# Strong Bases

## Strong bases dissociate completely in solution, generating hydroxide ions of the same concentration as the base.

#### Key Points

• In chemistry, a base is a substance that can accept hydrogen ions (protons) or, more generally, a substance that can donate a pair of valence electrons. A base can be thought of as the chemical opposite of an acid.

• Strong bases are commonly, though not exclusively, formed from the hydroxides of alkali metals and alkaline earth metals.

• Superbases are stronger than hydroxide ions and cannot be kept in water. They provide examples of bases that do not contain a hydroxide ion.

#### Terms

• A complex formed by the attachment of solvent molecules to that of a solute.

• A proton acceptor, or an electron pair donor.

• Referring to the process by which compounds split into smaller constituent molecules, usually in a reversible manner.

#### Figures

1. ##### Periodic Chart

Strong bases are often formed through the hydroxides of alkali metals and alkaline earth metals in groups I and II in the periodic chart.

2. ##### Sodium Hydroxide Pellets

Sodium hydroxide pellets, before being suspended in water to dissociate.

A base in chemistry is a substance that can accept hydrogen ions (protons) or more generally, a substance that can donate a pair of valence electrons. In water, by altering the autoionization equilibrium, bases give solutions with a hydrogen ion an activity lower than that of pure water, meaning the solutions will have a pH higher than 7.0 at standard conditions.

Bases can be thought of as the chemical opposite of acids. A reaction between an acid and base is called neutralization. Bases and acids are seen as opposites because the effect of an acid is to increase the hydronium ion (H3O+) concentration in water, whereas bases reduce this concentration. Bases and acids are typically found in aqueous solution forms. Aqueous solutions of bases react with aqueous solutions of acids to produce water and salts.

A strong base is a base that dissociates completely in water. This means that all the base molecules break up into ions and solvate to water molecules. Therefore, the concentration of hydroxide ions in a strong base solution is equal to the concentration of the base. Common examples of strong bases are the hydroxides of alkali metals and alkaline earth metals such as NaOH and Ca(OH)2 (Figure 2). Strong bases are capable of deprotonating even weak acids; very strong bases are able to deprotonate very weakly acidic C–H groups in the absence of water.

Some common strong bases include:

• Potassium hydroxide (KOH)
• Sodium hydroxide (NaOH)
• Barium hydroxide (Ba(OH)2)
• Caesium hydroxide (CsOH)
• Sodium hydroxide (NaOH)
• Strontium hydroxide (Sr(OH)2)
• Calcium hydroxide (Ca(OH)2)
• Lithium hydroxide (LiOH)
• Rubidium hydroxide (RbOH)

The cations of these strong bases appear in the first and second groups of the periodic table (alkali and earth alkali metals) (Figure 1). The conjugate bases of very weak acids (acids with a pKa of more than about 13) are strong bases. When writing out the dissociation equation of a strong base, assume that the reverse reaction does not occur, because the conjugate acid of a strong base is very weak.

## Superbases

Group 1 salts of carbanions, amides, and hydrides tend to be even stronger bases due to the extreme weakness of their conjugate acids—stable hydrocarbons, amines, and dihydrogen. Usually these bases are created by adding pure alkali metals such as sodium into the conjugate acid. They are called superbases, and it is not possible to keep them in water solution. This is due to the fact they are stronger bases than the hydroxide ion, so they will deprotonate the conjugate acid water. For example, the ethoxide ion (conjugate base of ethanol) in the presence of water will undergo this reaction:

CH3CH2O + H2O → CH3CH2OH + OH

Some superbases include:

• Butyl lithium (n-BuLi)
• Lithium diisopropylamide (LDA) (C6H14LiN)
• Lithium diethylamide (LDEA)
• Sodium amide (NaNH2)
• Sodium hydride (NaH)
• Lithium bis(trimethylsilyl)amide (((CH3)3Si)2NLi)

