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

  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 6.02x10^23
• What is the formula that links mass, molecular mass and moles together?

  Mass = Mr x Moles
• What is meant by a limiting reactant in chemical reactions?

  The reactant that is used up
• What are the two formulas that link concentration, mole/mass and volume together?

  Concentration (g per dm^3) = mass (g)/volume (dm^3)

  Concentration (mol per dm^3) = nr of moles/volume (dm^3)
• 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)
• What is the percentage yield?

  % yield = (actual mass of a product x 100) / maximum theoretical mass of product
• What is atom economy?

  A measure of the amount of starting materials that end up as useful products. It is the ratio of the relative formula mass of desired product to the stum of relative formula masses of reactants