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How many grams of water will 5 grams of Oxygen produce? 5 grams of Hydrogen? Tonight's Homework: Finish Lab Report pg 259 Numbers 2-10

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Lab Report Purpose Procedure Data Calculation (mass salt+dish)–(mass dish) Results Questions/Conclusion

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Limiting Reactant Percent Yield www.pedagogics.ca

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A Word About Mass Conversions Calculating the mass-mass conversion between compounds in a chemical reactions is not something that will disappear now that we are moving on

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A Word About Mass Conversions Calculating the mass-mass conversion between compounds in a chemical reactions is not something that will disappear now that we are moving on If you can not calculate conversions from mass-mass, mass –mole, mole-mole…..

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A Word About Mass Conversions Calculating the mass-mass conversion between compounds in a chemical reactions is not something that will disappear now that we are moving on If you can not calculate conversions from mass-mass, mass –mole, mole-mole….. You Will Fail

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Consider the following reaction 2 H 2 + O 2 2 H 2 O

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Reactants are combined in perfect proportions 6 molecules 3 molecules

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In reality this never happens 6 molecules 3 molecules

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Consider 4 molecules 4 molecules + leftover oxygen 3 molecules

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Consider LIMITING REACTANT Amount of PRODUCT is determined by limiting reactant EXCESS REACTANT

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Consider 6 molecules 4 molecules + leftover hydrogen 2 molecules

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Consider EXCESS REACTANT Amount of PRODUCT is determined by limiting reactant LIMITING REACTANT

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Given 24 grams of O 2 and 5.0 grams of H 2 determine the mass of H 2 O produced. 2 H 2 + O 2 2 H 2 O the mass of H 2 O produced will be determined by the limiting reactant - do TWO calculations

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Two Calculations

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Calculate the amount of product each reactant would produce

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Two Calculations Calculate the amount of product each reactant would produce In this case convert grams of O 2 to grams of H 2 O

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Two Calculations Calculate the amount of product each reactant would produce In this case convert grams of O 2 to grams of H 2 O Then convert grams of H 2 to grams of H 2 O

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Two Calculations Calculate the amount of product each reactant would produce In this case convert grams of O 2 to grams of H 2 O Then convert grams of H 2 to grams of H 2 O Whichever will produce the least amount of water will be the limiting reactant

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calculation for 24 grams of O 2 24 g O 2 2 H 2 O18.0 g mol -1 32.0 g mol -1 1 O 2 = 27 g of H 2 O

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calculation for 24 grams of O 2 24 g O 2 2 H 2 O18.0 g mol -1 32.0 g mol -1 1 O 2 = 27 g of H 2 O calculation for 5.0 grams of H 2 5 g H 2 2 H 2 O18.0 g mol -1 2.0 g mol -1 2 H 2 = 45 g of H 2 O

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calculation for 24 grams of O 2 24 g O 2 2 H 2 O18.0 g mol -1 32.0 g mol -1 1 O 2 = 27 g of H 2 O calculation for 5.0 grams of H 2 5 g H 2 2 H 2 O18.0 g mol -1 2.0 g mol -1 2 H 2 = 45 g of H 2 O O 2 is the LIMITING REACTANT and determines the amount of product H 2 is the EXCESS REACTANT (some would be left over)

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How much hydrogen gas would be left over? To calculate, first determine how much reacts with all of the oxygen

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How much hydrogen gas would be left over? To calculate, first determine how much reacts with all of the oxygen given 24 grams of O 2 24 g O 2 2 H 2 2.0 g mol -1 32.0 g mol -1 1 O 2 = 3.0 g of H 2 3.0 g of H 2 reacts so

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How much hydrogen gas would be left over? To calculate, first determine how much reacts with all of the oxygen given 24 grams of O 2 24 g O 2 2 H 2 2.0 g mol -1 32.0 g mol -1 1 O 2 = 3.0 g of H 2 3.0 g of H 2 reacts so 5.0 g – 3.0 g = 2.0 g of hydrogen remains

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Re-Cap What steps do you take to convert the mass of one substance to the mass of another in a chemical reaction? What steps do you take to determine which substance will be the limiting reactant in a reaction?

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Percent Yield 2 AuCl 3 +3 Pb 3 PbCl 2 + 2 Au Enoch the Red, an alchemist, wants to try to turn lead into gold (which you can’t do chemically). He finds that mixing lead with an unidentified compound (gold III chloride) actually produces small amounts of gold. The reaction is as follows:

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Percent Yield 2 AuCl 3 +3 Pb 3 PbCl 2 + 2 Au Enoch reacts 14.0 g of gold III chloride with excess lead metal. What would be the maximum, THEORETICAL yield of this reaction?

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Percent Yield 2 AuCl 3 +3 Pb 3 PbCl 2 + 2 Au Enoch reacts 14.0 g of gold III chloride with excess lead metal. What would be the maximum, THEORETICAL yield of this reaction?

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Percent Yield 2 AuCl 3 +3 Pb 3 PbCl 2 + 2 Au Enoch reacts 14.0 g of gold III chloride with excess lead metal. What would be the maximum, THEORETICAL yield of this reaction? given 14.0 g of AuCl 3 14.0 g AuCl 3 2 AuCl 3 196.97 g mol -1 303.5 g mol -1 2 Au = 9.09 g Au

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Percent Yield Enoch recovers only 1.05 g of gold from the reaction. This could be for many different reasons some product was lost in the recovery process the reaction did not go to completion the AuCl 3 is not pure

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Percent Yield the percentage yield expresses the proportion of the expected product that was actually obtained.

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Baking Soda Lab In the baking soda lab, the formula for the reaction should be : NaHCO 3 + HCl ------> NaCl + CO 2 + H 2 O Balance the equation Find the molar masses of NaHCO 3 & NaCl. Use the mass from you lab (mass baking soda) to calculate theoretical yield of NaCl

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What do we need to calculate the percent yield now that we have the theoretical yield?

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Lab Reports The discussion questions were designed to have you calculate a theoretical yield and calculate a percent yield from your actual result.

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Finding Limiting Reactant Determine the theoretical yield based on the masses of each reactant Whichever produces the least amount is your limiting reactant

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Finding Theoretical Yield Use the mass-mass conversion from the limiting reactant to the desired product The product produced by the mass of the limiting reactant is the theoretical yield

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Finding Percent Yield Use theoretical yield from your mass-mass (gram-gram) calcualtions Make sure you have the correct limiting reactant Divide the actual yield (given) by the theoretical yield (from calculation)

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