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

Раствор представляет собой однородную смесь двух основных веществ: растворенного вещества и растворителя. Растворитель присутствует в большем количестве, чем растворенное вещество.
В разбавленном растворе доля растворенного вещества по отношению к растворителю невелика, тогда как в концентрированном растворе она велика.
При образовании раствора растворенное вещество и растворитель не вступают в химическую реакцию. Вместо этого молекулы перераспределяются, при этом отдельные молекулы растворителя окружают молекулы растворенного вещества и взаимодействуют с помощью сил притяжения. Такой процесс растворения называется сольватацией.
Для того, чтобы способствовать сольватации, взаимодействия растворенного вещества и растворителя должны быть более сильными, чем взаимодействия растворитель-растворитель и растворенное вещество.
В растворе растворенное вещество и растворитель могут находиться в любом состоянии вещества. Само решение представляет собой одну «фазу».
Противоположностью сольватации является осаждение, вызванное сильными взаимодействиями между растворенными веществами. Когда скорость сольватации равна скорости выпадения осадков, устанавливается равновесие растворимости.
Растворимость растворенного вещества – это его максимально возможная концентрация при равновесии растворимости в данном количестве растворителя. На растворимость влияет температура и другие физические условия, такие как молекулярная полярность.
Неполярные растворенные вещества растворяются в неполярных растворителях за счет межмолекулярных дисперсионных сил Лондона, в то время как полярные или ионные растворенные растворы растворяются в полярных растворителях за счет ион-дипольных или диполь-дипольных взаимодействий.
Вода является полярным растворителем. Гидрофильные или водолюбивые соединения растворимы в воде благодаря ионным зарядам или полярным группам, которые обеспечивают достаточно сильные взаимодействия между водой и растворенным веществом. Они менее растворимы в неполярных растворителях, потому что взаимодействия между растворенными веществами намного сильнее, чем любое возможное взаимодействие между неполярным растворителем и полярными молекулами растворенного вещества.
Нерастворимые в воде, жирорастворимые неполярные соединения, такие как масла, являются гидрофобными или водобоязливыми, поскольку они не могут образовывать водородные связи, конкурирующие с растворителями.
Амфифильные или амфипатические соединения имеют как полярные, так и неполярные группы. Например, мыло – это металлические соли жирных кислот. В воде молекулы мыла агрегируются в сферы, называемые мицеллами. Их неполярные хвосты гидрофобных жирных кислот направлены внутрь, в то время как полярные гидрофильные головки находятся снаружи.
При удалении масляных пятен с помощью мыла хвосты окружают неполярное масло, образуя водорастворимые мицеллы, что позволяет смыть масло.

Растворимость

Раствор, растворимость и равновесие растворимости

Раствор представляет собой гомогенную смесь, состоящую из растворителя (основного компонента) и растворенного вещества (второстепенного компонента). Физическое состояние раствора — твердое, жидкое или газообразное — обычно такое же, как и у растворителя. Концентрации растворенных веществ часто описываются качественными терминами, такими как разбавленные (относительно низкой концентрации) и концентрированные (относительно высокой концентрации).

В растворе частицы растворенного вещества (молекулы, атомы и/или ионы) тесно окружены растворителями и взаимодействуют посредством сил притяжения. Этот процесс растворения называется сольватацией. Когда растворителем является вода, этот процесс известен как гидратация. Для сольватации взаимодействия растворенное вещество-растворитель должны быть более сильными, чем взаимодействия растворенное вещество-растворенное вещество и растворитель-растворитель. Осаждение является противоположностью сольватации и происходит из-за сильных взаимодействий между частицами растворенного вещества.

Растворимость – это мера максимального количества растворенного вещества, которое можно растворить в данном количестве растворителя. Температура, давление и молекулярная полярность являются одними из важных факторов, влияющих на растворимость. Равновесие растворимости устанавливается, когда растворение и осаждение растворенных веществ происходят с одинаковой скоростью.

