Name: strong acids, strong bases, and ph
Uploaded: 2020-09-24T15:06:51.000Z
Duration: 3 min 22 s
Channel: JoVE

K12 Standards

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North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Matter and its Interactions

PS.Chm.6.3

Strong Acid and Base Solutions

Os ácidos fortes dissociam-se completamente dentro de água. Por exemplo, o ácido nítrico dissocia-se completamente em íons de hidrónio e íons de nitrato. Como os íons de hidrónio gerados da autoionização da água são insignificantes, a concentração de íons hidrônicos na água é igual à concentração do ácido forte.O pH destas soluções pode ser determinado utilizando a concentração inicial do ácido forte. Por exemplo, numa solução 0, 10 mols de HCl, o HCl irá dissociar-se completamente em íons hidrônicos e íons de cloreto, e, portanto, a concentração de íons hidrônicos da solução também ser de 0, 10 mols. Ao tomar o logaritmo negativo desta concentração, o pH da solução é igual a um.Em contrapartida, o pH de uma solução pode ser utilizado para determinar a concentração de íons hidrônicos de uma solução. Por exemplo, para uma solução de pH 3, 60, a sua concentração de íons hidrônicos pode ser determinada através da resolução a equação 3, 60 é igual ao registo negativo da concentração de íons hidrônicos. Para resolver a concentração, multiplicar ambos os lados pelo lado negativo, e depois tomar a antilogia de ambos os lados.A concentração de íons hidrônicos é igual a 2, 5 10-⁴ mols. As bases fortes que são do grupo um de hidróxidos metálicos, como o Hidróxido de sódio e hidróxido de potássio, Dissociam-se completamente na solução. Por exemplo, 0, 20 mols de hidróxido de sódio irá dissociar-se completamente na água e produzir 0, 20 íons de sódio mols e 0, 20 íons de hidróxido mols.No entanto, o grupo dois de hidróxidos metálicos, como o hidróxido de bário e o hidróxido de cálcio, produzem dois moles de íons de hidróxido para cada mole de base. Por exemplo, 0, 020 mols de hidróxido de cálcio irá dissociar-se completamente dentro de água e produzir 0, 020 mols de íons de cálcio e 0, 040 mols de íons hidróxidos. Os óxidos de metais iónicos, como o óxido de sódio e o óxido de cálcio, são também bases fortes.O seu íon de óxido reage com a água e produz íons hidróxidos. A concentração de íons hidróxidos pode ser utilizada para calcular o pOH e pH da solução. Por exemplo, uma solução mols de hidróxido de potássio de 5 10-⁵ tem uma quantidade igual de íons hidróxidos como uma base forte e tem, portanto, um pOH de 4.30.Como o pH, o pOH da solução também pode ser utilizado para determinar a concentração de íons hidróxidos por resolução da equação:o pOH é igual ao registo negativo da concentração de íons hidróxidos. Uma vez que pH mais pOH é igual a 14 e a pOH é 4.3, o pH da solução é de 9, 7.

