AP Lab #2: Determine Mass of Mg(OH)2 in antacid by Back Titration * Milk of Magnesia states it contains 1200 mg of magnesium hydroxide in 15 mL. We will check to see how much is actually in 15 mL. 1. Place 15 mL of Milk of Magnesia into small Erlenmeyer flask. How many grams of Mg(OH)2 “should” be in the flask? (we will pretend this amount is unknown) 2. Place 1.0 M HCl into buret and record initial amount 3. Calculate the volume of 1.0M HCl needed to react with the “assumed” mass of your sample. 4. Place 10 mL above the amount determined in step two, so that you have gone past the endpoint and now have an excess amount of HCl in your flask. 5. Place 2-3 drops of BMB indicator into flask—what color should you see and why? 6. Place your standardized NaOH in a buret and record initial amount. 7. titrate your excess HCl (created in step 4) with your NaOH. What color transition should you see with this indicator? 8. Calculate the volume of HCl that reacted with the NaOH. 9. Subtract the volume of HCl from step 8 from the total volume of HCl used, to determine the volume of HCl used to titrate the Mg(OH)2 10. Save the contents of the flask for next experiment!!! Data: Initial volume HCl NaOH Final volume Volume used for NaOH Volume used for Mg(OH)2 N/A N/A Analysis Explain and show all calculations as you work through steps 1-9 Summarize the technique of back titration Calculate % Error from your calculated mass of Mg(OH)2 and the 1200 mg from the manufacture’s label. discuss the possible experimenter errors. AP Lab #3: Determine Mass of Mg(OH)2 in antacid by Gravimetric Analysis * Milk of Magnesia states it contains 1200 mg of magnesium hydroxide in 15 mL. We will check to see how much is actually in 15 mL. 1. Start with the solution from your titration in Lab #2 2. Calculate the amount of sodium dihydrogen phosphate monohydrate is needed to react “theoretically” with 1.2 grams of magnesium hydroxide Mg(OH)2 + 2NaH2PO4 → Mg(H2PO4)2 +2 NaOH 3. Add an “excess” amount of NaH2PO4 to the solution in the flask. (Why excess?) 4. Allow the precipitate to settle to the bottom of flask. 5. Pour off excess supernate (liquid above the precipitate—only that amount that you are sure contains no precipitate. 6. prepare your filter paper (fold and tear corner) mass the paper and record. 7. filter your supernate and precipitate through the filter paper. 8. set the precipitate aside to allow to dry overnight 9. mass the paper and precipitate subtract the mass of the paper 10. calculate the mass of Mg(OH)2 from your precipitate’s mass. Data: Mass of paper Mass of paper and precipitate Mass of precipitate Analysis Explain and show all calculations as you work through steps 1-10 Summarize the technique of gravimetric analysis Calculate % Error from your calculated mass of Mg(OH)2 and the 1200 mg from the manufacture’s label. discuss the possible experimenter errors.