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Related Concept Videos

Acid/Base Strengths and Dissociation Constants03:02

Acid/Base Strengths and Dissociation Constants

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The relative strength of an acid or base is the extent to which it ionizes when dissolved in water. If the ionization reaction is essentially complete, the acid or base is termed strong; if relatively little ionization occurs, the acid or base is weak. There are many more weak acids and bases than strong ones. The most common strong acids and bases are listed below:
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Polyprotic Acids03:38

Polyprotic Acids

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Acids are classified by the number of protons per molecule that they can give up in a reaction. Acids such as HCl, HNO3, and HCN that contain one ionizable hydrogen atom in each molecule are called monoprotic acids. Their reactions with water are:
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Polyprotic acids of the type H2M constitute two ionizable protons. As a result, on titration with a base, they exhibit two equivalence points in the titration curve. During titration, the species H2M, HM−, and M2− will be present in the solution at different points. The fractions of H2M, HM−, and M2− present at the various instances of the titration are denoted by α0, α1, and α2, respectively.
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This lesson defines the leveling effect in acidic and basic solutions and its role in aqueous and non-aqueous solutions. It is essential to understand the competing nature of various species in a chemical system.
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Extraction: Effects of pH00:53

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Consider a neutral form of an amine, B, with a partition coefficient, K, in a liquid mixture containing organic and aqueous phases. The pH of the aqueous phase affects the charge on acidic and basic solutes, and the charged form is usually more soluble in the aqueous phase. Suppose the conjugate acid form of the amine is soluble only in the aqueous phase while the base form is soluble in both phases. Then the distribution coefficient, D, can be given as the ratio of amine concentration in the...
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Titration of Polyprotic Base with a Strong Acid01:18

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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...
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Related Experiment Video

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Determination of the Gas-phase Acidities of Oligopeptides
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Squaramide equilibrium acidities in DMSO.

Xiang Ni1, Xin Li, Zhen Wang

  • 1State Key Laboratory of Elemento-Organic Chemistry, Department of Chemistry, Nankai University, and Collaborative Innovation Center of Chemical Science and Engineering , Tianjin 300071, China.

Organic Letters
|March 11, 2014
PubMed
Summary
This summary is machine-generated.

This study quantifies the acidity of squaramide organocatalysts using UV spectrophotometric titrations. The determined pKa values provide insights for designing novel squaramide catalysts.

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Area of Science:

  • Organic Chemistry
  • Catalysis

Background:

  • Squaramide derivatives are increasingly utilized as organocatalysts.
  • Understanding their acidity is crucial for predicting catalytic activity and selectivity.

Purpose of the Study:

  • To systematically determine the acidities (pKa values) of various popular squaramide organocatalysts.
  • To provide data that aids in the rational design of new squaramide catalysts.

Main Methods:

  • Utilized an overlapping indicator method for acidity determination.
  • Employed UV spectrophotometric titrations in dimethyl sulfoxide (DMSO) solvent.

Main Results:

  • Acidity (pKa) values for the studied squaramide organocatalysts were successfully determined.
  • The measured pKa values fall within the range of 8.37 to 16.46.

Conclusions:

  • The quantified acidities offer valuable data for the field of organocatalysis.
  • These findings can guide the development of more effective squaramide-based catalytic systems.