# Chemical Forums

• March 19, 2019, 12:40:30 AM
• Welcome, Guest

•

Pages: [1]   Go Down

### AuthorTopic: Polymer weight calculations  (Read 796 times) !function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="https://platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs"); (function() {var po = document.createElement("script"); po.type = "text/javascript"; po.async = true;po.src = "https://apis.google.com/js/plusone.js";var s = document.getElementsByTagName("script")[0]; s.parentNode.insertBefore(po, s);})();

0 Members and 1 Guest are viewing this topic.

#### Dugy

• Very New Member
• Mole Snacks: +0/-0
• Offline
• Posts: 2
##### Polymer weight calculations
« on: December 04, 2018, 01:43:51 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
Logged

#### mjc123

• Chemist
• Sr. Member
• Mole Snacks: +217/-9
• Offline
• Posts: 1531
##### Re: Polymer weight calculations
« Reply #1 on: December 04, 2018, 10:50:17 PM »

You need to show some effort before being given help, that is a forum rule.

Do you know any equations for molecular weight averages?
Logged

#### Dugy

• Very New Member
• Mole Snacks: +0/-0
• Offline
• Posts: 2
##### Re: Polymer weight calculations
« Reply #2 on: December 04, 2018, 11:19:01 PM »

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.
Logged

#### Borek

• Mr. pH
• Deity Member
• Mole Snacks: +1628/-395
• Offline
• Gender:
• Posts: 24861
• I am known to be occasionally wrong.
##### Re: Polymer weight calculations
« Reply #3 on: December 05, 2018, 12:59:24 AM »

Would assuming that you have 1000g sample of the polymer help?
Logged
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info, PZWT_s1

#### mjc123

• Chemist
• Sr. Member
• Mole Snacks: +217/-9
• Offline
• Posts: 1531
##### Re: Polymer weight calculations
« Reply #4 on: December 05, 2018, 02:16:46 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
Logged
Pages: [1]   Go Up

Mitch Andre Garcia's Chemical Forums 2003-Present.

Page created in 0.13 seconds with 19 queries.