Acid, Base and Salts: Definition, Physical & Chemical Properties, Examples and Similarities

Acid, Base and Salts

Have you ever wondered why everything has a different taste? Why is it the sour taste of lemon but sweet mango? It is because of the different percentages of acid, base and salts in their chemical composition. Acid, base and salts are the concepts that affect our daily life, and it's easy to identify the taste differences in them. Acid is sour in taste, and it turns the blue litmus to red, whereas the base is bitter and turns the red litmus to blue. Have you ever noticed that the curry stain on the white cloth will appear to be reddish-brown in colour when soap is scrubbed on it (basic in nature)? It turns the cloth yellow in colour again when washed with plenty of water. Is it interesting? Keep reading to know more about the definition and properties and understand the concepts from scratch.

Definition of Acid, Base and Salts

Numerous acids and bases are found naturally, such as citric acid in fruits like lemon, and orange, tartaric acid in tamarind, lactic acid in milk, etc. Similarly, bases can also be found naturally, such as lime water. We use these bases in our everyday life, such as vinegar in the kitchen, baking soda for cooking, washing etc. Several acids are not meant for domestic use; instead, they are used in laboratories and industries. For example, acids such as HCl, H2SO4 etc., and bases such as KOH, NaOH etc. When the acid and base are mixed in the right proportion, they form salt and water. Some of the naturally occurring salts such as KCl, NaCl etc. The following are the definition of the acid, base and salts:

What is Acid?

The term acid has been derived from the Latin word "acidus", meaning sour. It is defined as the substance whose solution is sour in taste, turns blue litmus to red and accepts electron pairs. When they react with metal, they release dehydrogenase. According to the Arrhenius hypothesis, acids are compounds that dissociate in water to create hydrogen ions H + (aq), while bases produce hydroxyl ions OH –. (aq) 

What is Base?

It is a substance whose aqueous solution taste bitter and feel soapy; it turns red litmus to blue and donates pair of electron. It becomes less basic when it is mixed with acid. According to Arius, bases are substances that dissolve in water and release hydroxide ions in solutions. Common bases include sodium bicarbonate, mainly used in cooking and household bleach, calcium hydroxide etc.

What is Salt?

It's an ionic compound, neutral, acidic and base in nature. It's an aqueous solution and doesn't affect litmus. It is formed through the neutralisation reaction by the combination of acid and base. Some common examples of Salts are sodium chloride, nitrate, barium sulphate and others.

Physical Properties of Acid, Base and Salts

The following are the physical properties of acid, base and salts:

Physical Properties of Acid

  • Taste: Acids have a sour flavour to them.

  • Physical state: Some acids are solids at normal temperature, whereas others are liquids. Examples such as oxalic acid, boric acid, and other solid acids are solids, whereas acetic acid, formic acid, and other liquid acids are liquids.

  • Corrosive nature: The majority of acids are corrosive. They cause a burning feeling on the skin and holes in the clothing they fall on.

  • Action of Indicator: It works by turning blue litmus red, changing the colour of methyl orange from orange to red, and keeping phenolphthalein colourless in acidic conditions.

Physical Properties of Base

  • Taste: Bases have a harsh taste, and their solution has a slick or soapy texture.

  • Corrosive nature: Severe bases have a strong burning impact on the skin, leading to blisters.

  • Action of the indicator: The markers convert the colour of red litmus solution to blue, methyl orange to yellow, and colourless phenolphthalein to pink.

  • Electricity conductivity: Bases in aqueous solutions, like acids, conduct electricity.

Physical Properties of Salt

  • Taste: It can be bitter, sweet or sour. Common NaCl is salty.

  • Corrosive nature: It is very corrosive.

  • Electricity conductivity: Dissolved salts conduct electricity.

Chemical Properties of Acid, Base and Salts

Chemical Properties of Acid

The following are the chemical properties of the acid:

  • Litmus turns from blue to red when exposed to acids.

  • They change Methyl Orange's colour from orange/yellow to pink.

  • Acids change Phenolphthalein's pink colour to a colourless colour.

  • Acids have the ability to carry electricity.

  • Some acids are extremely corrosive, meaning they will corrode or rust metals.

  • When acids react with an active metal such as Zn, Mg, or other metals, hydrogen gas is produced.

  • When combined with water, they form H+ ions.

1. Reaction with Active Metals

When acid reacts with the active metals, it generally displaces the hydrogen from acids, leading to the evolution of the hydrogen gas. The metals react with the residual acids to form a salt.



  1. Zinc Metal reacts with the dilute Sulphuric acid to form Zinc sulphate and evolves hydrogen gas.
  2. Zn+H2SO4→ZnSO4 +H2↑

  3. Magnesium reacts with the dilute sulphuric acid to form ferrous sulphate and evolves the hydrogen gas.

  4. Fe+H2SO4→FeSO4+H2↑

Less reactive metals such as copper and silver don’t react with the dilute acids.

