Base

Bases are the substances which give hydroxyl ion(OH^-) in aqueous solution. Almost all bases are oxide or hydroxide of metals. Most of bases form alkali on aqueous solution. That’s why all alkali are base but all bases are not alkali because all bases do not dissolve in water.

Classification of bases: Bases are classified as strong and weak base. The base which dissolve completely in water and gives sufficient amount of hydroxyl ion in aqueous solution are called strong bases. NaOH and KOH are example of strong bases. The bases which give little amount of hydroxyl ion on dissolving with water are weak base. for example Ca(OH)₂ and NH₄OH

Properties of bases

• Bases have generally bitter taste and are slippery on touch
• Solution of base turns red litmus to blue
• Strong bases like NaOH and KOH dissolve with oil, fat and grease
• Base react with acid to form salt and water
• Solution of base(alkali) react with carbon dioxide to form carbonate

2NaOH + CO₂ → Na₂CO₃ + H₂O

• Bases react with ammonium salts to form ammonia

NH₄Cl + NaOH → NH₃ + NaCl + H₂O

Uses of bases

• NaOH: making soap, paper production, purification of mineral oil
• KOH: making shampoo & saving cream
• Ca(OH)2: production of bleaching powder
• CaO: cement production, removing hardness of hard water
• Mg(OH)2: reducing acidity on stomach
• NH4OH: making chemical fertilizer, plastic production etc

Acid

Acid are the substances which give hydrogen(H⁺) ion on aqueous solution. Acids are found in nature in different forms. In most of sour fruits acids are found such as

• Citric acid in lemon and orange
• Tartaric acid in pomelo(भोगटे)
• Ascorbic acid in gooseberry(Vitamin C)
  
  
  

Similarly lactic acid in sour milk, fatty acid on fats, acetic acid in vinegar etc. In laboratory mostly hard acids are used both organic and inorganic. For example Nitric Acid(HNO₃), sulfuric acid(H₂SO₄), hydrochloric acid(HCl) etc.

HCl → H⁺ + Cl^-

H₂SO₄ → 2H⁺ + SO₄^2-

CH₃COOH → H⁺ + CH₃COO^-

Acids are classified with two ways

• On the basis of sources acids are classified as organic and inorganic. Acids found on plants and animal body are said to be organic(except HCl found on our stomach). Citric acid, ascorbic acid, tartaric acid acetic acid etc are organic acids. Similarly hydrochloric acid, nitric acid, sulfuric acid etc are inorganic acids.
• On the basis of ionization capacity acids are classified as strong and weak acid. Strong acids liberate more hydrogen ion in aqueous solution than weak acids. Tartaric acid, acetic acid, carbonic acid(H2CO3) etc are weak acid whereas HCL, H2SO4, HNO3 are strong acids.

Properties of acids

• Acids give H+ ion in aqueous solution
• Generally acids have sour taste.
• Acids burn skin
• Metals react with acid and hydrogen is displaced
• Acids reacts with carbonate and bicarbonates to form carbondioxide
• Acids react with bases to form salt and water

Uses of acids

• Sulfuric acid: in lead acid battery, in industries
• Hydrochloric acid: industrial use, to kill germs in our stomach
• Nitric acid: industrial use, metal etching
• Carbonic acid: making soda water
• Acetic acid: making pickles, chatpate(चटपटे)

Chemical Reaction

A chemical reaction is a process in which a chemical transformation takes place of one set of chemical

substances to another. This may combine two or more substances to single substance or vice versa. The substances before transformation are called reactants and substance formed after transformation are called products. There are four major types of chemical reactions as listed below

1. Combination reaction: In this reaction two or more substances combine to form a single substance. For example

2H₂ + O₂ → 2H₂O

2K + Cl₂ → 2KCl

N₂ + 3H₂ → 2NH₃

4Fe + 3O₂ → 2Fe₂O₃

2. Decomposition Reaction: In this reaction single substance breaks down to two or more substances. For example

CaCO₃ → CaO + CO₂

NH₄OH → NH₃ + H₂O

2KClO₃ → 2KCl + 3O₂

3. Displacement reaction: Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from its compound. Both metals and non-metals take part in displacement reactions. Foe examples

