Class 10 Science Chapter 2 Acids, Bases and Salts Notes PDF in English free
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Class 10 Science Notes : Chapter 2 Acids, Bases and Salts
|Chapter Name||Acids, Bases and Salts|
|Category||Class 10 Science Notes|
Introduction Acid and Base
Acid, Base and Salt
♦ General Introduction
• The word acid is derived from the Latin word “acids” meaning sour to taste.
• Acids are highly inflammable.
• Acids can change colour of litmus from blue to red.
• Bases are those substance which is bitter in taste and soft like soap.
• Bases change colour of litmus of litmus from red to blue.
• When acid and base react with each other then it form salt.
• Indicator is a compound which is used to detect the acidic or basic nature of given solution.
• Indicators are of two types
• Natural indicators
• Synthetic indicators
– Those indicators which are obtained from nature are called natural indicators.
A. Litmus- It is a mixture of water soluble dyes extracted from Lichens.
It is a purple coloured dye.
Acid base indicators- It is that substance which posses one colour in acidic medium and a different colour in alkaline medium.
Example-: Red cabbage juice and Turmeric juice.
Those indicators which are prepared in laboratories are called artificial indicators.
Example -: Methyl orange and phenolphthalein.
♦ Olfactory Indicators- Indicators giving different odours in acidic and basic medium are called olfactory indicators.
Example –: Onion, Vanilla etc.
Chemical properties of Acid and Base
♦ Chemical properties of Acid and Base
(i) Reaction with Metal :- Reactive metal displaces hydrogen from acid in the form of H2
and forms metal salt.
Metal + Dilute acid → Metal salt + hydrogen
For Ex. Zn(s) + H2SO4 (aq.) → ZnSO4(aq.) + H2(g)
1. H2SO4 is added to a test tube and a few pieces of Zinc granules to it.
2. A gas is evolved in test tube and it is passed into soap solution through a delivery tube.
3. As the gas reacted to soap solution, bubbles are formed in the solution.
4. When a lighted candle is brought near to gas filled bubble pop sound is produced there which proves that evolved gas is H2.
♦ Reaction of Acid with metal carbonates
Acid reacts with metal carbonates produces metal Salt, Water and CO2 etc.
Ex. CaCO3(s) + 2HCl(dil.) → CaCl2(aq.) + H2O(l) + CO2(g)
Metal + Acid → Salt + H2O + CO2
• First of all we will take two test tube and name it A and B.
• In test tube A we take some amount of sodium carbonate and in test tube we take Ca(OH)2 solution.
• When dil. HCl is added to test tube A and a gas is evolved which is passed through a tube to test tube B.
• When gas is passed to test tube B the colour of solution turned to white due to formation of a white precipitate called CaCO3. (Calcium Carbonate)
It proves that gas evolved gas CO2.
Na2CO3 + 2HCl → 2NaCl + H2O + CO2
2Ca(OH)2 + 2CO2 → 2CaCO3 + 2H2O
Note that :- If excess of CO2 is passed in above solution ppt. get dissolve and solution
CaCO3 + H2O + CO2 → Ca(HCO3)2
♦ Reaction with Metal hydrogen carbonate
• Acid reacts with metal hydrogen carbonate produces Salt, Water and CO2 gas.
Acid + Metal hydrogen carbonate → Salt + H2O + CO2
H2SO4 + 2NaHCO3 → Na2SO4 + 2H2O + 2CO2
♦ Reaction with Metal Oxide
• Acid react with metal oxides to form Salt and Water.
• As Metal oxide react with acids to produce neutral salts they are called basic oxides.
Metal Oxide + Acid → Salt + Water
Ex. CaO + 2HCl → CaCl2 + H2O
Note that :- Some metal oxides show acidic as well as basic properties hence are called amphoteric oxides.
Ex. ZnO, BeO, Al2O3.
♦ Reaction of base with non metallic oxide
• When base react with non metallic oxide it forms Salt and Water.
Ca(OH)2 + CO2 → CaCO3 + H2O
♦ Similarity between Acid and Base
• There are some similarities between acid and Base. That all acids and Bases are conductor of electricity.
(i) First of all we will take solutions of NaOH (sodium hydroxide), HCl (hydrochloric acid), glucose and alcohol etc. in separate beakers.
(ii) Now, fix two nails on a cork and place the cork in a each beaker.
(iii) Now we will connect nails to the two terminals of a 6 volt battery through a bulb and switch.
(iv) Now we will switch on key in each beaker.
As the current passes through solutions bulbs of beaker containing HCl, NaOH will glow but bulbs of beaker containing glucose and alcohol do not glow. It shows that glucose and alcohol do not conduct electricity.
