The Mole | Chemistry for Grade 11 (IGCSE) PDF Download

The Mole & the Avogadro Constant

• Chemical quantities are quantified using a unit called the mole.
• The mole, denoted as mol, is the standard unit of amount of substance in the International System of Units (SI).
• A mole of any substance contains an equivalent number of particles, whether they are atoms, molecules, ions, or other entities.
• This quantity is defined as 6.02 x 10²³ particles and is known as the Avogadro Constant.
• For instance:
  • One mole of sodium (Na) comprises 6.02 x 10²³  sodium atoms.
  • One mole of hydrogen (H₂) consists of 6.02 x 10²³  hydrogen molecules.
  • One mole of sodium chloride (NaCl) contains 6.02 x 10²³  formula units of sodium chloride.
• The mass of one mole of a substance is referred to as the molar mass.
• For elements, the molar mass equals the relative atomic mass expressed in grams.
• For compounds, it is equivalent to the relative formula mass or relative molecular mass, also measured in grams.

The Mole & Volume of Gas

Avogadro's Law explains that under the same temperature and pressure conditions, equal quantities of gases will occupy identical volumes of space.

• Avogadro's Law: This principle asserts that at consistent temperature and pressure, gases will occupy the same volume.
• Room Temperature and Pressure: One mole of any gas occupies 24 dm³ or 24,000 cm³ of space under these conditions.
• Molar Gas Volume at RTP: This term refers to the volume one mole of gas occupies at room temperature and pressure.
• RTP: Stands for "room temperature and pressure," specifically at 20°C and 1 atmosphere (atm).
• Formula Triangle: This triangle elucidates the relationship between moles of gas, volume in dm³, and the molar volume.
• Formula triangle showing the relationship between moles of gas, volume in dm³, and the molar volume:

• If the volume is given in cm³ instead of dm³, then divide by 24,000 instead of 24.
  
• Formula triangle showing the relationship between moles of gas, volume in cm³, and the molar volume.

Using the Formula Triangle

• The formula can be used to calculate the number of moles of gases from a given volume or vice versa.
• Simply cover the one you want, and the triangle tells you what to do.
  Volume = Moles x Molar Volume

Examples of Converting Moles into Volumes Table

To find the moles of a gas

• Moles = Volume ÷ Molar Volume

Examples of Converting Volumes into Moles Table