C3: Quantitative Chemistry

• What is the law of conservation of mass?


  The law of conservation of mass states that no atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants.
• Define relative atomic mass and relative formula mass


  RAM - average mass of atoms in an element taking into account masses and abundance of its isotopes, relative to ¹²C.

  
  

  RFM- sum of RAM's of all atoms in the formula.
• What is Avogadro's constant?


  The number of atoms, molecules or ions in a mole of a given substance. The value of the constant is 6.02 x 10²³.
• What is the formula that links mass, molecular mass and moles together?


  Mass = Mr x Moles
• State what we mean by a limiting reactant in a chemical reaction 


  In a chemical reaction involving two reactants, it is common to use an excess of one of the reactants to ensure that all of the other reactant is used. The reactant that is completely used up is called the limiting reactant because it limits the amount of products.
• Write down the two formulae that link concentration, mass and volume together.


  Concentration (g/dm³) = Mass (g)/Volume (dm³)

  Concentration (mol/dm³) = number of moles/volume (dm³)
• What is the molar volume of a gas at room temperature and pressure?


  1 mole of gas at room temperature and pressure occupies 24 dm³
• What is titration? 


  A technique for finding the concentration of a solution by reacting a known volume of this solution with a known concentration.
• Why is it not always possible to obtain the theoretical amount of product in a chemical reaction?

  The reaction may not go to completion because it is reversible.

  Some of the product may be lost when it is separated from the reaction mixture.

  Some of the reactants may react in ways different to the expected reaction (side reactions may occur)
• How do you work out the percentage yield of a product in a chemical reaction?


  %Yield = $\frac{ }{ }$$\frac{Actual\ mass\ of\ a\ product}{Maximum\ theoretical\ mass\ of\ product}$X 100
• What is atom economy?


  A measure of the amount of starting materials that end up as useful products.

  It is a ratio of the relative formula mass of desired product to the sum of relative formula masses of reactants.
• What is concentration?


  The amount of substance (e.g the mass) in a certain volume of a solution
• What is a mole?


  Chemical amounts are measured in moles. The mole is the unit for amount of substance. The symbol for the unit is mol.