, adding a soluble chromate indicator gives an initial yellow color to the analyte solution. As the titrant is added, the first excess of silver ions forms a red silver chromate precipitate, marking the endpoint. The solution pH should be maintained at about 8 by adding solid CaCO3.
In the Volhard method, a standard excess of AgNO3 is first added to the...
Ladder Diagrams: Acid&#8211;Base Equilibria01:32

Ladder Diagrams: Acid–Base Equilibria

Understanding the chemistry between the reagents is necessary for performing any experiment. To this end, scientists have designed a tool called a ladder diagram, which is a graphical representation that helps illustrate the chemistry of a system.
A ladder diagram for acid-base equilibria consists of a vertical axis that represents pH and horizontal bars (steps on the ladder) that help position all the pKa values in the system. At equilibrium, the pH value of the system corresponds to one of...

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An Assay for Measuring the Activity of Escherichia coli Inducible Lysine Decarboxyase
08:08

An Assay for Measuring the Activity of Escherichia coli Inducible Lysine Decarboxyase

Published on: December 19, 2010

Lapachol: a new acid-base indicator.

K C Joshi1, P Singh, G Singh

  • 1Chemistry Department, University of Rajasthan, Jaipur-302004, India.

Talanta
|April 1, 1976
PubMed
Summary
This summary is machine-generated.

Lapachol, a natural acid-base indicator, offers a distinct red color in alkaline solutions. Its pH transition range of 4.8-5.8 makes it suitable for titrating strong acids with various bases.

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Area of Science:

  • Analytical Chemistry
  • Natural Product Chemistry

Background:

  • Acid-base indicators are crucial for determining endpoints in titrations.
  • Natural products offer sustainable alternatives to synthetic reagents.

Purpose of the Study:

  • To evaluate Lapachol as a novel acid-base indicator.
  • To determine the transition range and utility of Lapachol in titrations.

Main Methods:

  • Spectrophotometric analysis to determine the color transition range.
  • Titration experiments using Lapachol as the indicator.

Main Results:

  • Lapachol exhibits a sharp color change to deep red in alkaline conditions.
  • The determined pH transition range for Lapachol is 4.8–5.8.
  • Lapachol proved effective for titrating strong acids with both strong and weak bases.

Conclusions:

  • Lapachol is a viable, naturally sourced acid-base indicator.
  • Its distinct color change and suitable pH range allow for accurate titrations.
  • Lapachol presents a sustainable option for analytical chemistry applications.