Some Revive About Chemistry form 4~

italian physicist Amedeo Avogadro (Name at birth: Lorenzo Romano Amedeo Carlo Avogadro)

• Born: 9 August 1776
• Birthplace: Turin, Piedmont, Italy
• Died: 9 July 1856
• Best Known As: The guy they named Avogadro’s number after

1. Avogadro constant / Avogadro’s number is 6.02 x 10²³
2. Atomic substances

• Elements – all the particles are atoms.
• Example: zinc (Zn), sodium (Na), aluminium (Al) and all noble gases, argon (Ar), helium (He) and neon (Ne).
• RAM (Relative Atomic Mass) of  Na = 23

3. Molecular substances

• Covalent compounds – the particles are molecules.
• Example: carbon dioxide (CO₂), water (H₂O) and non-metal elements, iodine (I₂), nitrogen (N₂) and oxygen (O₂).
• RMM (Relative Molecular Mass) of I₂ = 127 + 127 = 254

4. Ionic substances

• Ionic compounds – the particles are ions.
• Example: sodium chloride (NaCl), hydrochloric acid (HCl) and potassium iodide (KI).
• RFM (Relative Formula Mass) of HCl = 1 + 35.5 = 36.5

5. Avogadro’s Law / Gas Law states that equal volumes of all gases contain the same number of molecules under the same temperature and pressure.

• Example: equal volumes of molecular hydrogen and nitrogen would contain the same number of molecules under the same temperature and pressure.

6. Volume of gas (dm³) = Number of moles of gas x Molar volume
7. Room temperature and pressure (r.t.p.) = 24 dm³ mol^-1 (25°C and 1 atm)

• Example: What is the volume of 5.0 mol helium gas at s.t.p.?
• Volume of gas = Number of moles x Molar gas volume
  = 5.0 mol x 24 dm³ mol^-1
  = 120 dm³

8. Standard temperature and pressure (s.t.p.) = 22.4 dm³ mol^-1 (0°C and 1 atm)

• Example: What is the volume of 5.0 mol helium gas at s.t.p.?
• Volume of gas = Number of moles x Molar gas volume
  = 5.0 mol x 22.4 dm³ mol^-1
  = 112 dm³

9. Mass (g) = Number of moles x Molar mass
10. Number of particles = Number of moles x Avogadro constant
11. Volume (dm³) = Number of moles x Molar volume