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The diagram shows two horizontal bars. The first, labeled, “Relative acid strength,” at the top is red on the left and gradually changes to purple on the right. The red end at the left is labeled, “Stronger acids.” The purple end at the right is labeled, “Weaker acids.” Just outside the bar to the lower left is the label, “K subscript a.” The bar is marked off in increments with a specific acid listed above each increment. The first mark is at 1.0 with H subscript 3 O superscript positive sign. The second is ten raised to the negative two with H C l O subscript 2. The third is ten raised to the negative 4 with H F. The fourth is ten raised to the negative 6 with H subscript 2 C O subscript 3. The fifth is ten raised to a negative 8 with C H subscript 3 C O O H. The sixth is ten raised to the negative ten with N H subscript 4 superscript positive sign. The seventh is ten raised to a negative 12 with H P O subscript 4 superscript 2 negative sign. The eighth is ten raised to the negative 14 with H subscript 2 O. Similarly the second bar, which is labeled “Relative conjugate base strength,” is purple at the left end and gradually becomes blue at the right end. Outside the bar to the left is the label, “Weaker bases.” Outside the bar to the right is the label, “Stronger bases.” Below and to the left of the bar is the label, “K subscript b.” The bar is similarly marked at increments with bases listed above each increment. The first is at ten raised to the negative 14 with H subscript 2 O above it. The second is ten raised to the negative 12 C l O subscript 2 superscript negative sign. The third is ten raised to the negative ten with F superscript negative sign. The fourth is ten raised to a negative eight with H C O subscript 3 superscript negative sign. The fifth is ten raised to the negative 6 with C H subscript 3 C O O superscript negative sign. The sixth is ten raised to the negative 4 with N H subscript 3. The seventh is ten raised to the negative 2 with P O subscript 4 superscript three negative sign. The eighth is 1.0 with O H superscript negative sign.
This diagram shows the relative strengths of conjugate acid-base pairs, as indicated by their ionization constants in aqueous solution.

[link] lists a series of acids and bases in order of the decreasing strengths of the acids and the corresponding increasing strengths of the bases. The acid and base in a given row are conjugate to each other.

This figure includes a table separated into a left half which is labeled “Acids” and a right half labeled “Bases.” A red arrow points up the left side, which is labeled “Increasing acid strength.” Similarly, a blue arrow points downward along the right side, which is labeled “Increasing base strength.” Names of acids and bases are listed next to each arrow toward the center of the table, followed by chemical formulas. Acids listed top to bottom are sulfuric acid, H subscript 2 S O subscript 4, hydrogen iodide, H I, hydrogen bromide, H B r, hydrogen chloride, H C l, nitric acid, H N O subscript 3, hydronium ion ( in pink text) H subscript 3 O superscript plus, hydrogen sulfate ion, H S O subscript 4 superscript negative, phosphoric acid, H subscript 3 P O subscript 4, hydrogen fluoride, H F, nitrous acid, H N O subscript 2, acetic acid, C H subscript 3 C O subscript 2 H, carbonic acid H subscript 2 C O subscript 3, hydrogen sulfide, H subscript 2 S, ammonium ion, N H subscript 4 superscript +, hydrogen cyanide, H C N, hydrogen carbonate ion, H C O subscript 3 superscript negative, water (shaded in beige) H subscript 2 O, hydrogen sulfide ion, H S superscript negative, ethanol, C subscript 2 H subscript 5 O H, ammonia, N H subscript 3, hydrogen, H subscript 2, methane, and C H subscript 4. The acids at the top of the listing from sulfuric acid through nitric acid are grouped with a bracket to the right labeled “Undergo complete acid ionization in water.” Similarly, the acids at the bottom from hydrogen sulfide ion through methane are grouped with a bracket and labeled, “Do not undergo acid ionization in water.” The right half of the figure lists bases and formulas. From top to bottom the bases listed are hydrogen sulfate ion, H S O subscript 4 superscript negative, iodide ion, I superscript negative, bromide ion, B r superscript negative, chloride ion, C l superscript negative, nitrate ion, N O subscript 3 superscript negative, water (shaded in beige), H subscript 2 O, sulfate ion, S O subscript 4 superscript 2 negative, dihydrogen phosphate ion, H subscript 2 P O subscript 4 superscript negative, fluoride ion, F superscript negative, nitrite ion, N O subscript 2 superscript negative, acetate ion, C H subscript 3 C O subscript 2 superscript negative, hydrogen carbonate ion, H C O subscript 3 superscript negative, hydrogen sulfide ion, H S superscript negative, ammonia, N H subscript 3, cyanide ion, C N superscript negative, carbonate ion, C O subscript 3 superscript 2 negative, hydroxide ion (in blue), O H superscript negative, sulfide ion, S superscript 2 negative, ethoxide ion, C subscript 2 H subscript 5 O superscript negative, amide ion N H subscript 2 superscript negative, hydride ion, H superscript negative, and methide ion C H subscript 3 superscript negative. The bases at the top, from perchlorate ion through nitrate ion are group with a bracket which is labeled “Do not undergo base ionization in water.” Similarly, the lower 5 in the listing, from sulfide ion through methide ion are grouped and labeled “Undergo complete base ionization in water.”
The chart shows the relative strengths of conjugate acid-base pairs.

The first six acids in [link] are the most common strong acids. These acids are completely dissociated in aqueous solution. The conjugate bases of these acids are weaker bases than water. When one of these acids dissolves in water, their protons are completely transferred to water, the stronger base.

Those acids that lie between the hydronium ion and water in [link] form conjugate bases that can compete with water for possession of a proton. Both hydronium ions and nonionized acid molecules are present in equilibrium in a solution of one of these acids. Compounds that are weaker acids than water (those found below water in the column of acids) in [link] exhibit no observable acidic behavior when dissolved in water. Their conjugate bases are stronger than the hydroxide ion, and if any conjugate base were formed, it would react with water to re-form the acid.