soluções de Ácidos e bases fortes

Um ácido forte é um composto que se dissocia completamente em uma solução aquosa e produz uma concentração de iões hidrónio igual à concentração inicial de ácido. Por exemplo, o ácido hidrobrómico a 0,20 M irá dissociar-se completamente em água e produzir 0,20 M de iões hidrónio e 0,20 M de iões brometo.
<img alt="Eq1" src="/files/ftp_upload/11399/11399_Equation_1.png" style="height: 50px;" />
Por outro lado, uma base forte é um composto que se dissocia completamente em uma solução aquosa e produz iões hidróxido. Por exemplo, 0,015 M de KOH, hidróxido de metal do grupo 1, irá dissociar-se completamente e produzir 0,015 M de OH- e 0,015 M de K+.
<img alt="Eq2" src="/files/ftp_upload/11399/11399_Equation_2.png" style="height: 50px;" />
Os hidróxidos metálicos do grupo 2, como o hidróxido de bário [Ba(OH)2] e o hidróxido de estrôncio [Sr(OH)2], são também bases fortes e possuem dois iões hidróxido. Isto faz com que produzam uma solução mais básica comparada com NaOH ou KOH à mesma concentração. Por exemplo, 0,015 M de Ba(OH)2  produzem 0,015 M de Ba+  e 0,030 M hydroxide.
<img alt="Eq3" src="/files/ftp_upload/11399/11399_Equation_3.png" style="height: 50px;" />
Como os ácidos e bases fortes se dissociam completamente, as razões molares podem ser usadas para determinar as suas concentrações de hidrónio e hidróxido, que por sua vez podem ser usadas para calcular o pH ou pOH de uma solução. Por exemplo, uma solução de HCl a 0,030 M irá produzir 0,03 M de iões hidronónio. Por conseguinte, o pH desta solução será de
<img alt="Eq4" src="/files/ftp_upload/11399/11399_Equation_4.png" style="height: 135px;" />
O pOH da mesma solução pode ser determinado usando a fórmula
<img alt="Eq5" src="/files/ftp_upload/11399/11399_Equation_5.png" style="height: 50px;" />
Como o pH da solução é 1,52, o seu pOH pode ser calculado como
<img alt="Eq6" src="/files/ftp_upload/11399/11399_Equation_6.png" style="height: 50px;" />
Da mesma forma, a concentração de iões hidróxido produzidos por bases fortes pode ser utilizada para determinar o pOH de uma solução utilizando a equação
<img alt="Eq7" src="/files/ftp_upload/11399/11399_Equation_7.png" style="height: 50px;" />
A equação acima também pode ser usada para determinar a concentração de iões hidróxido quando se sabe o pOH. Por exemplo, se o pOH de uma solução for 3,00,
<img alt="Eq8" src="/files/ftp_upload/11399/11399_Equation_8.png" style="height: 50px;" />
A multiplicação de ambos os lados por −1 dá
<img alt="Eq9" src="/files/ftp_upload/11399/11399_Equation_9.png" style="height: 50px;" />
Agora, pegue o antilog de ambos os lados
<img alt="Eq10" src="/files/ftp_upload/11399/11399_Equation_10.png" style="height: 90px;" />
Assim, a concentração de iões hidrónio da solução com pOH 3 é de 1,0 × 10−3 M. Um método semelhante pode ser usado para determinar a concentração de iões hidrónio de uma solução se o seu pH for conhecido.

Soluções de Ácidos e Bases Fortes

Um ácido forte é um composto que se dissocia completamente em uma solução aquosa e produz uma concentração de íons hidrônio igual ao ...

Education

JoVE Core

Química

Acids and Bases

Ácidos e Bases

KEY TERMS AND CONCEPTS

TERMOS-CHAVE E CONCEITOS

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 completely. It produces 0.015 M OH- and 0.015 M K+.

Some group 2 metal hydroxides are also strong bases. Barium hydroxide, Ba(OH)2, and strontium hydroxide, Sr(OH)2, each contain two hydroxide ions. That means they create a more basic solution than NaOH or KOH at the same concentration. For example, 0.015 M Ba(OH)2 produces 0.015 M Ba+ and 0.030 M hydroxide.

The ion concentrations from strong acids and strong bases can be used to calculate pH and pOH. A 0.030 M HCl solution produces 0.03 M hydronium ions, so its pH can be found from that concentration. The same pH value can then be used to determine pOH. If the pH is 1.52, the pOH can be calculated from the relationship between them.

The same idea works for strong bases. The hydroxide ion concentration can be used to find pOH with the equation for pOH, and the equation can also be used in reverse when pOH is known. For example, if the pOH of a solution is 3.00, multiplying by -1 and taking the antilog gives a hydronium ion concentration of 1.0 × 10^-3 M. The same method can be used to find hydronium ion concentration when pH is known.

Strong Acids, Strong Bases, and pH

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 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...

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 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 strong acids and strong bases dissociate completely in water and how their ion concentrations are used to calculate pH and pOH.

Strong Acids, Strong Bases, and pH | JoVE K12

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Ohio’s Learning Standards and Model Curriculum

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9-12.PS.3.6.c

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New York State Science Learning Standards

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Strong Acids, Strong Bases, and pH

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