Acids and Bases are chemicals which are widely used in chemistry in our daily life. Acids are a substance which on dissolving in water gives H+ ions whereas bases are substances which on dissolving in water gives OH– ions.
Acids have a sour taste and are corrosive in nature i.e. exposure to acid on human skin can cause blisters. Some examples of acids are HCl, H2SO4 and others.
Bases are also corrosive in nature and they have a soapy texture. Some examples of bases are NaOH, KOH and others.
Let’s learn more about acids and bases, their properties, theories and others in this article.
What are Acids?
The term acid is derived from the Latin word ‘acidus’ or ‘acere’, which means sour. The most common characteristic is their sour taste. An acid is a substance that renders an ionizable hydronium ion (H3O+) in its aqueous solution. It turns blue litmus paper red.
The following image represents the aqueous solution of the acid.
Acids can be present in a variety of things, including food, but their presence in several fruits is particularly notable. For example
- Curd – Lactic Acid
- Vinegar – Acetic Acid
- Orange – Citric Acid
- Tamarind – Tartaric Acid
- Tomato – Oxalic Acid
- Lemon – Citric Acid
Apart from these, several acids, such as hydrochloric acid, sulphuric acid, and nitric acid, are commonly employed in laboratories. In the stomach, we have certain fairly common acids, such as weak hydrochloric acid, which causes food indigestion. We normally experience indigestion and a burning feeling in our stomach when the contents of our stomach become excessively acidic. When acids react with metals, hydrogen gas is produced. All acids have hydrogen as a component.
Metal + Acid ⇢ Salt + Hydrogen
Properties of Acids
Various properties of the acids are,
- When an acid is dissolved in water, it produces hydrogen ions (H+).
- Acids react with metals to form/release hydrogen gas.
- Acid has a sour flavour and is caustic in nature.
- Acids have a pH of less than 7.
- When acids react with limestone (CaCO3), carbon dioxide is produced.
- Blue litmus paper is generally converted to red litmus paper by acid.
- They obliterate bases’ chemical properties.
Classifications of Acids
Acid can be classified into various categories
On the Basis of Origin
On the basis of origin, acid can be classified into two categories which are discussed below,
Organic Acids: The acids that come from organic matter like plants and animals are known as Organic Acids. For Example, citric acid (Citrus fruits), Acetic acid (Vinegar), Oleic acid (Olive oil), etc.
Mineral Acids: The acids that come/are produced from minerals are known as Mineral Acis or Inorganic Acids. These acids do not contain carbon For Example H2SO4, and HCl. HNO3, etc.
On the Basis of Strength
On the basis of strength, acid can be classified into two categories which are discussed below,
Acids produce hydrogen ions when mixed with H2O, the strength of an acid depends on the concentration of the hydrogen ions present in a solution. A greater number of hydrogen ions means greater strength of the acid whereas, a lower number of hydrogen ions means that the acid is weak.
Strong Acids: A strong acid is one that can be totally or nearly completely dissociated in water. For Example, Sulphuric acid, Nitric acid, Hydrochloric acid, etc.
H+ + H2O ⇢ H3O+
HCl(aq) ⇢ H+(aq) + SO4–(aq)
H2SO4(aq) ⇢ 2H+(aq) + SO4–(aq)
Weak Acids: A weak acid is one that does not completely dissociate or dissociates very little in water. For Example, the acids that we consume on daily basis like citric acid, acetic acid, etc.
CH3COOH(aq) ⇢ CH3COO-(aq) + H+(aq)
HCOOH(aq) ⇢ HCOO-(aq) + H+(aq)
What are Bases?
Bases are ionic substances that when dissolved in water produce negative hydroxide (OH) ions. An ionic compound is one that contains a negative nonmetal ion and a positive metal ion that is held together by an ionic bond.
The following image represents the aqueous solution of the base.
Properties of Bases
Various properties of the bases are,
- Bases are chemicals that, when dissolved in water, produce the hydroxide ion (OH).
- Bases have a harsh taste and caustic properties. They frequently have a slick, soapy feel about them.
- Bases are excellent conductors of electricity and have a pH of more than 7.
- Soap molecules are formed when bases combine with oils and grease.
- Red litmus paper is converted to blue litmus paper by bases.
- Bases have a proclivity for corroding metal surfaces.
- When they come into contact with acids, they respond quickly.
Classification of Bases
The various classification of the base is,
- Strong Bases
- Super Bases
- Weak Bases
- Lewis Bases
In the acid-base reaction, a strong base is described as a basic chemical substance that can remove a proton (H+) from (or deprotonate) a molecule of even a relatively weak acid (like water). Hydroxides of alkaline earth metals and alkali metals, such as Ca(OH)2 and NaOH, are two common examples of strong bases.
