You are here:

Chemistry (including Biochemistry)/Molar ratio fraction reduction

Advertisement


Question
Hello Dr. Jeffery Raymond,

Chemistry noob here. I'm doing research, trying to replicate a study and need to use my resources wisely.

The stated molar ratio for my desired reaction is 1/35/8

The converted volumes are more than what I would like to start with.

Can I cut the ratios all in half (0.5/17.5/4) or even a quarter (0.25/8.75/2) and still get the same reaction?

Many thanks!

Answer
As a quick answer: yes.

More detailed: the ratios you are listing are still the same as the original.  What you are talking about is the quantities I presume.  Molar ratios have nothing to do with the scale you are working at.  Below I have an example:

You want to follow a published reaction with molar ratios of 8 A to 4 B to 1 C. In the reaction they used 28 g of A and 16 g of B and 3 g of C. If you used 14g A, 8g B and 1.5g C the ratios are the same, the scale is just halved.

Even more detailed: It will be important, if the reaction is occurring in solvent, to make sure that you scale the solvent as well. Why? Chemical reactions can only occur if you have interactions between molecules.  The more molecules you have in a given volume, the more reactions you get. This means that if you have a given volume of solvent and decrease the number of reactive molecules,the reaction will go slower, possibly way slower.  A second example:

If a synthetic formula calls for 5g A and 10g B in 1 liter of solvent, and you want to do the reaction at 1/10th scale (0.5 g and 1 g respectively) you should use 1/10th the solvent to get the same effect (in this case 100 mL).  If you do not, the reaction might not occur at all, or only occur really slowly/inefficiently.  

On a side note, if you use too little solvent, you run the risk of over populating the solution with product (whatever A+B+C turns into) and having a solution that has enough product to prevent further reactions from occurring. (This is based on things like reaction kinetics and entropic requirements of the system... more advanced topics which I would be happy to talk about, but which don't seem critical to your current question)

Chemistry (including Biochemistry)

All Answers


Answers by Expert:


Ask Experts

Volunteer


Dr. Jeffery Raymond

Expertise

Materials chemistry. Materials science. Spectroscopy. Polymer science. Physical Chemistry. General Physics. Technical writing. General Applied Mathematics. Nanomaterials. Optoelectronic Behavior. Science Policy.

Experience

Teaching: General Inorganic Chemistry I & II, Organic Chemistry I & II, Physical Chemistry I, Polymeric Materials, General Physics I, Calculus I & II
My prior experience includes the United States Army and three years as a development chemist in industry. Currently I am the Assistant Director of the Laboratory for Synthetic Biological Interactions. All told, 13 years of experience in research, development and science education.

Organizations
Texas A&M University, American Chemical Society, POLY-ACS, SPIE

Publications
Journal of the American Chemical Society, Nanoletters, Journal of Physical Chemistry C, Journal of Physical Chemistry Letters, Ultramicroscopy Proceedings of SPIE, Proceedings of MRS, Polymer News, Chemical and Engineering News, Nano Letters, Small, Chemistry.org, Angewandte

Education/Credentials
PhD Macromolecular Science and Engineering (Photophysics/Nanomaterials Concentration), MS Materials Science, BS Chemistry and Physics, Graduate Certificate in Science Policy, AAS Chemical Technology, AAS Engineering Technology

©2016 About.com. All rights reserved.