Acid base and salt

Acid: Acid is substance which is sour in taste containing hydrogen which can be replaced and gives rise to hydrogen ions when dissolved in water.

Most of the chemicals that we come across in our daily life can be classified as acid, base or salt. Fruits like orange, lemon, apples, grapes, etc. contains same sort of acid in them. It is found found in curd even the cold drinks has acid in it. Similarly, lime powder used for white wash is a base. Antacid tablets used in hyperacidity of our stomach is also a base. The common salt is one of the main ingredients of our food is a salt. Similarly, the soap that we use for washing or bathing is also a salt.

Term “acid ” is derived from latin word, ”acidus” meaning sour. Anything that tastes sour is an acid. Common laboratory acids .

1. Hydrochloric acid (HCl)
2. Sulphuric acid (H₂S0₄)
3. Nitric acid (HNO₃)
4. Acetic acid (CH₃ COOH)

If we look at formula of acids, they contain at least one replaceable Hydrogen atom in them. When acid is dissolved in water, it gives Hydrogen ion (H⁺aq). Hydrogen ion are called called proton. Therefore acid ore also called proton donors.

HCL  ⇌⇌ H⁺ + Cl^–

H₂S0₄  ⇌⇌ 2H⁺ + S0₄^–

HNO₃  ⇌⇌ H⁺ + NO₃^–

CH₃ COOH  ⇌⇌ H⁺ + CH₃ COO^–

Anything that tastes sour has at-least 1 replaceable Hydrogen atom and gives H⁺ ion on dissolving in water are called an acids.

Types of acid

Acid can be classified in 2 ways

1. On the basis of their strength
2. On the basis of the source where they are obtained

On the basis of their strength: On this basis or on the degree of ionization, they con classified into strong and weak acid.

Strong acid:The acids which gives larger concentration of H⁺ ion on dissolving in water due to complete ionization are called strong acid. They are highly corrosive in nature. Eg, Hydrochloric acid (HCI), H₂S0₄ and HNO₃

Weak acid: The acids which ionize partially to give smaller concentration of H⁺ ion on dissolving in water are called weak. They are less corrosive. Eg, Acetic acid, Citric acid, Maelic acid etc.

On the basis of source from where the acids are obtained: Acids can be classified as:

Inorganic acid: The acids which are obtained from minerals found earth’s crust are called inorganic acid. They are also called mineral acid as they’re obtained from minerals. Eg, HCI, H₂S0₄, HNO₃ H₂CO₃

Organic acid: The acids which are obtained from organism ie. plants and animals are called organic acids. They are weak acids and mild in nature. Eg, CH₃ COOH

Properties of acid

1. Acids have sour taste.
2. Acids change color of blue litmus to red, methyl orange to red and leaves phenolphthalein colorless.
3. Strong acids are corrosive.

Reactive metals like Mg, Fe, Zn displaces Hydrogen from an acid. Eg,

Zn + 2HCL → ZnCl₂ + H₂

Mg + H₂S0₄ → MgS0₄ + H₂

Fe + HCL → FeCl₂ + H₂

Acids react with a metal carbonate or bicarbonate to give a salt, CO₂ and H₂O  Eg,

2HCL + Na₂C0₃ → 2NaCl + CO₂ + H₂O

2HCL + NaHC0₃ → NaCl + CO₂ + H₂O

H₂S0₄ + CuC0₃ → CuS0₄ + CO₂ + H₂O

An acid neutralizes base to form salt and water

HCL + NaOH → NaCl + H₂O

H₂S0₄ + 2KOH → K₂S0₄ + H₂O

H₂S0₄ + CuO → CuS0₄ + H₂O

Acid dissolve in water to give H⁺ ion.

