# SPM Chemistry Form 4 Notes – Terminology and Concepts: Chemical Formulae and Equations (Part 2)

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This is the second part of the notes on Chemical Formulae and Equations that was posted on Berry Berry Easy some few days back. The first part focused on relative atomic mass, relative formula mass, relative molecular mass and the various scales from different atom types. So here we are, moving on to some tougher concepts. Let’s us get acquaintant with Mr Avogadro and see what we can further learn on this topic.

SPM Form 4 – Terminology and Concepts: Chemical Formulae and Equations (Part 2)

Berry Berry Scientist

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

Be sure to copy down all these formulae a few times on paper so that you will have a better chance recalling it in the future. Copying them onto a card to bring around will be very helpful.

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