Acids,Bases and Salts Important Notes

CBSE Class 10 ACIDS Bases and Salts Important Notes

Acids are chemical substances that release H+ ions in liquid solution in another words it dissociates on dissolving in water to produce hydrogen ions.Acids are sour in taste
Acids can be Classified on the basis of origin

1. Organic Acids:They are derived from plants and animals
2. Mineral Acids:They are derived from minerals

Organic Acids

1.An acid which is partially ionised in water and thus produces a small amount of

 hydrogen ions is called a weak acid.

 Examples of Organic Acids

a)Acetic Acid
b)Oxalic Acid
c)Malic Acid
d)Citric Acid
e)Tartaric Acid
f)Lactic Acid
g)Formic Acid

Mineral Acids

1.They are prepared from the minerals, these acids are highly corrosive as they 

competely release their H+ ions in water solution

 2.Mineral acids are highly corrosive and can cause severe burns

 3.Even dilute mineral acids are not safe to drink

 Examples of Mineral Acids
a)Hydrocholoric Acid
b)Sulphuric Acid
c)Nitric Acid
d)Carbonic Acid

Properties of Acids

• Acids have a sour taste
• Acids turn blue litmus paper to red
• Acid solution conduct electricity.They are electrolytes
• Acids react with metals to form hydrogen gas
• Acids react with metal carbonates to form carbon dioxide
• Acids react with base to form salt and water
• Acids are corrosive in nature

Storage of Acids
Since acids are highly corrosive they can not be stored in metals as they gradually corrode and eat up the metal container, therefore acids are generally stored in containers made of glass or ceramic as they are not attacked by acids

What is common in all acids
All acids have hydrogen in common.When acid is dissolved in water, it separates 

out as positively charged hydrogen ion.Hydrogen ions do not exist as H+ ions in 

solution, they attach themselves to the polar water molecule to form hydronium ions, H3O

It is the presence of hydrogen ions which gives an acid solution its acidic 

properties

All acids contain hydrogen but all hydrogen containing compounds are not acids

Hydrogen containing compounds such as glucose and alcohol do not behave as 

acids because they do not dissociate in water to produce hydrogen ions.

Dry HCl does not show acidic behaviour because it releases its H+ ions in water solutions

Uses of Mineral Acids
1.Sulphuric acid is used in the manufacture of fertilisers, paints dyes,

detergents,explosives.
2.Nitric Acid is used for making fertilizers, explosives(TNT),dyes and plastic

Bases They are bitter in taste and produce OH- ions in water solution.They are opposite of acids, they neutralize the effect of acids and vice versa All metal oxides and metal hydroxides and metal hydrocarbonates are considered basic in nature

Alkali: Those bases which are soluble in water are considered alkalis.some of the common alkalis are sodium hydroxide, potassium hydroxide,calcium hydroxide,ammonium hydroxide,magnesium hydroxide.
Strong Bases
A base which completely ionises in water and thus produces a large amount of hydroxide ions is called a strong base. Sodium hydroxide and potassium hydroxide are strong bases.
Weak Bases
A Base which is partially ionised in water and thus produces a small amount of hydroxide ions is called a weak base.Ammonium hydroxide, calcium hydroxide magnesium hydroxide are weak bases. Properties of Bases

1. Bases have bitter taste
2. Bases Feel soapy to touch
3. Bases turn red litmus paper to blue
4. Bases conduct electricity in a solution
5. Bases have bitter taste
6. Bases react with aluminium and zinc to form hydrogen gas
7. Bases react with acids to form salt and water

PH Scale In 1909 Sorenson devised a scale known as ph scale on which the strength of acid as well as basic solution could be represented by making use of the hydrogen ion concentration in them. The PH of solution is inversely proportional to the concentration of hydrogen ions in it.i.e a solution having higher concentration of hydrogen ions has low ph value and vice versa

The strength of an acid or base is measured on a scale of numbers called the 

pH scale.The pH scale has values from 0 to 14.

1.Neutral substances have a ph of exactly 7.Pure water is a neutral substance it

 is neither acidic nor basic.
2.Acids have a pH of less than 7., more acidic a solution is, the lower will be

 its pH.A solution of pH 1 is more acidic than solution with pH 5. 

The solutions having pH of 0,1,2, and 3 are usually considered strong acids,

 and pH of 4,5,6 are weak acids
3.Bases have a pH of more than 7.The higher the pH the stronger the base.

The solutions with ph 8,9, 10 are considered weak bases and solutions with

 ph 11,12,13,14 are strong bases

Universal Indicator
A common indicator like litmus paper can differentiate between acid or base but

 can not tell us how strong or weak an acid or base is.
Universal indicator is amixture of many different indicators which gives 

diferent colorus at different ph values of entire ph scale

Neutralisation reaction
When acid and base react they neutralise the effect of each other and 

form salt and water and energy is released inthe form of heat

Salt is a general name and it does not refer only to sodium chloride.

Salts are formed when acids react with baes.In a way we can say that a 

salt has two parents, an acid and a base, name of salt consists of two 

parts; the first part is derived from base and second part is derived from acid.

Just like acids and bases the solution of salts also conduct electricity

Salts are generaly neutral but some salts produce acidic or basic solution.

When strong acid reacts with strong base the salt produced is neutral in nature,

 but when strong acid reacts with weak base, the salt produced is acidic and vice versa

for e.g
Sodium chloride       neutral
Ammonium chloride     Acidic
Sodium carbonate      Basic
Sodium bicarbonate    Basic

Sodium Hydroxide
 It is commonly known as caustic soda.The chemical formula of sodium hydroxide is NaOH.  

