limiting reactant and percent yield

My last post on 12/10/2014 was about Stoichiometry.  A typical problem using Stoichiometry is to determine the Limiting Reactant in a situation.

A Limiting Reactant (or Reagent) is the reactant that produces the least amount of product.  A typical mathematical problem has values for two reactants – it is the chemist’s responsibility to calculate both amounts of product to determine the Limiting Reactant.

Upon producing a substance in lab, it is typical for a student to be asked to evaluate the quality of the lab result.  One typical way of performing this is calculating the Percent Yield.  This is a way to evaluate the quality of the experiment by examining the amount produced.

 
A formula for Percent Yield is:

% yield = Experimental Yield / Theoretical Yield x 100 %

Reminder, the % button is not used on the calculator for this problem.

Using Stoichiometry, a value for Theoretical Yield can be determined.  Lab results produce an Experimental Yield.  This calculation provides useful information as to the quality of lab results.

If percent yield is less than 100%, reflection/discussion would focus on how the mass was lost.  Typical answers could focus on the rinsing of the product, the quality of filtration, and an incomplete reaction.

If percent yield is greater than 100%, reflection/discussion would focus on how the mass was gained.  Not meaning to be repetitive, typical answers could also focus on the rinsing of the product, the quality of filtration, and an incomplete reaction.

This following video explains Limiting Reagent and Percent Yield and solves a few problems:

I like how he focuses on moles to figure out the Limiting Reactant.

Here are a few worksheets focusing on Limiting Reagent and Percent Yield:
 
This worksheet has several examples (and answers) with enough space between problems where it could be projected for use as a classroom lesson.  Notice that you’ll have to balance the reactions!

http://www2.palomar.edu/stem/WorkshopMaterials/Chem115/HO%205%20Limreact%20practice.pdf

 
This is several pages of problems and answers with solutions!

http://msmcraesscience.weebly.com/uploads/5/1/4/4/5144948/limiting_reagent_worksheet__14.pdf
 

This page contains several problems with space for solving the problems:

http://www.hemethigh.com/apps/download/1Q3LNrmRnm3KhN1UDFQ4vRAwjOnmPxUVUi6W46dA3VEeLJiF.pdf/Limiting%20Reactant%20Worksheet.pdf


Here are several limiting reagent / percent yield problems with answers:

http://theoakwoodschool.org/blog/kthompson/files/2011/08/Limiting-Reagent-Worksheets.pdf

 
Check out the Topic List to help you to find past Blog entries.  It can be a great help!
 

Most of you are preparing for a holiday break.  If you’re a new teacher, congratulations!  You’ve gotten this far!  And safe travelling for your holiday!


*During the holidays, buy my lab book "Chemistry on a Budget"  -- it is available for $20.54 at amazon.com or $23 at lulu.com. It will take a few weeks to get to you, so order now!

http://www.amazon.com/Chemistry-Budget-Marjorie-R-Heesemann/dp/0578129159/ref=sr_1_1?s=books&ie=UTF8&qid=1389410170&sr=1-1&keywords=chemistry+on+a+budget


http://www.lulu.com/shop/marjorie-r-heesemann/chemistry-on-a-budget/paperback/product-21217600.html


This book contains 13 labs using consumable materials purchased from local stores.  There are two versions of each lab, one with a ten-question conclusion and one with directions for a full lab report.  This way the teacher has the option!  Each lab is two pages to allow for one two-sided handout.  


Have a good holiday!  I’m taking a vacation too, but I plan to post again on January 2nd, 2015. 


Happy New Year!