quant chem

• How do you find the Ar?

  The mass number of the element on the periodic table.
• What is relative formula mass?

  Relative formula mass (Mr) is all of the relative atomic masses (Ar/ mass number) in the molecular formula added together.
• percentage mass of an element in a coumpound = Ar x number of atoms in that element / Mr of the coumpound x 100
• What is a mole?


  An amount of a substance. (6.02 x 10 power of 23)
• One mole of atoms or molecules in a substance will have a mass in grams equal to the relative formula mass (Ar / Mr )

  
  

  e.g Carbon has an Ar (mass number) of 12, so one mole of carbon weighs exactly 12g.
• What are moles measured in?

  Mol.
• number of moles = mass in grams (of an element or compound) / Mr (of the element or compound)
• In a chemical reaction, mass is always conserved.
• During a chemical reaction, no atoms are destroyed nor created, meaning there are the same number and types of atoms on each side of a reaction equation.
• If the mass seems to change, there's usually a gas involved.
• What is concentration?

  Concentration is a measure of how crowded things are.
• The amount of a substance (e.g. the mass or the number of moles)

  in a certain volume of a solution = concentration
• The more solute (the substance that is dissolved) there is in a given volume, the more concentrated the solution.
• concentration (g/dm³) = mass of solute (g) / volume of solvent (dm³)
• mass (g) = concentration (g/dm³) X volume of a solvent (dm³)
• 1 dm³ = 1000 cm³ (1 litre)