1)
Acids are sour in taste,
turn blue litmus red, and dissolve in water to release H+ ions e.g.
HCl, H2SO4, HNO3 etc.
2)
Bases are bitter in taste,
have soapy touch, turn red litmus blue and give hydroxide ions in solution.
e.g. NaOH, KOH etc.
3) A salt is a compound which is formed by neutralization reaction
between an acid and base.
e.g. sodium chloride.
3)
Indicators – Indicators are substances
which indicate the acidic or basic nature of the solution
by their colour
change.
The colour of some acid – base indicators in acidic and basic medium are
given below
|
Sr. No.
|
INDICATORS
|
COLOUR IN ACIDIC MEDIUM
|
COLOUR IN BASIC MEDIUM
|
|
1
|
Litmus
solution
|
Red
|
Blue
|
|
2
|
Methyl
Orange
|
Pink
|
Orange
|
|
3
|
Phenolphthalein
|
Colourless
|
Pink
|
|
4
|
Methyl
red
|
Yellow
|
Red
|
5)
Chemical properties of acids:
i) Acids react
with active metals to give hydrogen gas.
Zn + H2SO4àZnSO4 + H2
ii) Acids react with metal carbonate and metal hydrogen carbonate to
give carbon dioxide.
NaHCO3 +HCl àNaCl + H2O + CO2
iii) Acids react
with bases to give salt and water. This reaction is called as neutralization
reaction.
NaOH + HCl à NaCl +H2O
iv) Acids react
with metals oxides to give salt and water.
CuO + H2SO4 à CuSO4 + H2O
6)
Chemical properties of Bases:
i)
Reaction with Metals - Certain reactive metals such
as Zinc, Aluminium, and Tin react with alkali solutions on heating and hydrogen
gas is evolved.
2NaOH + Zn à Na2ZnO2
+H2
ii)
Reaction with acids -Bases react with acids to form
salt and water.
KOH +HCl à KCl +H2O
iii)
Reaction with Non -metallic oxides – These oxides
are generally acidic in nature. They react with bases to form salt and water.
2NaOH + CO2à Na2CO3 + H2O
7)
PH Scale: The concentration of hydrogen ion in
solution is expressed in terms of pH. The pH of a solution is defined as the
negative logarithm of hydrogen ion concentration in moles per liter.
pH = -
log [H+]
For water or neutral solutions, pH = 7 ; For
acidic solutions, pH < 7; For basic
solutions, pH > 7
8)
Some Important Chemical Compounds:
a)Common
Salt (NaCl)
Sodium chloride is known as common salt.
Its main source is sea water. It is also exists in the form of rocks and is called rock
salt.
Common salt is an important component of
our food. It is also used for preparing sodium hydroxide, baking soda, washing
soda etc.
b)Sodium
Hydroxide or Caustic Soda (NaOH)
It is prepared by passing electricity
through an aqueous solution of sodium chloride also known as brine.
2NaCl (aq) + 2 H2O (l) à 2NaOH (aq) + Cl2 (g) + H2 (g)
This process is known as chlor-alkali
process.
Properties:
1. It is white translucent solid.
2. Crystals of sodium hydroxide are
deliquescent.
3. It is readily soluble in water and gives
strong alkaline solution.
c)
Bleaching Powder (CaOCl2)
Its chemical name is calcium oxychloride.
It is prepared by passing chlorine gas through dry slaked lime.
Ca (OH) 2 + Cl2àCaOCl2 + H2O
Uses
–
1. For bleaching cotton and linen in
textile industry and wood pulp in paper industry
2. For disinfecting drinking water.
d)
Baking Soda (NaHCO3)
Chemical name is Sodium hydrogen carbonate.
It is prepared by passing CO2
gas through brine solution saturated with ammonia.
NaCl + H2O +CO2
+NH3à NH4Cl + NaHCO3
Properties:
1. It is white crystalline solid and
sparingly soluble in water at room temperature.
2. On heating it decomposes to give sodium
carbonate and carbon dioxide.
3. It reacts with acids to give carbon
dioxide gas.
4. It aqueous solution is weak alkaline due
to hydrolysis.
Uses:
1. It is used in soda – acid fire
extinguisher.
2. It acts as mild antiseptic and antacid.
3. It is used as a component of baking
powder. In addition to sodium hydrogen carbonate baking soda contains tartaric
acid.
e)
Washing Soda (Na2CO3.10 H2O)
Chemical name is sodium carbonate
decahydrate.
It is prepared by heating baking soda.
Recrystallisation of sodium carbonate gives washing soda.
2NaHCO3à Na2CO3 +H2O +CO2
Na2CO3
+10 H2O à Na2CO3. 10 H2O
Uses:
1. It is used for removing permanent
hardness of water.
2. It is used in glass, soap and paper
industries.
3. It can be used as a cleaning agent for
domestic purposes.
f) Plaster of Paris (CaSO4.1/2H2O)
Its chemical name is calcium sulphate
hemihydrates. It is obtained by heating Gypsum upto 373K.
CaSO4.2H2O à CaSO4.1/2H2O + 11/2H2O
On treatment with water it is again
converted into gypsum and sets as a hard mass.
CaSO4.1/2H2O+11/2H2OàCaSO4.2H2O
Uses:-
- It is used by doctors for setting
fractured bones.
- It is used for making statues, models and
other decorative materials.
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