CBSE Class 10 Science Chapter-2 Acids, Bases and Salts Notes

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CBSE Class 10 Science Chapter-2 Acids, Bases and Salts Notes
CBSE Class 10 Science Chapter-2 Acids, Bases and Salts Notes

CBSE Class 10 Science

Chapter-2 Acids, Bases and Salts Notes

Dear Students here we are uploading the best study notes of CBSE class 10 Science Ch. 2 i.e. Acids, Bases and Salts (study/revision notes) based on Latest CBSE syllabus and NCERT pattern. These notes are very useful for your studies especially for Board Exams.

In this we have also included the most important and frequently asked question in CBSE board exams from Chapter 2, Acids, Bases and Salts. The source of the notes are various science text books including NCERT Class 10 Science text book and various student support materials prepared by learned teachers of KVS. So without any confusion you can prepare from these authentic notes.

CHAPTER 2–ACIDS, BASES AND SALTS

Acids: Substances which turn blue litmus solution red are called acids. Acids are sour in taste. They give H+ ions in aqueous solution.  The term ‘acid’ has been derived from the Latin word, acidus, which means sour.

Strong Acids: Acids which dissociate into ions completely are called strong acids. E.g. H2SO4, HCl, HNO3.

Weak Acids: Acids which do not dissociate into ions completely are called weak acids E.g.. CH3COOH, Oxalic acid, Lactic acid.

Concentrated Acid : Having more amount of acid + less amount of water.

Dilute Acid : Having more amount of water + less amount of acid

Mineral Acids: Acids which are obtained from minerals like sulphates, nitrates, chlorides etc. are called mineral acids, e.g., H2SO4 (Sulphuric acid), HNO3 (Nitric acid) and HCl (Hydrochloric  acid).

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

 

Chemical properties of acids

 

(i) Acids react with active metals to give salt and hydrogen gas.

(ii) Acids react with metal carbonate and metals hydrogen carbonate to give salt, water and carbon dioxide.

(iii) Acids react with bases to give salt and water. This reaction is called neutralization reaction.

(iv) Acids react with metals oxides to give salt and water.

Bases: Substances which change red litmus solution blue are called bases. These are the substances which are bitter in taste and soapy in touch. They give OH− ions in aqueous solution.

Strong Bases : NaOH, KOH, Ca(OH) 2

Weak Bases : NH4OH

Alkalis : These are bases which are soluble in water [NaOH, KOH, Ca(OH) 2].

Chemical properties of Bases

  1.   Reaction with Metals – Certain metals such as Zinc, Aluminium and 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.

SALTS :These are the compounds formed from reaction of acid and base. Example : NaCl, KCl. 

INDICATORS :

Indicators are substances which indicate the acidic or basic nature of the solution by their colour change. These are the substances which change their color/smell in different types of substances.

TYPES OF INDICATORS

 

Natural indicators                  Synthetic indicators                          Olfactory indicators

Found in nature                   These are chemical                               These substances in plants.                                             substances.                                       have different                                                                                                                       odour in acid and                                                                                                                     bases.

Litmus, red                                     Methyl orange,                                                                cabbage leaves                              phenolphthalein                                                      extract, flowers of                                                                                                                     hydrangea plant,                                                                                                                         turmeric

 

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

Hydronium Ions: They are formed by reaction of H+ (from acid) and H2O. It is because H+ is unstable..


pH scale
: A scale for 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 liter.

pH =-log [H+]

pH =-log [H3O+]

where [H+] or [H3O+] represents concentrations of hydrogen ions in solution.

The pH of a neutral solution is 7

     The pH of a acidic solution is  < 7

     The pH of a basic  solution is  > 7

 

pH of Salts :

 

  1.  Strong Acid + Strong Base Neutral Salt : pH = 7
  2.  Salt of strong acid + Weak base Acidic salt : pH < 7
  3. Salt of strong base + Weak acid Basic salt : pH > 7

 

Some Important Compounds and their uses

Common Name Chemical name Chemical formula Uses
Washing soda Sodium carbonate decahydrate Na2CO3.10H2O Manufacture of borax, caustic soda, softening of hard water
Baking soda Sodium hydrogen carbonate NaHCO3 Used as antacid, ingredient of baking powder
Bleaching powder Calcium oxychloride CaOCl2 Bleaching clothes, used as oxidizing agent, disinfecting water, manufacture of chloroform
Plaster of  Paris Calcium sulphate hemihydrate CaSO4 .1/2H2O Plastering fractured bones, making toys ,decorative materials ,statues

 

  1. Sodium Hydroxide (NaOH) : When electricity is passed through an aqueous solution of NaCl (brine), it decompose to form NaOH. (Chlor-alkali process)

2NaCl + 2H2O 2NaOH + Cl2 + H2

At anode : Cl2 gas

At cathode : H2 gas

Near cathode : NaOH solution is formed.

 Uses :

H2 : Fuels, margarine

Cl2 : Water treatment, PVC, CFC’s

HCl : Cleaning steels, medicines

NaOH : Degreasing metals, soaps and paper making

Cl2 + NaOH → Bleach : Household bleaches, bleaching fabrics

  1. Bleaching Powder (CaOCl2) : It is produced by the action of chlorine on dry

slaked lime.

Cl2 + Ca(OH)2 CaOCl2 + H2O

Uses :

(a) Bleaching cotton and linen in textile industry.

(b) Bleaching wood pulp in paper factories.

(c) Oxidizing agent in chemical industries.

(d) Disinfecting drinking water.

