Name: ph and poh in water
Uploaded: 2020-09-24T15:06:51.000Z
Duration: 2 min 41 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.6.3

pH Scale

La concentración de iones de hidronio en una solución acuosa generalmente se escribe con exponentes negativo y puede ser tan pequeña como 1 10⁻¹⁴ Mol. La escala de pH fue desarrollada por el químico Soren Sorenson en 1909 como una forma más conveniente de comparar rápidamente la acidez de diferentes soluciones. El pH de una solución es el logaritmo negativo de su concentración de iones de hidronio.Por ejemplo, una solución con una concentración de hidronio 1 10⁻⁵ Mol tiene un pH de 5. Cuanto mayor sea la concentración de iones de hidronio de una solución, menor será su pH. Como el pH se expresa en una escala logarítmica, un cambio de una sola unidad corresponde a un aumento o disminución de 10 veces la concentración de iones de hidronio.Una solución con un pH de 3 tendrá diez veces más iones de hidronio que una solución con un pH de 4 y cien veces más que una solución con un pH de 5. Una solución ácida tiene una concentración más alta de iones de hidronio que iones de hidróxido y un pH menor a 7 mientras que una solución básica tiene una concentración menor de iones de hidronio que iones de hidróxido y un pH mayor que 7. Una solución neutra con una concentración igual de iones de hidronio e hidróxido tiene un pH de 7.La concentración de iones de hidróxido también se puede expresar como pOH. pOH es el logaritmo negativo de la concentración de iones de hidróxido. Cuanto mayor sea la concentración de iones de hidróxido, menor será su valor de pOH.Un valor de pH o pOH de una solución acuosa varía entre 0-14. Esto se debe a que Kw, la constante de equilibrio para la autoionización del agua, es igual a 1 10⁻¹⁴. Si consideramos el logaritmo negativo de ambos lados de la ecuación da como resultado una ecuación en la que pKw es igual a la suma de pH y pOH.Dado que el logaritmo negativo de 1 10⁻¹⁴ es 14, la suma del pH y el pOH de una solución acuosa siempre será 14. Esto se puede utilizar para determinar el valor del pH cuando se conoce el valor de pOH y viceversa. Por ejemplo, una solución con un pOH de 10 tiene un pH de 4.

<ol>
	<li>van Lubeck, Henk. "¿Por qué no reemplazar el pH y el pOH por un solo grado de acidez real, AG?. Revista de Educación Química 76, no. 7 (1999): 892. <a href="https://pubs.acs.org/doi/pdf/10.1021/ed076p892">https://pubs.acs.org/doi/pdf/10.1021/ed076p892</a></li>
</ol>

