NCERT chemistry Class 11 chapter 1 important notes
Law of conservation of mass: In a chemical reaction,The mass in the reactant side is always equal to the product side.It states that matter can neither be created nor be destroyed .
Law of Definite Proportions (Law of definite composition): This law was proposed by Joseph Proust. It
states that a given compound always contains exactly the same proportion of elements by weight. Or, the
same compound always contains the same elements combined in a fixed ratio by mass.
Law of Multiple Proportions: This law was proposed by John Dalton. It states that if two elements can
combine to form more than one compound, the different masses of one of the elements that combine with a
fixed mass of the other element, are in small whole number ratio.
Gay Lussac’s Law of Gaseous Volumes: This law was proposed by Gay Lussac. It states that when gases
combine to form gaseous products, their volumes are in simple whole number ratio at constant temperature
and pressure.
Avogadro’s Law: This law was proposed by Amedeo Avogadro. It states that equal volumes of all gases at
the same temperature and pressure should contain equal number of moles or molecules.
Atomic mass unit(AMU) : It is defined as the 1/12th weight of a carbon-12 atom.
1amu= 1.66 x 10-27 kg
DALTON’S ATOMIC THEORY
The term atom was first used by John Dalton from the Greek word a-tomio (means indivisible). He proposed
the first atomic theory. The important postulates of this theory are:
1. Matter is made up of minute and indivisible particles called atoms.
2. Atoms can neither be created nor be destroyed.
3. Atoms of same element are identical in their properties and mass. While atoms of different elements
have different properties and mass.
4. Atoms combined to form compound atoms called molecules.
5. When atoms combine, they do so in a fixed ratio by mass.
Dalton’s theory could explain the laws of chemical combination.
Based on the type of atoms, there are two types of molecules – homonuclear molecule and heteronuclear
molecule.
Mass percent (w/w or m/m): It is defined as the number of parts solute present in 100 parts by mass of
solution.
i.e. Mass % of a component = Mass of solute × 100/ masa of solution
Mole fraction: It is defined as the ratio of the number of moles of a particular component to the total
number of moles of solution.
i.e. Mole fraction of a component = Number of moles of the component /
Total number of moles of all the component
Molarity (M): It is defined as the number of moles of solute dissolved per litre of solution.
i.e. Molarity (M) = Number of moles of solute (n) / Volume of solution in litre(V)
Molality (m): It is defined as the number of moles of the solute present per kilogram (kg) of the solvent.
i.e. Molality (m) = Number of moles of solute/ Mass of solvent in kg
Among the above concentration terms, molarity depends on temperature because it is related to volume, which
changes with temperature. All the others are temperature independent.
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