July 27, 2018 , , , ,

ACID, BASES AND SALTS
ACID
  • Acids are sour in taste
  •  its pH is less than 7
Example
Natural resources
 acid
 vinegar
 acetic acid
 orange and lemon
 citric acid
 tomato
 oxalic acid
 curd
 lactic acid
  • It turns blue Litmus red
Hydrochloric acid (HCl)
Sulphuric acid(H2SO4)
Nitric acid (HNO3)
Chemical properties of acids
1.Reaction with metals
Acids like dilute hydrochloric acid and dilute sulphuric acid react with certain active metals like iron  to form salt and evolve hydrogen gas

Note

we should not kept acid in metal containers  because acid  corrode the container

 Example
 metal + dilute acid ------------------> salt + hydrogen gas

Zn + H2SO4 ---------------> ZnSO4 + H2
2.Reaction with metal carbonate and hydrogen carbonate

Acid react with metal carbonate and hydrogen carbonate to produce their corresponding salt carbon dioxide gas and water

Metal carbonate / metal hydrogen carbonate + acid ----> salt + carbon dioxide + water

CaCO3(s)+2HCl-------->CaCl2+H2O+CO2
Test for Carbon dioxide gas

When carbon dioxide gas is passed through lime water it turns milky due to the formation of white precipitate of calcium carbonate

Ca(OH)2+CO2--------->CaCO3+H2O
3.reaction with metal oxide

Acid react with certain metal oxide to form salt and water

CuO+2HCl--------------->CuCl2+H2O


BASES
  • Bases are bitter in taste
  • It turns red litmus blue
  • Its pH is greater than 7
Chemical properties of bases
1.Reaction with metals

Strong bases react with active metals to produce hydrogen gas

Metal + base-------------> salt + hydrogen gas
Example
Zn(s)+2NaOH-------->Na2ZnO2(aq)+H2(g)

2.Reaction with non metallic oxide 
  • Bases react with non metallic oxide to produce salt and water
  • Non metallic oxides are acidic in nature
Base + non metallic oxide ----------------> salt + water

CO2(g)+Ca(OH)2(aq)----------->CaCO3(s)+H2O(l)
Acid / bases in  water solution
In presence of water acids Give hydrogen ion( H+) as hydrogen ion (H+) cannot exist alone so it combines with water molecules and form hydronium ion(H3O+)
Example
HCl+H2O----------->H3O++Cl-
 In the same way in presence of water bases give Hydroxide ions(OH-)
NaOH(s)----->Na+(aq) + OH- (aq)
Reaction between acid and bases

When acid react with base it gives salt and water this reaction is also known as neutralization reaction
Base + acid ------> salt + water
Example
NaOH(aq) + HCl(aq)---------->NaCl(aq) + H2O(l)
Dilution

  • mixing of an acid or base with water is called dilution
  • Dissolving an acid or a base in water is a highly exothermic reaction so care must be taken while doing it .The acid must always be added slowly to water with constant steering.
NOTE:-
Water should not be added to concentrated acid because if water is added the heat generated may cause the mixture to Splash out and cause burns
Indicators

Indicators are the substances that changes their colour or order when added into an acid or an alkaline solution
Types of indicators

1.Natural indicators

These indicators are found in nature in the plants  example Litmus, turmeric juice

2.Synthetic indicator 

the indicator which are synthesized in the laboratory or industry are known as synthetic indicator examplemethyl orange, phenolphthalein etc 
3.Olfactory indicator

