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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)

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Plan for Wed, 8 Oct 08

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  1. 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: 2AgNO3(aq) + BaCl2(aq)  2AgCl(s) + Ba(NO3)2(aq) To determine the limiting reactant using chemical tests and dimensional analysis. Read the experimental procedure carefully!! Plan for Wed, 8 Oct 08

  2. Tips for success • Avoid touching the AgNO3 solution. It will turn your skin black!! • If you get HNO3 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!! • NEVERput 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 NOToverfill the liquid waste containers. Let me know if they are getting too full and I will replace them. • PUT EVERYTHING AWAY!!

  3. BaCl2.2H2O(s) AgNO3(aq) BaCl2(aq) + AgNO3(aq) Cl- NO3- Cl- NO3- Ba2+ Ag+ Ag+ Cl- Cl- Cl- Ba2+ Ag+ Ag+ NO3- Ba2+ Cl- NO3- Ba2+ Cl- Cl- 2AgNO3(aq) + BaCl2(aq)  2AgCl(s) + Ba(NO3)2(aq) Barium and nitrate ions are left in aqueous solution. Solid silver chloride precipitates out of solution.

  4. Cl- NO3- Cl- NO3- NO3- NO3- Isolate supernatant Ba2+ Ba2+ Ba2+ Cl- Ba2+ Cl- What happens if you put BaCl2 in the supernatant? Nothing. There are no Ag+ ions for the chloride to react with, so you should observe no changes in the solution. What happens if you put AgNO3 in the supernatant? 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 BaCl2 was the reactant present in excess. Therefore, AgNO3(aq) was the limiting reagent.

  5. 1 mol BaCl2 1 mol BaCl2.2H2O 2 mol AgCl 1 mol BaCl2.2H2O g BaCl2.2H2O 1 mol BaCl2 Determining Limiting Reagent • Take care when determining the number of moles of BaCl2(aq). • The mass of the barium chloride you weigh out includes water molecules that you must account for when calculating the MM. • Ionic formula: BaCl2.2H2O(s) 2AgNO3(aq) + BaCl2(aq)  2AgCl(s) + Ba(NO3)2(aq) ? mol AgCl = x g BaCl2.2H2O The amount of BaCl2.2H2O(s) you weigh out MM of BaCl2.2H2O

  6. 1 L AgNO3 0.1 mol AgNO3 2 mol AgCl 1000 mL AgNO3 1 L AgNO3 1 mol AgNO3 Determining Limiting Reagent • To determine the number of moles of AgNO3, use the molarity and the volume. 2AgNO3(aq) + BaCl2(aq)  2AgCl(s) + Ba(NO3)2(aq) ? mol AgCl = x mL AgNO3 Volume of AgNO3 you measure. Molarity of AgNO3. Write down the EXACT concentration!!

  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.

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