Description Of Acid & Base

Acid

A chemical that releases hydrogen ions in water and combines with certain metals to make salts. Acids taste sour and turn some colors red. Some acids that the body makes, like gastric acid, can help organs work properly. Hydrochloric acid is one type of acid. The pH scale is a way to measure how acidic something is. On this scale, a value of 7 is neutral, and a value of less than 7 or equal to 0 means that the acidity is getting worse.

Examples of Acid

The most common examples of Acid are:

• Hydrochloric Acid.
• Sulfuric Acid.
• Nitric Acid.
• Formic Acid.
• Citric Acid.

Base

In chemistry, an alkali is a substance that can take in hydrogen ions from water and make an acid neutral. Bases make the skin feel soapy or slippery, and they can turn some dyes blue. Sodium hydroxide is an example of a base. The pH scale is a way to measure how basic something is. On this scale, a pH value of 7 is neutral, and a pH value between 7 and 14 shows that the substance is becoming more basic.

Examples of Base

The most common examples of Base are:

• sodium hydroxide
• calcium carbonate
• potassium oxide

Historical theories of Acid & Base

To explain what acid and base are, three different ideas have been put forward. The Arrhenius theory, the Bronsted-Lowry theory, and the Lewis theory of acid and base are some of these ideas. Here is an explanation of each of these ideas.

Arrhenius’s theory about Acid & Base

The Swedish chemist Svante Arrhenius came up with the Arrhenius theory of acid and base in 1884. He suggested that you could tell if a compound is an acid or a base by what kind of ions it makes when you mix it with water.

Arrhenius acid

Any substance that increases the hydrogen ion (H⁺)when dissolved in an aqueous solution is called Arrhenius acid. Hydronium ions (H₃O⁺) is formed when hydrogen ion (H⁺) react with water in an aqueous solution.

HCl (aq) → H⁺ (aq) + Cl⁻ (aq)

When an aqueous solution of HCL (Hydrochloric Acid) is formed HCl dissociates into H+ ions and OH- ions. So this increases the number of protons (H+).

Arrhenius Base

Any substance that increases the hydroxide ion (OH^–) when dissolved in an aqueous solution is called an Arrhenius base. Most of the time, when an Arrhenius acid and a base react, they make water and salt. This is called an acid-base or neutralization reaction.

NaOH (aq) → Na⁺ (aq) + OH⁻ (aq)

When an aqueous solution of NaOH (Sodium Hydroxide) is formed NaOH dissociates into Na⁺ ions and OH⁻ ions. So this increases the number of Sodium Hydroxide ions ( OH⁻ ).

Limitations of Arrhenius’s theory

The Arrhenius theory isn’t perfect because it can only explain acid-base chemistry in water. But similar reactions can also happen between molecules in the gas phase and in solvents that are not water. One big problem with Arrhenius’s definitions of acid and base is that they don’t explain how matters that don’t have hydroxide ions can form basic solutions when dissolved in water like NO₂^– and F^–. Because of this, most modern chemists prefer the Brnsted-Lowry theory, which can be used for a wider range of chemical reactions.

Bronsted Lowry Theory of Acid and Base

The Bronsted-Lowry theory explains how acid and base interact in terms of how protons move from one chemical to another. A Bronsted-Lowry acid is any substance that can give up a proton, and a Bronsted-Lowry base is any substance that can take up a proton. In terms of chemical structure, this means that any Bronsted-Lowry acid must have hydrogen shown as (H⁺). For a Bronsted-Lowry base to accept a proton, it must have at least one pair of free electrons that can form a new bond with the proton. One good thing about the Bronsted-Lowry definition of acids and bases is that it can explain why ionic species are acidic or basic.

Bronsted Lowry Acid

The Bronsted-Lowry theory says that acid is something that gives away protons (H⁺) or hydrogen ions. Bronsted acids break apart to give off protons, which makes the concentration of (H⁺) ions in the solution higher.

Bronsted Lowry Base

A Bronsted-Lowry base is any substance that can accept a proton, which needs a pair of free electrons to bond to the H⁺. Bronsted bases take protons from the solvent, which is water, to make hydroxide ions.

• Water is amphoteric, which means that it can act as both a Bronsted-Lowry acid and a Bronsted-Lowry base.
• In water, acids, and bases that are strong ionize completely, while acids and bases that are weak only ionize partially.

Conjugate acid

A conjugate acid has one more hydrogen atom and one more positive charge than the base from which it was made. When an acid gives a proton to a base, this gives rise to a conjugate acid. A conjugate base has one less hydrogen atom and one more negative charge than the acid from which it was made. When an acid loses its hydrogen ion, this is what is left.

CH₃COOH  +  H₂O  ⇋  CH₃COO^–  + H₃O⁺ 

In the above reaction H₃O⁺ act as Conjugate Acid.

Examples

The most common examples of Conjugate acids are

• hydronium ion (H₃O)
• produced from reactants nitric acid (HNO₃)
• water (H₂O). 

Conjugate Base

A conjugate base has one less hydrogen atom and one more negative charge than the acid from which it was made. When an acid loses its hydrogen ion, this is what is left. Basically, a conjugate base is an acid that has lost its hydrogen ion. It has the same formula as an acid but without the hydrogen ion.

