Basic Stoichiometry PhET Lab rvsd 2/2011 Let’s make some sandviches! _ Introduction: When we bake/cook something, we use a specific amount of each ingredient. Imagine if you made a batch of cookies and used way too many eggs, or not enough sugar. YUCK! In chemistry, reactions proceed with very specific recipes. The study of these recipes is stoichiometry. When the reactants are present in the correct amounts, the reaction will produce products. What happens if there are more or less of some of the reactants present? Procedure: Load the “Reactants, Products, and Leftovers” simulation by going to http://phet. olorado. edu/ or googling “phet. ” You may have to download or update the version of Java on your computer. Complete each exercise on your own. Remember to use proper units and labels. PhET Simulations _ Play with the Sims _ Chemistry _ Reactants, Products, and Leftovers_ If a yellow bar drops down in your browser, click on it and select “Allow Blocked Content” Part 1: Making Sandviches: _ The _ is a simulation of a two-reactant synthesis reaction.
In this case, one reactant will be limiting, while the other will be in excess. Take some time and familiarize yourself with the simulation.
Set the reaction to a simple mole ratio of 2:1:1_ Complete the table below while making tasty cheese sandwiches: Bread Used Cheese Used Sandwiches Made Excess Bread Excess Cheese 5 slices 5 slices 2 sandwiches 1 slice 3 slices 4 slices 3slices 2 sandwiches 0 slices 1 slice 5 slices 2 slices 2 sandwiches 1 slice 0 slices 6 slices 7 slices 3 sandwiches 0 slices 4 slices Part 2: Real Chemical Reactions: _ _Now let’s work with real chemical reaction, one that creates a very entertaining BOOM! What is the mole ratio for the reaction of hydrogen and oxygen to produce water?
The mole ratio is 2 to1 to 1_ Complete the table below while making water H2O from hydrogen H2 and oxygen O2: Hydrogen Molecules H2 Oxygen Molecules O2 Water Molecules H2O Excess H2 Excess O2 4 molecules 4 molecules 2 molecules 0 molecules 2 molecules 7 molecules 6 molecules 3 molecules 1 molecule 3 molecules 8 molecules 4 molecules 4 molecules 0 molecules 0 molecules 9 moles 8 moles 4. 5 moles 0 moles 3. 5 moles 9 moles 4 moles 4 moles 1 moles 0 moles 4. 0 moles 2. 5 moles 2 moles 0 moles .5 moles 1. 5 moles .75 moles 1. 5 moles 0 moles 0 moles _Notice that the labels changed from molecules to moles.
This does not change the mole ratio, as a mole is simply a large number of molecules. How many molecules is a mole? 6. 023 x 10^23 _________________ Now try producing ammonia, a very important chemical in industry and farming. What is the mole ratio for the production of ammonia? Ratio is 1:3:1_ Complete the table below: Moles N2 Moles H2 Moles NH3 Excess N2 Excess H2 3 moles 6 moles 2 moles 1 mole 0 moles 6 moles 3 moles 1 mole 5 moles 0 moles 4 moles 12 moles 4 moles 2 moles 0 moles 1. 5 moles 4. 0 moles 1 mole .5 moles 1 mole Combustion of hydrocarbons like methane CH4 produce two products, water and carbon dioxide CO2.
What is the mole ratio for the combustion of methane? Ratio is 1:2_ Complete the table below: WATCH FOR FRACTIONS mol CH4 mol O2 mol CO2 mol H2O Excess mol CH4 Excess mol O2 4 mol 4 mol 2 mol 4 mol 2 mol 0 mol 3 mol 6 mol 3 mol 6 mol 0 mol 0 mol 2 mol 4 mol 2 mol 4 mol 0 mol 0 mol 3 mol 6 mol 3 mol 6 mol 0 mol 0 mol The BEST PART: _. Your First Score:_______lvl__ Your Best Score:________lvl__ Basic Stoichiometry Post-Lab Exercises rvsd 2/2011 Vocabulary:Before your begin, please define the following. The following site has a good chemistry glossary – http://antoine. frostburg. du/chem/senese/101/index. shtml Limiting Reactant:The reactant that limits the amount of product produced in a chemical reaction. Excess Reactant: A reactant that remains after a chemical reaction because there is nothing it can react with. Synthesis Reaction: Two or more chemical species combine to form a more complex product. Combustion Reaction: A chemical reaction between a fuel and an oxidizing agent that produces heat. Mole Ratio: Ratio between the amounts in moles of any two compounds involved in a chemical reaction. Diatomic Molecule: A molecule that contains only two atoms.
Mole: SI unit for amount of substance, defined as the number of atoms in exactly 12 g of carbon-12. Hydrocarbon: Organic compounds that contain only hydrogen and carbon. Actual yield: The measured amount of product produced in a chemical reaction. Theoretical Yield: The amount of the product obtained when all of the limiting reagent react. Percent Yield: Equals expiremental yield divided by theoretical yield times 100%. Stoichiometry: A branch of chemistry that deals with the relative quantities of reactants and products in chemical reactions. . For the reaction _determine the correct lowest mole ratio. 2. For the reaction _determine the correct lowest mole ratio. 3. For the reaction_, determine how many moles of chlorine Cl2 would be needed to react with moles of phosphorus P4 to entirely use up all the phosphorus. 3)________________ 4. If 5 moles of P4 reacted with 22 moles Cl2 according to the above reaction, determine: a) How many moles PCl3 are produceda)________________ b) How many moles of P4 are left in excess after the reaction (if any)b)________________ c) How many moles of Cl2 are left in excess after the reaction (if any)c)________________ _
In reality, reactants don’t have to react in perfect whole-numbers of moles. In a two-reactant synthesis reaction, usually one reactant gets entirely used up (and determines how much product is made), even if that means using fractions of a mole of reactant. For instance, when solid, metallic aluminum Al and red, liquid bromine Br2 are brought together, they make a white solid according to the reaction _. If 5. 0 moles of aluminum Al was reacted with 10 moles bromine Br2, all five moles of aluminum would react, with only 7. 5 moles bromine. (2:3 mole ratio) This would produce only 5. 0 moles of AlBr3, leaving 2. moles of excess Br2 behind. 5. Now assume 3 moles Al and 4 moles Br2 react a)Which chemical is the limiting reactant? a)________________ b)Which chemical must be the excess reactant? b)________________ c)How much (in moles) AlBr3 gets produced? c)________________ SHOW WORK HERE: d)If all the limiting reactant gets used up, how much of the excess reactant is left? d)________________ SHOW WORK HERE: 7. What is the maximum amount (in moles) of NaCl that can be produced from 4. 5 moles of Na and 3. 5 moles of Cl2 according to the reaction _(left for you to balance). SHOW WORK HERE: 7)________________
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