Examples of base in the following topics:
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- Most base reagents are alkoxide salts, amines or amide salts.
- Since alcohols are much stronger acids than amines, their conjugate bases are weaker than amide bases, and fill the gap in base strength between amines and amide salts.
- Hünig's base is relatively non-nucleophilic (due to steric hindrance), and like DBU is often used as the base in E2 elimination reactions conducted in non-polar solvents.
- Barton's base is a strong, poorly-nucleophilic, neutral base that serves in cases where electrophilic substitution of DBU or other amine bases is a problem.
- Finally, the two amide bases see widespread use in generating enolate bases from carbonyl compounds and other weak carbon acids.
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- A weak base is a chemical base that does not ionize fully in an aqueous solution.
- As Brønsted-Lowry bases are proton acceptors, a weak base may also be defined as a chemical base with incomplete protonation.
- A general formula for base behavior is as follows:
- This results in a relatively low pH compared to that of strong bases.
- The pH of bases in aqueous solution ranges from greater than 7 (the pH of pure water) to 14 (though some bases have pH values greater than 14).
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- Lewis bases are electron-pair donors, whereas Lewis acids are electron-pair acceptors.
- A Lewis base, therefore, is any species that donates a pair of electrons to a Lewis acid.
- By treating acid-base reactions in terms of electron pairs instead of specific substances, the Lewis definition can apply to reactions that do not fall under other definitions of acid-base reactions.
- Nearly all reactions in organic chemistry can be considered Lewis acid-base processes.
- This lesson continues to describe acids and bases according to their definition.
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- Originally, acids and bases were defined by Svante Arrhenius.
- Keep in mind that acids and bases must always react in pairs.
- Therefore, according to the Brønsted-Lowry definition, an acid-base reaction is one in which a conjugate base and a conjugate acid are formed (note how this is different from the Arrhenius definition of an acid-base reaction, which is limited to the reaction of H+ with OH- to produce water).
- Here, ammonia is the Brønsted-Lowry base.
- Chemistry 12.1 What are Acids and Bases?
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- As discussed in the previous concepts on bases, a base is a substance that can: donate hydroxide ions in solution (Arrhenius definition); accept H+ ions (protons) (Bronsted-Lowry definition); or donate a pair of valence electrons (Lewis definition).
- Strong bases are capable of deprotonating weak acids; very strong bases can deprotonate very weakly acidic C–H groups in the absence of water.
- Generally, the alkali metal bases are stronger than the alkaline earth metal bases, which are less soluble.
- 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.
- Unlike weak bases, which exist in equilibrium with their conjugate acids, the strong base reacts completely with water, and none of the original anion remains after the base is added to solution.
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- Acid-base titration can determine the concentrations of unknown acid or base solutions.
- An acid-base titration is an experimental procedure used to determined the unknown concentration of an acid or base by precisely neutralizing it with an acid or base of known concentration.
- Acid-base titrations can also be used to quantify the purity of chemicals.
- strong acid-weak base titration: methyl orange indicator the base is off the scale (e.g., pH > 13.5) and the acid has pH > 5.5: alizarine yellow indicator
- A weak acid will react with a strong base to form a basic (pH > 7) solution.
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- The conjugate base is the ion or molecule that remains after the acid has donated its proton, and the conjugate acid is the species created after the base accepts the proton.
- Water is amphoteric, which means it can act as either an acid or a base.
- The acetate ion CH3CO2- is the conjugate base of acetic acid, and the hydronium ion H3O+ is the conjugate acid of the base, water:
- The hydroxide ion is the conjugate base of water, which acts as an acid, and the ammonium ion is the conjugate acid of the base, ammonia.
- Identify the Brønsted acid, Brønsted base, conjugate acid, and conjugate base in an acid-base reaction.
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- A strong acid will react with a weak base to form an acidic (pH < 7) solution.
- An example of a strong acid-weak base titration is the reaction between ammonia (a weak base) and hydrochloric acid (a strong acid) in the aqueous phase:
- The acid is typically titrated into the base.
- In the case of titrating the acid into the base for a strong acid-weak base titration, the pH of the base will ordinarily start high and drop rapidly with the additions of acid.
- In strong acid-weak base titrations, the pH at the equivalence point is not 7 but below it.
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- Acid names are based on the anion they form when dissolved in water; base names follow the rules for ionic, organic, or molecular compounds.
- Most strong bases contain hydroxide, a polyatomic ion.
- For example, methyl amine (CH3NH2) is a weak base.
- Some weak bases have "common" names.
- Convert between the structure of an acid or base and its chemical name
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- A buffer is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid.
- You can use one of these acid/conjugate base pairs:
- What amount of acid and base should you use to create the buffer?
- Extrapolating further from this, a buffer is most effective when the concentrations of acid and conjugate base (or base and conjugate acid) are approximately equal—in other words, when the log [base]/[acid] equals 0 and the pH equals the pKa.
- The change is minimized if the concentrations of acid and conjugate base are equal.