CBSE Class 11 Notes Chapter 1 - Some Basic Concepts of Chemistry

Chemistry is referred to as Central Science as it interconnects geology, biology, environmental science, and physics to each other. Chemistry is a discipline where people of ancient India had the knowledge of scientific phenomenon before the emergence of modern science. Any substance on earth contains matter. A substance that occupies physical space and has inertia is called matter. There are three states of matter viz solid, gas, liquid. Matter can also be
classified into compounds, mixtures or elements.

Laws Of Chemical Combination

  • Law of Conservation of Mass – It states that during a chemical reaction, the mass of the products and reactants will always be equal.
  • Law of Definite Proportions – It states that every chemical compound will contain a fixed and constant proportion by mass, of its constituent elements. Joseph Proust proposed this law.
  • Law of Multiple Proportions – It is a rule of stoichiometry formulated by John Dalton.
  • Gay Lussac’s Law of Gaseous Volumes – Gay Lussac gave this law in the year 1808. This law was properly explained by Avogadro.
  • Avogadro Law – It states that when the temperature and pressure conditions are same, gases of equal volumes contain the same number of molecules.

The above-described laws led to Dalton’s atomic theory.


Few Important Questions

  1. Define mass and write its SI unit?
  2. Calculate the number of atoms in 52 moles of Ar and 52 g of He.
  3. What is the mass percent of elements present in Na2SO4
  4. What is the difference between 0.50 mol Na2CO3 and 0.50 M Na2CO3

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