Both aqueous solution of acid and base contain ions. which helps in conduction of electricity.
Definition of acid and base
♦ Acid: Acids are those substances which dissociate in aqueous solution to give H+ ions. (hydronium ions)
Example : HCl, HNO3, CH3COOH etc.
Acids are classified into two categories :
(A) Strong acid (B) Weak acid
(A) Strong acid : Those acids which completely dissociate in aqueous solution and gives large amount of H+ ions are called strong acid.
Example : HCl, HNO3 and H2SO4.
(B) Weak acid : Those acids which do not dissociate completely in aqueous solution and produce small amount of H+ ions are called weak acid.
Example : CH3COOH, H2CO3 etc.
♦ Base : Bases are those substance which dissociate in aqueous solution to give Oh– ions.
Example : NaOH, KOH, Ca(OH)2 etc.
Bases are classified into two categories :
(A) Strong base (B) Weak base
(A) Strong base : The base which completely dissociate in aqueous solution and gives a large amount of OH– hydroxide ions is called strong base.
Example : NaOH, KOH etc.
(B) Weak base : The base which does not dissociate completely in aqueous solution and gives a small amount of OH– ions is called weak base.
Example : Ca(OH)2, Mg(OH)2 etc.
Note : All acids and based give their respective ions when they are present in aqueous solution. As dry HCl gas does not change the colour of litmus paper.
♦ Water with Acid
• The process of dissolving an acid or a base in water is highly exothermic process.
• Acid must always be added slowly to water with constant stirring. Because if water is added to a concentrated acid, the heat generated may cause the mixture to splash out and cause burns.
♦ Concentrated Acid : Pure form of acid is called concentrated acid.
♦ Dilute Acid : When water mixed with acid then such acid is called dilute acid.
• Mixing of acid or base with water results in decrease in concentration of ions (H3O+ /
OH–) per unit volume. Such a process is called dilution.
• It is a scale to measure the strength of Arrhenius acids and bases.
• In PH ‘P’ stands for ‘Potenz’ (meaning power) and ‘H’ stands for hydrogen ions.
• PH scale measures hydrogen ion concentration in given solution.
♦ Standard definition : PH can be defined as logarithm of reciprocal of H3O+ ions in
PH = -log [H+] or [H+] = 10–PH
• In PH scale values are there from 0 to 14.
• All substance having PH value between 0 and 7 are called acids.
• All substance having PH value between 0 and 7 are neutral.
• All substance having PH value between 7 and 14 are called bases.
• Stronger the acid; lesser the PH.
• Stronger the base ; higher the PH.
Lemons -: PH range (2.2 – 2.4) (Acids)
Tears -: PH range (7.4) (Basic)
H2O -: PH range (7.0) (Acids)
♦ Importance of PH in daily life
1. PH of our digestive system
• Our stomach produces hydrochloric acid. (HCl)
• It helps in digestion of our food by converting it into simple particles.
• The PH range of HCl is about (1.3 – 1.8).
• When excess amount of HCl is produced in stomach, the PH get lower down as a result of it pain, irritation and feeling of burning occur. Such condition is called acidity.
• To get relief from this pain; antacids tablets are given.
• Sometime mild bases are also used to get relief from this pain.
2. pH in Rain
Living organisms can survive only in narrow range of pH change. Due to
environmental pollution harmful gases like SO2 and NO2 are released in environment and when these gases are combined with H2O it forms H2SO4 and HNO3 respectively which results in decrease of pH of rain. As the pH get below than 5.6 then such rain is called acid rain.
3. pH change leads to tooth decay
The outer white covering of teeth is made up of enamel. Enamel is the hardest substance chemically made up of calcium phosphate. But aa bacteria increase in mouth it breakdown sugar to lactic acid. As a result of it these acids cause decrease in pH. And as the pH of mouth falls down below than 5.5, the enamel get damaged. Hence it is advised to keep mouth clean.
4. pH Of Soil
Growth of plants in soil is related to its pH.
Different kind of particle have different pH.
Preferred pH Range
♦ pH in self defence by Plants and Animals
• Stings of bees and ants contain methanoic acid (formic acid). When stung, they cause lot of pain and irritation because as acid is highly inflammable and skin is sensitive to acids.
• These effects can be neutralised by applying base on that site.
• There are some herbaceous plants called nettle plants which contain sharp hairs which contain methanoic acid. If due to any reason these stings get in contact with our body then these stings are quite painful as methanoic acid get injected into our body. Hence they are called stinging nettles.
• Those areas are rubbed by the leaves of ‘dock plants’.
