Acids and Bases

Acids and bases are common molecules that, when combined, result in the production of salt and water. The origin of the word acid is the Latin word acere, which means sour.

In our daily lives, we utilize a variety of chemicals that scientists refer to as acids. Citric acid is included in the orange or grapefruit juice you drink for breakfast (also known as Vitamin C). When milk gets sour, it includes lactic acid. The salad dressing vinegar contains acetic acid. According to this theory, a chemical bond is composed of an acid-base combination.

Therefore, the properties of a molecule can be comprehended by separating it into acid and basic components.

Acids and Bases Definition

An acid is any chemical that contains hydrogen and can donate a proton (hydrogen ion) to another material. A base is a molecule or ion that can accept an ion of hydrogen from an acid.

Typically, acidic chemicals are distinguished by their sour flavour. A fundamental definition of an acid is a molecule that can donate an H+ ion and remain energetically favourable after losing H+. It is known that acids turn blue litmus crimson.

Bases, on the other hand, have a bitter flavour and a slippery consistency. Alkali is the term for a base that can be dissolved in water. When these compounds combine with acids, salts are produced. It is known that bases turn red litmus blue.

Acid Definition Chemistry

According to one’s perspective on the qualities of acidity and basicity, the terms acid and base have been defined in a variety of ways. Arrhenius initially defined acids as substances that ionise to produce hydrogen ions and bases as substances that ionise to produce hydroxide ions. An acid is a proton donor according to the Lowry-Bronsted definition, while a base is a proton acceptor.

According to the Lewis definition, acids are molecules or ions capable of coordinating with unshared electron pairs, whereas bases are molecules or ions possessing unshared electron pairs that are available for coordination with acids. For a molecule to be acidic in the Lewis sense, it must be electron-deficient. This is the most general concept of acid and base. In addition to all Lowery Bronstead acids being Lewis acids, the Lewis definition also includes many additional reagents, such as boron trifluoride, aluminium chloride, etc.

Theories of Acids and Bases

In order to define acids and bases, three distinct theories have been proposed. The Arrhenius hypothesis, the Bronsted-Lowry theory, and the Lewis theory of acids and bases are examples of these hypotheses. In this section, a brief summary of each of these theories is presented.

There are three distinct theories for defining acids and bases.

• According to the Arrhenius theory of acids and bases, an acid produces H+ ions in its solution, while a base produces OH– ions.
• According to the Bronsted-Lowry theory, an acid is a proton giver and a base is a proton acceptor.
• The Lewis definition of acids and bases concludes that “acids are electron-pair acceptors and bases are electron-pair donors.”

the pH of Acids and Bases

The pH scale (where pH stands for “potential of hydrogen”) can be used to determine the numeric value of a substance’s acidity or basicity. The pH scale is the most popular and reliable method for determining whether a substance is acidic or basic. A substance’s pH value can range from 0 to 14, with 0 being the most acidic and 14 the most basic.

Litmus paper is an alternative method for determining if a chemical is acidic or basic. There are two varieties of litmus paper that can be used to distinguish between acids and bases: red and blue. Under acidic conditions, blue litmus paper turns red, and red litmus paper turns blue under basic or alkaline conditions.

Properties of Acids and Bases

1.Properties of Acids

• Acids are corrosive in nature.
• They are good conductors of electricity.
• Their pH values are always less than 7.
• When reacted with metals, these substances produce hydrogen gas.
• Acids are sour in taste.
• Examples: Sulfuric acid [H₂SO₄], Hydrochloric acid [HCl], and Acetic acid [CH₃COOH].

2.Properties of Bases

Some characteristics, such as a bitter flavour, are shared by all bases. The bases also felt slick. Imagine what slippery soap would look like. And this is the basis. In addition, when dissolved in water, bases conduct electricity because they are composed of charged particles.

• They have a soapy feel when they are touched.
• When dissolved in water, these compounds release hydroxide ions.
• In their aqueous solutions, bases are excellent electrical conductors.
• The pH values of bases are greater than 7.
• Bases are chemicals with a bitter taste that can turn red litmus paper blue.

3. Neutral Substances

The neutral substance is one that is neither acidic nor basic, possesses the equal number of hydrogen and hydroxyl ions, and does not alter the colour of the litmus surface.

• These chemicals show neither acidic nor basic properties.
• Their pH values are roughly 7.
• There is no effect of neutral chemicals on red or blue litmus paper.
• Pure water has a pH of exactly 7.

