(747241516) Solutions Report Sheet W16

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Questions: 1. Rob, Billy, Yulia, and Devin are each trying to make a solution that requires 30 mL of stock to be added. Rob uses a 25 mL pipette and a 5 mL pipette; Billy uses a 5 mL pipette 6 times; Yulia uses a 50 mL burette; and Devin uses a 25 mL graduated cylinder. Assuming that the only error introduced was by the variance in the glassware, determine the cumulative error for each person. Add the uncertainties of the respective equipment they use Rob used 25 mL Graduated Cylinder +/- 0.03 mL and + 5 mL pipette +/- 0.01 mL To obtain cumulative error, take the sum of the uncertainties. 25 mL +/- 0.03 mL + 5 mL +/- 0.01 mL=30 ml +/- 0.04 ml Therefore the cumulative error for rob is +/- 0.04 ml. Billy used 5 mL pipette +/- 0.01 mL 6 times To obtain cumulative error, take the sum of the uncertainties. (Same as adding 6 times) 6*(5 mL +/- 0.01 mL) = +/- 0.06 mL Therefore the cumulative error for Billy is +/- 0.06 ml. Yulia uses a 50 mL burette Burette 50 mL +/- 0.05 mL Therefore Yulia’s cumulative error is +/- 0.05 mL. Devin uses a 25 mL graduated cylinder 25 mL +/- 5% To calculated how much 5% is: 25ml*5/100=+/-1.25 ml Therefore Devin’s cumulative error is +/-1.25 ml. Pipettes 5 mL +/- 0.01 mL 0.03 25 mL +/Burette mL 50 mL +/- 0.05 mLCylinder Graduated 25 mL +/- 5%

2. Timmy is making a 4 M HCl solution in a 1 L volumetric flask. The dilution is quite exothermic. He fails to wait for the solution to cool before making it up to the mark. How would this effect the concentration of the resultant solution? Explain. If the forward reaction is exothermic, then the reverse reaction must be endothermic. As the heat is still within the solution, then the reaction has not reached an equilibrium temperature with the room. The reaction will continue to cool, the concentration of reactants and products would continue to change as it is not in equilibrium. If the forward reaction is exothermic, then the excess heat will drive the reaction in the reverse direction via le Chatelier's principle By allowing the temperature of the water to establish equilibrium with the temperature of the air, the concentration of products and reaction swill not change.

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Solution 1 8 Solution 2 8 Questions #1

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