The extent to which a base forms hydroxide ion in aqueous solution depends on the strength of the base relative to that of the hydroxide ion, as shown in the last column in [link] . A strong base, such as one of those lying below hydroxide ion, accepts protons from water to yield 100% of the conjugate acid and hydroxide ion. Those bases lying between water and hydroxide ion accept protons from water, but a mixture of the hydroxide ion and the base results. Bases that are weaker than water (those that lie above water in the column of bases) show no observable basic behavior in aqueous solution.

The product K a × K b = K w

Use the K b for the nitrite ion, NO 2 , to calculate the K a for its conjugate acid.

Solution

K b for NO 2 is given in this section as 2.17 × 10 −11 . The conjugate acid of NO 2 is HNO 2 ; K a for HNO 2 can be calculated using the relationship:

K a × K b = 1.0 × 10 −14 = K w

Solving for K a , we get:

K a = K w K b = 1.0 × 10 −14 2.17 × 10 −11 = 4.6 × 10 −4

This answer can be verified by finding the K a for HNO 2 in Appendix H .

Check your learning

We can determine the relative acid strengths of NH 4 + and HCN by comparing their ionization constants. The ionization constant of HCN is given in Appendix H as 4.9 × 10 −10 . The ionization constant of NH 4 + is not listed, but the ionization constant of its conjugate base, NH 3 , is listed as 1.8 × 10 −5 . Determine the ionization constant of NH 4 + , and decide which is the stronger acid, HCN or NH 4 + .

Answer:

NH 4 + is the slightly stronger acid ( K a for NH 4 + = 5.6 × 10 −10 ).

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The ionization of weak acids and weak bases

Many acids and bases are weak; that is, they do not ionize fully in aqueous solution. A solution of a weak acid in water is a mixture of the nonionized acid, hydronium ion, and the conjugate base of the acid, with the nonionized acid present in the greatest concentration. Thus, a weak acid increases the hydronium ion concentration in an aqueous solution (but not as much as the same amount of a strong acid).

Questions & Answers

Define the term chemistry
Ahmed Reply
explain law of definite proportion
MOTIA Reply
yes same idea
DEMGUE
wat?
Advic
what's kinetic energy
Charity Reply
energy possessed by an object in motion
Asare
what is anion?
Hussniz Reply
an anion is a positively charge ion
ade
Thnkz
Hussniz
an anion is a negatively charged ion
Johnson
And anion is a negatively charged ion which move towards the anode which is positively charged.
Ngwesse
a negatively charged ion formed by the gain of an electron(s)
Asare
H
Cyril
What is a electron cause I'm New to chemistry
Joshua
what is matter
Henry Reply
what is pressure
Henry
what is water?
Scarcies Reply
hydrogen gas burned into oxygen gas which forms a polar molecule, has a defenate shape volume but not shape. at 20 degrees Celsius exists as an aqueous solution. Is a solvent that dissolves many solutes into solution. And can act as an acid or a base.
David
HOW CAN ETHANOL BE PREPARED FORM CASSAVA.... (WITH EQUATION)
Obi Reply
by mixing
Henry
it is less dense than water
Erastus Reply
can cooking gas be durable in gallon. ..
mowete
no
PRINCESS
reason pls
mowete
What is happening
Oluchi Reply
Why does ice float on water?
Ngwesse
it is less denser than water
Advic
and why does a boat don't sink in water
DEMGUE
because the boat has a large surface area and the water surface contains molecules that are attracted together by a weak force of attraction
Maxime
brief the water surface has a wall
Maxime
As it cools, olive oil slowly soldifies and froms a solid over a range of temperatures. Which best describes the solid?
Tammie Reply
definition of a sample
ashley Reply
a small part or quantity intended to show what the whole is like
Abdull
What does kj stand for ? or just k. example - 371K
Katr Reply
kilojoules or Kelvin
Annie
what is atom
divinegift Reply
atom is anything that has weight and can occupy space
Neutons
atom is the smallest particle of an element that can neitherbe divided nor destroyed
clin
atom is the smallest indivisible particle of an element.
Igbayima
atom is the smallest particle of an element that can neither be created,subdivided or destroyed
Gbolahan
All wrong
Gift
Do you know that atoms can further be devided
Gift
Go and read 📘 up Dalton atomic theory and who disproved.. Read 📘 up atomic theory
Gift
an atom is the smallest particle of an element that can take part in a chemical reaction
Anyebem
good@anyebem
Henry
what is anion?
Hussniz
No, that's incorrect. Atom is the smallest indivisible particles of an element.
Abdulroheem
atom is the smallest particle of an element which can have a separate existence of a n element and still retail as the chemical properties of the element.
Fawaz
Atom is the smallest particle which involve in chemical reactions
YUSUF
atoms are the smallest that a giving element can go they are however not the smallest particles in nature those are elementary particles which are what protons and neutrons are consisted of or made up of. electrons are leptons in ordinary matter then you have tau neutrinos
Kendrick
Chemistry can be defined as the study of the properties, composition, structure of matter the changes they undergo and the energies accompanying those changes.
Emmanuel
but thats particle physics which is story for another day
Kendrick
what is a structure of atomic
Deren Reply
WATS atomic structure?
mowete
what is the meaning of intermolecular force
Eunice Reply
is the force of attraction that exist between two or more molecules
Johnson
What is a primary standard solution ?
Duval
a known solution
Fiko
Characteristic of a primary standard solution
Duval
Practice Key Terms 5

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Source:  OpenStax, Chemistry. OpenStax CNX. May 20, 2015 Download for free at http://legacy.cnx.org/content/col11760/1.9
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