2K + 2HCl → 2KCl + H₂

Ca + H₂SO₄ → CaSO₄ + H₂

Zn + H₂SO₄ → ZnSO₄ + H₂

NaCl + AgNO₃ → NaNo₃ + AgCl

4. Acid-Base Reaction: The chemical reaction between acid and base is called acid-base reaction. In almost cases the products are salt and water.for examples

HCl + NaOH → NaCl + H₂O

HNO₃ + KOH → KNO₃ + H₂O

2HCl + CaO → CaCl₂ + H₂O

H₂SO₄ + FeO → FeSO₄ + H₂O

Factors affecting chemical reaction:

1. Temperature: Generally increase of temperature causes increase in rate of chemical reaction because increase of temperature causes increase in internal kinetic energy of reactants and collision process becomes faster.
2. Pressure: In general increase in pressure causes increase in rate of chemical reaction especially in case of gases.
3. Area of contact: Area of contact between reacting substances increases rate of chemical reaction.
4. Light: Some silver compounds react in presence of light. Photosynthesis takes place in presence of light.
5. Catalyst: The substance which increases the rate of reaction is called catalyst. In many reactions catalyst play key role. For example hydrogen peroxide decomposes by catalyst manganese dioxide.
6. Concentration of solution: Increase of concentration of reactant solution generally increases rate of chemical reaction.

Endothermic reaction: The chemical reaction which takes place by absorbing heat is called endothermic reaction. For example, production of Lime from limestone.

CaCO₃ → CaO + CO₂
Exothermic Reaction: The chemical reaction in which heat is released is called exothermic reaction. For example reaction of quick lime with water.

CaO + H₂O → Ca(OH)₂ + Heat

Reactivity of Elements

In every group of periodic table reactivity of elements either increases or decreases from top to bottom. In case of metal reactivity increases from top to bottom and that decreases in case of non metals. The reactivity of element depend upon two major factors

• The number of electrons in outermost orbit
• Radius of atom

Reactivity of metals: In general reactivity of metallic element increases from top to bottom in the group of periodic table. As we move from top to bottom radius of atom increases and hence probability of losing electron from outermost orbit also increases as the distance of free electron from nucleus become high and electrostatic force between nucleus and the free electron becomes weak.
Q. Why potassium is more reactive than sodium?
Ans: As potassium is larger than sodium, potassium's valence electron is at a greater distance from the attractive nucleus and is so removed more easily than sodium's valence electron. As it is removed more easily, it requires less energy, and can be said to be more reactive.
Reactivity of non-metals: In case of metal it is most reactive if it has valence electron 1 or valency 1 but in case of non metal most reactive one is that which has number valence electrons 7 and valency 1. Unlike in case of metal, reactivity of non metal in a group as we move from top to bottom. The cause same as explained above but opposite with radius of atom. As we move from top to bottom in a group atomic radius increases and capacity of pulling external electron dcreases.

Q. Why is fluorine more reactive than chlorine?
Ans: This is because the valence/bonding electrons are closer to the nucleus in Fluorine than they are Chlorine and others and thus more strongly attracted. Fluorine is most electronegative, thus it is most reactive.

Modern Periodic Table

Modern periodic table : Scientists kept on the research of finding the solution of the drawbacks found

on Mendeleev’s periodic table. In 1913 Henery Moseley found that the physical and chemical properties of elements are periodic function of their atomic number and not like as stated by Mendeleev.On the basis of this principle he published new periodic table which is known as Modern Periodic Table.
Modern periodic rule: the physical and chemical properties of elements are periodic function of their atomic numbers.
Features of modern periodic table:

• There are seven periods on modern periodic table and the feature is like below

 

Period	First	Second	Third	Fourth	Fifth	Sixth	seventh
No of elements	2	8	8	18	18	32	26
Feature of period	Very short	Short	Short	Long	Long	Very long	Incomplete long

 

•   There are 9 groups along with group VIII and group 0

• The lanthanide series includes elements 58 to 71, which fill their 4f sublevel progressively. The actinides are elements 89 to 103 and fill their 5f sublevel progressively. 
• The elements with valency 0 are placed on last group of periodic table(18), which are called elements of zero group
• 10 elements from group IIIB to group IIB are placed between reactive metals and non metals. They are called Transition Elements. 

