Buffers Pre-Lab Assignment

Buffers Pre-Lab Assignment Purpose: Many titrations will be conducted on a weak acid and buffer with the previous titrations techniques in Experiment 7. First, an acetic acid solution will be prepared and titrated with sodium hydroxide in order to determine the equivalence and half equivalence points of the titration. Additionally, a buffered acetic acid solution will be produced to titrate with NaOH and hydrochloric acid to demonstrate what happens when buffering after adding a strong acid or base, to which the buffering capacity of the buffered acetic acid solution will then be experimentally deduced. Objectives: 1. Conduct titrations on multiple solutions of acetic acid and buffered acetic acid with a 50 mL burette and a pH probe. 2. Create a second derivative plot and determine the equivalence point for each titration with Logger Pro 3.14 3. Find the experimental pKa of acetic acid and calculate its value of Ka. 4. Find the buffering capacity of the buffered acetic acid solution Compounds: 0.5 M acetic acid 0.5 M NaOH 0.5 M HCl sodium acetate trihydrate deionized H2O Materials: Vernier LabQuest 250 mL beaker 150 mL beaker 100 mL beaker 50 mL graduated cylinder 10 mL graduated cylinder 10 mL volumetric pipette 50 mL burette Chemical Hazards: Vernier pH sensor plastic funnel pipette bulb analytical balance stir plate magnetic stir bar burette clamp 3 prong/utility clamp Acetic acid, HCl, and NaOH are corrosive to flesh meaning it can cause serious burns Physical Hazards: Broken glassware Step stool slipping when using the burette Equation: 1) NaOH (aq) + CH3COOH(aq) -> NaCH3COO(aq) + H2O(l) 2) NaCH3COO(aq) + NaOH (aq) -> NaCH3COO (aq) + H2O (l) 3) NaCH3COO(aq) +HCl(aq) -> CH3COOH (aq) + NaCl(aq) Outline: Acetic acid vs NaOH - - Prepare acetic acid solution - Add acetic acid and water to beaker Prepare NaOH solution - Add water and NaOH to beaker LabQuest - Turn it on - “Sensors” - “Data Collection” - Mode: “events with entry” - Name: “volume” Condition burette - Secure burette to ring stand and close stopcock and add water - Remove from stand and invert many times with finger over open part - Reclamp and drain - Repeat 4 times twice with water twice with NaOH With funnel fill until the 0mL line Position burette correctly Start collecting data with pH probe - “collect” Click keep for 0 and enter initial volume - Proceed with titration: Add NaOH until close to pH 6 When stabilized ‘keep’ and enter current volume At pH 6 keep adding small amounts of NaOH ‘Stop” and clean pH probe and dispose of reaction - - - Change partners and repeat for total 3 times Buffered Acetic acid vs NaOH - Prepare buffered acetic acid solution - Add solid sodium acetate trihydrate, water, and acetic acid to beaker Prepare NaOH solution - Add water and NaOH to beaker Dispose of NaOH in burette and recondition and fill burette back up Rinse pH probe and submerge in acetic acid solution Start collecting data, keep 0 and enter intital volume Add NaOH until pH changes dramatically After change, keep adding small amounts of NaOH Stop and dispose of reaction Buffered Acetic Acid vs HCl - Prepare HCl solution - Add HCl and water to beaker Discard previous NaOH from burette and recondition burette Fill burette with HCl solution Add water, HCl buffer and stir on stirring plate Rinse pH probe “Collect” and begin titration Add HCl until pH changes dramatically Keep adding even after changes ‘Stop’, dispose, and turn off lab quest