Name: why some substances dissolve in water
Uploaded: 2025-05-22T09:05:33.000Z
Duration: 3 min
Channel: JoVE

K12 Standards

Minnesota Academic Standards in Science

9-12

Chemistry

3.2.1 9C.3.1.1.3

Solubility

溶液是由两种主要物质组成的均一混合物：溶质和溶剂。&#160;溶剂的量多于溶质。
在稀溶液中，溶质相对于溶剂的比例较小，而在浓溶液中，该比例较大。
在形成溶液时，溶质与溶剂之间不会发生化学反应。相反，分子会重新分布，单个溶剂分子会包围溶质分子，并通过吸引力相互作用。这种溶解过程称为溶剂化。
为了有利于溶剂化，溶质-溶剂相互作用应强于溶剂-溶剂和溶质-溶质相互作用。
在溶液中，溶质和溶剂可以是任何物态。溶液本身为单一“相”。
与溶解相反的过程是沉淀，由强烈的溶质-溶质相互作用引发。当溶解速率等于沉淀速率时，便建立了溶解度平衡。
溶质的溶解度是指在给定量的溶剂中，达到溶解平衡时其可能存在的最大浓度。溶解度受温度及分子极性等其他物理条件的影响。
非极性溶质通过分子间的伦敦色散力溶解于非极性溶剂中，而极性或离子型溶质则通过离子-偶极或偶极-偶极相互作用溶解于极性溶剂中。
水是一种极性溶剂。亲水性（即喜水）化合物由于带有离子电荷或极性基团，能够与水分子发生足够强的相互作用，因此可溶于水。这些化合物在非极性溶剂中溶解度较低，因为溶质分子之间的相互作用远强于非极性溶剂与极性溶质分子之间可能发生的任何相互作用。
像油类这样不溶于水、可溶于脂肪的非极性化合物具有疏水性，即“惧水性”，因为它们无法形成氢键以与溶剂-溶剂之间的相互作用相竞争。
两亲性或双亲性化合物同时具有极性和非极性基团。例如，肥皂是脂肪酸的金属盐。在水中，肥皂分子会聚集形成称为胶束的球形结构，其非极性的疏水性脂肪酸尾部向内，而极性的亲水性头部则朝外。
使用肥皂去除油渍时，肥皂分子的尾部会包围非极性的油污形成可溶于水的胶束，从而使油污被水冲洗掉。

溶解度

<h4>溶液、溶解度和溶解平衡</h4>


 溶液是由溶剂（主要成分）和溶质（次要成分）组成的均匀混合物。 溶液的物理状态（固体、液体或气体）通常与溶剂的物理状态相同。 溶质浓度通常用定性术语描述，例如稀释（相对较低浓度）和浓缩（相对较高浓度）。


 在溶液中，溶质颗粒（分子、原子和/或离子）被溶剂分子紧密包围，并通过吸引力相互作用。 这个溶解过程称为溶剂化。 当水作为溶剂时，该过程称为水合。 溶剂化需要溶质-溶剂相互作用强于溶质-溶质和溶剂-溶剂相互作用。 沉淀与溶剂化相反，因强烈的溶质-溶质相互作用而发生。


 溶解度是在给定量的溶剂中可以溶解的最大溶质量。 温度、压力和分子极性是影响溶解度的重要因素。 当溶质的溶解和沉淀以相同的速率发生时，就达到了溶解平衡。


 <h4>相似相溶</h4>


 为了预测溶质是否可溶于某种溶剂，经验法则是"相似相溶"。 由于与溶剂分子产生离子-偶极或偶极-偶极相互作用，极性或离子溶质可以溶解在极性溶剂中。 这种相互作用对于非极性溶剂是无法实现的。 非极性溶质通过分子间色散力溶解在非极性溶剂中。


 <h4>亲水性、疏水性和两亲性化合物</h4>


 水是极性溶剂。 可溶于水的溶质被称为"亲水"或"喜水"。 例如，当将固体KCl添加到水中时，极性水分子的正（氢）端被负氯离子吸引，而水的负（氧）端被正钾离子吸引。 水分子包围着单个 K+ 和 Cl− 离子，减小了将离子结合在一起的强力，让它们以溶剂化离子的形式移入溶液中。



 不溶于水的溶质被称为"疏水"或"恐水"。 由于溶质-溶质相互作用较强，此类溶质（如油）无法与周围的水分子形成氢键。 结果，溶质颗粒聚集在一起并且保持不溶解。



 同时具有极性和非极性基团的化合物称为"两亲"或"两性化合物"。 例如，肥皂是脂肪酸的盐。，具有非极性碳氢化合物的疏水尾部和极性亲水头部。 肥皂和洗涤剂的清洁作用可以用分子结构来解释。 肥皂或洗涤剂分子的碳氢化合物（非极性）末端溶解在非极性物质中或被非极性物质吸引，例如油脂或污垢颗粒。，而离子末端被水（极性）吸引。 结果，肥皂或洗涤剂分子在污垢颗粒和水之间起到桥梁作用，使污垢颗粒悬浮为胶体颗粒并容易被冲走。



 本文改编自 <a href="https://openstax.org/books/chemistry-2e/pages/11-1-the-dissolution-process">OpenStax Chemistry 2e, Section 11.1: The Dissolution Process</a>, <a href="https://openstax.org/books/chemistry-2e/pages/11-3-solubility">Section 11.3: Solubility</a>, and <a href="https://openstax.org/books/chemistry-2e/pages/11-5-colloids">Section 11.5: Colloids

溶液、溶解度与溶解平衡
溶液是由溶剂（主要组分）和溶质（次要组分）组成的均一混合物。……

Education

教育

JoVE Core

Organic Chemistry

有机化学

Unit 1

第一单元

Covalent Bonding and Structure

共价键与结构

KEY TERMS AND CONCEPTS

关键术语与概念

why some substances dissolve in water

Solution formation depends on how solutes and solvents interact. A solution is a homogeneous mixture made of a solvent, which is the larger part, and a solute, which is the smaller part. The physical state of a solution is usually the same as the solvent. Concentration is often described as dilute for a low amount of solute or concentrated for a high amount of solute.

