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

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Strong Acid and Base Solutions

Les acides forts se dissocient complètement dans l'eau. Par exemple, l'acide nitrique se dissocie complètement en ions hydronium et en ions nitrate. Comme les ions hydronium générés par l'auto-ionisation d'eau sont négligeables, la concentration des ions hydronium dans l'eau est égale à la concentration de l'acide fort.Le pH de ces solutions peut être déterminé en utilisant la concentration initiale de l'acide fort. Par exemple, dans une solution de HCl de 0, 10 molaire, le HCl se dissociera complètement en ions hydronium et en ions chlorure, et donc la concentration en ions hydronium de la solution sera également de 0, 10 molaire. En prenant le logarithme négatif de cette concentration, le pH de la solution est égal à un.Inversement, le pH d'une solution peut être utilisé pour déterminer la concentration d'ion hydronium d'une solution. Par exemple, pour une solution de pH 3, 60, sa concentration en ions hydronium peut être déterminée en résolvant l'équation 3.60 est égale au log négatif de la concentration en ions hydronium. Pour résoudre la concentration, multipliez les deux côtés par moins un, puis prenez l'antilog des deux côtés.La concentration en ions hydronium est égale à 2, 5 10⁻⁴ molaire. Les bases fortes qui sont des hydroxydes métalliques du groupe 1, comme l'hydroxyde de sodium et l'hydroxyde de potassium, se dissocient complètement en solution. Par exemple, l'hydroxyde de sodium de 0, 20 molaire se dissociera complètement dans l'eau et produira des ions sodium de 0, 20 molaire et des ions hydroxyde de 0, 20 molaire.Cependant, les hydroxydes de métaux du groupe 2, comme l'hydroxyde de baryum et l'hydroxyde de calcium, produisent deux moles d'ions hydroxyde pour chaque mole de base. Par exemple, l'hydroxyde de calcium de 0, 020 molaire se dissociera complètement dans l'eau et produira 0, 020 molaire d'ion calcium et 0, 040 ions hydroxyde molaire. Les oxydes métalliques ioniques, comme l'oxyde de sodium et l'oxyde de calcium, sont également des bases fortes.Leur ion oxyde réagit avec l'eau et produit des ions hydroxyde. La concentration d'ions hydroxyde peut être utilisée pour calculer un pOH et un pH de la solution. Par exemple, une solution molaire de 5 10⁻⁵ d'hydroxyde de potassium contient une quantité égale d'ions hydroxyde comme base forte et a donc un pOH de 4, 30.Comme le pH, un pOH de la solution peut également être utilisé pour déterminer la concentration en ions hydroxyde en résolvant l'équation:pOH est égal au log négatif de la concentration en ions hydroxyde. Alors que le pH plus pOH est égal à 14 et le pOH est de 4, 3, le pH de la solution est de 9, 7.

acides forts et solutions basiques

Un acide fort est un composé qui se dissocie totalement dans une solution aqueuse et produit une concentration d'ions hydronium égale à la concentration initiale d'acide. Par exemple, l'acide bromhydrique 0,20 M se dissocie complètement dans l'eau et produit 0,20 M d'ions hydronium et 0,20 M d'ions bromure. 
 <img alt="Eq1" src="/files/ftp_upload/11399/11399_Equation_1.png" style="height: 50px;" />
 D'autre part, une base forte est un composé qui se dissocie totalement dans une solution aqueuse et produit des ions hydroxyde. Par exemple, 0,015 M de KOH, l'hydroxyde d'un métal du groupe 1, se dissociera complètement et produira 0,015 M de OH- et 0,015 M de K+. 
 <img alt="Eq2" src="/files/ftp_upload/11399/11399_Equation_2.png" style="height: 50px;" />
 Les hydroxydes des métaux du groupe 2, comme l'hydroxyde de baryum [Ba(OH)2] et l'hydroxyde de strontium [Sr(OH)2], sont également des bases fortes et ils possèdent deux ions hydroxyde. Cela les amène à produire une solution plus basique que NaOH ou KOH à la même concentration. Par exemple, 0,015 M de Ba(OH)2  produit 0,015 M de Ba+  et 0,030 M d'hydroxyde. 
 <img alt="Eq3" src="/files/ftp_upload/11399/11399_Equation_3.png" style="height: 50px;" />
 Comme les acides forts et les bases fortes se dissocient totalement, les rapports molaires peuvent être utilisés pour déterminer leurs concentrations en hydronium et hydroxyde, qui peuvent à leur tour être utilisées pour calculer le pH ou le pOH d'une solution. Par exemple, une solution de HCl 0,030 M produira des ions hydronium 0,03 M. Par conséquent, le pH de cette solution sera de 
 <img alt="Eq4" src="/files/ftp_upload/11399/11399_Equation_4.png" style="height: 135px;" />
 Le pOH de la même solution peut être déterminé à l'aide de la formule 
 <img alt="Eq5" src="/files/ftp_upload/11399/11399_Equation_5.png" style="height: 50px;" />
 Comme le pH de la solution est de 1,52, son pOH peut être calculé comme suit 
 <img alt="Eq6" src="/files/ftp_upload/11399/11399_Equation_6.png" style="height: 50px;" />
 De même, la concentration des ions hydroxyde produits par des bases fortes peut être utilisée pour déterminer le pOH d'une solution à l'aide de l'équation 
 <img alt="Eq7" src="/files/ftp_upload/11399/11399_Equation_7.png" style="height: 50px;" />
 L'équation ci-dessus peut également être utilisée pour déterminer la concentration en ions hydroxyde lorsque le pOH est connu. Par exemple, si le pOH d'une solution est 3,00, 
 <img alt="Eq8" src="/files/ftp_upload/11399/11399_Equation_8.png" style="height: 50px;" />
 La multiplication des deux côtés par −1 donne 
 <img alt="Eq9" src="/files/ftp_upload/11399/11399_Equation_9.png" style="height: 50px;" />
 Maintenant, prenez l'antilog des deux côtés 
 <img alt="Eq10" src="/files/ftp_upload/11399/11399_Equation_10.png" style="height: 90px;" />
 Ainsi, la concentration en ions hydronium de la solution ayant un pOH de 3 est de 1,0 × 10−3 M. Une méthode similaire peut être utilisée pour déterminer la concentration en ions hydronium d'une solution si son pH est connu.

Acides forts et solutions basiques

Un acide fort est un composé qui se dissocie complètement dans une solution aqueuse et produit une concentration d’ions hydronium égale à la concentration initiale ...

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Acides et bases

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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

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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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Strong Acids, Strong Bases, and pH

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