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

Strong Acid and Base Solutions

強酸は水中で完全に解離します。例えば、硝酸はヒドロニウムイオンと硝酸イオンに完全に解離します。水の自己イオン化から生成されるヒドロニウムイオンはごくわずかであるため、水中のヒドロニウムイオンの濃度は強酸の濃度と等しくなります。
これらの溶液のpHは、強酸の初期濃度を使用して決定できます。
例えば、0.10モルのHCl溶液では、HClはヒドロニウムイオンと塩化物イオンに完全に解離するため、溶液のヒドロニウムイオン濃度も0.10モルになります。この濃度の負の対数を取ることにより、溶液のpHは1に等しくなります。
逆に、溶液のpHを使用して、溶液のヒドロニウムイオン濃度を決定できます。例えば、pH 3.60の溶液の場合、そのヒドロニウムイオン濃度は、式3.60がヒドロニウムイオン濃度の負の対数に等しいことを解くことによって決定できます。
濃度を解くには、両側に負の 1 を掛けてから、両側の逆数を取ります。ヒドロニウムイオン濃度は、負の4モルの10の2.5倍に等しくなります。
水酸化ナトリウムや水酸化カリウムなどのグループ1の金属水酸化物である強塩基は、完全に解離して溶液になります。たとえば、0.20モルの水酸化ナトリウムは水で完全に解離し、0.20モルのナトリウムイオンと0.20モルの水酸化物イオンを生成します。
ただし、水酸化バリウムや水酸化カルシウムなどのグループ2の金属水酸化物は、塩基の1モルごとに2モルの水酸化物イオンを生成します。たとえば、0.020モルの水酸化カルシウムは水中で完全に解離し、0.020モルのカルシウムイオンと0.040モルの水酸化物イオンを生成します。
酸化ナトリウムや酸化カルシウムなどのイオン性金属酸化物も強塩基です。それらの酸化物イオンは水と反応し、水酸化物イオンを生成します。
水酸化物イオンの濃度は、溶液のpOHとpHを計算するために使用できます。例えば、5×10〜マイナスの5モルの水酸化カリウム溶液は、強塩基と同量の水酸化物イオンを有しており、したがってpOHは4.30である。
pHと同様に、溶液のpOHも、pOHは水酸化物イオン濃度の負の対数に等しいという方程式を解くことにより、水酸化物イオン濃度を決定するためにも使用できます。
pH と pOH の合計は 14 に等しく、pOH は 4.3 であるため、溶液の pH は 9.7 です。

強酸、強塩基性溶液

強酸とは、水溶液中で完全に解離し、酸の初期濃度と同じ濃度のヒドロニウムイオンを生成する化合物のことです。例えば、0.20 Mの臭化水素酸は水中で完全に解離し、0.20 Mのヒドロニウムイオンと0.20 Mの臭化物イオンを生成します。
 <img alt="Eq1" src="/files/ftp_upload/11399/11399_Equation_1.png" style="height: 50px;" />
 一方、強塩基とは、水溶液中で完全に解離して水酸化物イオンを生成する化合物のことです。例えば、1族金属の水酸化物である0.015 MのKOHは、完全に解離して0.015 MのOH-と0.015 MのK+を生成します。
 <img alt="Eq2" src="/files/ftp_upload/11399/11399_Equation_2.png" style="height: 50px;" />
 水酸化バリウム[Ba(OH)2]や水酸化ストロンチウム[Sr(OH)2]などの2族金属水酸化物も強塩基であり、2つの水酸化物イオンを持っています。そのため、同じ濃度のNaOHやKOHに比べて、より塩基性の強い溶液を生成します。例えば、0.015 MのBa(OH)2  は0.015 MのBa+  と0.030 Mの水酸化物イオンを生成します。
 <img alt="Eq3" src="/files/ftp_upload/11399/11399_Equation_3.png" style="height: 50px;" />
 強酸と強塩基は完全に解離するので、モル比からヒドロニウムイオンと水酸化物イオンの濃度を求め、それをもとに溶液のpHやpOHを算出することができます。例えば、0.030 Mの塩酸溶液は、0.030 Mのヒドロニウムイオンを生成します。したがって、この溶液のpHは次の通りです。
 <img alt="Eq4" src="/files/ftp_upload/11399/11399_Equation_4.png" style="height: 135px;" />
 同じ溶液のpOHは、次の式で求めることができます。
 <img alt="Eq5" src="/files/ftp_upload/11399/11399_Equation_5.png" style="height: 50px;" />
 溶液のpHは1.52なので、そのpOHは次のように計算できます。
 <img alt="Eq6" src="/files/ftp_upload/11399/11399_Equation_6.png" style="height: 50px;" />
 同様に、強塩基によって生成される水酸化物イオンの濃度は、次式を用いて溶液のpOHに変換することが出来ます。
 <img alt="Eq7" src="/files/ftp_upload/11399/11399_Equation_7.png" style="height: 50px;" />
 上の式は、pOHが既知の場合、水酸化物イオン濃度を求めるのにも使用できます。例えば、溶液のpOHが3.00の場合は次の通りです。
 <img alt="Eq8" src="/files/ftp_upload/11399/11399_Equation_8.png" style="height: 50px;" />
 両辺に −1 を乗じると、
 <img alt="Eq9" src="/files/ftp_upload/11399/11399_Equation_9.png" style="height: 50px;" />
 Now, take the antilog of both sides
 <img alt="Eq10" src="/files/ftp_upload/11399/11399_Equation_10.png" style="height: 90px;" />
 したがって、pOH 3の溶液のヒドロニウムイオン濃度は1.0 × 10−3 Mとなります。同様の方法で、溶液のpHがわかっている場合には、ヒドロニウムイオン濃度を求めることができます。

強酸は、水溶液中で完全に解離し、初期に等しい濃度のヒドロニウムイオンを生成する化合物です...

Education

JoVE Core

化学

Acids and Bases

酸と塩基

KEY TERMS AND CONCEPTS

主要用語と概念

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...

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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

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acid strength and molecular structure

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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

chemistry

JoVE Core 化学は、簡潔で理解しやすいアニメーションビデオレッスンを使用して、一般的な化学の概念を生き生きとしたものにします。さらに、活動する科学者のビデオでは、現在世界中の実験室で行われている古典的そして独創的な研究・実験をお見せします。

Physical Science

PS.PSc.2.5

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

Minnesota Academic Standards in Science

1.2.1 9L.4.2.2.1

Texas Essential Knowledge and Skills

High School

CHEM.12

CHEM.12.C

Alabama Course of Study Science

Matter and Its Interactions

9-12.C.1.6.a

9-12.PS.3.6.c

new-york-state-science-learning-standards

New York State Science Learning Standards

HS. Chemical Reactions

HS-PS1-11.

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Strong Acids, Strong Bases, and pH

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