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相关概念视频

Relative Strengths of Conjugate Acid-Base Pairs02:29

Relative Strengths of Conjugate Acid-Base Pairs

Brønsted-Lowry acid-base chemistry is the transfer of protons; thus, logic suggests a relation between the relative strengths of conjugate acid-base pairs. The strength of an acid or base is quantified in its ionization constant, Ka or Kb, which represents the extent of the acid or base ionization reaction. For the conjugate acid-base pair HA / A−, the ionization equilibrium equations and ionization constant expressions are
Weak Base Solutions03:21

Weak Base Solutions

Some compounds produce hydroxide ions when dissolved by chemically reacting with water molecules. In all cases, these compounds react only partially and so are classified as weak bases. These types of compounds are also abundant in nature and important commodities in various technologies. For example, global production of the weak base ammonia is typically well over 100 metric tons annually, being widely used as an agricultural fertilizer, a raw material for chemical synthesis of other...
Titration of a Polyprotic Acid02:08

Titration of a Polyprotic Acid

A polyprotic acid contains more than one ionizable hydrogen and undergoes a stepwise ionization process. If the acid dissociation constants of the ionizable protons differ sufficiently from each other, then the titration curve for such polyprotic acid generates a distinct equivalence point for each of its ionizable hydrogens. Therefore, titration of a diprotic acid results in the formation of two equivalence points, whereas the titration of a triprotic acid results in the formation of three...
Acid and Bases: Ka, pKa, and Relative Strengths02:35

Acid and Bases: Ka, pKa, and Relative Strengths

This lesson delves into a critical aspect of the relative strengths of acids and bases. The strength of an acid is evaluated by the acid dissociation into its conjugate base and a hydronium ion in water. The complete dissociation of a strong acid is confirmed with a very high concentration of hydronium ions. As a result, an incomplete dissociation process affirms a weak acid. Therefore, the equilibrium is in the forward direction for strong acids and backward for weak acids in these reactions.
Position of Equilibrium in Acid-Base Reactions02:05

Position of Equilibrium in Acid-Base Reactions

In any solution, the value of pKa indicates whether an acid is completely dissociated or not. A negative pKa corresponds to a stronger acid, whereas a positive pKa corresponds to a weaker acid. Consider the reaction between ammonia and an ethoxide ion. In this reaction, ethanol with a pKa of 15.9 is a stronger acid than ammonia with a pKa of 38. Recall that the strong acid forms a weak conjugate base, and a weak acid forms a strong conjugate base. Hence, the ethoxide ion is a weak base.
Extraction: Effects of pH00:53

Extraction: Effects of pH

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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相关实验视频

Updated: Jul 20, 2026

PIP-on-a-chip: A Label-free Study of Protein-phosphoinositide Interactions
10:58

PIP-on-a-chip: A Label-free Study of Protein-phosphoinositide Interactions

Published on: July 27, 2017

绝对pK ((a) 替代的测定

Matthew D Liptak1, Kevin C Gross, Paul G Seybold

  • 1Department of Chemistry, Hamilton College, 198 College Hill Road, Clinton, New York 13323, USA.

Journal of the American Chemical Society
|May 30, 2002
PubMed
概括

这项研究使用计算化学准确预测了酸度 (pK(a)). 在溶液中优化结构对于精确的计算至关重要,有利于化学界.

科学领域:

  • 计算化学的计算化学
  • 物理化学 物理化学
  • 量子化学 是一个量子化学.

背景情况:

  • 预测的酸度 (pK (a) 值) 对于各种化学应用是必不可少的.
  • 需要精确的计算方法来确定pK (a) 值,而无需实验装配.

研究的目的:

  • 准确计算 20 种的绝对pK (a) 值,使用明确的计算方法.
  • 评估溶解模型对pK (a) 预测准确性的影响.

主要方法:

  • 使用CBS-QB3方法进行气相自由能计算.
  • 用CPCM连续溶解模型对及其离子进行分析.
  • 在气体和溶剂阶段进行了优化.

主要成果:

  • 在标准偏差和RMSE低于0.4 pK (a) 单位的情况下实现了高精度.
  • 证明了化相优化结构对于精确的离子计算至关重要.
  • 该研究代表了非常准确的PK的绝对确定.

结论:

  • 通过连贯的计算策略,可以准确预测pK (a) 值.
  • 溶解效应,特别是离子,显著影响pK (a) 计算.

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In Vivo EPR Assessment of pH, pO2, Redox Status, and Concentrations of Phosphate and Glutathione in the Tumor Microenvironment
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In Vivo EPR Assessment of pH, pO2, Redox Status, and Concentrations of Phosphate and Glutathione in the Tumor Microenvironment

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A New Straightforward Method for Lipophilicity (logP) Measurement using 19F NMR Spectroscopy
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A New Straightforward Method for Lipophilicity (logP) Measurement using 19F NMR Spectroscopy

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PIP-on-a-chip: A Label-free Study of Protein-phosphoinositide Interactions
10:58

PIP-on-a-chip: A Label-free Study of Protein-phosphoinositide Interactions

Published on: July 27, 2017

In Vivo EPR Assessment of pH, pO2, Redox Status, and Concentrations of Phosphate and Glutathione in the Tumor Microenvironment
10:46

In Vivo EPR Assessment of pH, pO2, Redox Status, and Concentrations of Phosphate and Glutathione in the Tumor Microenvironment

Published on: March 16, 2018

A New Straightforward Method for Lipophilicity (logP) Measurement using 19F NMR Spectroscopy
09:32

A New Straightforward Method for Lipophilicity (logP) Measurement using 19F NMR Spectroscopy

Published on: January 30, 2019

  • 这种方法提供了一种可靠的,非实证的方法来确定化合物的酸度.