1. Plan for Wed, 8 Oct 08 Turn in Exp 1 Post-lab and Exp 2 Pre-lab Today: Exp 2, Limiting Reactant Purpose: –To determine the actual and theoretical yields of the reaction: 2AgNO 3 (aq) + BaCl 2 (aq)  2AgCl(s) + Ba(NO 3 ) 2 (aq) –To determine the limiting reactant using chemical tests and dimensional analysis. Read the experimental procedure carefully!!

2. Tips for success Avoid touching the AgNO 3 solution. It will turn your skin black!! If you get HNO 3 on your skin, rinse with plenty of water. DO NOT put hot plates away hot!! –If they are not cool enough to put away at the end of lab, you may leave them on your lab bench. USE PEN!! WRITE CLEARLY!! NEVER put a spatula, etc into a reagent bottle. NEVER return unused reagent to the reagent bottle. Any unused reagent must be placed in the waste container. DO NOT start your vacuum filtration until I have checked your set up! DO NOT overfill the liquid waste containers. Let me know if they are getting too full and I will replace them. PUT EVERYTHING AWAY!!

3. BaCl 2.2H 2 O(s) Ba 2+ Cl - AgNO 3 (aq) Ag + NO 3 - BaCl 2 (aq) + AgNO 3 (aq) Ag + NO 3 - Ba 2+ Cl - 2AgNO 3 (aq) + BaCl 2 (aq)  2AgCl(s) + Ba(NO 3 ) 2 (aq) Solid silver chloride precipitates out of solution. Barium and nitrate ions are left in aqueous solution.

4. NO 3 - Ba 2+ Cl - NO 3 - Ba 2+ Cl - Isolate supernatant What happens if you put AgNO 3 in the supernatant? What happens if you put BaCl 2 in the supernatant? Nothing. There are no Ag + ions for the chloride to react with, so you should observe no changes in the solution. Precipitate forms. There are excess Cl - ions for the silver cations to react with, so you should observe the formation of a solid. What can we conclude from testing the supernatant like this? Since there was excess Cl - in the supernatant for the Ag + to react with to form AgCl(s), this means that BaCl 2 was the reactant present in excess. Therefore, AgNO 3 (aq) was the limiting reagent.

5. Determining Limiting Reagent Take care when determining the number of moles of BaCl 2 (aq). The mass of the barium chloride you weigh out includes water molecules that you must account for when calculating the MM. Ionic formula: BaCl 2.2H 2 O(s) 1 mol BaCl 2.2H 2 O 1 mol BaCl 2 2AgNO 3 (aq) + BaCl 2 (aq)  2AgCl(s) + Ba(NO 3 ) 2 (aq) ? mol AgCl = x g BaCl 2.2H 2 O g BaCl 2.2H 2 O 1 mol BaCl 2.2H 2 O 1 mol BaCl 2 2 mol AgCl MM of BaCl 2.2H 2 O The amount of BaCl 2.2H 2 O(s) you weigh out

6. Determining Limiting Reagent To determine the number of moles of AgNO 3, use the molarity and the volume. 1000 mL AgNO 3 1 L AgNO 3 2AgNO 3 (aq) + BaCl 2 (aq)  2AgCl(s) + Ba(NO 3 ) 2 (aq) ? mol AgCl = x mL AgNO 3 1 L AgNO 3 0.1 mol AgNO 3 1 mol AgNO 3 2 mol AgCl Molarity of AgNO 3. Write down the EXACT concentration!! Volume of AgNO 3 you measure.

7. Determining Actual Yield You must dry your precipitate in the Gooch filter until next week before you take the new mass. This means you will not be able to calculate Actual Yield until next week’s lab. SO, unlike your other lab reports, this lab report will be due at the END of lab, rather than at the beginning. This will give you time to mass your Gooch filter + precipitate and determine the actual yield.