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:
(ii) Bases and
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:
|Indicator||Colour in the neutral solution||Colour in the acidic solution||Colour in the basic solution|
|2. Red cabbage leave extract||Red||Red||Green|
|3. Flowers of hydrangea plant||Blue||Blue||Pink|
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 Source||Acid Present|
|1.||Oranges, lemons||Citric acid|
|4.||Tamarind (Imli)||Tartaric acid|
|5.||Sour milk or curd||Lactic acid|
Some common acids and their chemical formulas
|S. No.||Name of the Acid||Chemical Formula|
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 OH–IONS = 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 OH–ion 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.
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
Q1. The three Categories of Compounds are?
Q2. Difference between P.O.P. and Gypsum?
Q3. What is pH?