Mole Concept
The word mole was introduced by Wilhelm Ostwald. In Latin, mole means heap or collection or pile.
- A mole is defined as the amount of a substance that contains as many particles (atoms, molecules or ions) of the substance as there are atoms in exactly 12 g of carbon-12.
- The number of particles present in a mole of any substance is fixed, with a value of 6.022 x 10^23. This number is called Avogadro number or Avogadro constant, named in honour of the Italian scientist Amedeo Avogadro. It is represented by N0.
- In other words, a mole of a substance is that amount of the substance that contains 6.022 x 1023particles of the substance.
-Mole is the SI unit of amount of substance.
-The atomic mass of an element expressed in grams is called gram atomic mass of the element.
- The molecular mass of a substance expressed in grams is called gram molecular mass of the substance.
- Gram atomic mass or gram molecular mass also represents molar mass of the substance.
- The mass of 1 mole of a substance is called molar mass of the substance.
1 mole = 6.022 x 1023 particles = Gram atomic mass (or gram molecular mass)
The word mole was introduced by Wilhelm Ostwald. In Latin, mole means heap or collection or pile.
- A mole is defined as the amount of a substance that contains as many particles (atoms, molecules or ions) of the substance as there are atoms in exactly 12 g of carbon-12.
- The number of particles present in a mole of any substance is fixed, with a value of 6.022 x 10^23. This number is called Avogadro number or Avogadro constant, named in honour of the Italian scientist Amedeo Avogadro. It is represented by N0.
- In other words, a mole of a substance is that amount of the substance that contains 6.022 x 1023particles of the substance.
-Mole is the SI unit of amount of substance.
-The atomic mass of an element expressed in grams is called gram atomic mass of the element.
- The molecular mass of a substance expressed in grams is called gram molecular mass of the substance.
- Gram atomic mass or gram molecular mass also represents molar mass of the substance.
- The mass of 1 mole of a substance is called molar mass of the substance.
1 mole = 6.022 x 1023 particles = Gram atomic mass (or gram molecular mass)
ATOMS AND MOLECULES NUMERICALS-
1. Calculate the number of moles of magnesium present in a magnesium ribbon weighing 12 g. Molar atomic mass of magnesium is 24g/ mol
2. Verify by calculating that
(a) 5 moles of CO2 and 5 moles of H2O do not have the same mass.
(b) 240 g of calcium and 240 g magnesium elements have a mole ratio of 3:5.
3. Find the ratio by mass of the combining elements in the following compounds.
(a) CaCO3 (b) MgCl2 (c) H2SO4 (d) C2H5OH (e) NH3 (f) Ca(OH)2
4. Calcium chloride when dissolved in water dissociates into its ions according to the following equation.
CaCl2 (aq) → Ca2+ (aq) + 2Cl– (aq)
Calculate the number of ions obtained from CaCl2 when 222 g of it is dissolved in water.
5. The difference in the mass of 100 moles each of sodium atoms and sodium ions is 5.48002 g. Compute the mass of an electron.
6. Cinnabar (HgS) is a prominent ore of mercury. How many grams of mercury are present in 225 g of pure HgS? Molar mass of Hg and S are 200.6 g /mol and 32 g/ mol respectively.
7. The mass of one steel screw is 4.11g. Find the mass of one mole of these steel screws. Compare this value with the mass of the Earth (5.98 × 1024kg). Which one of the two is heavier and by how many times?
8. A sample of vitamin C is known to contain 2.58 ×1024 oxygen atoms. How many moles of oxygen atoms are present in the sample?
9. Compute the difference in masses of 103 moles each of magnesium atoms and magnesiumions. (Mass of an electron = 9.1×10–31 kg)
10. Compute the number of ions present in 5.85 g of sodium chloride.
11. A gold sample contains 90% of gold and the rest copper. How many atoms of gold are present in one gram of this sample of gold?
12. Compute the difference in masses of one mole each of aluminium atoms and one mole of its ions. (Mass of an electron is 9.1×10–28 g). Which one is heavier?
13. A silver ornament of mass ‘m’ gram is polished with gold equivalent to 1% of the mass of silver. Compute the ratio of the number of atoms of gold and silver in the ornament.
14. A sample of ethane (C2H6) gas has the same mass as 1.5 ×1020 molecules of methane (CH4). How many C2H6 molecules does the sample of gas contain?
15. Fill in the blanks
(a) In a chemical reaction, the sum of the masses of the reactants and products remains unchanged. This is called ————.
(b) A group of atoms carrying a fixed charge on them is called ————.
(c) The formula unit mass of Ca3 (PO4)2 is ————.
(d) Formula of sodium carbonate is ———— and that of ammonium sulphate is ————.