A few of the bases, such as alkaline earth hydroxides, can be employed when the solubility requirement is ignored due to their poor solubility. “Several antacids were suspensions of the metal hydroxides like magnesium hydroxide and aluminium hydroxide,” says one proponent of the low solubility.
For Example – Sodium hydroxide – NaOH, Lithium hydroxide – LiOH, and Potassium hydroxide – KOH.
Because their conjugate acids, amines, stable hydrocarbons, and dihydrogen, are extremely weak, Group 1 salts of hydrides, amides, and carbanions tend to be stronger bases. In general, these bases are made by mixing conjugate acid with pure alkali metals like sodium. They are known as superbases, and keeping them in water is nearly impossible because they are classified as stronger bases than the hydroxide ion. As a result, conjugate acid water is deprotonated.
For Example – Sodium hydride (NaH), Sodium amide (NaNH2), and Butyl lithium (n-C4H9Li).
A weak base is one that does not completely ionize in an aqueous solution or one whose protonation is incomplete. At 25 °C, the equilibrium constant for the above-mentioned reaction is 1.8 x 10-5, implying that the degree of ionization or reaction is quite minimal.
A Lewis base, also known as an electron-pair donor, is a molecule that has a high-energy pair of electrons that can be shared with a low-energy empty orbital in an acceptor molecule to form an adduct. Other possible acceptors (known as Lewis acids) include neutral molecules like BF3 and metal ions like Fe3+ or Ag+, in addition to the H+ molecule. Adducts containing metal ions, on the other hand, are known as coordination complexes.
An electric stress state occurs when a neutral base forms a bond with a neutral acid, according to the original Lewis formulation. The electron pair that used to belong only to the base is now shared by acid and base.
pH of Acid and Base
Soren Peter (Biochemist) was the first to coin the term pH in 1909. We utilize a universal indicator to determine the strength of acids and bases, which shows distinct colours at varying quantities of hydrogen ions in a solution. The pH value is commonly used to determine the strength of acid and base in a quantitative manner. The logarithm of H+ ion concentration is defined as pH, which stands for the Power of Hydrogen. Any material or solution’s pH value indicates whether it’s acidic, neutral, or alkaline.
What is the pH scale?
A pH scale is a tool for determining acid and base concentrations. The scale goes from zero to fourteen, with zero being the lowest and fourteen being the highest. A litmus test reveals whether a substance is acidic or basic. The colour of the paper matches the pH scale numbers, indicating the sort of chemical being tested.
What is pH value?
A pH scale is used to determine the pH value of a component. The pH scale ranges from 0 to 14, with 0 indicating extremely acidic and 14 indicating extremely alkaline. If a pH value of 7 is found in any solution, it indicates that the solution is neutral in nature. Values less than 7 suggest an acidic solution, whereas values more than 7 indicate an alkaline solution.
The acidity of the solution increases as the pH value decreases from 7 to 1, i.e. a solution with a pH value of 2 is more acidic than a solution with a pH value of 3. The alkalinity of a solution increases from 7 to 14 (in the opposite direction of acidity), i.e. a solution with a pH of 11 is more alkaline than a solution with a pH of 9.
The litmus test of acid and base is shown in the following image.
Strength of Acid
Acids are defined as substances with a pH less than 7.0. As the amount of H+ ions in the solution increases, the value decreases. Strong acids are compounds that rapidly release H+ ions or are completely ionizable in solution. As a result, strong acids have a lower pH value, close to 0 to 1. The higher the concentration of H+ ions in the solution, and hence the stronger the acid, the lower the pH value.
For example, Hydrochloric acid, Sulfuric acid, Nitric acid, Perchloric acid, Chloric acid, etc.
Strength of Weak Acid
A weak acid is one that does not entirely ionize in solution. In low quantities, it releases the H+ ion, resulting in a pH range of 5 to 7. Formic acid (HCOOH), acetic acid (CH3COOH), and many more acids are examples.
Strength of Base
The nature of certain substances is determined by their pH. Bases, on the other hand, are substances having a pH greater than 7.0. As the amount of H+ in the solution drops, the value continues to rise. Strong bases are chemicals that rapidly release the OH– ion in a solution. The H+ ion in the solution is scooped up by these ions, which raises the pH value of the solution. As a result, strong bases commonly have pH values of around 13 or 14.
For example, Lithium hydroxide, Sodium hydroxide, Potassium hydroxide, Rubidium hydroxide, Cesium hydroxide, etc.
Strength of Weak Base
Chemicals that do not completely dissociate are known as weak bases (have a pH value in the range of 7 – 10). As a result, the concentration of OH– ions decreases, and the pH value rises. Methylamine and ammonia are two such examples.