As a result, not all metals react with the same acid in the same way. Highly active metals in the activity range above hydrogen react vigorously with dilute acids to liberate hydrogen gas, whereas less active metals react less aggressively with dilute acids.

2. Reaction of Metal Carbonates/Bicarbonates with Acid

When dilute acid reacts with metal carbonate, it generates salt, water and carbon dioxide.

Metal carbonates/bicarbonates+Acid→Salt+water+carbondioxide


  1. Sodium carbonate reacts with dilute sulphuric acid. It forms sodium sulphate and water and evolves carbon dioxide.

  2. Na2CO3 +H2SO4 →Na2SO4+H2O+CO2↑

  3. Sodium hydrogen carbonate reacts with dilute hydrochloric acid. It forms sodium chloride and water and evolves carbon dioxide.

  4. NaHCO3 +HCl→NaCl+H2O+CO2↑ 

3. Reaction of Acid with Base

When acid reacts with the base, it generates salts and water, and this reaction is called neutralisation.



When hydrochloric acid combines with sodium hydroxide solutions, sodium chloride and water are formed due to a neutralisation process.


4. Reaction of Metal Oxide with Acid

When acid reacts with metal oxide, it forms salts and water; therefore, it is a kind of neutralisation process.



A black metallic oxide combined (copper oxide) with hydrochloric acid forms blue-green copper chloride and water.


Chemical Properties of Base

The following are the chemical properties of the base:

  • Litmus' colour changes from red to blue due to the bases.

  • They have a bitter flavour.

  • When acids are combined with bases, the basicity of the base is lost.

  • Salt and water are formed when bases combine with acids. Neutralisation Reaction is the name given to this process (Read).

  • They have the ability to conduct electricity.

  • Bases have a slick or soapy feel to them.

  • Some bases are excellent electrical conductors.

  • Electrolytes include bases such as sodium hydroxide, potassium hydroxide, and others.

  • When alkalis are combined with water, they generate hydroxyl ions (OH-).

Alkali: It is a base that dissolves in water. It is a chemical that produces hydroxyl ions (OH–) as the sole negative charge ions when dissolved in water. Alkalis are not bases that are not soluble in water. As a result, all bases are alkalis, but not all alkalis are bases.

1. Reaction with Acid

The bases combine with the acid to form salt and water. It is called neutralisation.



  1. Sodium hydroxide combines with hydrochloric acid to form sodium chloride and water.

  2.  NaOH+HCl→NaCl+H2O

2. Reaction of Alkalis with Metal Oxide

Bases such as sodium hydroxide and potassium react with active metals such as aluminium and zinc and evolve hydrogen gas.


  1. When zinc reacts with sodium hydroxide, it produces sodium zincate and evolves hydrogen gas.

  2. Zn+2NaOH→Na2ZnO2+H2

  3. When aluminium reacts with sodium hydroxide, it produces sodium aluminate and evolves hydrogen gas.

  4. 2Al+2NaOH+2H2O→2NaAlO2+3H2

3. Reaction of Base with Non-Metallic Oxide

When the base reacts with non-metallic oxide, it produces salt and water.


  1. When sodium hydroxide reacts with carbon dioxide, it generates sodium carbonate and water.

  2. 2NaOH(aq)+CO2(g)→Na2CO3(aq)+H2O(l) 

  3. When calcium hydroxide reacts with sulphur dioxide, it generates calcium sulphite and water.

  4. Ca(OH)2(s)+SO2(g) →CaSO3(aq)+H2O(l)

Similarity between Acid and Base

The following is the list of the similarities between the two: 

  • The majority of strong acids and bases are corrosive by nature. They have a proclivity for corroding or rusting metals.

  • Litmus paper changes colour in both acids and bases. A base changes the colour of red litmus paper to blue, whereas an acid changes the colour of blue litmus paper to red.

  • When strong acids come into touch with the skin, they can cause serious burns.

  • We use acid and bases in our day to day life; common examples such as citric fruit, such as lemon, grapefruit, orange etc., contain critic acid, and grapes contain tamarind acid. Sopas and toothpaste have a base in them, and baking soda is also basic in nature.

  • Both produce ions in the water solution. Acid releases positive hydrogen ions (H+), whereas base releases negative ions such as (OH–).

Acid, base and salts are important topics. It will not only help you to score good marks in your academics but also help you to crack the competitive exams. Therefore, it is essential to understand the topic from the basics. You can also join our Chemistry class to develop a strong foundational base on the subject. The following are the additional key benefits you can avail of:

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