Подобное растворяется в подобном

Чтобы предсказать, будет ли растворенное вещество растворимым в данном растворителе, применяется эмпирическое правило: «подобное растворяется подобным». Полярные или ионные растворенные вещества растворяются в полярных растворителях в результате ион-дипольных или диполь-дипольных взаимодействий с молекулами растворителя. Такое взаимодействие будет невозможно с неполярным растворителем. Неполярные растворенные вещества растворяются в неполярных растворителях за счет сил межмолекулярной дисперсии.

Гидрофильные, гидрофобные и амфифильные соединения

Вода – полярный растворитель. Растворенные вещества, растворимые в воде, называются «гидрофильными» или «водолюбивыми». Например, когда к воде добавляется твердый KCl, положительный (водородный) конец полярных молекул воды притягивается к отрицательным ионам хлорида, а отрицательные (кислородные) концы воды притягиваются к положительным ионам калия. Молекулы воды окружают отдельные ионы K+ и Cl−, уменьшая сильные силы, связывающие ионы вместе, и позволяя им переходить в раствор в виде сольватированных ионов.

Растворенное вещество, нерастворимое в воде, называется «гидрофобным» или «водобоязненным». Такие растворенные вещества, как нефть, не способны образовывать водородные связи с окружающими молекулами воды из-за более сильных взаимодействий между растворенными веществами. В результате частицы растворенного вещества собираются вместе и остаются нерастворенными.

Соединения, имеющие как полярные, так и неполярные группы, называются «амфипатическими» или «амфифильными». Например, мыло, представляющее собой соли жирных кислот. Они имеют гидрофобный хвост из неполярных углеводородов и полярную гидрофильную головку. Очищающее действие мыла и моющих средств можно объяснить структурой молекул в их составе. Углеводородный (неполярный) конец молекулы мыла или моющего средства растворяется или притягивается к неполярным веществам, таким как масло, жир или частицы грязи. Ионный конец притягивается водой (полярный). В результате молекулы мыла или моющего средства ориентируются на границе раздела частиц грязи и воды и действуют как своего рода мост между двумя разными типами материи: неполярной и полярной. В результате частицы грязи оказываются взвешенными в виде коллоидных частиц и легко смываются.

Раствор, растворимость и равновесие растворимости
Раствор представляет собой однородную смесь, состоящую из растворителя, основного компонента, и растворенного вещества, ...

Education

JoVE Core

Organic Chemistry

Органическая химия

Unit 1

Раздел 1

Covalent Bonding and Structure

Ковалентная связь и структура

KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

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

what is organic chemistry?

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...

electronic structure of atoms

Atomic Orbitals and Quantum Numbers

Atomic orbitals and quantum numbers describe how electrons are arranged around the nucleus. An atom has a small, positively charged nucleus with electrons surrounding it. The nucleus contains protons and neutrons, and the quantum mechanical model gives a better picture of this structure than older models. Protons carry a +1 charge and have a mass of 1.0073 amu. Neutrons have no charge and have a mass of 1.0087 amu. Electrons carry a −1 charge and have a mass of 0.00055 amu. The number of...

electron configurations

How Electrons Fill Atomic Orbitals

Electron filling in atoms follows a set order based on orbital energy. The Aufbau principle says each new electron enters the lowest-energy subshell available. The Pauli exclusion principle says no two electrons can share the same set of four quantum numbers. Hund’s rule of maximum multiplicity says electrons stay unpaired in equal-energy orbitals when possible. The order of filling follows the relative energies of the subshells. A common sequence is 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, and so on.

chemical bonds

Chemical Bonds: Types and Strength

Chemical bonds help atoms reach a full valence shell like the nearest noble gas. The main bond types are ionic, covalent, and metallic. Bond energy and bond length also help explain how strong a bond is. An ionic bond forms from electrostatic attraction between cations and anions. In many cases, one atom transfers electrons to another atom, and the ions form from that transfer. Ionic bonds have no defined direction because the attraction spreads evenly through three-dimensional space. A...