Those substances whose odour changes in acidic and basic medium are known as olfactory indicators example Vanilla extract and onion can be used as olfactory indicators
The pH scale
  • It is a scale used for measuring hydrogen ion concentration the p in pH stand for potenz which means power in German
  •  it has values ranging from 0 (very acidic) to 14 (very alkaline) pH is a number which indicates the acidic or basic nature of a solution
  • Higher the hydrogen Ion concentration present in the solution lower is its PH value [pH means power of hydrogen ions]
  1. If pH is greater than 7 solution is basic
  2. If pH is less than 7 solution is acidic 
  3. if pH is equals to 7 solution is neutral
Importance of PH in daily life
  •  pH sensitivity of plant and animals human body pH lies between 7 to 7.8
  •  pH of acid rain is less than 5.6
  •  when acid rain water flows into the river then pH of river water also lower it make survival of Aquatic life in such river difficult
  •  pH of soil:- plants require a specific pH range for their healthy growth
  •  PH in digestive system:- as we know our stomach produces HCL acid which help in digestion of food without harming the stomach. During digestion in stomach produces large amount of acid in order to digest food its causes pain and irritation to get rid of the pain people  use antacid Like magnesium Hydroxide or milk of magnesia or mild base
  • Tooth decay start when the pH of mouth is lower than 5.5. enamel (calcium phosphate) hardest substance in the body enamel  does not dissolve in water but they get corrode when pH of mouth is less than 5.5 bacteria present in our mouth produce acid because of degradation of sugar and food particle remaining in the mouth
Prevention of  tooth decay
  • Clean mouth open after eating food
  • Use toothpaste
Self defence by animal and plants through chemical warfare

As we know when Honey Bee stung on our skin leaves Acid which cause pain and irritation   to overcome this pain we use baking soda (mild base) which gives Relieve in stung area.

 SALTS
  • Salts of strong acid and strong base are neutral (pH value 7)
  • salts of strong acid and weak base (pH less than 7)
  • salts of weak acid and strong base (pH value greater than 7)
Common salt ( NaCl )

common salt used as raw material for various material of daily use such as Sodium Hydroxide, baking soda, washing soda, bleaching powder and many others
Sodium hydroxide(NaOH)
Chlor-alkali process
When electric is passed through an aqueos solution NaCl(aq) BRINE it decomposes to form sodium hydroxide
2NaCl(aq) + 2H2O(l) ------>2NaOH(aq)+Cl2(g)+H2(g)
Cl-anode
H2-cathode
NaOH-near cathode
  • It is also known as caustic soda
Bleaching powder ( CaOCl2 )
  • The chlorine gas is used for manufacturing of bleaching powder
  • Bleaching powder is obtained by the action of chlorine on the dry slaked lime
Ca(OH)2 + Cl2 ----------> CaOCl2 + H2O
Uses
  • For bleaching cotton and linen in the textile industry
  • Bleach wood Pulp and Paper factory
  • Bleach waste cloth in laundry
  • Oxidizing agent in chemical industry
  • Disinfectant in drinking water
Baking soda  (NaHCO3)

It Produced using sodium chloride

NaCl + H2O + CO2 + NH4 --------> NH4 + NaHCO3
 Uses
  • It is used in kitchen for making bread cakes
following reaction takes place during cooking

2NaHCO3 --------------> Na2CO3 + H2O + CO2

carbon dioxide produced during the reaction cause bread fluffy and become soft and spongy
  •  for making baking powder
  •  used as a ingredient in antacid
  •  it is also  for fire extinguisher
 washing soda
  •  recrystallization of sodium carbonate gives washing soda
  •  sodium carbonate obtained by heating of baking soda
Na2CO3 + 10H2O ------->Na2CO3.10H2O

 it is also known as  basic salt
 Uses
  •  used in glass, soap and paper industry
  •  used for removing permanent hardness of water
  •  cleaning agent for domestic purpose
  •  manufacture of sodium compound like borax
plaster of Paris(CaSO4 . ½ H2O)
On heating gypsum at 370 Kelvin it losses water molecules and becomes calcium sulphate hemihydrate
CaSO4 . ½ H2O
It is also known as plaster of Paris

CaSO4 . ½ H2O +  ½ H2O------------>CaSO4 .2 H2O
Uses
  •  plaster of paris is used for making toys materials for decoration and for making surface smooth
Water of crystallization
Water of crystallization is fixed number of water molecules present in one formula unit of salt
Example

CuSO4.5H2O