Mendeleev's Periodic Table

Till now about 118 elements are found in nature. About 150 years ago new elements were found day to

day and their physical and chemical properties were different. To study their properties it was going to be nuisance task. So scientists started classifying them according to their physical and chemical properties. They formed a table by classification of elements which is known as periodic table.
Mendeleev’s periodic Table:  The first periodic table was published by Russian chemist  Dmitri Mendeleev in 1869. It was published under Mendeleev’s periodic law which states that “ The physical and chemical properties of elements are periodic function of their atomic weight”. Which explains that after certain number of elements, going on increase of atomic weight, similar element repeats(with similar properties). The elements on horizontal row were called period and elements on vertical column were called group.

Importance of Mendeleev’s periodic table:

• It was the first event to study elements by classification
• Space was provided to the elements which were not discovered
• It made easy to do correction of atomic weight of several elements like gold, platinum, uranium etc.

Drawbacks of Mendeleev’s periodic table:

• Hydrogen was placed in group I with alkali metal though it was a non metal.
• Highly reactive alkali metals like Lithium(Li), Sodium(Na) and potassium(K) were placed with less reactive metals like copper, silver and gold.
• Cobalt was placed before Nickel though atomic weight of  Ni was less than that of Co.

Ammonia II

 Chemical Properties of ammonia gas

1. When dissolved in water it forms an alkali ammonium hydroxide.

NH₃ + H₂O → NH₄OH

2. Ammonia reacts with acids to form salt.

2NH₃ + H₂SO₄ → (NH₄)₂SO₄

3. Aqueous solution of ammonia(Ammonium Hydroxide) reacts with acids to form salt and water

NH₄OH + HCl → NH₄Cl + H₂O

4. When ammonia reacts with hydrogen chloride, solid ammonium chloride is formed.

NH₃ + HCl → NH₄Cl

5. If ammonia is heated with carbon dioxide under pressure and temperature of 1500^oC, a chemical fertilizer urea is formed.

2NH₃ + CO₂ → NH₂CONH₂ + H₂O

6. If ammonia is reacted with oxygen, nitrogen gas is formed

4NH₃ + 3O₂ → 2N₂ + 6H₂O

Uses of ammonia gas:

1. Liquid ammonia is used as cooling agent in refrigerator
2. Ammonia is used to make blue prints of land maps
3. It is used in production of chemical fertilizers like urea, ammonium sulphate, ammonium phosphate etc
4. It is used in manufacturing of nitric acid
5. It is used in plastic production
6. It is used to make washing soda
7. It is used as cleansing agent to wash grease

8. It is used on manufacturing of ammonium chloride which is electrolyte of dry cell

Ammonia

 Ammonia has molecular weight of 17 amu. It is formed by the combination of nitrogen and hydrogen gases. For the first time ammonia was prepared by Lavoisier by heating the mixture of ammonium chloride and calcium hydroxide. Some soil bacteria create natural ammonia underground. Ammonia is also formed when protein rich materials decay in absence of oxygen. In the form of compounds it is found on ammonium chloride and ammonium sulphate.

Ammonia was first discovered by the ancient Egyptians, the Egyptians found this chemical compound by accident as it occurs naturally in cracks near volcanoes, and when it is warmed it decomposes into the pungent ammonia. This was then used in their religious rites. The worshippers of the Egyptian god Amun - known as the Ammonians named this chemical compound 'Ammonia'.

Laboratory Preparation of Ammonia gas: As shown in fig below, ammonia is prepared by heating ammonium chloride and calcium hydroxide in 2:1 ratio on hard glass test tube.

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

As shown in fig, when delivery tube is heated ammonia gas is formed and passes through delivery tube. To collect fully dry gas it is passed through calcium oxide tower. Via another delivery tube gas is collected on inverted gas jar as it is lighter than air.

Manufacturing of Ammonia gas: In large scale ammonia is obtained by reacting hydrogen and nitrogen in 1:3 ratio under the temperature of 500^oC, pressure of 200 to 300 atm on the presence of iron as catalyst and molybdenum as promoter. This process is also called Haber’s Process.

 N₂ + 3H₂ → 2NH₃

Physical Properties of Ammonia

1.  It is colorless gas with strong smell and tears on eye

2. It is lighter than air

3. It is highly soluble in water

4. It forms alkali when dissolved in water

5. It is neither combustible nor supports combustion

Read Chemical Properties and Uses of ammonia in next post.