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Transcript
Names: ____________________________________________ Period: ______ Basic Stoichiometry PhET Lab Let's make some sandwiches! Introduction: When we bake or 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: Go to: http://phet.colorado.edu and click the following links: Play with sims…> PhET Simulations 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 Sandwiches: 1. The is a simulation of a two-reactant synthesis reaction. In this case, the reactants are either in exact stoichiometric ratios, or one reactant will be limiting, while the other will be in excess. 2. Take some time and familiarize yourself with the simulation. 3. If you have 6 pieces of bread and 4 slices of cheese, predict how many cheese sandwiches of type A you can make. Then predict how many of type B you can make. A: B: 4. Now check your predictions using the “Sandwich Shop” tab. Do the results make sense? 5. In case A, the bread could be called the “limiting reactant” while the cheese could be called the “excess reactant.” How would you define a(n): a) “limiting reactant” b) “excess reactant”? 6. What is the limiting reactant for case B and why? What is the excess reactant? 1 7. Set the reaction to a simple ratio of 2:1:1 8. Complete the table below while making tasty cheese sandwiches: Bread Used Cheese Used 5 slices 5 slices 4 slices 3 slices 6 slices Sandwiches Made Excess Bread Excess Cheese 2 sandwiches 1 slice 0 slices 3 sandwiches 4 slices Part 2: Real Chemical Reactions: Now let's work with real chemical reaction, one that creates a very entertaining BOOM! 9. What is the mole ratio for the reaction of hydrogen and oxygen to produce water __ H 2 __ O2 __ H 2O 10. Complete the table below while making water H2O from hydrogen H2 and oxygen O2: Hydrogen Molecules H2 4 molecules Oxygen Molecules O2 4 molecules 7 molecules 6 molecules 9 moles Water Molecules H2O Excess H2 Excess O2 4 molecules 0 molecules 0 molecules 4 moles 1 moles 0 moles 8 moles Notice that the labels changed from molecules to moles. This does not change the relationship between reactants and products. A balanced chemical reaction can be interpreted in terms of the number of molecules or moles reacting. The only difference is that a mole Data can be divided into fractions of a mole while a molecule cannot be divided. That is, we Stamp could work with 0.5 or 0.75 of a mole of reactant rather than a whole-number multiple of a mole. The coefficients of a balanced equation show, in terms of moles, how much of each substance is involved in the reaction. Stoichiometry is the study of the relationships of quantities of substances in a chemical reaction. Obtain a data stamp before proceeding to the following section. 2 Consider the reaction: FeCl3 (aq) + 3NaOH (aq) → Fe(OH)3 (s) + 3NaCl (aq) This balanced equation tells us: one mole of iron(III) chloride reacts with three moles of sodium hydroxide to produce one mole of iron(III) hydroxide and three moles of sodium chloride. Several mole ratio fractions are possible: or or You recognize these as conversion factors. The first relates moles of the two reactants; the second and third relate one of the reactants to one of the products. 11. Use dimensional analysis to complete the table below. Show your work in the space below. Have your work stamped before proceeding to the next section. Moles of FeCl3 Moles of NaOH Moles of Fe(OH)3 Moles of NaCl Data Stamp 0.50 moles 1.5 moles 3 12. Now try producing ammonia, a very important chemical in industry and farming. 13. What is the mole ratio for the production of ammonia? __ N 2 __ H 2 __ NH 3 14. Complete the table below: Moles N2 Moles H2 3 moles 6 moles 6 moles 3 moles 1.5 moles (requires a 4.5 moles(requires a calculation) calculation) Moles NH3 Excess N2 Excess H2 4 moles 2 moles 0 moles 15. Combustion of hydrocarbons like methane CH4 produce two products, water and carbon dioxide CO2. 16. What is the mole ratio for the combustion of methane? __ CH 4 __ O2 __ CO2 __ H 2O 17. Complete the table below: WATCH FOR FRACTIONS mol CH4 mol O2 mol CO2 mol H2O Excess mol CH4 4 mol 4 mol 3 mol 6 mol 2 mol Excess mol O2 4 mol 3 mol 0 mol 18. The BEST PART: Challenge your lab partner to the hidden. Lab Partner 1: ______________________ Level 1 Score: _______ Lab Partner 2: ______________________ Level 1 Score: _______ 0 mol . Begin at Level 1with nothing Data Stamp 4 Basic Stoichiometry Post-Lab Homework Exercises 1. Load the "Reactants, Products, and Leftovers" simulation and work through each of the levels of the Game! At http://phet.colorado.edu/ or googling "phet." You may have to download or update Java on your computer. Show your work for all calculations. Remember: Labels, units, sig figs and cancellation! 2. For the reaction P4 6Cl2 4 PCl3 , determine how many moles of chlorine Cl2 would be needed to react with 4.0 moles of phosphorus P4 to entirely use up all the phosphorus. 4)________________ 3. If 3.00 moles of P4 reacted with 22.0 moles Cl2 according to the above reaction, determine: a) How many moles PCl3 are produced a)________________ 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 2 Al 3Br2 2 AlBr3 . 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 2.5 moles of excess Br2 behind. 6. Now assume 3.0 moles Al and 4.0 moles Br2 react. a) How much (in moles) AlBr3 gets produced? a)________________ b) Which chemical must be the excess reactant? b)________________ c) Which chemical is the limiting reactant? c)________________ d) If all the limiting reactant gets used up, how much of the excess reactant is left? d)________________ 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 __ Na __ Cl2 __ NaCl (left for you to balance). 7)________________