escala del ph

Los iones hidronio e hidróxido están presentes tanto en agua pura como en todas las soluciones acuosas, y sus concentraciones son inversamente proporcionales según lo determinado por el producto iónico del agua (Kw). Las concentraciones de estos iones en una solución son a menudo determinantes críticos de las propiedades de la solución y de los comportamientos químicos de sus otros solutos. Dos soluciones diferentes pueden diferir en sus concentraciones de iones hidronio o hidróxido en un millón, mil millones o incluso billones de veces. Un medio común de expresar cantidades que pueden abarcar muchos órdenes de magnitud es utilizar una escala logarítmica. Por lo tanto, el pH de una solución se define como se muestra aquí, donde [H3O+] es la concentración molar de iones hidronio en la solución:
  <img alt="Eq1" src="/files/ftp_upload/11397/11397_Equation_1.png" style="height: 50px;" />
 La reorganización de esta ecuación para aislar la molaridad del ion hidronio produce la expresión equivalente:
  <img alt="Eq2" src="/files/ftp_upload/11397/11397_Equation_2.png" style="height: 50px;" />
 Asimismo, la molaridad de los iones hidróxido puede expresarse como una función p o pOH: 
  <img alt="Eq3" src="/files/ftp_upload/11397/11397_Equation_3.png" style="height: 50px;" />
 o bien
  <img alt="Eq4" src="/files/ftp_upload/11397/11397_Equation4.png" style="height: 50px;" />
 Por último, la relación entre estas dos concentraciones de iones expresadas como funciones p se obtiene fácilmente de la expresión Kw:
  <img alt="Eq5" src="/files/ftp_upload/11397/11397_Equation_5.png" style="height: 135px;" />
 A 25 °C, el valor de Kw es de 1,0 × 10−14, por lo que:
  <img alt="Eq6" src="/files/ftp_upload/11397/11397_Equation_6.png" style="height: 50px;" />
 La molaridad de iones hidronio en agua pura (o cualquier solución neutra) es de 1,0 × 10−7 M a 25 °C. Por lo tanto, el pH y el pOH de una solución neutra a esta temperatura son:
  <img alt="Eq7" src="/files/ftp_upload/11397/11397_Equation_7.png" style="height: 95px;" />
 Y así, a esta temperatura, las soluciones ácidas son aquellas con molaridades de iones hidronio superiores a 1,0 × 10−7 M y molaridades de iones hidróxido inferiores a 1,0 × 10−7 M (correspondientes a valores de pH inferiores a 7,00 y valores de pOH superiores a 7,00). Las soluciones básicas son aquellas con molaridades de iones hidronio inferiores a 1,0 × 10−7 M y molaridades de iones hidróxido superiores a 1,0 × 10−7 M (correspondientes a valores de pH superiores a 7,00 y valores de pOH inferiores a 7,00).
 Dado que la constante de autoionización Kw depende de la temperatura, estas correlaciones entre los valores de pH y los adjetivos ácido/neutro/básico serán diferentes a temperaturas distintas de 25 °C. Por ejemplo, la molaridad del hidronio del agua pura a 80°C es de 4,9 × 10−7 M, que corresponde a los valores de pH y pOH de:
  <img alt="Eq8" src="/files/ftp_upload/11397/11397_Equation_8.png" style="height: 95px;" />
 A esta temperatura, las soluciones neutras muestran pH = pOH = 6,31, las soluciones ácidas muestran un pH inferior a 6,31 y un pOH superior a 6,31, mientras que las soluciones básicas muestran un pH superior a 6,31 y un POH inferior a 6,31. Esta distinción puede ser importante cuando se estudian ciertos procesos que ocurren a otras temperaturas, como reacciones enzimáticas en organismos de sangre caliente a una temperatura alrededor de 36 – 40 °C. A menos que se indique lo contrario, se presumirá que las referencias a los valores de pH son aquellas a 25 °C.
 Este texto es adaptado de<a href="https://openstax.org/books/chemistry-2e/pages/14-2-ph-and-poh"> Openstax, Química 2e, Sección 14.2: pH y pOH. </a>

Escala del pH

Los iones hidronio e hidróxido están presentes tanto en el agua pura como en todas las soluciones acuosas, y sus concentraciones son inversamente proporcionales ...

Education

Educación

JoVE Core

Química

Acids and Bases

Ácidos y bases

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

ph and poh in water

pH and pOH show how hydronium and hydroxide ions behave in water and other aqueous solutions. These ion concentrations are linked by the ion product of water, K w , so when one goes up, the other goes down.

Because ion concentrations can differ by huge amounts, a logarithmic scale is used to describe them. pH is defined from the hydronium ion concentration, [H3O+], and pOH is the matching p-function for hydroxide ion concentration. These two values are also connected through the K w relationship.

At 25 °C, K w is 1.0 × 10−14. In pure water, or any neutral solution at this temperature, the hydronium ion concentration is 1.0 × 10−7 M. That gives pH = 7.00 and pOH = 7.00.

At 25 °C, acidic solutions have hydronium ion concentrations greater than 1.0 × 10−7 M and hydroxide ion concentrations less than 1.0 × 10−7 M. This means acidic solutions have pH values below 7.00 and pOH values above 7.00. Basic solutions show the opposite pattern, with pH above 7.00 and pOH below 7.00.

