c4- chemical calculations

• What is the conservation of mass

  No atoms are lost or made during a chemical reaction - mass of products is equal to mass of reactants
• what is an ion

  Atom with a charge - metals form positive Ions and non metals form negative ions
• what is the charge on a metal ion often 


  the same as the group number on the periodic table
• Which non metals are positive

  Hydrogen - H+

  Ammonium - NH4+
• overall charge of ionic compounds

  charges on the ions cancel out to leave an overall charge of zero
• What is relative atomic mass

  The average mass of the isotopes of hat element weighted to take into account to abundance of each isotope
• what is relative formula mass

  • sum of the relative atomic masses of the atoms in the numbers shown in the formula
  • no units
  • never involves big number
• symbol for relative atomic mass


  A$^r$
• Steps for relative formula mass

  1. identify how many of each element there is
  2. Times the relative atomic mass by the number of each element
  3. Add all together
• percentage by mass of an element equation

  (total relative atomic mass of the atoms in an element/relative formula mass of compound) x 100
• Number of moles equation (element)

  Mass/relative atomic mass
• number of moles (compound)

  mass/relative formula mass
• rearranged equation to calculate mass

  Mass = number of moles x relative formula mass
• What is avagadros constant

  1 mole - 6.02 x 10$^{23}$
• Calculate moles of atoms

  • calculate how many atoms in the molecule
  • Number of atoms is equivalent to number of moles in the molecule
• calculate number of atoms in one mole of hydrogen chloride

  • 1 mole of HCL contains avogadros constant of molecules
  • 2 times 6.02 x 10$^{23}$
  • 1.204 x $10^{24}$
• Calculate number of atoms in a given mass

  • find number of moles - mass/relative atomic mass
  • Times number of moles by avagadros constant to find number of atoms
• number of atoms in a compound

  • work out relative formula mass of compound (add atomic masses)
  • find number of moles - mass/relative formula mass
  • times number of moles by avagadros constant to find number of molecules
  • times number of molecules by number of different compounds to find number of atoms
• Finding mass of products when given mass of reactant

  • calculate molar ratio
  • Find number of moles of reactant - mass/relative atomic mass
  • Find mass Of product - number of moles = mass/relative atomic mass
• What is concentration

  • the mass f a solute in a given volume of solution
  • A solute is a chemical dissolved in a solvent
  • Water is often a solvent
• concentration equation

  concentration = mass/volume
• Concentration equation

  Concentration = mass/volume