HCL   ⇌⇌ H⁺ + Cl^–

H₂S0₄  ⇌⇌ 2H⁺ + S0₄^–

HNO₃  ⇌⇌ H⁺ + NO₃^–

CH₃ COOH  ⇌⇌ H⁺ + CH₃ COO^–

Use of some acids

1. Sulphuric Acid, HCL nitric acid are strong acids. So, they are used in lab for different experiments. They are equally used in industries to prepare drugs, dyes etc.
2. Carbonic acid (H₂C0₃) is used to make soft drinks.
3. Vinegar i.e. acetic acid (CH₃ COOH) and citric acids are used to make pickle and different food items.
4. Citric acid (C₆H₈O₇) con be used as source of vitamin C.
5. Phenol i.e. carbolic acid (C₆H₅OH) can be used as germicide.

Base: Metallic oxides and Hydroxides which neutralizes an acid to form salt and water is called base. Bases like Sodium Hydroxide, Potassium Hydroxide, Ammonium Hydroxide etc are soluble in water. Soluble bases are called alkali.

“All alkalis are base but all bases aren’t alkali.”

Preparation of base:

By heating metals in air

2Na + 0₂ → 2Na₂O (on heating)

2K + 0₂ → 2K₂O (on heating)

2Mg + 0₂ → 2MgO (on heating)

2Ca + 0₂ → 2CaO (on heating)

By heating metal compounds like metal carbonate or metal nitrate.

2CaC0₃ → CaO + CO₂ (on heating)

2Cu(N0₃)₂ → 2CuO + O₂ + 4NO₂(on heating)

Common alkalis

1. Sodium Hydroxide (NaOH)
2. Potassium Hydroxide (KOH)
3. Calcium Hydroxide [Ca(OH)₂]
4. Ammonium Hydroxide [NH₄OH]

When alkalis are dissolved in water, they produce Hydroxide ion. Eg.

NaOH   ⇌⇌ Na⁺ + OH^–

Ca(OH)₂  ⇌⇌ Ca⁺ + 2OH^–

NH₄OH  ⇌⇌ NH₄⁺ + OH^–

Types of base

Bases can also be strong or weak.

Strong base/Alkali – Alkali that dissociate completely on dissolving on water to form large concentration of Hydroxide ion is called strong alkali. Eg, Sodium Hydroxide, Potassium Hydroxide

Weak base/Alkali – The alkali that dissociate partially to give smaller concentration of Hydroxide ion are called weak alkali

Eg Calcium Hydroxide, Ammonium Hydroxide, Magnesium Hydroxide

Properties of base

1. Most of the bases (alkalis) have bitter taste.
2. Alkali have soapy feeling i.e they are slippery on touch.
3. A base solution turns red litmus to blue, methyl orange is yellow and phenolphthalein to pink.
4. Strong alkali like Sodium Hydroxide (NaOH) and Potassium Hydroxide (KOH) are highly corrosive. They dissolve muscle, skin and other organic matter.
5. A base neutralizes acid to form salt and water. Eg,

NaOH + HCl  → NaCl + H₂O

CuO + H₂SO₄  → CuSO₄ + H₂O

6. When CO₂ gas is passed in alkali solution, it gives a metal carbonate.

CO₂ + 2NaOH  → NaCl + H₂O

CO₂ + Ca(OH)₂  → CaCO₃ ⇣+ H₂O

7. The mixture of an alkali and ammonium salt on heating gives ammonia gas.

2NH₄Cl + Ca(OH)₂ → CaCl₂ + NH₃ + 2H₂O (on heating)

NH₄NO₃ + NaOH → NH₃⇡ + NaNO₃ + 2H₂O (on heating)

8. When an alkali solution is mixed with certain salt solution, it forms an insoluble hydroxide.

NaOH (aq) + CuSO₄ (aq) → Cu(OH)₂⇣ + Na₂SO₃

KOH + FeCl₃ →  Fe(OH)₃ + KCl

Uses of Bases

1. Sodium Hydroxide (NaOH) – To prepare soap, paper, petroleum refinery.
2. Potassium Hydroxide (KOH) – To prepare soft soap.
3. Calcium oxide (CaO) – Softening water, cement production, sugar purification.
4. Ammonium Hydroxide (NH₄OH) – To prepare urea, nitric acid, dyes.
5. Magnesium Hydroxide [Mg(OH)₂] and Aluminum Hydroxide [Al(OH)₃] – As antacid against stomach acidity.
6. Slaked lime [Ca(OH)₂] – White washing of walls