polar covalent bonds

Electronegativity in Polar Covalent Bonds

Polar covalent bonds form when atoms share electrons unevenly. This happens in covalent bonds between atoms that have similar, but not identical, tendencies to attract electrons. Nonmetal atoms often make these bonds with other nonmetals. Hydrogen gas, H2, is a simple example of a covalent bond between two hydrogen atoms. A covalent bond begins when two atoms move close enough for their valence orbitals to overlap. In hydrogen, the 1s orbitals overlap and the single electrons on each atom...

lewis structures and formal charges

Lewis Structures, Bonds, and Formal Charge

Lewis structures show how atoms share electrons in covalent bonds and in polyatomic ions. Lewis symbols help draw these structures, and the periodic table helps predict how many valence electrons an atom has and how many bonds it can form to reach an octet. Group 18 elements, such as argon and helium, already have filled electron configurations. They rarely take part in chemical bonding. Atoms in group 17, such as bromine and iodine, need one more electron to reach an octet, so they can form...

vsepr theory

Molecular Shapes from Electron Pairs

Molecular shape can be predicted from the way electron pairs arrange around a central atom. Valence shell electron-pair repulsion theory, or VSEPR theory, uses a Lewis structure to count bonding pairs and lone electron pairs. The main idea is simple: electron pairs spread out as far as possible to reduce repulsion. In a molecule, the valence electrons around the central atom can be bonding pairs or lone pairs. Bonding pairs are found mainly between bonded atoms. Lone pairs stay on one atom and...

molecular geometry and dipole moments

Predicting Shape and Molecular Polarity

Molecular shape and molecular polarity can be predicted with VSEPR theory and dipole moments. Start by writing the Lewis structure of the molecule or polyatomic ion. Then count the electron groups around the central atom. Lone pairs and bonds both count as electron groups, and a single, double, or triple bond each counts as one region of electron density. Use that count to identify the electron-pair geometry. Next, use the number of lone pairs to determine the molecular structure. If more than...

resonance and hybrid structures

Resonance in Nitrite and Carbonate Ions

Resonance explains why some Lewis structures do not match the measured properties of a molecule or ion. When two or more Lewis structures have the same atom arrangement, the real electron distribution is an average of the structures shown. The nitrite anion, NO2−, is one example. It can be drawn in two ways, with the N–O and N=O bonds in different places. If nitrite had one single bond and one double bond, the two bond lengths should be different, because a double bond is shorter and stronger...

valence bond theory and hybridized orbitals

valence-bond-theory-and-hybridized-orbitals

Covalent Bond Overlap and Orbital Hybridization

Covalent bonds form when orbitals on two atoms overlap and their single electrons pair up. The bond is stronger when the overlap is greater. Maximum overlap happens when the orbitals meet along a direct line between the two nuclei. A sigma bond, or σ bond, is the kind of covalent bond found in a single bond in a Lewis structure. In a σ bond, electron density is concentrated along the internuclear axis. A pi bond, or π bond, forms when two p orbitals overlap side by side. In a π bond, the...

mo theory and covalent bonding

Bond Order and Molecular Orbitals

Molecular orbital theory explains how electrons are arranged in molecules. It treats electron regions in a molecule much like atomic orbitals in an atom. A molecular orbital is the region of space where a valence electron is most likely to be found. Molecular orbitals form through the linear combination of atomic orbitals, or LCAO. When atomic wave functions combine in phase, they create regions with high electron density. When they combine out of phase, they create nodes, or regions with no...

intermolecular forces and physical properties

intermolecular-forces-and-physical-properties

How Intermolecular Forces Affect Matter

Intermolecular forces are the attractions between molecules, and they help explain how matter behaves. These forces influence melting points, boiling points, and whether substances mix with one another. Water has a much higher boiling point than hexane, which shows that water has stronger intermolecular forces. Three main kinds of intermolecular interactions are covered here. They include ion-dipole forces, dipole-dipole interactions, and van der Waals forces, which include London dispersion...

solubility

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...

