Acid, Bases and Salts comes under unit Chemical substances. It’s an important unit covering 33 marks of the first term exam. Read the whole class 10 General Science syllabus. Read Acid Bases Salts Class 10 General Science Notes.
Acids, bases and salts syllabus: Their definitions in terms of furnishing of H+ and OH- ions, General properties, examples and uses, concept of pH scale (Definition relating to logarithm not required), importance of pH in everyday life; preparation and uses of sodium hydroxide, Bleaching powder, Baking soda, Washing soda and Plaster of Paris.
Acid Bases Salts Class 10 General Science Notes
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.
4) 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|
5) Chemical properties of acids:
i) Acids react with active metals to give hydrogen gas.
Zn + H2SO4 → ZnSO4 + H2
ii) Acids react with metal carbonate and metal hydrogen carbonate to give carbon dioxide.
NaHCO3 +HCl → NaCl + H2O + CO2
iii) Acids react with bases to give salt and water. This reaction is called as neutralization reaction.
NaOH + HCl → NaCl +H2O
iv) Acids react with metals oxides to give salt and water.
CuO + H2SO4 → 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 → Na2ZnO2 +H2
ii) Reaction with acids –Bases react with acids to form salt and water.
KOH +HCl → 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 + CO2 → 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 litre.
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) → 2NaOH (aq) + Cl2 (g) + H2 (g)
This process is known as chlor-alkali process.
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 + Cl2 → CaOCl2 + H2O
1. For bleaching cotton and linen in textile industry.
2. For disinfecting drinking water.
3. For bleaching wood pulp in paper industry.
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 +NH3 → NH4Cl + NaHCO3
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.
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.
2NaHCO3 → Na2CO3 +H2O +CO2
Na2CO3 +10 H2O → Na2CO3 . 10 H2O
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 → CaSO4.1/2H2O + 11/2H2O
On treatment with water it is again converted into gypsum and sets as a hard mass.
CaSO4.1/2H2O+11/2H2O → CaSO4.2H2O
1. It is used by doctors for setting fractured bones.
2. It is used for making statues, models and other decorative materials.
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