The link between pH and acidity changes with temperature because K w changes with temperature. For example, pure water at 80 °C has a hydronium ion concentration of 4.9 × 10−7 M, which gives pH and pOH values of 6.31. At this temperature, neutral solutions have pH = pOH = 6.31, acidic solutions have pH below 6.31, and basic solutions have pH above 6.31.

This temperature effect matters in processes that happen away from 25 °C, including enzyme reactions in warm-blooded organisms at about 36–40 °C. Unless another temperature is stated, pH values are usually assumed to refer to 25 °C.

pH and pOH in Water

bronsted-lowry acids and bases

Proton Transfer in Acids and Bases

Acids and bases can be understood through proton transfer. Early scientists described acids by their sour taste, their effect on dyes, and their reaction with limestone, which releases carbon dioxide. Robert Boyle also noted that acid solutions can lose these properties after contact with alkali, or base, solutions. The modern view developed step by step. Humphry Davy showed that hydrogen is the essential part of acids. Joseph Louis Gay-Lussac then described acids as substances that neutralize...

water: a bronsted-lowry acid and base

Water as an Amphiprotic Substance

Water can act as both a Brønsted-Lowry acid and a Brønsted-Lowry base. When hydrogen fluoride dissolves in water, it donates protons to water. This is acid ionization. The products are hydronium ions and fluoride ions. Water can also accept protons from another substance. When pyridine dissolves in water, it accepts a proton from water molecules. This is base ionization. The products are hydroxide ions and pyridinium ions. These reactions show that water can play either role. A substance that...

ph scale

pH and pOH show how hydronium and hydroxide ions behave in water and other aqueous solutions. These ion concentrations are linked by the ion product of water, K w , so when one goes up, the other goes down. Because ion concentrations can differ by huge amounts, a logarithmic scale is used to describe them. pH is defined from the hydronium ion concentration, [H3O+], and pOH is the matching p-function for hydroxide ion concentration. These two values are also connected through the K w...

relative strengths of conjugate acid-base pairs

relative-strengths-of-conjugate-acid-base-pairs

How Ka and Kb Show Acid-Base Strength

Brønsted-Lowry acid-base chemistry is based on proton transfer. That idea helps show how the strength of an acid is linked to the strength of its conjugate base, and vice versa. Acid and base strength is measured with ionization constants, Ka and Kb, which tell how far an ionization reaction goes. For the conjugate pair HA and A−, the acid ionizes in water and the base reaction can be written for the partner species. When the two reactions are added, they give the autoionization of water. The...

strong acid and base solutions

Strong Acids, Strong Bases, and pH

Strong acids and strong bases change the pH of a solution by dissociating completely in water. A strong acid produces hydronium ions, which are H3O+ ions, and a strong base produces hydroxide ions, OH-. Because the dissociation is complete, the ion concentration can be found from the starting concentration and the molar ratio. For example, 0.20 M hydrobromic acid dissociates fully in water. It produces 0.20 M hydronium ions and 0.20 M bromide ions. A 0.015 M KOH solution also dissociates...

weak acid solutions

Weak Acid Equilibrium in Water

Weak acid equilibrium in water explains why many acids only partially react when dissolved. Most weak acid molecules stay in their original form, and only a small amount of hydronium ions forms. Weak acids are common in nature. They help create the tangy taste of citrus fruits, the stinging sensation from insect bites, and the smells linked to body odor. Acetic acid is a familiar weak acid. It is the main ingredient in vinegar. Its equation uses a double arrow to show that the reaction with...

weak base solutions

Weak Base pH and Kb Calculations

Weak base pH and Kb calculations show how partially reacting bases change water chemistry. Weak bases produce hydroxide ions when they dissolve by reacting with water molecules. Because the reaction only happens partly, these compounds are classified as weak bases. Weak bases are common in nature and in technology. Ammonia is one major example. Global production of ammonia is typically well over 100 metric tons each year. It is used as an agricultural fertilizer, a starting material for...