Learn more about Base
Difference between Acids and Bases
The difference between acid and base are discussed below in the table.
|Acids are substances which on dissolving in water release H+ ions.||Bases are substances which on dissolving in water release OH– ions.|
|Acid has a sour taste.||Acid has a bitter taste. Acid has a soapy texture.|
|Acid turns blue litmus red.||Base turns red litmus blue.|
|Acid has pH values ranging from 1 to 7.||Base has pH value ranging from 7 to 14.|
|Examples of acids are HCl, H2SO4 etc.||Examples of bases are NaOH, KOH etc.|
Theories of Acid and Base
There are various concepts of acid and base and some of them are
- Lewis’s Concept of Acids and Bases
- Arrhenius’s Concept of Acids and Bases
- Bronsted Lowry’s Theory of Acids and Bases
They are discussed below in the article
Lewis Concept of Acids and Bases
According to Lewis, “Acids are the substance which accepts an electron pair and are electrophilic in nature i.e. they have incomplete valance orbital which can accept electron pairs.”
Examples of Lewis acids are, Cu2+, Fe3+, etc.
Similarly,” Bases are the substance which has an electron pair in their outermost valence shell and they can easily donate those electron pair, they are nucleophilic in nature.”
Examples of Lewis bases are Cl–, NH3, etc.
The Lewis definition of an acid states that it is a species that has a vacant orbital and therefore, has the ability to accept an electron pair.
Arrhenius Concept of Acids and Bases
Arrhenius’s concept of acid and bases is the basic concept which explains the concept of acid and base.
According to Arrhenius, “Acids are the substance that on dissolving in water releases H+ ions.” These H+ ions combine with H2O molecules to form hydronium ions (H3O+).
Examples of acids are HCl, H2SO4, etc.
Similarly, “Bases are the substance that on dissolving in water releases OH– ions.”
Examples of bases are NaOH, Ca(OH)2, etc.
Bronsted Lowry Theory of Acids and Bases
Another theory which explains the definition of Acid and Base is the Bronsted-Lowry theory of acid and base which says that,
“Acids are the substance which is categorised as protons (or H+) acceptors whereas bases are the substance which accepts protons (or H+) from the water.”
The limitation of this theory is that it is unable to explain the acidic behaviour of BF3 and AlCl3 as they lack to give protons in their aqueous solution and still are considered to be acidic.
Uses of Acids and Bases
Acids and Bases are highly used chemicals which are used for various purposes. Various uses of acid and bases are discussed below in the article,
Uses of Acids
Various uses of the acid are,
- Acetic acid (Vinegar) is a highly used acid which is used for various household purposes.
- Sulphuric acid is widely used for Lead- Acid batteries.
- Acids are used in various industries for making paints, varnishes, fertilizers and others.
- Nitric Acid is used for the production of explosives.
Uses of Bases
Various uses of the base are,
- Bases are used for the production of various soaps.
- Bases are used as laboratory reagents.
- Bases are used in various industries.
- Bases are highly used for metallurgical purposes.
- Calcium Hydroxide [Ca(OH)2] is used for the manufacturing of bleaching powder.
- Magnesium Hydroxide [Mg(OH)2] also called milk of magnesia is used as an antacid.
FAQs on Acid and Bases
Q1: How can we differentiate between Acid and Base?
Acid and Bases can be differentiated by using a litmus paper. Litmus paper/solution turns red in acidic solutions and blue in alkaline solutions.
Q2: List some acids present in fruits and vegetables.
Some acid present in fruits and vegetables are,
- Orange – Citric Acid
- Tamarind – Tartaric Acid
- Tomato – Oxalic Acid
- Lemon – Citric Acid
Q3: Acids react with metals to release which gas?
Acids react with metals to release hydrogen gas.
Q4: How do Acid and Base react with metal?
Acids and Bases react with metals to form salt and release hydrogen gas.
Q5: How do Acids and Bases react with each other?
Acids and Bases react with each other to form salt and water this reaction is called a neutralization reaction. Example,
Acid + Base —> Salt + Water
HCl + NaOH —-> Nacl + H2O
Q6: What is the pH range of Acid and Base?
Solutions with pH less than 7 are acidic in nature, whereas solutions with pH higher than 7 are basic in nature.
Q7: What is a strong acid?
Strong acids are compounds that rapidly release H+ ions or are completely ionizable in solution. As a result, strong acids have a lower pH value, close to 0 to 1. The higher the concentration of H+ ions in the solution, and hence the stronger the acid, the lower the pH value.
For Example: Hydrochloric Acid, Sulfuric Acid, Nitric Acid etc.
Q8: What is a strong base?
Strong bases are chemicals that rapidly release the OH– ion in a solution. The H+ ion in the solution is scooped up by these ions, which raises the pH value of the solution. As a result, strong bases commonly have pH values of around 13 or 14.
For Example: Lithium Hydroxide, Sodium Hydroxide, Potassium Hydroxide etc.