Question

my dear frnds
pls guys tmrw test solve this

Answer 1

Mole:  Mole is the measurement in chemistry. It is used to express the amount of a chemical substance.
One mole is defined as the amount of substance of a system which contains as many entities like, atoms, molecules and ions as there are atoms in 12 grams of carbon - 12".

Avogadro number:  The number of the particles present in one mole of any substance is equal to 6.022x1023. This is called avogadro’s number or avogadro’s constant.

Number of particles in 1 mole: 
1 mole of hydrogen atoms represents 6.022 × 1023 hydrogen atoms.
1 mole of hydrogen molecules represents 6.022 × 1023 hydrogen molecules.
1 mole of water molecules represents 6.022 × 1023 water molecules.


Atomic mass:  The atomic mass of an element is the mass of one atom of that element in atomic mass units or (u).

Atomic mass unit (amu):  1/12th of the mass of an atom of carbon-12 is called atomic mass unit. It is a unit of mass used to express atomic masses and molecular masses.
 
Molar mass:  The molar mass of an element is equal to the numerical value of the atomic mass. However, in case of molar mass, the units change from ‘u’ to ‘g’. The molar mass of an atom is also known as gram atomic mass.
For example, the atomic mass of carbon =12 atomic mass units. So, the gram atomic mass of carbon = 12 grams.

Molecular mass of the molecule:  The sum of the atomic masses of all the atoms in a molecule of a substance is called the molecular mass of the molecule.

Molecular mass - calculation: Generally we use relative atomic masses of atoms for calculating the molecular mass of 1 mole of any molecular or ionic substances.
Example: Molecular mass of H2SO4
Atomic mass of Hydrogen = 1 
Atomic mass of sulphur = 32
Atomic mass of oxygen = 16
Molecular mass of H2SO4 = 2(Atomic mass of Hydrogen) + 1 (Atomic mass of sulphur) + 4 (Atomic mass of oxygen)
 = 2×1 + 32 + 4× 16 = 98 u.

Calculation of molecular mass of hydrogen chloride:
Atomic mass of hydrogen + Atomic mass of chlorine = 1 + 35.5 = 36.5 u.
 
Formula unit mass:  The formula unit mass of a substance is the sum of the atomic masses of all atoms in a formula unit of a compound. The term ‘formula unit’ is used for those substances which are made up of ions.
Formula unit mass of NaCl: 1 X Atomic mass of Na + 1 X Atomic mass of Cl
1x23 +1 x 35.5 = 58.5 atomic mass units.

Formula unit mass of ZnO: 
= 1 X Atomic mass of Zn + 1 X Atomic mass O 
= 1 X 65 + 1 X 16 = 81 u.

Avogadro's number, number of particles and moles - conversion formulae:
    Number of moles (n) = Given number of particles (N) / Avogadro number (N0)
Example: Find the number of moles present in 24.088X1023 particles of carbon dioxide
1 mole of carbon dioxide contains 6.022x1023
Solution: The number of moles (n ) = Given number of particles (N) / Avogadro number (N0).
                                                   = 24.088X1023 / 6.022x1023
                                                   = 4 moles.
   Number of atoms (n) = Given mass (m) / Molar mass (M) x Avogadro number (N0)
Example: Calculate the number of atoms in 48g of Mg
Solution: Number of atoms (n) = Given mass (m) / Molar mass (M) x Avogadro number (N0).
                                            = 48/24 X 6.022x1023
                                            = 12.04 X1023 atoms.
Number of molecules (n) = Given mass (m) / Molar mass (M) x Avogadro number (N0)
Example: Calculate the number of molecules in 3.6 g of water
Solution: The molecular weight of H2O = 18
                                            18g of water - 6.022x1023 molecules
                                            3.6g of water - 6.022x1023 X 3.6/18
                                            = 1.206 X 1022 molecules.
     Number of particles (n) = Number of moles of particles (n) x Avogadro number (N0)
Example:  Calculate the number of atoms in 0.5 moles of carbon
Solution: Number of atoms = 0.5 X 6.022x1023
                                        = 3.0115 atoms

Extra problems:

1) Calculate the number of moles in 12g of oxygen gas
Ans: 32g of oxygen gas = 1 mole
        12g of oxygen gas = ?
         = 12 X 1 / 32 =  0.375 mole.

2) Calculate the number of moles present in 14g of carbon monoxide .
Ans: 28g of CO = 1 mole
14g of CO = ?
= 14 X 1 / 28 = 1/2 = 0.5 mole.

3) Find the mass of 5 moles of aluminium atoms?
Ans: Atomic mass of aluminium atom = 27g
5 moles of aluminium atoms = 5 X 27g = 135 g.