March 19, 2024, 12:24:15 AM
Forum Rules: Read This Before Posting


Topic: Polymer weight calculations  (Read 1657 times)

0 Members and 1 Guest are viewing this topic.

Offline Dugy

  • Very New Member
  • *
  • Posts: 2
  • Mole Snacks: +0/-0
Polymer weight calculations
« on: December 04, 2018, 07:43:51 PM »
Need to work out number average and weight average of a polymer that contains two different chains. Only weight fraction and the mass of each chain is given. How can I work it out?

Mass one: 2000 g mol-1
Weight fraction: 0.5

Mass two: 250000 g mol-1
Weight fraction: 0.5

Offline mjc123

  • Chemist
  • Sr. Member
  • *
  • Posts: 2049
  • Mole Snacks: +296/-12
Re: Polymer weight calculations
« Reply #1 on: December 05, 2018, 04:50:17 AM »
You need to show some effort before being given help, that is a forum rule.

Do you know any equations for molecular weight averages?

Offline Dugy

  • Very New Member
  • *
  • Posts: 2
  • Mole Snacks: +0/-0
Re: Polymer weight calculations
« Reply #2 on: December 05, 2018, 05:19:01 AM »
I know these equations:

Number average = ΣiNiMiiNi

Weight average = ΣiNiMi2iNiMi

Where Ni is number of chains and Mi is the mass.

However the number of chains is not given.

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27624
  • Mole Snacks: +1799/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Polymer weight calculations
« Reply #3 on: December 05, 2018, 06:59:24 AM »
Would assuming that you have 1000g sample of the polymer help?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline mjc123

  • Chemist
  • Sr. Member
  • *
  • Posts: 2049
  • Mole Snacks: +296/-12
Re: Polymer weight calculations
« Reply #4 on: December 05, 2018, 08:16:46 AM »
Your equations, in terms of number fractions, are correct, but in your case equations in terms of weight fractions would be more useful.
The mass of species i is NiMi, and its weight fraction Wi is NiMi/ΣNiMi
The average equations can then be rewritten as
Number average = ΣWi/Σ(Wi/Mi)
Weight average = ΣWiMi/ΣWi

Sponsored Links