Production of Sodium Hydroxide (Caustic Soda) The raw material for producing sodium hydroxide is common salt.Sodium hydroxide is produced by the electrolysis of concentrated aqueous solution of sodium chloride which is called brine When electricity is passed through a concentrated solution of Sodium Chloride, it decomposes to form sodium hydroxide,chlorine and hydrogen During electrolysis, chlorine gas is produced at anode and hydrogen is produced at cathode.Sodium chloride solution is formed near the cathode. This process is also reffered to as chloralkali process because of the products formed: chlor for chlorine and alkali for sodium hydroxide

2Nacl + 2H₂O------------------> 2NaOH + Cl₂ +H₂  


Uses of 

Sodium Hydroxide 1.Used in making soaps and detergents 2.Used for making artificial textile fibres 3.It is used in manufacturing of paper 4.It is used in purifying bauxite ore from which aluminum is extracted  

Uses of Chlorine gas 1.It is used to sterilise drinking water supply 2.It is used in production of bleaching powder 3.It is used in production of hydrochloric acid 4.It is used to make plastics such as pvc  

Uses of hydrogen 1.It is used in hydrogenation of oils 2.It is used in production of hydrochloric acid 3.used to make ammonia for fertilisers 4.used to make methanol

Baking Soda The chemical name of baking soda is sodium hydrogencarbonate.The formula of baking soda is NaHCO₃

  Production of Sodium Hydrogencarbonate Sodium hydrogencarbonate is produced on a large scale by reacting cold and concentrated solution of sodium chloride with ammonia and carbon dioxide.

NaCL + NH₃ +H₂O + CO₂-------------------------------> NaHCO₃ + NH₄Cl  

Properties of Sodium hydrogencarbonate
1.Sodium hydrogencarbonate consists of white crystals which are sparingly soluble in water
2.Sodium hydrogencarbonate is mild and non corrosive base.
 3.When sodium hydrogencarbonate is heated Carbon dioxide gas is released  

Uses of Sodium Hydrogen carbonate 1,It is used in making antacid tablets to get relief from acidity 2.It is used in making baking powder.Baking powder is the mixture of baking soda and tartaric acid. 3.It is used in fire extinguishers


 Washing Soda Washing soda is sodium carbonate containing 10 molecules of water of crystallisation.Washing soda is sodium carbonate decahydrate.The formula for washing soda is Na₂CO₃  

Production of WAshing soda
On heating, Sdoium hydrogencarbonate decomposes to form sodium carbonate. 2NahCO₃-----------------------------> Na₂CO₃ + H₂O

Anhydrous Sodium carbonate obtained here is called soda ash Anhydrous Sodium carbonate is dissolved in water and recrystallised to gt washing soda crystals containing 10 molecules of water of crystallisation

Na₂CO₃ + 10H₂O + CO₂ + H₂O  

Properties of Washing soda
 1.Washing soda is transparent crystalline solid
2.Washing soda is one of the few metal carbonates which are soluble in water
3.The solution of washing soda in water is alkaline which turns red litmus to blue.  

Uses of Sodium carbonate
1/It is used as cleansing agent
 2.It is used for removing permanent hardness of water
 3.It is used in manufacturing of glass soap and paper
 4/It is used in making borax

Bleaching powder is calcium oxychloride.
The chemical formula of bleaching powder is CaOCl₂

Prepration of Bleaching powder It is prepared by passing chlorine gas over dry slaked lime
Ca(OH)₂ + Cl₂ ------------------------> CaOCl₂ + H₂O

 Properties of Bleaching powder 1.It is a white powder which gives a strong smell of chlorine 2.It is soluble in cold water 3.It reacts with dilute acids to produce chlorine.

  Uses of Bleaching Powder 1/It is used for bleaching cotton and linen in textile industry and for bleaching wood pulp in paper industry 2.It is used for disinfecting drinking water supply. 3.It is used for the manufacture of chloroform 4.It is used for making wool unshrinkable Plaster of Paris Plaster of Pris is calcium sulphate hemihydrate.The formula of plaster of paris is CaSO₄.1/2H₂O.The name plaster of paris came from the fact that it was first of all made by heating gypsum which was mainly found in paris.

  Preprataion of Plaster of Paris Plaster of paris is prepared from gypsum.Gypsum is calcium sulphate dihydrate.that is calcium sulphate containing two molecules of water of crystallization. It is prepared by heating gypsum to a temperature of 100 celcius in a kiln.When gypsum is heated to that temperature it loses three-fourths of its water of crystallisation and forms plaster of paris.
 CaSO₄----------------------> CaSO₄.1/2H₂O + 1 1/2H₂O

Properties of plaster of paris 
1.Plaster of Paris is a white powder 2.Plaster of paris sets into hard mass on wetting with water.The setting of plaster of paris is due to its hydration to form crystals fo gypsum which set to form hard,  

Water of Crystallisation The water molecules which form part of structure of crystal are called water of crystallisation.The salts which contain water of crystallisation are called hydrated salts.Every hydrated salt has a fixed number of molecules of water of crystallisation in its one formula unit.

 1.Copper sulphate crystals contain 5 molecules of water of crystallisation in one formula unit and hence written as CuSO₄.5H₂O
 2.Sodium carbonate crystals contain 10 molecules of water of crystallisation. Na₂CO₃.10H₂O
3.Calcium sulphate crystals contain 2 molecules of water of crystallisation CuSO₄.2H₂O
 4.Iron Sulpahte crystals contain 7 molecules of water of crystallisation. FeSO₄.7H₂O

Water of crystallisation is part of crystal structure of a salt.Since water of crystallisation is not free water, it does not wet the salt The water of crystallisation gives the crystals of the salts their shape and in some cases imparts them colour.