#### Key Term Glossary

acid
an electron pair acceptor; generally capable of donating hydrogen ions
##### Appears in these related concepts:
activity
In chemical thermodynamics, activity (symbol a) is a measure of the “effective concentration” of a species in a mixture, meaning that the species' chemical potential depends on the activity of a real solution in the same way that it would depend on concentration for an ideal solution.
##### Appears in these related concepts:
alkali metal
Any of the soft, light, reactive metals of Group 1 of the periodic table; lithium, sodium, potassium, rubidium, cesium, and francium.
##### Appears in these related concepts:
alkaline
Having a pH greater than 7.
##### Appears in these related concepts:
Alkaline earth metals
A group of chemical elements in the periodic table with very similar properties: they are all shiny, silvery-white, somewhat reactive metals at standard temperature and pressure and readily lose their two outermost electrons to form cations with charge +2.
##### Appears in these related concepts:
amide
Any derivative of an oxoacid in which the hydroxyl group has been replaced with an amino or substituted amino group; especially such derivatives of a carboxylic acid, the carboxamides.
##### Appears in these related concepts:
amine
organic compounds or functional group that contains a basic nitrogen atom with a lone pair
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aqueous
Consisting mostly of water.
##### Appears in these related concepts:
base
A proton acceptor, or an electron pair donor.
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cation
A positively charged ion, as opposed to an anion.
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chemistry
The branch of natural science that deals with the composition and constitution of substances and the changes that they undergo as a consequence of alterations in the constitution of their molecules.
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concentration
the proportion of a substance in a mixture
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conjugate acid
The species created when a base accepts a proton.
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conjugate base
The species that is created after the donation of a proton.
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deprotonate
to remove one or more protons from a molecule
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dissociation
Referring to the process by which compounds split into smaller constituent molecules, usually in a reversible manner.
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electron
The subatomic particle having a negative charge and orbiting the nucleus; the flow of electrons in a conductor constitutes electricity.
##### Appears in these related concepts:
equilibrium
the state of a reaction in which the rates of the forward and reverse reactions are the same
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group
A vertical column in the periodic table, which signifies the number of valence shell electrons in an element's atom.
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hydride
a compound of hydrogen with a more electropositive element
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hydrocarbon
A compound consisting only of carbon and hydrogen atoms.
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hydronium
The hydrated hydrogen ion, $H_3O^+$.
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hydroxide
An univalent anion (OH-1) based on the hydroxyl functional group.
##### Appears in these related concepts:
ion
An atom or group of atoms bearing an electrical charge, such as the sodium and chlorine atoms in a salt solution.
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metal
Any of a number of chemical elements in the periodic table that form a metallic bond with other metal atoms; generally shiny, somewhat malleable and hard, often a conductor of heat and electricity
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molecule
the smallest particle of a specific element or compound that retains the chemical properties of that element or compound; two or more atoms held together by chemical bonds
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neutralization
A chemical reaction in which an acid and a base react to form a salt.
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pH
the negative of the logarithm to base 10 of the concentration of hydrogen ions, measured in moles per liter; a measure of acidity or alkalinity of a substance, which takes numerical values from 0 (maximum acidity) through 7 (neutral) to 14 (maximum alkalinity)
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pKa
A quantitative measure of the strength of an acid in solution; a weak acid has a pKa value in the approximate range −2 to 12 in water and a strong acid has a pKa value of less than about −2.
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proton
A positively charged subatomic particle forming part of the nucleus of an atom and determining the atomic number of an element; the nucleus of the most common isotope of hydrogen; composed of two up quarks and a down quark
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reduce
to add electrons/hydrogen or to remove oxygen
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salt
An ionic compound that is composed of cations and anions The product is electrically neutral. The two ions are held together by ionic bonds, not covalent bonds.
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solution
A homogeneous mixture, which may be liquid, gas or solid, formed by dissolving one or more substances.
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Solution
A homogeneous mixture, which may be liquid, gas or solid, formed by dissolving one or more substances.
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solvate
A complex formed by the attachment of solvent molecules to that of a solute.
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standard
something used as a measure for comparative evaluations
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Standard conditions
In chemistry, IUPAC established standard temperature and pressure (informally abbreviated as STP) as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of 100 kPa (14.504 psi, 0.986 atm, 1 bar),[1] An unofficial, but commonly used, standard is standard ambient temperature and pressure (SATP) as a temperature of 298.15 K (25 °C, 77 °F) and an absolute pressure of 100 kPa (14.504 psi, 0.986 atm). The STP and the SATP should not be confused with the standard state commonly used in thermodynamic evaluations of the Gibbs free energy of a reaction.
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strong base
A strong base is a basic chemical compound that is able to deprotonate very weak acids in an acid-base reaction. Common examples of strong bases are the hydroxides of alkali metals and alkaline earth metals, such as NaOH and Ca(OH)2. Very strong bases are even able to deprotonate very weakly acidic C–H groups in the absence of water.
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substance
Physical matter; material.
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valence
the combining capacity of an atom, radical or functional group determined by the number of electrons that it will lose, gain, or share when it combines with other atoms, etc.
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valence electron
Any of the electrons in the outermost shell of an atom; capable of forming bonds with other atoms.
##### Appears in these related concepts:
valence electrons
In chemistry, valence electrons are the electrons of an atom that can participate in the formation of chemical bonds with other atoms. Valence electrons are their "own" electrons, present in the free neutral atom, that combine with valence electrons of other atoms to form chemical bonds.
##### Appears in these related concepts:
weak acid
one that dissociates incompletely, releasing only some of its hydrogen atoms into solution