Chemical Combinations Notes Chemistry IX


Chemical Combinations - Theory Notes and Question Answers - Chemistry IX
Theory Notes and Question Answers from Chapter No 02 "Chemical Combinations" for class 9th, IX, Ninth Class 


2.1 LAWS OF CHEMICAL COMBINATIONS
Chemical Combinations Theory Notes and Question Answers


Q 1: What does the chemistry deal?

ANS :

     CHEMISTRY:

              Chemistry deals with the matter and the changes occurring i it. Th chemical changes are governed by some empirical laws known as laws of c mica! combinations.

These laws are
  • Law of conservation of mass.
  • Law of constant composition or definite pro
  • Law of multiple proportions.
  • Law of reciprocal 


Q.2: State the law of conservation of mass and  explain with examples.
Ans:  LAW OF CONSERVATION OF MASS
Introduction:
Antoine Lavoisier discarded the worm out Of ideas about the changes that occur during a chemical reaction. By making careful quantitative measurements, he established the mass is neither created destroyed during a chemical change. 

Statement:

Its state that mass is neither create nor destroyed during a chemical reaction. In other Words,.

In any Chemical reaction the initial weight of reacting substances is equal to the final weight of the products. 

        OR
 Mass is neither created nor destroyed during a chemical reaction but it only changes from one form to another form.

Examples:
An iron (Fe) increase in weight on rusting is because of it combination of oxygen from the air and increase in weight is exactly equal to the weight of oxygen combined. 
           
                              4Fe + 3O2     ---------->   2Fe2O3
  • The most important chemical reaction that Lavoisier performed was the decomposition of the red oxide of mercury to form metallic mercury and a gas, he named this gas as oxygen.

Lavoisier summarized his finding by formulating a law, which is known as law of conversation of mass. 

The law of conservation of mass may be demonstrated by the union of hydrogen (H2) and oxygen (O2) to form water. If the H 2 and O2 are weighed before they unite, it will be found that their combined weight is equal to the weight of water (H2O) formed.

 Q.3: Describe Landolt experiment for practical verification of law of conservation of mass?
Ans: LANDOLT EXPERIMENT:
German Chemist tested the A validity of Law of conservation of mass, 
Procedure:
  • He took H-shaped tube as shown in figure
  • He filled the two limbs A and B with silver nitrate (AgNO3) In Limb A and hydrochloric acid (HCI) in limb B.
  • The tube was sealed so that the material could not escape outside.
  • The tube was weighed initially in a vertical position so that the solutions should not intermix with each
    Chemical Combinations Theory Notes and Question Answers 1
    other.
  • The reactants were mixed by inverting and shaking the tube.
  • The tube was weighed after mixing (on the formation of white precipitate of (AgCI). 








Observation:
He observed that weight remains same.
Ag NO3(aq) + HCl(aq) AgCl(s) + HNO3(aq)
Result:
Thus total mass of the substance before the reaction is equal to the total mass of the substances after the reaction. 

Q.4: Describe Einstein Theory about the relationship between mass and energy?

Ans: EINSTEIN THEORY:

The relationship between mass and energy was first proposed by AIbert EGstein in 1906. The relationship between mass that is lost and the energy that is released in chemical reaction is given by the equation.
E = mc2 

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