Chemistry test 2

• Formulae of compounds

  • the formula of a molecular compound tells you the type and # of each atom in each molecule
  • the formula of an ionic compound tells you the type and ratio of ions in the compound
• Valency of an element

  the # of electrons its atoms lose, gain and share
• Molecular Formula


  is a formula that shows the actual # of atom and electrons making up the compound
• Empirical Formula 


  is a formula that shows the simpler # ratio of atoms and electrons making up the compound
• Relative atomic mass (Ar)

  is the average mass of the isotopes of an element compound
• Relative molecular mass (Mr)


  is the sum of relative atomic masses
• Two laws of chemistry

  • the total mass does not change during a chemical reaction
  • elements always react in the same ratio, to form given compounds
  • total mass of reaction = total mass of products
• The mole


  is the amount of substance that contains 6.02 × 10^23 particles
• • The SI unit for the mole is mol.
  • 6.02 × 10^23 = Avogadro's Constant
  • number of moles (n) = mass (g)/ molar mass (g/mol)
• Limiting reagent/reactant


  is the reactant that is completely used up in the reaction
• Excess reagent


  will remain at the end of the reaction ( it's not totally used up)
• Avogadro's Law


  1 mole of every gas has the game volume at a given temp. and pressure.

  At room temp. and pressure, this volume is 24dm^3
• • 1 ml = 1 cm^3
  • 1000 ml = 1000 cm^3 = 1 L = 1 dm^3
• • number of moles= Volume/Volume taken up by 1 mole of gas
  • n= V/ Vm
• Concentration of a Solution


  is the amount of solute in grams/ moles, that is dissolved in 1 dm^3 of solution

  Units: ( mol / dm^3 ) or ( g / dm^3 )
• • concentration (mol/dm^3) = amount of solute (mol)/ Volume of solution (dm^3)
  • c=n/V