Chemistry C3: The mol concept, chemical formula and equation

• Carbon 12 atom is chosen as the standard to calculate relative mass because it can be handled easily, exists as a solid
• RAM: atom

  RMM: molecule

  RFM: ionic compund
• No. of particles in 1 mole of substance equals to Avogadro constant
• no. of particles= n×NA
• n=no. of particles÷NA
• n=mass of substance÷molar mass
• n=volume÷molar volume
• STP: 22.4 dm³

  Room condition: 24 dm³
• Find the no. of moles and no. of molecules in 7g of Nitrogen gas.

  1. Find the molar mass
  2. Calculate no. of moles
  3. Calculate no. of molecules
• How many grams of.....?


  1. Find no. of moles
  2. Mass of ....
• A chemical formula: chemical representation using letters to represent an element and numbers to represent number of atoms
• Empirical formula: chemical formula which shows the simplest ratio of the no. of atoms for each element in a compound.
• Molecular formula: chemical formula which shows the actual no. of atoms for each element in a molecule.
• How to find the molecular formula?

  Let molecular formula = (empirical formula) n
• How to find empirical formula?

  1. Mass
  2. No. of moles
  3. Ratio of element
  4. Simplest ratio
  5. Write empirical formula
• The most reactive metal is K
• Reactivity series

  K

  Na

  Ca

  Mg

  Al

  C

  Zn

  H

  Fe

  Sn

  Pb

  Cu
• Less reactive metal react slowly with oxygen gas
• How to determine the empirical formula of metals?

  There are 2 method:

  1. Combustion of metal in air
  2. Reduction of metal oxide by Hydrogen gas
• Combustion of metal in air: Al, Mg, Zn
• Reduction of metal oxide by Hydrogen gas: PbO, FeO, CuO
• Why we need to lift the lid when the exp of combustion?

  Reason: to allow air enter into crucible for completed combustion.
• Why we need to use sandpaper to clean the metal ?

  Reason: to remove oxide layer
• Drying agent: anhydrous calcium chloride, concentrated sulphuric acid
• What reactans can be used to make Hydrogen gas?

  Answers: Zinc/Magnesium and HCl
• Why Mg and Zn not using method of reduction of metal oxide using Hydrogen gas?

  Reason: Mg and Zn is more reactive than hydrogen
• NO = nitrogen monoxide
• Qualitative: reactans and products

  Quantitative: no. of moles
• A+B --> C+D

  From the above equation, we can conclude that:

  A/B = A react with B

  A/C = A produce C

  C/A = C is produce by A