Salt: Salt is a compound formed by replacing hydrogen atom partly or completely by a metal or Ammonium radical from an acid. If Hydrogen from an acid is completely replaced by a metal or ammonium, it gives a normal salt. Eg, NaCL, CuSO₄, CaNO₃, NH₄Cl. When hydrogen is replaced partially, the resultant salt is called acid salt. Eg, NaHS0₄ , NaHC0₃ If you look at formula of salt, we can see two parts in it, one is derived from acid and another from base. They are called basic radical and another part is acidic radical. Part of Salt where the salt gets from a base is called basic radical. It is a metal ion or  NH₄⁺ ion. Acid radical is the port of salt which it gets from acid. It is electronegative in nature.

Depending on behavior towards an indicator, a salt can be neutral, acidic or basic.

Hydrated salt: The salt where certain number of water molecules are loosely held with a molecule of salt are called hydrated salt. The water molecule present with salt gives their crystalline structure. When such salts are heated, the crystalline structure is lost. E.g,

CuSO₄ 5H₂0 (Pentahydrate Copper Sulphate)

CaSO₄ 2H₂0 (Dihydrate calcium Sulphate)

Na₂CO₃ 10H₂0 (Decahydrate calcium carbonate)

CuSO₄ 5H₂0 → CuSO₄(heat) (anhydrous salt) white powder (Amorphous)

Properties

1. Salts have different tastes. They have salty taste like NaCl, bitter taste and most of the salt are tasteless.
2. Most of the salt are soluble in water. Solution of salt act as electrolyte i.e. they undergo electrolysis.
3. Salt can be neutral like NaCl, acidic like Copper Sulphate and basic like Sodium Carbonate.
4. Salts of Na, K, Ca, Mg, Zn etc are white salts of Cu, Mn, Cr, Fe, Ni, Co etc are colored.
5. All salts of Na, K and NH₄ are soluble in water. Similarly, all nitrates and bicarbonates are also soluble in water except Ag and Pb (lead) similarly all sulphates are soluble in water except Ag and Ba (Barium). All carbonates are insoluble in water except Na, K and NH₄

Uses of salt

1. NaCl – As edible salt
2. Sodium carbonate – As a soap, glass industries and to prepare detergent
3. Ammonium sulphate – As chemical fertilizer
4. Ammonium sulphate –  As electrolyte in dry cell
5. Calcium sulphate – To make chalk ,cement and plaster of Paris

Neutralization reaction and its application: The reaction between acid and a base give neutral products i.e. salt and water is called neutralization reaction. It has several practical applications in our everyday life. Different types of manufacturing industries produce useful materials along with waste products. If such wastes are mixed in environment, it is harmful to the nature. The acidic effluences (liquid waste) of industries are treated by using lime. The acidic gases are treated by using powdered lime (CaO) and (CaCO₃) powder

Laboratories: In labs acids spillage is neutralized by using base and vice versa.

Health: In health, by hyperacidity due to excess HCl produced in stomach is neutralized by using baking soda or with an antacid which is a mixture of Mg(OH)₂ and Al(OH)₂. Similarly, in case of wasp sting an alkali is injected into our skin causing burning sensation. It can be neutralized by using vinegar. In case of burning by ants bite, bettle and bee sting, baking soda is applicable.

In agriculture: Acidic soil is treated with lime (CaOH₂) to neutralizes.

At home: Toothpaste we use is basic in nature which to neutralize the acid produced into our mouth due to bacterial action on food particles stuck between our teeth.

Q. When an acid reacts with base, salt and water is formed.

When acid reacts with base, salt and water is formed due to their neutralization property of acid.