Difference between Acids and Bases

Acids	Bases
When dissolved in water, acid releases hydrogen ions.	In the presence of water, bases emit hydroxyl ion.
It turns blue colour litmus paper into red.	It turns red colour litmus paper into blue.
It has a sour taste.	It has a bitter taste and is soapy to touch.
Its pH value ranges from 1 to 7.	Its pH value ranges from 7 to 14.
Example: HCl, H2SO4 etc.	Examples: NaOH, KOH etc.

Arrhenius’s Concept of Acids and Bases

• The Swedish scientist Svante August Arrhenius classified acids as compounds that, when dissolved in water, increase the concentration of H+ ions.
• Hydronium ions (H3O+) are formed when these protons combine with water molecules.
• Similarly, the Arrhenius definition of a base specifies that bases are compounds that raise the concentration of OH– ions in water when dissolved in it.
• This theory successfully explains the reaction between acids and bases that results in the formation of salts and water.
• Importantly, the Arrhenius definitions of acids and bases fail to explain how compounds without hydroxide ions, such as NO2– and F–, form basic solutions when dissolved in water.

Bronsted Lowry’s Theory of Acids and Bases

• According to the Bronsted-Lowry theory, an acid is a proton donor.
• This theory defines a base as a proton acceptor (or H+ ion acceptor).
• Bronsted acids dissociate to produce protons, hence increasing the concentration of H+ ions in a solution.
• Bronsted bases, on the other hand, take protons from water (the solvent) to produce hydroxide ions.
• The capacity of the Bronsted-Lowry definition of acids and bases to describe the acidic or basic character of ionic species is one of its advantages.
• A significant weakness of this theory is that it fails to explain how molecules lacking hydrogens, such as BF3 and AlCl3, display acidic characteristics.

Conjugate Acids and Bases

• According to the Bronsted-Lowry idea, an acid is a material that can donate H+, while a base can take H+.
• The acid and base that differ by a single proton are said to create a conjugate acid-base pair.
• When a proton is given to a base, a conjugate acid is made, and when a proton is withdrawn from an acid, a conjugate base is produced.

Lewis Concept of Acids and Bases

• According to the Lewis definition, an acid is a species that possesses an empty orbital and can therefore accept an electron pair.
• A Lewis base is a species that possesses a lone pair of electrons and, as a result, can function as an electron-pair donor.
• In its definition of acids and bases, this hypothesis does not include the hydrogen atom.
• The nature of Lewis acids is electrophilic, whereas Lewis bases are nucleophilic.
• The Lewis acids Cu2+, BF3, and Fe3+ are examples. The Lewis bases F–, NH3 and C2H4 are examples (ethylene).
• A Lewis acid takes a pair of electrons from a Lewis base to create a coordinated covalent bond. The resulting molecule is known as a Lewis adduct.
• Numerous substances can be characterized as acids or bases by this notion, which is a noteworthy advantage. However, it provides scant information regarding the strength of these acids and bases.
• The failure of this theory to explain acid-base reactions that do not involve the creation of a coordinated covalent bond is one of its shortcomings.

Uses of Acids and Bases

The various uses of acids and bases are listed in this subsection.

1. Uses of Acids

• Vinegar, a diluted solution of acetic acid, has numerous applications in the home. Primarily, it is employed as a food preservative.
• Citric acid is a fundamental component of both lemon juice and orange juice. It can also be used for food preservation.
• In batteries, sulfuric acid is commonly employed. Typically, batteries used to start automotive motors contain this acid.
• Sulphuric acid and nitric acid are used in the industrial production of explosives, dyes, paints, and fertilizers.
• Phosphoric acid is an essential component of numerous soft drinks.

2. Uses of Bases

• In the production of soap and paper, sodium hydroxide is utilized. Additionally, NaOH is employed in the production of rayon.
• Ca(OH)2, commonly known as hydrated lime or calcium hydroxide, is employed in the production of bleaching powder.
• Calcium hydroxide is used to create dry mixtures for use in painting and decorating.
• As a laxative, magnesium hydroxide, often known as milk of magnesia, is frequently employed. In addition to reducing excess acidity in the human stomach, it is utilized as an antacid.
• Ammonium hydroxide is a very useful laboratory reagent.
• Using slaked lime, excess acidity in soils can be neutralized.

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