272_Exp4BC

At the equivalence point the first acidic proton has

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Unformatted text preview: r knowledge about acid- base equilibrium and the behavior of buffers to predict not only the amount of NaOH necessary to reach each equivalent point, but also the pH at each equivalence point. First equivalence point: Starting with 25.0 mL of 0.0628 M C2H2O4, (1) predict the amount of 0.100 M NaOH necessary to reach the first equivalence point and (2) predict the pH at this point. (1) At the equivalence point, the number of moles of hydroxide added is equal to the number of moles of protons in the solution. We can calculate the number of moles of OH- needed because we know the number of moles of protons in our acid sample: " 0.0628 mol C2 H 2O4 %" 1mol H + % + 0.025 L C2 H 2O4 $ '$ ' = 0.0015 7 mol H # &#1mol C2 H 2O4 & L volume of acid acid concentration mole ratio number of moles of H + € (Note that we are carrying an extra significant figure to avoid rounding errors.) We know the concentration of the standardized NaOH solution, so we can predict the amount of NaOH we would need to add to reach this equivalence point: # 1 mol OH − &# 1 mol NaOH &# & L 0.0015 7 mol H + % ( = 0.0157 L = 15.7 mL + (% − (% $ 1mol H '$ 1 mol OH '$ 0.100 mol NaOH ' € moles of H+ mole ratio mole ratio concentration of NaOH volume from above at equivalence needed point (2) To predict the pH once this volume of NaOH has been added, we need to identify all of the species present that will...
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This lab report was uploaded on 04/06/2014 for the course CHEM 272 taught by Professor Dr.brooks during the Summer '08 term at Maryland.

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