STOICHIOMETRY
Major PointsBalancing Equations
Conversions: - grams to moles / moles to grams (use molar mass) - atoms to moles / moles to atoms (use Avogrado's number) - moles of element x to moles of element y (use molar ratio) Steps for stoichiometry (see below) Finding Excess and Limiting Reagents Finding Percent Yield Steps for Stoichiometry1. Identify what you're given and the target unit/compound
2. Balance the equation you are given 3. Set up the problem (convert to moles if necessary) 4. Use mole ratio(s) to convert from compound to compound 5. convert to grams of the desired compound if necessary |
Example ProblemsBALANCING THE EQUATION (answer with the ratio)
__Fe(NO3)3 + __NaOH ----> __Fe(OH)3 + __ NaNO3 Answer: 1:3:1:3 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GRAMS TO MOLES You have 46.23kg Fe. Find the number of moles Fe. Answer: 827.8 mol Fe ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ MOLES TO MOLES (using the balanced equation from above, solve this problem) 2 mol Fe(OH)3. Find the # of moles of NaOH needed to form the compound. Answer: 6 mol NaOH Find the # of moles of NaOH to react with 5.50 mol Fe(NO3)3 Answer: 16.5 mol NaOH ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ MOLES--->MOLES--->GRAMS (given this balanced equation, answer the question.) 2H2 + O2 --> 2H2O. If you have 4.96 mol of H2, how many grams of H2O will be produced? Answer: 89.4g H2O ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ GRAMS-->MOLES-->MOLES-->GRAMS Balance the equation. How many grams of I2 will you need if you have 3.50 grams of Al? Al(s) + I2 ---> AlI3 Answer: Balanced equation is 2:3:2. You will need 494 grams of I2 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Using the previous now-balanced equation, determine the excess reagent and the limiting reagent of the equation. You will have 45.3g of Al and 45.3 g of I2. Answer: Excess reagent= Al, Limiting reagent= I2 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ Magnesium hydroxide reacts with hydrobromic acid (HBr) to produce Magnesium Bromide and water. You start the reaction with 1.0 gram of HBr. A- what is the limiting reactant? B- If you collected .55 grams of magnesium bromide, what is the percent yield of the reaction? Answer- limiting reactant is MgOH2. The percent yield of the reaction is 50%. |
Online Resources
Finding the limiting or excess reagent: http://www.chem.tamu.edu/class/majors/tutorialnotefiles/limiting.htm
Theoretical and percent yield: http://danielleamorim.tripod.com/
Theoretical and percent yield: http://danielleamorim.tripod.com/
Video Resources
Percent Yield: http://www.youtube.com/watch?v=LQN9lH9WAVQ
Basics of Stoichiometry (By Me!): https://vimeo.com/59017336
Basics of Stoichiometry (By Me!): https://vimeo.com/59017336
Activity resources
Balancing Act! Game: http://education.jlab.org/elementbalancing/
Soluble or Insoluble Worksheet (With Answers!): http://chemistry.bd.psu.edu/halmi/wks4b1.pdfIf you can't get the .pdf to come up, save linked file as download and go to your downloads. It should be there!
Soluble or Insoluble Worksheet (With Answers!): http://chemistry.bd.psu.edu/halmi/wks4b1.pdfIf you can't get the .pdf to come up, save linked file as download and go to your downloads. It should be there!