mixtures of acids

pH of Acid Mixtures

The pH of acid mixtures depends on the acids present, their dissociation constants, and their starting concentrations. When a solution contains two different acids, the pH can be found by choosing the method that fits their relative strengths. This makes acid mixtures a useful case for applying acid-base rules in chemistry. In a mixture of a strong acid and a weak acid, the strong acid dissociates completely and supplies almost all of the hydronium ions in the solution. The weak acid...

ions as acids and bases

Salt Hydrolysis and pH of Solutions

Salt hydrolysis explains why some salt solutions are acidic, basic, or neutral. Salts are ionic compounds made of cations and anions. In water, either ion may react with water through an acid or base ionization reaction. The pH of the solution depends on the relative acid-base strength of the ions in the salt. Ammonium chloride is a good example of an acidic salt. When it dissolves, it separates into ammonium ions and chloride ions. The ammonium ion is the conjugate acid of ammonia, so it can...

determining the ph of salt solutions

Salt Hydrolysis and pH in Solutions

Salt hydrolysis and pH in solutions depend on the ions released when a salt dissolves. Some ions react with water, while others do not. The balance between the cation and anion helps show whether the solution becomes acidic, basic, or neutral. Salts with pH-neutral anions and cations that produce hydronium ions give acidic solutions with pH below 7. Ammonium nitrate is one example. In NH4NO3, NO3− does not react with water, but NH4+ forms hydronium ions, so the solution is acidic. Other salts...

acid/base strengths and dissociation constants

acidbase-strengths-and-dissociation-constants

Acid and Base Strength in Water

Acid and base strength in water depends on how much a substance ionizes after it dissolves. If ionization is nearly complete, the substance is called strong. If only a small amount ionizes, it is called weak. Weak acids and weak bases are much more common than strong ones. The most common strong acids are HClO4, HCl, HBr, HI, HNO3, and H2SO4. The most common strong bases are LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2, and Ba(OH)2. These strong acids and bases ionize essentially completely in water. <br...

polyprotic acids

Stepwise Ionization of Polyprotic Acids

Polyprotic acids lose hydrogen ions in steps. The number of ionizable protons in a molecule determines whether an acid is monoprotic, diprotic, or triprotic. This video also shows that polyprotic bases can accept more than one proton. Monoprotic acids have one ionizable hydrogen atom per molecule. Examples include HCl, HNO3, and HCN. Their reactions with water form hydronium ions and the matching anion. Acetic acid, CH3CO2H, is also monoprotic because only the hydrogen in the carboxyl group...

acid strength and molecular structure

How Bonding Affects Acid Strength

Acid strength depends on bonding, electronegativity, and oxidation number. These factors help explain why some hydrogen compounds act as strong acids, while others behave as weak acids or bases. For binary acids, which are hydrogen compounds with one other nonmetal, acidity increases as the H-A bond gets weaker down a group. That is why the order for group 17 is HF &lt; HCl &lt; HBr &lt; HI, and for group 16 it is H2O &lt; H2S &lt; H2Se &lt; H2Te. Across a period, acid strength increases as...

lewis acids and bases

Electron-Pair Reactions in Acid-Base Chemistry

Electron-pair reactions explain Lewis acid-base chemistry. In 1923, G. N. Lewis described acids and bases by how they accept or donate a pair of electrons. When that electron pair forms a coordinate covalent bond, one atom supplies both bonding electrons. This bond is also called a dative bond. A simple example is the reaction of water with a hydrogen ion to make a hydronium ion. Ammonia can also combine with a hydrogen ion to form an ammonium ion. In both cases, the reaction creates a Lewis...

key terms and concepts

Learn how hydronium and hydroxide ion levels define pH and pOH, why neutral water changes with temperature, and how acidic or basic solutions are identified.

pH and pOH in Water | JoVE K12

chemistry

JoVE Core Química da vida a los conceptos de química general mediante lecciones de vídeo basadas en animaciones, concisas y fáciles de entender. Además, en los vídeos de científicos en acción, se muestran experimentos de investigación clásicos y originales realizados en laboratorios de todo el mundo.

