CHAPTER 2
                  ACIDS,BASES AND SALTS
                                                               CLASS 10
  Acids: Substance which are turn blue litmus solution red are called acids. Acids are sour in taste.

Bases: Substances which change red litmus solution blue are called bases. They are bitter in taste.

Mineral Acids: Acids which are obtained from minerals like sulphates, nitrates, chloride etc. are called mineral acids. example: H2SO4 ,HNO3, and HCL.

Organic Acids: Acids which are obtained from plants and animals are called organic acids. Example: citric acid, ascorbic acid, tartaric acids, acetic acids.

Universal indicators: A universal indicators is a mixture of indicators which shows a gradual but well-marked series of colour changes over a very wide range of change in concentration of H+ ions.

Strong Acids: Acids which dissociate into ions completely are called strong acids.
Weak Acids: Acids which do not dissociate into completely are called weal acids. Example: citric acids, acetic acids.

Chemical properties of acids:

1. acids react with active metals to give salt and hydrogen gas.
2. Acids react with metal carbonates and metal hydrogen carbonate to give salt, water and carbon dioxide.
3. Acids react with base to give salt and water. This reaction is called neutralization reaction.
4. Acids react with metal oxides to give salt and water.

Chemical properties of bases:

1. Reaction with Metals: certain metals such as zinc ,aluminium ans tin react with alkali solutions on heating and hydrogen gas is evolved.
2. Reaction With acids: Bases react with acids to form salt and water.

Indicators: indicators are substances which indicate the acidic or basic nature of the solution by their colour change.

pH scale: A scale measuring hydrogen ion concentration in a solution. The pH of a solution is defined as the negative logarithm of hydrogen ion concentration in moles per liters.

1. The pH of a neutral solution is 7
2. The pH of an acidic solution is <7
3. The pH of a basic solution is > 7

SOME IMPORTANT COMPOUNDS AND THEIR USES:

                                                  WASHING SODA

Chemical name -    Sodium carbonate decahydrate

Chemical formula – Na₂CO₃, 10H₂O

Common name – washing soda

Washing soda can be obtained by recrystallisation of sodium carbonate of sodium  carbonate sodium carbonate can be obtained by heating baking soda

                    Na₂co₃ + 10H₂O – Na₂CO₃. 10H₂O

  Uses of washing soda

• Sodium carbonate is used in glass, soap and paper industries
• It is used in the manufacture of sodium compound such as borax
• Sodium carbonate can be used as a cleaning agent for domestic purposes
• It is used for removing permanent hardness

                                               BAKING SODA

  Chemical name – sodium hydrogen carbonate

 Common name – baking soda

            In the preparation of baking soda, a solution of sodium chloride in water is saturated  with ammonia and then CO₂ is passed into the liquid,

                        Nacl + H₂O + CO₂ + NH₃ – NH₄Cl + NaHCO₃

            

Baking soda is a mild non corrosive The following reaction takes place when it is heated  during cooking

                                         2HaHCO₃ D Na₂CO_3. + H₂O + CO₂

Uses of baking soda

• For making baking powder, which is mixture of baking soda and a mild edible acid as tartaric acid when baking powder is heated or mixed in water it release carbon dioxide that causes bread or cake to rare making them soft and spongy
• It is also an ingredient in antacids and it neutralizes excess acid in stomach
• It is also used in soda acid fire extinguishes

                                                BLEACHING POWDER

Chemical name: Calcium oxychloride

chemical formula: Ca(OCl)₂  

Uses: Bleaching clothes, used as oxidizing agent,disinfecting water, manufacture of chloroform.

 Preparation of Bleaching Power :

1. Chlorine gas is produced during electrolysis of aqueous sodium chloride.
2. This chlorine gas is used for the manufacture of bleaching powder.
3. Bleaching powder is produced by the action of a chlorine on slaked lime. 

                                                      PLASTER OF PARIS

Calcium sulphate with half a molecule of water per molecule of the salt (hemi-hydrate) is called plaster of paris (plaster of paris).

Preparation

plaster of paris is prepared by heating gypsum (CaSO₄.2H₂O) at 120°C in rotary kilns, where it gets partially dehydrated.

The temperature should be kept below 140°C otherwise further dehydration will take place and the setting property of the plaster will be partially reduced.

Properties

It is a white powder. When mixed with water (1/3 of its mass), it evolves heat and quickly sets to a hard porous mass within 5 to 15 minutes. During setting, a slight expansion (about 1%) in volume occurs so that it fills the mould completely and takes  a sharp impression. The process of setting occurs as follows:

The first step is called the setting stage, and the second, the hardening stage. The setting of plaster of Paris is catalyzed by sodium chloride, while it is reduced by borax, or alum.

Uses

• In surgery for setting broken or fractured bones
• For making casts for statues, in dentistry, for surgical instruments, and toys etc
• In making black board chalks, and statues
• In construction industry

                                  EQUATIONS OF ACIDS,BASES AND SALTS

Chapter 1 Chemical Reaction and Equation (class10)

1 Chemical Reaction :  During chemical  reaction, chemical composition of substances changes or new substances are formed.

2. Chemical Equation: Chemical reactions can be written in chemical equation form which should always balanced .

3. Types of Chemical Reaction
   (1) Combination reaction: A single product is formed from two or more reactants.
                                        2 Mg + O2 -> 2 MgO

   (2) Decomposition reaction : A single product breaks down to yield two or more products:

1. Thermal decomposition :   PB(NO₃)₂ = 2 PBO + 4 NO₂ + O2
2. Electrolysis  : 2H2 + O2 = 2H2O
3. Photochemical reaction : 2AgBr(s)+ Sunlight → 2Ag(s) + Br2(g)

(3) Displacement reaction : one element is displaced by another element.

                                Fe + CuSO₄ → FeSO₄ + Cu 

(4) Double displacement reaction : Exchange of ions between reactants.

                                  AB + CD → AD + CB

                           AgNO₃ + NaCl → AgCl + NaNO₃

(5)Redox reaction : Both oxidation and reduction take place simultaneously.

                                 Cuo + H2 ------ Cu + H2O

(6) Exothermic reaction: A chemical reaction in which heat energy is evolved.

                                 C+ O2 = CO2 ( heat)

(7) Endothermic reaction: A chemical reaction in which heat energy  is absorbed .

                               ZnCO3+ Heat =  ZnO + CO2

(8) Redox reaction : chemical reaction in which both oxidation and reduction take place simultaneously.

(9) Oxidation: reaction that involves the gain of oxygen or loss of hydrogen .

(10) Reduction: Reaction that shows the loss of oxygen or gain of hydrogen.

                         ZnO+ C = Zn+ CO

    ( ZnO is reduced to Zn,  C is oxidized to CO - oxidation)

(4) Corrosion : It is an undesirable change that occurs in metals , when they are attacked by moisture, air, acids and bases.

    Example: Corrosion( Rusting Of iron) : Fe2O3.n H2O (hydrated iron oxide)

               Corrosion of Sliver: Ag2S (Sliver Sulphide)

               Corrosion Of Aluminium :  Al2O3 ( Aluminum Oxide)

(5) Rancidity: Undersirable change that takes palce in oil containing food items due to the oxidation of fatty acids.

  Prevention methods of rancidity : Adding antioxidants to the food materials storing food in air tight container ,flushing out air with nitrogen gas and refrigerator.