Friday, Oct. 12 th : A Day Monday, Oct. 15 th : B Day Agenda Finish Lab: Stoichiometry and Gravimetric Analysis In-Class Assignment: Chapter 9 review,

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Friday, Oct. 12 th : A Day Monday, Oct. 15 th : B Day Agenda Finish Lab: Stoichiometry and Gravimetric Analysis In-Class Assignment: Chapter 9 review, pg. 329-331: #1-8, 13-15, 21a, 24a, 27b, 29b, 31, 34, 37 Homework: Concept Review Chapter 9 Test/Concept Review due: Thursday 10-18/Friday, 10-19 Reminder: Late concept reviews WILL NOT be accepted!

Finish Lab: Stoichiometry and Gravimetric Analysis Get your beaker, paper towel, filter paper and dried precipitate out of the drying oven and record the total mass (#5). 1.Organizing Data Write a balanced equation for the reaction. Na 2 CO 3 (aq) + SrCl 2 (aq) 2 NaCl (aq) + SrCO 3 (s) What kind of reaction was this? Double Displacement What is the precipitate? SrCO 3 (strontium carbonate)

Finish Lab: Stoichiometry and Gravimetric Analysis 2.Examining Data Calculate the mass of the dry precipitate (#6) by subtracting the mass of the filter paper (#3) and the mass of the beaker with paper towel (#4) from the total mass of beaker, paper towel, filter paper, and dried precipitate (#5). (#6 = #5 - #3 - #4) Record the mass of the dry precipitate in table. (#6) Use the molar mass of SrCO 3 to calculate the number of moles of precipitate formed.

Finish Lab: Stoichiometry and Gravimetric Analysis 3.Examining Data Use the mole ratio from the balanced equation in question #1 to change moles SrCO 3 moles Na 2 CO 3.

Finish Lab: Stoichiometry and Gravimetric Analysis 4.Evaluating Methods Calculate the #moles of SrCl 2 that were added if there was 0.30 mol SrCl 2 in every liter of solution. Was SrCl 2 or Na 2 CO 3 the limiting reactant? Na 2 CO 3 Would this experiment have worked if SrCl 2 was the limiting reactant? No, we wouldnt be able to determine how much Na 2 CO 3 was in the vat if we had excess Na 2 CO 3 left over after the reaction.

Finish Lab: Stoichiometry and Gravimetric Analysis 5.Evaluating Methods Why was the SrCO 3 rinsed in step 11? To remove any impurities. What soluble impurities could have been on the filter paper along with the precipitate? NaCl How would the results vary if the precipitate had not been completely dry? The mass would have been greater due to the mass of the water.

Finish Lab: Stoichiometry and Gravimetric Analysis 6.Applying Conclusions Start with the #moles of Na 2 CO 3 from question #3 and use the molar mass of Na 2 CO 3 to change moles Na 2 CO 3 grams Na 2 CO 3

Finish Lab: Stoichiometry and Gravimetric Analysis 7.Applying Conclusions How many grams of Na 2 CO 3 are present in the 575 L drum? Hint: you just calculated how many grams of Na 2 CO 3 were in the 15 mL sample. Use that information as a conversion factor.

Finish Lab: Stoichiometry and Gravimetric Analysis 8.Evaluating Methods We used a 0.5M solution, which means that there was 0.795 g Na 2 CO 3 for every 15 mL (this is the theoretical yield) Use your answer from question #6 as the actual yield and calculate the percentage yield: Actual yield X 100% Theoretical Yield

Finish Lab: Stoichiometry and Gravimetric Analysis 1.Designing Experiments What possible sources of error can you identify with your procedure? Could have done multiple trials Precipitate wasnt washed thoroughly Precipitate wasnt dried thoroughly Could have put dried precipitate back in beaker, washed with distilled water, and re-filtered Errors in mass measurements

Finish Lab: Stoichiometry and Gravimetric Analysis Dont forget your reflection statement: Was your hypothesis correct? How could you minimize the sources of errors that were mentioned in the lab in future trials? Did this lab help you to understand how stoichiometry could be used outside of the lab? Complete sentences!