Physical Science

PS.PSc.2.5

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

Virginia  Standards of Learning

HIgh School

CH.5

CH.5.d

Texas Essential Knowledge and Skills

High School

CHEM.12

CHEM.12.E

Alabama Course of Study Science

Matter and Its Interactions

9-12.C.1.6

9-12.C.1.6.a

9-12.C.1.6.d

9-12.PS.3.6.c

Florida Department of Education

SC.912.P.8

SC.912.P.8.11

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-11.

Georgia Standards of Excellence

SPS6.

pH and Acidity/Basicity

SC6.

acids-and-bases-percent-dissociation-and-ph

Acids and Bases: Percent Dissociation and pH

Scientific Laws and Theories

Scientific Laws

In science, a law is defined as a concise, verbal or mathematical, statement that summarizes a vast number of experimental observations. ...

The Scientific Method

Chemistry is an empirical science. Scientists often pose questions to understand the chemistry in everyday life and seek answers to these questions. To ...

Classifying Matter by State

Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air, ...

Classifying Matter by Composition

Matter: Pure Substances and Mixtures
According to its composition, the matter can be classified into two broad categories &mdash; pure substances and ...

The Atomic Theory of Matter

The earliest recorded discussion of the basic structure of matter comes from ancient Greek philosophers. Leucippus and Democritus argued that all matter ...

Subatomic Particles

Dalton was only partially correct about the particles that make up matter. All matter is composed of atoms, and atoms are composed of three smaller ...

Elements: Chemical Symbols and Isotopes

A chemical symbol is an abbreviation used to indicate an element or an atom of an element. For example, the symbol for mercury is Hg. The same symbol is ...

Use models to explain how the scientific understanding of atomic structure has evolved.

PS.Chm.1.1

Radioactivity and Nuclear Equations

Nuclear chemistry is the study of reactions that involve changes in nuclear structure. The nucleus of an atom is composed of protons and, except for ...

Types of Radioactivity

The most common types of radioactivity are &#945; decay, &#946; decay, &#947; decay, neutron emission, and electron capture.
Alpha (&#945;) decay is the ...

Nuclear Stability

Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10&#8722;15 meters, a nucleus is ...

Nuclear Binding Energy

The difference between the calculated and experimentally measured masses is known as the mass defect of the atom. In the case of helium-4, the mass defect ...

Radioactive Decay and Radiometric Dating

Radioactivity is a spontaneous disintegration of an unstable nuclide and is a random process, as all the nuclei in the sample do not decay simultaneously. ...

Nuclear Fission

Many heavier elements with smaller binding energies per nucleon can decompose into more stable elements that have intermediate mass numbers and larger ...

Nuclear Power

Controlled nuclear fission reactions are used to generate electricity. Any nuclear reactor that produces power via the fission of uranium or plutonium by ...

Nuclear Fusion

The process of converting very light nuclei into heavier nuclei is also accompanied by the conversion of mass into large amounts of energy, a process ...

Nuclear Transmutation

Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with ...

Use models to compare nuclear reactions including alpha decay, beta decay and gamma decay; nuclear fusion and nuclear fission.

PS.Chm.1.2

Atomic Orbitals

An atomic orbital represents the three-dimensional regions in an atom where an electron has the highest probability to reside. The radial distribution ...

The Pauli Exclusion Principle

The arrangement of electrons in the orbitals of an atom is called its electron configuration. We describe an electron configuration with a symbol that ...

The Energies of Atomic Orbitals

In an atom, the negatively charged electrons are attracted to the positively charged nucleus. In a multielectron atom, electron-electron repulsions are ...

The Aufbau Principle and Hund's Rule

To determine the electron configuration for any particular atom, we can build the structures in the order of atomic numbers. Beginning with hydrogen, and ...

electron-configuration-of-multielectron-atoms

Electron Configuration of Multielectron Atoms

The alkali metal sodium (atomic number 11) has one more electron than the neon atom. This electron must go into the lowest-energy subshell available, the ...