When a solute dissolves, its particles are surrounded by solvent species. This process is called solvation. If water is the solvent, it is called hydration. For solvation to happen, solute-solvent attractions must be stronger than the attractions within the solute and within the solvent. The opposite process is precipitation, which happens when solute particles are pulled together strongly enough to leave solution.

Solubility is the maximum amount of solute that can dissolve in a given amount of solvent. Temperature, pressure, and molecular polarity can all affect solubility. Solubility equilibrium occurs when dissolution and precipitation happen at the same rate. At that point, the amount dissolved stays constant.

A useful rule for predicting solubility is “like dissolves like.” Polar or ionic solutes usually dissolve in polar solvents because of ion-dipole or dipole-dipole attractions. These interactions do not work well with nonpolar solvents. Nonpolar solutes usually dissolve in nonpolar solvents through dispersion forces.

Water is a polar solvent, so substances that dissolve well in water are called hydrophilic, or water-loving. For example, when KCl is added to water, the hydrogen end of water is attracted to chloride ions, and the oxygen end is attracted to potassium ions. Water molecules surround the ions, weaken the forces holding them together, and allow them to move into solution as solvated ions. Substances that do not dissolve in water are called hydrophobic, or water-fearing. Oil is one example. It cannot form hydrogen bonds with water, so the particles cluster together and stay undissolved.

Some compounds contain both polar and nonpolar parts. These are called amphipathic, or amphiphilic. Soaps are an example because they are salts of fatty acids. They have a nonpolar hydrocarbon tail and a polar hydrophilic head. This structure helps soaps and detergents clean because the nonpolar end interacts with oil, grease, or dirt, while the ionic end interacts with water. The molecules line up at the boundary between the dirt and the water. They act like a bridge between polar and nonpolar matter, which helps suspend dirt as colloidal particles so it can be washed away.

Why Some Substances Dissolve in Water

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Carbon Compounds in Everyday Life

Organic chemistry focuses on carbon compounds called organic compounds. These compounds may come from living things or be made by chemists. Carbon is the main element in them, and it bonds with other carbon atoms as well as hydrogen, oxygen, nitrogen, and sulfur. Carbon can form up to four strong bonds. That ability lets carbon atoms build chains and rings of many sizes, shapes, and levels of complexity. Not every carbon-containing substance is classified as organic. Carbonates, cyanides, and...

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Atomic Orbitals and Quantum Numbers

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How Electrons Fill Atomic Orbitals

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chemical bonds

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polar covalent bonds

Electronegativity in Polar Covalent Bonds

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lewis structures and formal charges

Lewis Structures, Bonds, and Formal Charge

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Molecular Shapes from Electron Pairs

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Predicting Shape and Molecular Polarity

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valence bond theory and hybridized orbitals

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intermolecular forces and physical properties

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Learn how solution formation, solvation, solubility, and the rule “like dissolves like” explain why some substances dissolve in water and others do not.

Why Some Substances Dissolve in Water | JoVE K12

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Arizona Science Standards

High School

Physical Science

HS+C.P1

HS+C.P1U1.4

Molecular Orbital (MO) Theory

Source: Tamara M. Powers, Department of Chemistry, Texas A&#38;M University
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Effect of Temperature Change on Reaction Rate

The Arrhenius equation,

relates the activation energy and the rate constant, k, for many chemical reactions.
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Factors Influencing the Rate of Chemical Reactions

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Concentration and Rate Law

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Measuring Reaction Rates

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Temperature Dependence

Chemical Kinetics 
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Reaction Rate

The rate of reaction is the change in the amount of a reactant or product per unit time. Reaction rates are therefore determined by measuring the time ...

Concentration Dependence

Chemical Kinetics and the Reaction Rate Law
Chemical kinetics refers to the rate or speed of a chemical reaction. The rate depends on the mechanism, ...

Matter and Its Interactions: Develop a model based on evidence to illustrate that the release or absorption of energy from a chemical reaction system depends upon the changes in total bond energy. (P: 2, CC: 5, CI: PS1)

9C.3.1.1.2

Solution Formation

There is no one solvent that can dissolve every type of solute. Some substances that readily dissolve in a certain solvent might be insoluble in a ...

Energetics of Solution Formation

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General Properties of Solutions

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Solutions and Concentrations

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Solubility
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Solution, Solubility, and Solubility Equilibrium
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Solution Equilibrium and Saturation

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Chemical and Solubility Equilibria

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9C.3.2.1.2

3 Developing possible explanations of phenomena or designing solutions to engineering problems
 3.2 Constructing explanations and designing solutions 
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Why Some Substances Dissolve in Water

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