Stoichiometry Lab – The reaction of iron with copper(II) sulfate The study of stoichiometry deals with the calculation of quantities in a chemical reaction.  How much product will be produced?  How much reactant do you need to make that much product? These are questions that can be answered by a stoichiometric calculation. When we wrote thermochemical equations, we learned that the coefficients of a balanced equation can be interpreted as mole ratios. This interpretation is central to all stoichiometry calculations, as well as this laboratory investigation. In this lab, you will perform a metal replacement reaction using solid elemental iron and aqueous copper(II) sulfate. With careful mass measurements, and then conversion to moles, you will determine whether the elemental iron forms a +2 or a +3 ion during the reaction. This is the purpose of the lab – to experimentally determine the charge of iron in the iron sulfate product. Careful mass measurements need to be taken, so that the correct relationship can be determined. Prelab question 1. Finish this reaction equation, assuming iron forms a +2 ion in iron sulfate. ___ Fe (s) + ___ CuSO4 (aq) → Prelab question 2. Finish this reaction equation, assuming iron forms a +3 ion in iron sulfate. ___ Fe (s) + ___ CuSO4 (aq) → Prelab question 3. If reaction equation 1 is correct, the moles of elemental iron reacting and the moles of elemental copper produced are in a ___:___ ratio. Prelab question 4. If reaction equation 2 is correct, the moles of elemental iron reacting and the moles of elemental copper produced are in a ___:___ ratio. Prelab question 5. Define supernatant liquid. Prelab question 6. What do iron filings look like? Describe their appearance. Procedure: 1. Mass an empty, clean 100 or 150 mL beaker. Record this mass. 2. Measure out approximately 4 grams of CuSO4 crystals into the beaker. Record the mass of the beaker + crystals exactly. Do not tare the balance. 3. Measure approximately 50 mL of distilled water in a graduated cylinder, and add to the crystals in the beaker. You do not need to record the volume of this water. 4. Heat the mixture in the beaker to just below boiling, using a hot plate. Stir occasionally with a glass stirring rod. Do not allow the liquid to boil. Heat until the crystals are completely dissolved. 5. Record the mass of a piece of weighing paper. Then mass out 1.12 grams of iron filings onto the paper. Try to get as close to 1.12 grams as you can. Take your time with this step! 6. Using beaker tongs, remove the beaker from the hot plate, and carefully add the iron filings, a little at a time, to the hot copper sulfate solution. Stir continuously. After all of the iron has been added, allow the beaker to sit for 10 minutes while the reaction proceeds. Record observations of the reaction. 7. Decant the supernatant liquid into a 250 mL beaker. Do not pour out the solid! You may observe a thin copper‐colored sheen on the surface of the liquid which does not settle out. You may ignore this while decanting. 8. Add about 10 mL of distilled water to the solid copper in the small beaker. Gently swirl the beaker, then let the solid settle to the bottom. Again decant the supernatant liquid into the 250 mL beaker. Keep the copper in the small beaker! 9. Repeat step 8 again. 10. Bring your small beaker up to the teacher desk, and add 5 mL of acetone to the beaker. Swirl and allow to stand for a few minutes. Decant off the acetone into the waste beaker provided. Repeat with another 5 mL of acetone. The acetone dissolves any remaining water and removes it from your solid copper product. 11. Gently shake your beaker to spread the copper in an even layer on the bottom of the beaker. Place the small beaker containing the solid on the tray provided by your teacher – we will let the remaining water/acetone evaporate overnight. 12. Pour the decanted liquid in the 250 mL beaker down the sink, with plenty of running water. 13. On day 2, mass your beaker containing the copper product and record in your data table.