Use models to explain how electrons are distributed in atoms.

PS.Chm.1.3

Periodic Classification of the Elements

The periodic table arranges atoms based on increasing atomic number so that elements with the same chemical properties recur periodically. When their ...

The Periodic Table

As early chemists discovered more elements, they realized that various elements could be grouped by their similar chemical behaviors. One such grouping ...

Atomic Mass

Atoms &mdash; and the protons, neutrons, and electrons that compose them &mdash; are extremely small. For example, a carbon atom weighs less than 2 ...

Molar Mass

The identity of a substance is defined not only by the types of atoms or ions it contains but by the quantity of each type of atom or ion. For example, ...

Use the Periodic Table as a model to predict the relative properties of elements based on the pattern of valence electrons in the outermost energy levels of atoms.

PS.Chm.2.1

atomic-radii-and-effective-nuclear-charge

Atomic Radii and Effective Nuclear Charge

The elements in groups of the periodic table exhibit similar chemical behavior. This similarity occurs because the members of a group have the same number ...

Ionic Radii

Ionic radius is the measure used to describe the size of an ion. A cation always has fewer electrons and the same number of protons as the parent atom; it ...

Ionization Energy

The amount of energy required to remove the most loosely bound electron from a gaseous atom in its ground state is called its first ionization energy ...

Electron Affinity

The electron affinity (EA) is the energy change for adding an electron to a gaseous atom to form an anion (negative ion).



This process can be either ...

Construct an explanation to infer the atomic size, reactivity, electronegativity, and ionization energy of an element based on its position in the Periodic Table.

PS.Chm.2.2

Types of Chemical Bonds

Chemical bonding theories were pioneered by American chemist Gilbert&#xA0;N. Lewis. He developed a model called the Lewis model to explain the type and ...

Lewis Symbols and the Octet Rule

Chemical bonds are complex interactions between two or more atoms or ions, which reduce the potential energy of the molecule. Gilbert N. Lewis developed a ...

Ionic Bonding and Electron Transfer

Ions are atoms or molecules bearing an electrical charge. A cation (a positive ion) forms when a neutral atom loses one or more electrons from its valence ...

The Born-Haber Cycle

Lattice Energy&#xA0;

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a ...

trends-in-lattice-energy-ion-size-and-charge

Trends in Lattice Energy: Ion Size and Charge

An ionic compound is stable because of the electrostatic attraction between its positive and negative ions. The lattice energy of a compound is a measure ...

Covalent Bonding and Lewis Structures

Compared to ionic bonds, which results from the transfer of electrons between metallic and nonmetallic atoms, covalent bonds result from the mutual ...

Electronegativity

Whether a bond is nonpolar or polar covalent is determined by a property of the bonding atoms called electronegativity.&#xA0;

Electronegativity values of ...

bond-polarity-dipole-moment-and-percent-ionic-character

Bond Polarity, Dipole Moment, and Percent Ionic Character

Bond Polarity

The absolute value of the difference in electronegativity (&Delta;EN) of two bonded atoms provides a rough measure of the polarity to be ...

lewis-structures-of-molecular-compounds-and-polyatomic-ions

Lewis Structures of Molecular Compounds and Polyatomic Ions

To draw Lewis structures for complicated molecules and molecular ions, it is helpful to follow a step-by-step procedure as outlined:


	Determine the ...

Resonance

The Lewis structure of a nitrite anion (NO2&minus;) may actually be drawn in two different ways, distinguished by the locations of the N-O and N=O ...

Formal Charges

In some cases, there are seemingly more than one valid Lewis structures for molecules and polyatomic ions. The concept of formal charges can be used to ...

Analyze and interpret data to explain the mechanisms and properties of the two main types of intramolecular (ionic and covalent) bonds.

PS.Chm.3.1

Analyze the structure of atoms and isotopes.

pH and pOH in Water

Description

Transcript

Tags

More videos by Standards