 

  1. Baking Soda (Sodium Hydrogen Carbonate) (NaHCO3) :

 

NaCl + H2O + CO2 + NH3NH4Cl + NaHCO3

 

Baking soda

  • It is mild non-corrosive base.
  • When it is heated during cooking :

2NaHCO3 ____ Na2CO3 + H2O + CO2

 

Uses :

(a) For making baking powder (mixture of baking soda and tartaric acid). When baking powder is heated or mixed with water, CO2 is produced which causes bread and cake to rise making them soft and spongy.

(b) An ingredient in antacid.

(c) Used in soda acids, fire extinguishers.

  1. Washing Soda (Na2CO3.10H2O) : Recrystallization of sodium carbonate gives washing soda. It is a basic salt. 

Na2CO3 + 10H2O Na2CO3.10H2O

Uses :

(a) In glass, soap and paper industry.

(b) Manufacture of borax.

(c) Cleaning agent for domestic purposes.

(d) For removing permanent hardness of water.

 

  1. Plaster of Paris (Calcium sulphate hemihydrates) (CaSO4.½H2O) :

On heating gypsum (CaSO4.2H2O) at 373K, it loses water molecules and becomes Plaster of Paris (POP). It is a white powder and on mixing with water it changes to gypsum.

 

CaSO4.½H2O + 1½H2O CaSO4.2H2O

Uses :

(a) Doctors use POP for supporting fractured bones.

(b) For making toys, material for decoration.

(c) For making surfaces smooth.

 

Water of Crystallization : It is a fixed number of water molecules present in one formula unit of a salt. 

E.g., CuSO4.5H2O has 5 water molecules.

Na2CO3.10H2O has 10 water molecules.

CaSO4.2H2O has 2 water molecules.

Important Questions For  Board Exams

Acids, Bases and Salts Important VERY SHORT QUESTIONS (1 Mark) 

  1. Name the acid present in ant sting.
  2. What happens when egg shell is added to nitric acid ?
  3. Name a salt which does not contain water of crystallization.
  4. Name two constituents of baking powder.
  5. What is the pH of gastric juices released during digestion ?
  6. Which solution is used to dissolve gold ?
  7. How will you test a gas which is liberated when HCl acid reacts with an active metal ?
  8. Why does flow of acid rain water into a river make the survival of aquatic life in the river difficult ?
  9. When conc. acid is added to water, whether the process is exothermic or endothermic ?
  10. Which by-product of chlor-alkali process is used for manufacturing bleaching powder ?
  11. Write the name of the products formed by heating gypsum at 373K.Write one use of it.
  12. Write the chemical name and formula of the compound which is used as an antacid.

Acids, Bases and Salts Important SHORT TYPE QUESTIONS (2 Marks)

  1. Why does bleaching powder smell strongly of chlorine and does not dissolve completely in water ?
  2. Hold one moist and one dry strip of blue litmus paper over dry HCl acid gas. Which strip will turn red and why ?
  3. What is Plaster of Paris ? How is it obtained from gypsum ?
  4. What is the role of toothpastes in preventing cavities ?
  5. Explain why sour substances are effective in cleaning copper vessels ?
  6. A white powder is added while baking breads and cakes to make them soft and fluffy. What is the name of the powder ? What are its main ingredients ?
  7. How washing soda is prepared from baking soda ?
  8. Though the compounds such as glucose and alcohol have hydrogen atoms in their molecule, yet they are not categorized as acids. Why ?
  9. What is the reaction called when an acid reacts with base to produce salt and water ? Give example also.
  10. Why pickles and curd are not stored in copper and brass utensils ?
  11. What is baking powder? How does it make the cake soft and spongy?

Acids, Bases and Salts Important SHORT TYPE QUESTIONS (3 Marks)

 

  1. On passing excess CO2 through lime water, it first turns milky and then becomes colourless. Explain why ? Write chemical equations.
  2. How are bases different from alkalis ? Are all bases alkalis ?
  3. While constructing a house, a builder selects marble flooring and marble top for kitchen where vinegar and juices of lemon, tamarind. etc. are more often used for cooking. Will you agree to this selection and why ?
  4. Indicate with the help of a diagram the variation of pH with change in concentration of H+ (aq) and OH− (aq) ions.
  5. Write the name and formulae of three hydrated salts.
  6. What happens when calcium carbonate is made to react with hydrochloric acid ? Give the equation of reaction.
  7. Why metallic oxides are called basic oxides and non-metallic oxides are called acidic oxides ?
  8. What is pH scale ? What is pH value of salt formed by a

(a) weak acid and strong base ?

(b) strong acid and strong base ?

9.Write the chemical name of Plaster of Paris. Write a chemical equation to show the reaction between Plaster of Paris and water. Name the compound produced in this reaction.

10. A gas X reacts with lime water and forms a compound Y which is used as bleaching agent in the chemical industry. Identify X and Y .Give the chemical equation of the reaction involved.

Acids, Bases and Salts Important LONG ANSWER TYPE QUESTIONS (5 Marks)

  1. What is water of crystallization ? Write the common name and chemical formula of a commercially important compound which has ten water molecules. How is this compound obtained ? Write chemical equations also. List any two uses of this compound.
  1. Identify the compound X on the basis of the reactions given below. Also, write the name and chemical formulae of A, B and C.

X + Zn A + H2 (g)

X + HCl B + H2O

X + CH3COOH C + H2O

  1. An element P does not react with dil. H2SO4. If forms an oxide PO which turns red litmus into blue. Will you call P as a metal or a non-metal ? Give reason.

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