• Dock plants grow besides nettle plants.
• Leaves of dock plants contain chemicals which neutralises acidic effect.
Some Natural Occuring Acids
Some General Salts
♦ Salt : When acid react with base salts are formed.
♦ Family of Salts :
• The salts of ‘hydrochloric acid’ are called ‘Chlorides’.
• The salts of ‘Sulphuric acid’ are called ‘Sulphates’.
• The salts of ‘Nitric acid’ are called ‘Nitrates’.
♦ pH of Salts
Strong acid + Strong base = Neutral Salt
(pH = 7)
Strong acid + Weak base = Acidic Salt
(pH less than 7)
Weak acid + Strong base = Basic Salt
(More than 7)
Weak acid + Weak base = Neutral Salt
(Nearly equal to 7)
♦ Some Common Salts
1. Sodium Chloride (NaCl) -:
• Chemical formula -: NaCl
• Common Name -: Rock Salt
• Method of preparation -:
Salty water is subjected to evaporation in open air in fields which leaves behind residue of impure NaCl. Then this impure NaCl is purified.
• Specific property -:
Common Salt is the starting material for the preparation of all other sodium compounds.
E.g. Na2CO3, NaOH etc.
• Uses -: (i) For making sodium compounds.
(ii) An essential constituent of food.
2. Sodium hydroxide (NaOH) -:
• Chemical formula -: NaOH
• Common Name -: Caustic Soda
• Method of preparation -:
The process of preparation of NaOH is called chlor-alkali process.
In this chlor-alkali process; electrolysis of an aqueous solution of sodium chloride (brine) take place as a result of it NaOH, Cl2 and H2 get formed.
2NaCl(aq) + 2H2O(l) 2NaOH + Cl2 + H2
In this reaction Cl2 gas is formed at anode and H2 is formed at cathode.
♦ Specific property
It is a crystalline solid and highly soluble in water.
♦ Uses (NaOH uses)
(i) Soap manufacture
(ii) Ragent in laboratory
♦ Uses of Cl2
• In PVC
• In disinfectant
♦ Uses of H2
• In fuels
• In ammonia for fertilizers
Common Salts (part-II)
♦ Sodium carbonate (Na2CO3)
Chemical formula : Na2CO3.10H2O
Common name : Washing Soda
♦ Method of preparation :- The important method for the preparation of sodium carbonate is called solvay process.
In Solvay process brine solution is treated with NH3 and CO2 as a result of it NH4Cl and insoluble substance NaHCO3 is formed.
When NaHCO3 is heated it get decomposed into Na2CO3.
NaCl + H2O + CO2 + NH3 → NaHCO3 ↓ + NH4Cl
2NaHCO3 ⟶Δ Na2CO3 + H2O + CO2
♦ Special properties
It is soluble in water with the evolution of considerable amount of heat and show alkaline nature due to hydrolysis.
Na2CO3 + 2H2O → 2NaOH + H2CO3
i. In laundry and in softening of water.
ii. In textile and manufacture of glass.
♦ Sodium hydrogen carbonate :- (NaHCO3)
Chemical formula :- NaHCO3
Common name :- Baking Soda
♦ Method of preparation :-
It is obtained as intermediate product in the Solvay process.
Na2CO3 + H2O + CO2 → 2NaHCO3
♦ Special property :-
Baking Soda converts into washing soda and release CO2 which makes food soft.
2NaHCO3 → Na2CO3 + H2O + CO2
♦ Uses :-
i. In fire extinguishers
ii. For the production of CO2.
♦ Calcium Sulphur hemihydrates :- (CaSO4. 12H2O)
Chemical formula :- CaSO4. 12H2O
Common name :- Plaster of Paris
♦ Method of preparation :-
• When gypsum is heated at 100. C, 112H2O get evaporated and plaster of Paris is obtained.
CaSO4 . 2H2O →100∘� CaSO4 . 12H2O + 12H2O
♦ Specific property :- Plaster of Paris is kept in dry bottle as it can absorb water from surroundings and get converted into gypsum.
♦ Uses :-
(i) As a fire proofing material.
(ii) In making ornamental casts and idols.
♦ Bleaching Powder :- (CaOCl2) (Calcium oxy chloride)
Chemical formula :- CaOCl2
Common name :- Bleaching Powder
♦ Method of preparation :-
It is prepared by action of Cl2 on dry slaked lime.
Ca(OH)2 + Cl2 → CaOCl2 + H2O
♦ Specific property :-
• It is pale yellow powder.
♦ Uses :-
(i) As bleaching agent in textile, paper industry.
(ii) As disinfectant.
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