Acids, Bases and Salts: Definition, Classification, Properties and Uses

Many acids and bases exist naturally in nature, such as malic acid in apples, hydrochloric acid in gastric fluids, tartaric acid in tamarind, lactic acid in milk and milk products, and citric acid in fruits like lemon and orange.

Lime water, on the other hand, has a lot of bases. Baking soda is used to create cakes and other baked goods, washing soda is used to clean, boric acid is used in laundry, and vinegar or acetic acid is used in the kitchen, among other things.

Many acids and bases, such as HCl, H₂SO₄, NaOH and KOH are utilised in labs. When these acids and bases are combined in appropriate and precise amounts, salt and water are formed. Some salts, such as NaCl and KCl, are found naturally, like in natural rock formations or in saltwater.

Let's take a deeper look at the characteristics of various acids, bases, and salts.

Read More: VSEPR Theory

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Definitions of Acids, Bases and Salts

Acid:- A chemical that neutralises bases, turns blue litmus red, and has a sour taste is characterised as an acid. 

Acid is derived from the Latin word 'acere', which means sour. In its aqueous solution, acid is defined as a chemical that produces ionizable hydronium ions (H₃O⁺).

As illustrated in the instances below, acids dissociate in their aqueous solution and give birth to their component ions.

Base:- If a material neutralises acids or turns red litmus blue, and if its aqueous solution tastes bitter, it is called a base. Bases have a soapy texture and a bitter flavour. In aqueous solution, a base produces the hydroxyl ion (OH^–). When red litmus paper comes into touch with base, its colour changes to blue.

Salt:- Salt is a tasteless neutral material and in an aqueous solution it has no effect on litmus. Salt is produced by neutralisation between bases and acids. Salts are made up of cations, which are positively charged, and anions, which are negatively charged. In nature, salts are either organic or inorganic. The presence of these ions neutralises the salt's nature.

Salt is formed as a result of the chemical processes depicted in the equations below.

The bases dissociate in aqueous solution to produce component ions, as shown in the examples below.

The pH of a salt solution is determined by the strength of acids and bases mixed in the neutralisation process.

Example:

• NaOH + HCl→ NaCl + H₂O
• HCl + NH₄OH → NH₄Cl + H₂O
• CH₃COOH + NaOH → CH₃COONa + H₂O
• CH₃COOH + NH₄OH → CH₃COONH₄+ H₂O

Table salt, also known as sodium chloride, is made by the combination an acid, hydrochloric acid, and a strong base, sodium hydroxide.

HCl(aq)+NaOH(aq)→NaCl(aq)+H₂O(l)

Other examples include:

• Baking soda (NaHCO₃) is a common ingredient used while cooking.

• Ammonium nitrate (NH₄NO₃) and ammonium nitrate (NH4NO₃) is used in fertilizers.

• Epsom salt (MgSO₄) is a common ingredient in bath salts.

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Classification of Acids, Bases and Salts

1. ACIDS: 

Acids can be categorised based on their occurence into natural and mineral acids

1. Acids obtained from natural sources, such as animal and fruit products, are known as natural acids like tartaric, citric, and lactic acids.
2. Mineral Acids are acids that are made from minerals and are commonly used in labs. Sulphuric acid (H₂SO₄), hydrochloric acid (HCl), and nitric acid (HNO₃) are some examples of mineral acids.

Acids are classified as follows based on the number of hydrogen ions in them:

1. Monoprotic Acid – Acids that generate one mole of H⁺ ions per mole of acid, such as HCl.
2. Diprotic Acid – Acids that generate two moles of H⁺ ions per mole of acid, such as H₂SO₄.
3. Triprotic Acid – Acids that generate three moles of H⁺ ions per mole of acid, such as H₃PO₄.

Acids are classified as follows based on their ability to donate hydrogen ions:

1. Acids that get fully ionised in aqueous solutions are known as Strong Acids. As a result, at equilibrium, the concentration of hydrogen ions is at its highest, while the concentration of acid molecules is at its lowest; for example, HCl, HNO₃, and HClO₄.
2. Weak Acids: Weak acids are only partly ionised in solution at equilibrium. At equilibrium, the concentration of hydrogen ions is lower, and acid molecules, such as HF and CH₃COOH, are present in significant amounts.

