can someone explain mole concept
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Mole is a unit used to measure the amount of a substance.
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In chemistry, the term mole represents a pile or mass of atoms, molecules, ions or electrons. Just as common man measures quantity in terms of kilograms or dozens, a chemical scientist deals with a 'mole' of atoms, molecules, ions or electrons.
Mole is defined as the amount of a substance, which contains the same number of chemical units (atoms, molecules, ions or electrons) as there are atoms in exactly 12 grams of pure carbon-12. A mole represents a collection of 6.023 x 1023 ( Avogadro's number) chemical units. Thus a mole represents the quantity of material, which contains one Avogadro's number of chemical units of any substance. The unit of mole is denoted as 'mol'.
For example
One mole of hydrogen atoms = 6.023 x 1023 atoms of hydrogen
One mole of hydrogen molecules = 6.023 x 1023 molecule of hydrogen
One mole of electrons = 6.023 x 1023 electrons
One mole of sodium ions (Na+) = 6.023 x 1023Na+ ions
It can be thus concluded that,
One mole of atoms = 6.023 x 1023 atoms = Gram atomic mass of the element.
One mole of molecules = 6.023 x 1023 molecules = Gram molecular mass.
Molar Volume
The volume occupied by one mole of any substance is called its molar volume. It is denoted by Vm. Molar volume of the substance depends on temperature and pressure. One mole of all gaseous substances at 273 K and 1 atm pressure occupies a volume equal to 22.4 litre or 22,400 mL. The unit of molar volume is litre per mol or millilitre per mol.
Problems
10. Calculate the average atomic weight of silicon having 92.2% of Si-28 isotope of relative mass 27.98 amu, 4.7% of Si-29 isotope of relative mass 28.98 amu and 3.1% of Si-30 isotope of relative mass 29.97 amu.
Solution
Data given: 92.20% of silicon of mass 27.98 amu
4.7% of silicon of mass 28.98 amu
3.1 % of silicon of mass 29.97 amu
Average atomic weight
= 25.80 + 1.36 + 0.93
= 28.09 amu.
Average atomic weight of silicon is 28.09 amu.11. One million silver atoms weigh 1.79 x 1016 g. Calculate the gram atomic mass of silver.
Solution
Number of silver atoms = 1 million = 1 x 106
Mass of one million Ag atoms = 1.79 x 1016 g
= 107.8 g
Gram atomic mass of silver is equal to the mass of 6.023 x 1023 atoms of silver. So, the gram atomic mass of silver is 107.8 g
12. Chlorophyll, the green colouring matter of plants responsible for photosynthesis, contains 2.68% of magnesium by weight. Calculate the number of Mg atoms in 2.00 g of chlorophyll.
Solution
100 g of chlorophyll contains 2.68 g of Mg
1 mole of Mg = 24 g of Mg = 6.023 x 1023 atom of Mg
24 g of Mg contains, 6.023 x 1023 atom of Mg
=1.34 x 1021 Mg atoms
13. A sample of gaseous substance weighing 0.5 g occupies a volume of 1.12 litre under NTP conditions. Calculate the molar mass of the substance.
Solution
1 mole of any gaseous substance at NTP occupies 22.4 L.
1.12 L of gaseous substance = 0.5 g
The molar mass of the substance therefore is 10 g/mol.
Mole is defined as the amount of a substance, which contains the same number of chemical units (atoms, molecules, ions or electrons) as there are atoms in exactly 12 grams of pure carbon-12. A mole represents a collection of 6.023 x 1023 ( Avogadro's number) chemical units. Thus a mole represents the quantity of material, which contains one Avogadro's number of chemical units of any substance. The unit of mole is denoted as 'mol'.
For example
One mole of hydrogen atoms = 6.023 x 1023 atoms of hydrogen
One mole of hydrogen molecules = 6.023 x 1023 molecule of hydrogen
One mole of electrons = 6.023 x 1023 electrons
One mole of sodium ions (Na+) = 6.023 x 1023Na+ ions
It can be thus concluded that,
One mole of atoms = 6.023 x 1023 atoms = Gram atomic mass of the element.
One mole of molecules = 6.023 x 1023 molecules = Gram molecular mass.
Molar Volume
The volume occupied by one mole of any substance is called its molar volume. It is denoted by Vm. Molar volume of the substance depends on temperature and pressure. One mole of all gaseous substances at 273 K and 1 atm pressure occupies a volume equal to 22.4 litre or 22,400 mL. The unit of molar volume is litre per mol or millilitre per mol.
Problems
10. Calculate the average atomic weight of silicon having 92.2% of Si-28 isotope of relative mass 27.98 amu, 4.7% of Si-29 isotope of relative mass 28.98 amu and 3.1% of Si-30 isotope of relative mass 29.97 amu.
Solution
Data given: 92.20% of silicon of mass 27.98 amu
4.7% of silicon of mass 28.98 amu
3.1 % of silicon of mass 29.97 amu
Average atomic weight
= 25.80 + 1.36 + 0.93
= 28.09 amu.
Average atomic weight of silicon is 28.09 amu.11. One million silver atoms weigh 1.79 x 1016 g. Calculate the gram atomic mass of silver.
Solution
Number of silver atoms = 1 million = 1 x 106
Mass of one million Ag atoms = 1.79 x 1016 g
= 107.8 g
Gram atomic mass of silver is equal to the mass of 6.023 x 1023 atoms of silver. So, the gram atomic mass of silver is 107.8 g
12. Chlorophyll, the green colouring matter of plants responsible for photosynthesis, contains 2.68% of magnesium by weight. Calculate the number of Mg atoms in 2.00 g of chlorophyll.
Solution
100 g of chlorophyll contains 2.68 g of Mg
1 mole of Mg = 24 g of Mg = 6.023 x 1023 atom of Mg
24 g of Mg contains, 6.023 x 1023 atom of Mg
=1.34 x 1021 Mg atoms
13. A sample of gaseous substance weighing 0.5 g occupies a volume of 1.12 litre under NTP conditions. Calculate the molar mass of the substance.
Solution
1 mole of any gaseous substance at NTP occupies 22.4 L.
1.12 L of gaseous substance = 0.5 g
The molar mass of the substance therefore is 10 g/mol.
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