introduction to functional groups

Functional Groups and Organic Molecules

Functional groups are groups of atoms with specific chemical properties that appear within organic molecules. They are sometimes shown as "R." These groups sit along the carbon backbone of macromolecules, which can form chains or rings of carbon atoms. Functional groups help functionalize a compound. That means they can give the molecule different physical and chemical properties. In organic chemistry, this change in group structure can strongly affect how a compound behaves. Common...

overview of advanced functional groups

Advanced Functional Groups in Organic Chemistry

Advanced functional groups are atom clusters in organic molecules that give those molecules specific chemical properties. They are sometimes shown as "R" in formulas. By changing the atoms attached to a carbon skeleton, a functional group can make a compound behave differently in physical and chemical reactions. This topic covers several major classes of organic compounds with advanced functional groups. Aromatic hydrocarbons include benzene. Phenol is another example and is also called...

key terms and concepts

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

organic chemistry

JoVE Core Organic Chemistry explains basic concepts of stereochemistry, reactions, and mechanisms using concise and easy-to-understand animated video lessons. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

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
This protocol serves as a guide in the synthesis of two metal complexes ...

Electron Behavior

Electrons are negatively charged subatomic particles that are attracted to an orbit around the positively-charged nucleus of an atom. They reside in ...

effect-of-temperature-change-on-reaction-rate

Effect of Temperature Change on Reaction Rate

The Arrhenius equation,

relates the activation energy and the rate constant, k, for many chemical reactions.
In this equation, R is the ideal gas ...

factors-influencing-the-rate-of-chemical-reactions

Factors Influencing the Rate of Chemical Reactions

A variety of factors influence the rate of chemical reactions. For a chemical reaction to happen, atoms must collide with enough energy to overcome the ...

Concentration and Rate Law

The rate of a reaction is affected by the concentrations of reactants. Rate laws (differential rate laws) or rate equations are mathematical expressions ...

Measuring Reaction Rates

Polarimetry finds application in chemical kinetics to measure the concentration and reaction kinetics of optically active substances during a chemical ...

Temperature Dependence

Chemical Kinetics 
The reaction rate is the speed at which a chemical reaction occurs. The reaction rate is defined as the change in concentration of a ...

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

The formation of a solution is an example of a spontaneous process, which is a process that occurs under specified conditions without energy from some ...

General Properties of Solutions

Many common substances around us exist as a solution, such as ocean water, air, and gasoline. All solutions are mixtures of substances that are composed ...

Solutions and Concentrations

Source: Laboratory of Dr. Michael Evans &#8212; Georgia Institute of Technology
A solution is a homogeneous mixture containing some components in small ...

Solubility
Solubility describes how much of a solute can dissolve in a given volume of a specific solvent. Solubility is usually reported in terms of ...

Solution, Solubility, and Solubility Equilibrium
A solution is a homogeneous mixture&#160;composed of a solvent, the major component, and a solute, the ...

Solution Equilibrium and Saturation

Imagine adding a small amount of sugar to a glass of water, stirring until all the sugar has dissolved, and then adding a bit more. You can repeat this ...

Intermolecular Forces in Solutions

The formation of a solution is an example of a spontaneous process, a process that occurs under specified conditions without energy from some external ...

Matter and Its Interactions: Develop models to illustrate the changes in the composition of the nucleus of the atom and the energy released during the processes of fission, fusion, and radioactive decay. (P: 2, CC: 5, CI: PS1)

Chemical and Solubility Equilibria

The free energy change associated with dissolving a solute in a liter of solvent is called the free energy of a solution, &#916;Gsolution. The overall ...

Matter and Its Interactions: Apply scientific principles and evidence to provide an explanation about the effects of changing the surface area, agitation, temperature, and concentration of the reacting particles on the rate at which the reaction occurs. (P: 6, CC: 1, CI: PS1)

9C.3.2.1.2

3 Developing possible explanations of phenomena or designing solutions to engineering problems
 3.2 Constructing explanations and designing solutions 
  3.2.1 Students will be able to apply scientific principles and empirical evidence (primary or secondary) to explain the causes of phenomena or identify weaknesses in explanations developed by the students or others.

Why Some Substances Dissolve in Water

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