The Acid Base Chemistry – Maharashtra Board Class 10 Solutions for Science and Technology (English Medium)
- Most of the acidic substances are sour in taste.
- Phenolphthalein is synthetic type of indicator.
- The strength of basic substance is represented by pOH.
- pH scale ranges from 0 to14.
- Acids and bases neutralize each other to form salt and water.
- Sodium or potassium salts of higher fatty acids are termed as soap.
- In FeSO4.7H2O; H2O represents water of crystallisation.
- 10% NaCl is known as brine.
The acidic or basic nature of the compound can be indicated by some natural or synthetic substances. These substances are known as indicators.
Indicators are of four types:
Natural indicators: Some natural substances can be used as indicators. They are called natural indicators.
Examples: Rose petals, turmeric, beetroot
Synthetic indicators: Some chemical substances can be used as indicators. They are called synthetic indicators. Examples: Phenolphthalein, methyl orange, eosin
Universal indicators: A mixture of several indicators is known as a universal indicator.
Olfactory indicators: Substances whose odour changes in acidic or basic medium are called olfactory indicators. Examples: Eucalyptus oil, clove extract
pH is a number which indicates the strength of the acidic or basic nature of a solution. The p in pH stands for ‘potenz’ and means strength in German. On the pH scale, we can measure the pH from 0 (most acidic) to 14 (most basic) The pH scale is used for measuring hydrogen ion concentration in a solution. When the pH value is in between 0 to 7, the solution is acidic, and when it is at 7, the solution is neutral. When pH is between 7 and 14, the solution is basic.
The normal pH scale ranges from 0 to 14 as given below:
Water of crystallisation is a fixed number of water molecules present in the crystal structure. On heating or on exposure to air, salts lose water of crystallisation and form anhydrous substances.
Copper sulphate (CuSO4.5H2O) has 5 molecules of water of crystallisation.
Sodium carbonate (Na2CO3.10H2O) has 10 molecules of water of crystallisation.
When a metal carbonate reacts with an acid, it forms a corresponding salt and carbon dioxide gas is evolved.
Na2CO3(s) +2HCl(aq) → 2NaCl(aq) + H2O(l) + CO2(g)
Al2(CO3)3 + 6HCl → 2AlCl3 + 3H2O + 3CO2(g)
The strength of an acid is measured in terms of number of hydrogen ions in an aqueous solution of that acid. Higher the H+ ion concentration, stronger is the acid. Hydrogen ion (H+) does not exist alone. H+ ion combines with water to form hydronium ion (H3O+).
HCl (aq)→ H++ Cl–
H2O + H+ → H3O+
A universal indicator is a mixture of several indicators. It gives different colours to solutions for different pH values of the pH scale. Mg(OH)2 does not react with sodium hydroxide because both are bases.
- Baking soda (NaHCO3) is used in bakery products such as bread and cake. It is also used in making dhoklas and pakoras.
- It is used in antacid. Being alkaline, it helps to reduce acidity in the stomach.
- It is useful in preparing CO2 and is a fire extinguisher compound.
An acid generates H+ ions and a base generates OH– ions in aqueous medium. The H+ ions of acid and the OH– ions of base react with each other to form unionised water. The process is called neutralisation. The products of this reaction are the corresponding salt and water.