Bases
By Charlene Mae Cuizon
BASE
A base is a substance that, in aqueous solution, is slippery to the touch, tastes bitter, changes the colour of indicators, reacts with acids to form salts, and promotes certain chemical reactions.
For a substance to be classified as an Arrhenius base, it must produce hydroxide ions in solution—in order to do so, Arrhenius believed the base must contain hydroxide in the formula. This makes the Arrhenius model limited, as it cannot explain the basic properties of aqueous solutions of ammonia (NH3) or its organic derivatives (amines). According to Brønsted–Lowry acid–base theory, a base is a substance that can accept hydrogen ions or otherwise known as protons. In the Lewis model, a base is an electron pair donor.
A soluble base is called an alkali if it contains and releases OH- ions quantitatively. However, it is important to realize that basicity is not the same as alkalinity. Metal oxides, hydroxides, and especially alkoxides are basic, and counteranions of weak acids are weak bases.
Bases can be thought of as the chemical opposite of acids. Bases and acids are seen as opposites because the effect of an acid is to increase the hydronium (H3O+) concentration in water, whereas bases reduce this concentration. A reaction between an acid and base is called Neutralization. In a neutralization reaction, an aqueous solution of a base reacts with an aqueous solution of an acids to produce a solution of water and salt in which the salt separates into its component ions. If the aqueous solution is saturated with a given salt solute, any additional such salt precipitates out of the solution.
Some properties of bases includes:
· Bases are bitter in taste.
· The pH level of a basic solution is higher than 7.
Strong- 12-14 pH
Weak- 7.1-11.9 pH
· Aqueous solutions or molten bases dissociate in ions and conduct electricity.
· Detergents
· Soap
· Lye (NaOH)
· Household Ammonia (Aqueous)
Alkalinity of Non-Hydroxides
Bases are generally compounds that can neutralize an amount of acids. Both sodium carbonate and ammonia are bases, although neither of these substances contains OH− groups. Both compounds accept H+ when dissolved in protic solvents such as water:
Na2CO3 + H2O → 2 Na+ + HCO3- + OH-
NH3 + H2O → NH4+ + OH-
From this, a pH, or acidity, can be calculated for aqueous solutions of bases. Bases also directly act as electron-pair donors themselves:
CO32- + H+ → HCO3-
NH3 + H+ → NH4+
Carbon can act as a base as well as nitrogen and oxygen. This occurs typically in compounds such as butyl lithium, alkoxides, and metal amides such as sodium amide. Bases of carbon, nitrogen and oxygen without resonance stabilization are usually very strong, or superbases, which cannot exist in a water solution due to the acidity of water. Resonance stabilization, however, enables weaker bases such as carboxylates; for example, sodium acetate is a weak base.
Neutralization
Neutralization is a chemical reaction in which an acid and a base react to form a salt. Water is frequently, but not necessarily, produced as well. Neutralizations with Arrhenius acids and bases always produce water where acid–alkali reactions produce water and a metal salt.
Neutralization reactions are exothermic. For example, the reaction of sodium hydroxide and hydrochloric acid. However, forms of endothermic neutralization do exist, such as the reaction between sodium bicarbonate (baking soda) and acetic acid (vinegar).
Strong Bases
A strong base is a basic chemical compound that deprotonates very weak acids in an acid-base reaction. Common examples of strong bases include hydroxides of alkali metals and alkaline earth metals like NaOH and Ca(OH)2. Very strong bases can even deprotonate very weakly acidic C–H groups in the absence of water.
By Charlene Mae Cuizon
BASE
A base is a substance that, in aqueous solution, is slippery to the touch, tastes bitter, changes the colour of indicators, reacts with acids to form salts, and promotes certain chemical reactions.
For a substance to be classified as an Arrhenius base, it must produce hydroxide ions in solution—in order to do so, Arrhenius believed the base must contain hydroxide in the formula. This makes the Arrhenius model limited, as it cannot explain the basic properties of aqueous solutions of ammonia (NH3) or its organic derivatives (amines). According to Brønsted–Lowry acid–base theory, a base is a substance that can accept hydrogen ions or otherwise known as protons. In the Lewis model, a base is an electron pair donor.
A soluble base is called an alkali if it contains and releases OH- ions quantitatively. However, it is important to realize that basicity is not the same as alkalinity. Metal oxides, hydroxides, and especially alkoxides are basic, and counteranions of weak acids are weak bases.
Bases can be thought of as the chemical opposite of acids. Bases and acids are seen as opposites because the effect of an acid is to increase the hydronium (H3O+) concentration in water, whereas bases reduce this concentration. A reaction between an acid and base is called Neutralization. In a neutralization reaction, an aqueous solution of a base reacts with an aqueous solution of an acids to produce a solution of water and salt in which the salt separates into its component ions. If the aqueous solution is saturated with a given salt solute, any additional such salt precipitates out of the solution.
Some properties of bases includes:
· Bases are bitter in taste.
· The pH level of a basic solution is higher than 7.
Strong- 12-14 pH
Weak- 7.1-11.9 pH
· Aqueous solutions or molten bases dissociate in ions and conduct electricity.
- Slippery in touch.
- Concentrated or strong bases are caustic on organic matter and react violently with acidic substances.
- Litmus paper changes from red to blue.
· Detergents
· Soap
· Lye (NaOH)
· Household Ammonia (Aqueous)
Alkalinity of Non-Hydroxides
Bases are generally compounds that can neutralize an amount of acids. Both sodium carbonate and ammonia are bases, although neither of these substances contains OH− groups. Both compounds accept H+ when dissolved in protic solvents such as water:
Na2CO3 + H2O → 2 Na+ + HCO3- + OH-
NH3 + H2O → NH4+ + OH-
From this, a pH, or acidity, can be calculated for aqueous solutions of bases. Bases also directly act as electron-pair donors themselves:
CO32- + H+ → HCO3-
NH3 + H+ → NH4+
Carbon can act as a base as well as nitrogen and oxygen. This occurs typically in compounds such as butyl lithium, alkoxides, and metal amides such as sodium amide. Bases of carbon, nitrogen and oxygen without resonance stabilization are usually very strong, or superbases, which cannot exist in a water solution due to the acidity of water. Resonance stabilization, however, enables weaker bases such as carboxylates; for example, sodium acetate is a weak base.
Neutralization
Neutralization is a chemical reaction in which an acid and a base react to form a salt. Water is frequently, but not necessarily, produced as well. Neutralizations with Arrhenius acids and bases always produce water where acid–alkali reactions produce water and a metal salt.
Neutralization reactions are exothermic. For example, the reaction of sodium hydroxide and hydrochloric acid. However, forms of endothermic neutralization do exist, such as the reaction between sodium bicarbonate (baking soda) and acetic acid (vinegar).
Strong Bases
A strong base is a basic chemical compound that deprotonates very weak acids in an acid-base reaction. Common examples of strong bases include hydroxides of alkali metals and alkaline earth metals like NaOH and Ca(OH)2. Very strong bases can even deprotonate very weakly acidic C–H groups in the absence of water.