What Is Chemistry And Its Laws:

 

What Is Chemistry
& It's Laws

What Is Chemistry?

Chemistry is the branch of science that deals with the properties,composition and structure of matter.It also deals with the changes involved in the matter.
These chemical changes are governed by some empirical laws known as laws of chemical combinations.

Laws of chemical combinations:

1- Law of Conservation of mass

2- Law of constant composition OR definite proportions

3- Law of multiple proportions

4- Law of Reciprocal Proportions

Law Of Conservation Of Mass:

Introduction:

In 1785, French Chemist Lavoisier make a careful quantitative measurement,he established that mass is neither created nor destroyed during a chemical change.

statement:

Its states that:

"Mass is neither created nor destroyed during a chemical reaction."

OR

"In any chemical reaction, the initial weight of reacting substances is equal to final weight of the products."

Examples:

1- 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.

2-The decomposition of the Red Oxide of mercury to form metallic mercury and a gas,he named this gas as Oxygen

Practical Verification: (Landolt Experiment)

German Chemist H. Landolt tested the validity of law of conservation of mass.

Procedure:

• He took H-shaped tube.
• He filled the two limbs A and B,with silver nitrate (AgNO3) in limb A and hydrochloric acid (HCl) 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 solutions should not intermix with each other.
• The reactants were mixed by inverting and shaking the tube.
• The tube was weighed after mixing (on the formation of white precipitate of AgCl.

Observation:

He observed that weight remains same.

AgNO3+HCl⟶AgCl+HNO

3

Result:

Thus total mass of the substances before the reaction is equal to the total mass of the substances after the reaction

2- Law Of Constant Composition:

Louis Proust in 1799 proposed the law of constant proportion.

statement:

It states that:

"Different samples of the same compound always contain the same elements combined together in the same proportions by mass."

Example:

Every sample of pure water,though prepared in the laboratory or obtained from rain, river or water pump contains one part hydrogen (H) and eight parts oxygen (O) by mass.

e.g. H₂O

       2:16

      1 : 8