Chem 1212 Lab Experiment 4

Chem 1212 Lab Experiment 4 - Exploring Buffers and Buffer...

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Unformatted text preview: Exploring Buffers and Buffer Capacity Sidney Sherrill Emily Teeter Alexander T. February 21, 2011 I certify this work is my own. ______________________ Part A. Acetic Acid/Sodium Acetate Buffer Assigned pH 4.2 Mass of NaCH COO*3H O used 3.88 g Measured pH 4.1 Procedure to test buffer: Fill two beakers with 30 mL of buffer solution Add .5 mL of HCl to one beaker Record pH change Add .5 mL of NaOH to the other beaker Record pH change Equation for the reaction of buffer with strong acid, HCl:- + +-( ) CH3COO aq HClaq CH3COOHaq Cl aq Volume of Buffer Tested (mL) 30 30 Volume of HCl added (mL) 0.5 1.0 Molarity of HCl used (M) 0.5 0.5 Measured pH after acid addition 4.03 3.72 Calculated pH after acid addition 4.01 3.75 Equation for the reaction of buffer with strong base, NaOH: + - + + +( ) CH3COOHaq NaOHaq CH3COO aq H2Ol Na aq Volume of Buffer Tested (mL) 30 30 Volume of NaOH added (mL) 0.5 1.0 Molarity of NaOH used (M) 0.5 0.5 Measured pH after base addition 3.92 4.15 Calculated pH after base addition 4.35 4.48 Procedure to test control: Fill two beakers with 30 mL D.I. water Add .5 mL of HCl to one beaker Record pH change Add .5 mL of NaOH to the other beaker Record pH change Volume of control Tested (mL) 30 30 Volume of HCl added (mL) 0.5 1.0 Molarity of HCl used (M) 0.5 0.5 Measured pH after acid addition 2.17 1.75 Calculated pH after acid addition 2.08 1.78 . Volume of control Tested (mL) 30 30 Volume of NaOH added (mL) 0.5 1.0 Molarity of NaOH used (M) 0.5 0.5 Measured pH after base addition 11.71 12.02 Calculated pH after base addition 11.92 12.22 Part A. Sample Calculations 1. Mass of sodium acetate trihydrate NaCH 3 COO*3H 2 O used to make buffer = + [ -][ ] pH pKa log A HA = . assigned pH 4 2 =- =- =- .- = . pKa logKa logacetic acid Ka log1 8e 5 4 74 . = . +-. 4 2 4 74 logA 1M-. =-. 54 logA 1M-. =-. =. A 1M 10 54 288 mols Na * CH3COO 3H2O 1 L = M1V1 M2V2 ( . 288 M Na * )( )=( )(. ) CH3COO 3H2O 1 L x M 1 L =. M 00288 mols Na * CH3COO 3H2O . 136 082 g Na * CH3COO 3H2O 1 mol Na * CH3COO 3H2O =. 388 g Na * CH3COO 3H2O...
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Chem 1212 Lab Experiment 4 - Exploring Buffers and Buffer...

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