Header Ads

Acids, Bases and Salts

" Acids, Bases and Salts"




ACIDS:

These are sour in taste, turn blue litmus red and release H+ ions.
According to “Arrhenius”, acids are the substance that give hydrogen ion(H+) in water. e.g HCl, HNO3 etc.
According to “Lewis”, acids have a tendency to accept an electron pair . e.g electron deficient species like BF3, AlCl3, transition metals etc.

CLASSIFICATION OF ACIDS:

1) On the basis of its origin:

(a) Organic acid:

•These acids are found from living- things.
•These are mild and weak acids.
•For example: oxalic acid( found in spinach, tomato)
•Formic acid ( found in ant sting) etc.

(b) Mineral acid:

•These acids are found from minerals.
•These are corrosive and strong acids.
•For example: nitric acid(HNO3),Sulphuric acid (H2SO4) etc.

2) On the basis of its composition:

(a) Strong acid: It produces large number of H+ ions and easily/completely ionized.
e.g HCl→ H+  + Cl-

(b) Weak acid: It produces less number of H+ ions and partially ionized.
e.g CH3COOH→ CH3COO- + H+

3) On the basis of its concentration:

(a) Concentrated acid: It contains approx. 90% acid and 10% water.
e.g mineral acids.

(b) Dilute acid: It contains approx. 10% acid and 90% water.
 e.g dilute HCl.

Physical Properties of Acids:
                       
1.They have a bitter taste.
2.They have slippery touch.
3.They conduct electrically.
4.It turns red litmus to blue.
5.It turns colorless phenolphthalein to pink
6.They are corrosive in nature.
7.They evolve hydrogen with active metals.
8.They react with base to give salts and water. This reaction is called neutralization reaction.

Chemical Properties of Acids:

BASE + ACID =SALT + WATER
KOH + HCl = KCl + H2O

Reactions with Salts
FeCl3 + 3NaOH = Fe(OH)3 + 3NaCl

Reaction with Metals
2Al + 2NaOH + 2H2O =2NaAlO2 + 3H2

Uses of Acids:




1.Vinegar, used in the kitchen, is a liquid containing 3-6% acetic acid. It is used in pickles and in many food preparations.
2.Lemon and orange juice contains citric acid. Citric acid is used in the preparation of effervescent salts and as a food preservative.
3.Acids have been put to many uses in industry. Nitric acid and sulphuric acid are used in the manufacture of fertilizers, dyes, paints, drugs and explosives.
4.Sulphuric acid is used in batteries, which are used in cars, etc. 
5.Hydrochloric acid is used to make aqua regia, which is used to dissolve noble metals such as gold and platinum.
6.Sulphuric acid is used in manufacturing fertilizers such as super phosphate, ammonium sulphate etc.

BASES:

Bases have bitter taste, turns red litmus blue and release OH- ions. 

According to "Arrhenius", bases are the substance that gives hydroxyl ion (OH-) in water. 
e.g Ca(OH)2, NaOH, NH4OH etc.

According to "Lewis" , bases have a tendency of donating an electron pair.
e.g NH3, H2O etc.  

NOTE: Water soluble bases are called alkalis. Thus, all alkalis are bases but all bases are not alkali. This is because all bases are not water soluble. 

Physical Properties of Bases:

1.They have a bitter taste.
2.They have slippery touch.
3.They conduct electrically.
4.It turns red litmus to blue.
5.It turns colorless phenolphthalein to pink
6.They evolve hydrogen only with certain metals.
7.They form salt and water when react with acids.

Chemical Properties of Bases:

BASE + ACID =SALT + WATER
(NaOH + HCl = NaCl + H2O)

Reaction with salts

FeCl3 + 3NaOH = Fe(OH)3 + 3NaCl
2CrCl3 + 6NaOH = 2Cr(OH)3 + 6NaCl

Reaction with metals

2Al + 2NaOH + 2H2O = 2NaAlO2 + 3H2
Zn + NaOH + H2O = Na2ZnO2 + 2H2

Uses of Bases in Daily Life:




1)Ammonia: Production of fertilizers (ammonium and nitrate salts), used in the manufacture of nitric acid, neutralize the acid (in the petroleum industry) and prevent premature coagulation in natural / synthetic latex.
2)Aluminium hydroxide: Manufacture other aluminium compound and to make gastric medicine (antacid).
3)Calcium hydroxide: To make cement, lime water, neutralize the acidity of soil and application of sewage treatment.
4)Sodium hydroxide: Used in the manufacturing of soaps, detergents, and cleaners.
5)Magnesium hydroxide: Suspension of magnesium hydroxide in water are used as an antacid, used as an antiperspirant armpit deodorant and as a non-hazardous alkali to neutralize acidic wastewater.

INDICATORS:


Substances having different colors in acids and bases are called indicators. Indicators may be a natural substance like litmus, turmeric, China rose etc. or a synthetic substance like phenolphthalein, methyl orange etc. 

Some important indicators and their color in acid and base solutions:


"Indicators remain unaffected by neutral substances"

Some important chemicals with their chemical formulas:

1. Caustic Soda – NaOH (It is used in Paper industry, soap industry, for degreasing metal etc.)
2. Baking Soda – NaHCO3 (It is an antibacterial, antifungal, antiseptic and anti-inflammatory properties. It is also a powerful medical tool effective at combating everything from colds to oral problems to skin issues.
3. Washing Soda – Na2CO3.10H2O (It is used for removing permanent hardness of water and also used as fire extinguisher).
4. Plaster of Paris- CaSO4.1/2H2O (It is used for making sculptures and casts, as an additive for lime plasters, and for making casts for setting broken limbs).
5. Bleaching Powder- CaOCl2 (It is used as disinfectant i.e purification of water, to decolourize i.e bleaching agent Cl2).

pH Scale:



To measure the acidity/basicity of dilute solutions, Sorenson developed a scale on which number from 1 to 14 are marked. It should be thought of simply as a number that indicates the acidic or basic nature of solution.
The pH of a solution is defined as the –ve logarithm of the concentration (in mole/L) of hydrogen ions which are present in the solution. 
The pH of a neutral solution is 7. Values less than 7 on the pH scale indicate an acidic solution and more than 7, basic medium.

NEUTRALIZATION:


 The acid-base reactions, in which both acids and bases lose their character, i.e their acidity or basicity is destroyed, such reaction is called as neutralization reaction.

ACID + BASE = SALT + WATER
(HCl + NaOH = NaCl + H2O)

SALTS:

When a metal displaces H+ ion of an acid, then salt is formed. 
                                       Or
Salts are the product of neutralization reaction of acid and base. e.g NaCl, K2SO4 etc. 

CLASSIFICATION OF SALTS:


1. Simple Salts: These are obtained by complete neutralization of acid and base. 
       (HCl + Na = NaCl + H2 )
2. Acidic Salts: These are obtained by incomplete neutralization of a poly basic acid. Such salts still contain one or more replaceable hydrogen atoms.
      (Strong acid + Weak base = Acidic salt)
       ( HCl + NH4OH = NH4Cl + H2O )
3. Basic Salts: Alkali salts or basic salts are salts that are the product of the neutralization of a strong base and a weak acid. 
        ( CH3COOH + NaOH = CH3COONa + H2O )
4. Double Salts: The addition compounds formed by the combination of two simple salts are termed as double salts. These salts are stable in solid state only.
e.g potash alum , ferrous ammonium salt etc
5. Complex Salts: These are obtained by the reaction of two compounds and have properties quite different from the compound used. They are stable in solid as well as in aqueous solutions.
e.g potassium Ferro cyanide etc.