unit 1.3 chemical calculations

• what is relative atomic mass


  average mass of that of a carbon 12 atom
• what is relative isotopic mass


  mass of an atom of an isotope relative to 1/12 a carbon 12 atom
• what is this

  mass spectrometer

  
• what are the 5 stages of the mass spec 


  -vapourisation

  -ionisaiton

  -acceleration

  -deflection

  -detection
• what happens in stage one of the mass spec 


  the sample must be gas
• what happens in stage two of the mass spec


  an electron gun collides with outer shell electrons knocking one or more electrons out of the sample

  most of the ions are made to be +1
• what happens in stage three of the mass spec


  positively charged plates repel the ions accelerating them
• what happens in stage four of the mass spec


  different ions are deflected by the magentic fields in different amounts.
• what does different amounts of deflection depend on


  • the mass of an ion. lighter ions deflect more than heavier ones
  • the charge on an ion. ions with two or more postive charges are deflected more than those with only one
• what is the symbol for mass to cahrge ratio

  m/z
• what happens in stage five of the mass spec


  the machine detects the beam of ions passinf through electrically
• what can the mass spec be used for 


  crime scene sampling

  sport drug testing
• whats the ratio of the chlorine mass spec 


  3(cl35) : 1(cl37)
• whats the ratio for Cl2 


  9(Cl35+35) : 6 (Cl35+Cl37) : 1 (CL37+37)
• what is the equation for moles 


  mass/Mr
• whats the definition of a mole


  the amount of substance which contains as many particls as there are carbon atoms in 12g of the carbon-12 isotope
• what is empirical formula 


  simplest whole number ratio of atoms of eachelement present in a compound
• example of empirical formula


  ethane:C2H4->CH2
• what is the molecular formula 


  the actual number of atoms of each element in a molecule
• whats the equation for moles at standard temperature and pressure


  if dm^3: n=v/24.5

  if cm^3: n=v/24500
• how do you work out K temperature


  C+273=K
• what is the ideal gas equation


  pV=nRT
• what do the letters mean in the equation pV=nRT

  p: pressure (Pa)

  V: volume (m^3)

  n: number of moles

  R: gas constant

  T: temperature (K)
• moles=volumexconcentration

  100
• what is stoichiometry


  • molar relationship between relative quantitites of substances taking part in reaction (numbers balancing an equation)
• what is this equation

  percentage yield

  
• what is this equation

  atom economy

  
• what are the benefits of high atom economy 


  • less waste, therefore less goes to landfill
  • saves money as less cost goes to dealing with waste
  • less chance of hazardous waste
• what are procedural errors


  due to the procedure itself (you)
• what are precision errors 


  due to inaccuracy within equipment
• whats an uncertainty


  half of the smallest possible reading
• the smaller the uncertainty the more precise the measurement
• what is the calculation for % error 


  % error= error

  reading x100
• more than one measurement increases error 2 readings = double error