Number Average Molecular Weight

Example numbers: 2,2,2,2,3,3,3,7,7
  4(2) + 3(3) + 2(7)     8 + 9 + 14     31
  -------------------- = ------------ = ---- = 3.444
      4 + 3 + 2              9           9
From this it should be obvious that the numbers 2,3, and 7 correspond to "molecular weights" which are represented by the variable M(i), and the numbers 4,3 and 2 correspond to "number average counts", which are represented by the variable N(i).

The symbol i is just an index. For the above data we would have
M(1)=2, N(1)=4
M(2)=3, N(2)=3
M(3)=7, N(3)=2

Weight Average Molecular Weight

Example numbers: 2,2,2,2,3,3,3,7,7
      2       2       2
  4(2)  + 3(3)  + 2(7)     16 + 27 + 98    141
  ---------------------- = ------------ = ----- = 4.548
   4(2) + 3(3) + 2(7)           31          31
It should be clear that M(i) and N(i) are the same as for the Number Average Molecular Weight example.



Z Average Molecular Weight

Example numbers: 2,2,2,2,3,3,3,7,7
      3       3       3
  4(2)  + 3(3)  + 2(7)      32 + 81 + 686    799
  ---------------------- = --------------- = --- = 5.666
      2       2       2         141          141
  4(2)  + 3(3)  + 2(7)

Last Update- May 24, 1995- wld