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2. BASES:

1. Strong Bases: These are the bases that, when fully ionised in water, create hydroxide ions, such as sodium hydroxide.

NaOH(s)⇔Na⁺(aq)+OH⁻(aq)

2. Weak Bases: These are bases in which equilibrium is mostly on the side of the reactants and are partly ionised, such as ammonia in water.

NH₃(aq)+H₂O(l)⇔NH₄⁺(aq)+OH⁻(aq)

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Properties of Acids, Bases and Salts

1. ACIDS

• Acids are chemicals that produce hydrogen ions (H⁺) when dissolved in water.

HCl + H₂O → H⁺ + Cl^-

• Acid is corrosive in nature, with a pH of less than 7 and a sour flavour.

• When acids react with metal, they produce hydrogen gas. For example, when zinc metal interacts with hydrochloric acid, zinc chloride and hydrogen gas are produced.

Zn + 2HCl → ZnCl₂ + H₂

• When acids react with limestone (CaCO₃), carbon dioxide is produced. For example, when HCl interacts with limestone, it produces calcium chloride and carbonic acid.

CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O

• Acids turn blue litmus to red.

Read More: Gay-Lussac’s Law

2. BASES

Bases have a pH value of more than 7, are caustic, and have a bitter taste. They generally have a soapy feel to them.

• They are excellent electrical conductors.
• When bases react with grease and oils, soap molecules develop.
• Red litmus cahnges to blue litmus by bases.
• When these chemicals are dissolved in water, they produce hydroxide ions (OH^– ions).

Examples: Sodium hydroxide [NaOH], milk of magnesia [Mg(OH)₂], and calcium hydroxide [Ca(OH)₂] are other examples.

Read More: Fehling Test

3. SALTS

Salt is a material with no acid or basic characteristics, the equal number of hydrogen and hydroxyl ions, and no effect on the litmus colour.

• There are no acidic or basic properties in these compounds.
• Their pH levels are close to 7.
• On red or blue litmus paper, neutral chemicals have no impact.
• Pure water has a pH of precisely 7.
• Examples: Common salt, water (NaCl)

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Uses of Acid and Bases

1. Acids and Their Applications

Vinegar is a diluted solution of acetic acid that has a variety of uses in the home and is mostly utilised in the food industry as a preservative.

• Lemon and orange juice contain a significant amount of citric acid.
• Sulfuric acid is extensively utilised in batteries and is often found in batteries used to start car motors.
• Sulfuric and nitric acid are used in the industrial manufacturing of explosives, dyes, paints, and fertilisers.
• Many soft drinks include phosphoric acid as a component.

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2. Bases and Their Applications

Sodium hydroxide is used in the production of soap and paper. Sodium hydroxide (NaOH) is also utilised in the production of rayon.

• Bleaching powder is made from Ca(OH)₂, commonly known as slaked lime or calcium hydroxide.
• Calcium hydroxide is used to create dry mixtures for painting and decorating.
• Magnesium hydroxide, often known as milk of magnesia, is a laxative that is frequently used. It is also used as an antacid since it lowers excess acidity in the human stomach.
• Ammonium hydroxide is a critical reagent used in laboratories.
• Slaked lime can be used to neutralise any excess acidity in soils.

Read More: Electrochemical Cells

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Things to Remember

1. pH scale can be used to determine the quantitative value of a substance's level of acidity or basicity. pH scale is the most widely used and accepted method of determining how acidic or basic a material is. A pH scale ranges from 0 to 14, with 0 indicating the most acidic and 14 indicating the most basic.
2. Litmus paper can also be used to determine if a material is acidic or basic. Red and blu are two forms of litmus paper that may be used to detect acids and bases. Under acidic conditions, blue litmus paper turns red, whereas red litmus paper turns blue under basic or alkaline conditions.

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