Acids Bases and Salts for class 10 notes

Class x acid base and salt Notes

Classification of substances into acids, bases and salts

The two main sources of most of the chemical substances are:

(1) Animals and plants

(2) Minerals and rocks

The chemical substance obtained from animals and plants (living organisms) are called organic compounds whereas those obtained from minerals and rocks are called inorganic compounds.

On this basis, the compounds were classified into the following three categories:

(i) Acids

(ii) Bases and 

(iii) Salts

Acids are the substances which have sour taste.

Bases are the substances which have bitter taste.

Salts are the compounds formed from acids and bases.

Tests to distinguish between acids and bases:

There are many substances which show one colour (or odour) in the acidic medium and a different colour (or odour) in the basic medium. Such substances are called as acid-base indicators.

The colours of some natural indicators are summed up in the table below:

IndicatorColour in the neutral solutionColour in the acidic solutionColour in the basic solution
1. Litmus PurpleRedBlue
2. Red cabbage leave extractRed RedGreen
3. Flowers of hydrangea plantBlueBluePink

General characteristic properties of Acids

1. Sour taste.

2. Action on litmus paper.

3. Action on methyl orange

4. Corrosive nature.

5. Reaction with metals.

Metal + Acid → Metal salt + Hydrogen gas

Some naturally occurring sources of acidsand the acids present

S. No.Natural SourceAcid Present
1.Oranges, lemonsCitric acid
2.ApplesMalic acid
3.TomatoesOxalic acid
4.Tamarind (Imli)Tartaric acid
5.Sour milk or curdLactic acid
6.VinegarAcetic acid
7.ProteinsAmino acids

Some common acids and their chemical formulas

S. No.Name of the AcidChemical Formula
1.Hydrochloric acidHCl
2.Sulphuric acidH2SO4
3.Nitric acidHNO3
4.Acetic acidCh3COOH
5.Formic acidHCOOH
6.Carbonic acidH2CO3
7.Phosphoric acidH3PO4

Acids are the substances which contain hydrogen and which when dissolved in water give hydrogen ions (H+) in the solution.

General characteristic properties of bases

1. Bitter taste.

2. Slippery or soapy touch.

3. Action on litmus paper.

4. Action on phenolphthalein.

5. Corrosive nature.

6. Conduction of electricity.

A base is a substance which when dissolved in water gives hydroxide (OH) ions in the solution.

The bases which are soluble in water and give hydroxide ions in the aqueous solution are called alkalies.

Neutralization is defined as a process in which an acid reacts with a base to form salt and water, i.e.,

Acid + Base → Salt + Water 

The number of hydroxide (OH) ions produced on dissociation of one molecule of the base is called its acidity.

Expressing acidity or alkalinity of a solution in terms of pH

Concentration of H+ions = Concentration of OHIONS = 10-7mole per litre

pH of a solution is the magnitude of the negative power to which 10 must be raised to express the hydrogen ion concentration of the solution in moles per litre.

(i) For neutral solution, pH=7

(ii) For acidic solutions, pH < 7 and greater the H+ion concentration than 10-7M, less is the pH value and more acidic is the solution.

Thus, acidic character of solutions of different pH will be in the order:

pH = 0 > pH = 1 > pH = 2 > pH = 3 > pH = 4 > pH = 5 > pH = 6

(iii) For basic solutions, pH > 7 and greater the OHion concentration than 10-7M, less is the H+ion concentration and hence greater is the pH value and more basic is the solution.

Preparation of Plastic of Paris

It is prepared from gypsum which is calcium sulphate dehydrate (CaSO­4.2H2O). Gypsum is heated in a kiln to a temperature of 100oC (373K). At this temperature, it loses three-fourth of its water of crystallization forming plaster of Paris.

 100oC (373K)

CaSo4.2 H2O    −−−−−→            CaSO4. H2O + 1 H2O

Gypsum                                                        Plaster of Paris

The temperature not allowed to rise beyond 100oC as otherwise whole of water of crystallization is lost producing anhydrous calcium sulphate which is called dead burnt plaster.

Answer These Questions

Q1The three Categories of Compounds are?

Q2. Difference between P.O.P. and Gypsum?

Q3. What is pH?

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