CH₃COOH  +  H₂O  ⇋  CH₃COO^–  + H₃O⁺ 

In the above reaction CH₃COO^– acts as Conjugate Base

Examples

The most common examples of Conjugate Bases are

• HSO₄^–
• SO₄^2-
• Cl⁻

Overview of Conjugate acid & Conjugate Base

Advantages of Bronsted-Lowry theory

Overall, the Bronsted-Lowry theory is better than the Arrhenius theory because it can explain why more species are acidic or basic. For instance: Bases that don’t have ions of hydroxide like ammonia (NH₃).

limitations of Bronsted Lowry Theory

In real life, it is possible for acidic oxides and basic oxides to react without a solvent to make salt. Another limitation of Bronsted Lowery theory includes an inability to explain the acidic properties of some specific compounds which do not have any proton in their chemical formula but still act as an acid. Because there are no H+ or OH- ions in this reaction, the Brnsted Theory of Acids and Bases can’t explain how it works. So, the Lewis Acid and Base Theory helps us understand how other species and complex ions that don’t usually have hydronium or hydroxide ions form.

Lewis Theory of Acids and Bases

The Bronsted Theory says that acids and bases give and take protons. Around the same time as Johannes N. Brnsted and Thomas M. Lowry, Gilbert N. Lewis came up with his own theory about acids and bases. Lewis’ theory is based on the transfer of electrons, while the Brnsted-Lowry theory is based on the transfer of protons. Acids and bases are not defined by this theory in terms of the hydrogen atom.

Lewis Acid

Lewis acids are molecules with a central atom that can have more than 8 electrons in its valence shell and can accept electrons. Lewis acids are made up of molecules that have more than one bond between atoms with different amounts of electronegativity.

Lewis acids are electron-deficient species. They cause the halogen molecule to split apart in a way called heterolytic fission. Lewis acid’s job is to make an electrophile. The electrophile will attack the benzene ring, which has a lot of electrons. This will make aryl bromides and chlorides. For example; Boron trifluoride (BF3) and Aluminum fluoride (AlF3)

Lewis Base

Lewis Base is a type of molecule that has a filled orbital with an unbonded electron pair that can form a dative bond with a Lewis acid to make a Lewis adduct. A chemical that gives up an electron pair. A covalent bond is made when a pair of electrons from a Lewis base is “donated” to an electron acceptor. Lone-pair electrons will be in a Lewis Base. Since they give up electrons, all anions are Lewis Bases. For example, NH3 is a Lewis base because it can give away its only pair of electrons.

What is Lewis Acid-Base reaction?

When a base gives an acid a pair of electrons, this is called a Lewis acid-base reaction. In many Lewis acid-base reactions, a Lewis acid-base adduct is made. This is a compound in which the Lewis acid and the Lewis base are linked by a covalent bond.

Examples

Characteristics

The Characteristics in the form of advantages and disadvantages are as follows:

Advantages of Acids

• Acid is used in cleaning products that kill germs and are used to clean the toilet, tiles, and other places.
• When the acids and bases come together, they make a high-value salt.
• Acid can help get rid of clogs in the sewer system.
• The immune system gets a boost from ascorbic acid.
• Hydrochloric acid is found in the stomach, where it helps break down food.
• Acids dissolved in water are electrolytes, which means they move electricity.
• The taste of acids is sour.
• Some acid-base indicators change color when acid is added.
• Acids react with metals that are doing work to make hydrogen gas.
• When acids meet bases, a salt compound and water are made.

Disadvantages of Acids

• Acid can irritate the skin and cause burns that are very painful.
• The acid can hurt the eyes and even make people go blind.
• If the stomach makes more hydrochloric acid than usual, it may make the stomach acidic.
• Clothes and fabrics can be burned by the acid.
• Because acids are corrosive, they can’t be kept in metal containers. Instead, they have to be kept in plastic or glass containers.
• Working with acids and bases is dangerous to your health because they are corrosive, which means they break down tissue.
• Hydrofluoric acid, or HF, has the sneaky property of being able to get through the skin without burning and destroying a lot of tissue underneath.
• Sulfuric acid is a chemical that can burn the skin and eyes very badly.
• When you breathe in sulfuric acid mist, it can irritate your eyes, nose, throat, and lungs. At higher concentrations, it can also cause fluid to build up in your lungs (pulmonary oedema).
• Acidic substances cause coagulation necrosis, which leads to cytotoxicity. There are also changes in the mucous membranes or skin that may stop the toxicity from getting worse and limit absorption.

Advantages of Bases

• Soaps and detergents are made with the bases.
• The bleaching agent is made with the help of calcium hydroxide.
• In the lab, reagents are things like sodium hydroxide, which is a base.
• Cement is made with calcium hydroxide.
• The waste sodium hydroxide is used to clean up oil.
• Some Bases are great at moving power around.
• Electrolytes are bases like sodium hydroxide, potassium hydroxide, and so on.
• When a metal reacts with a base, hydrogen gas is made.
• When bases are mixed with acids, salt, and water are made. Neutralization response is the name for this process.
• They can pass electricity through them.

Disadvantages of Bases

• The base could make the skin red and itchy.
• Porcelain and glass can be broken down by bases.
• If the base solution gets in your eye by accident, it can make you blind for life.
• The fumes from the reaction with the base could make it hard to breathe.
• Some bases are dangerous to people.
• Ammonia is a strong acid. How long you are exposed, how much you are exposed, and how you get exposed all affect how bad the health effects are.
• High levels of ammonia in the air burn the eyes, nose, throat, and breathing passages right away. This can lead to blindness, lung damage, or death.
• Ammonia emissions can lead to more acid rain and too many nutrients in the soil, rivers, or lakes, which can hurt aquatic ecosystems and hurt forests, crops, and other plants.
• There are two main reasons why you shouldn’t use ammonia as a coolant: It doesn’t work with copper, so it can’t be used in pipes made of copper. In large amounts, ammonia is poisonous.

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