Answer Happy

Acid Dissociation Constant, Ka Acetic Acid, HC,H,O,, is a weak acid that dissociates according to his equation: HCHO(aq) —— H*(aq) + CHO, (a p) In this experiment, you will experimentally determine the dissociation constant, K, for acetic acid, starting with solutions of different initial concentrations. OBJECTIVES In this experiment, you will . Gain experience mixing solutions of specified concentration. Experimentally determine the dissociation constant, K., of an cid. Investigate the effect of initial solution concentration on the e uilibrium constant. MATERIALS computer Vernier computer interface Logger Pro Vernier pH Sensor 100 ml. beaker 200M HC HỒ wash bottle distilled water Chemistry with Computers Experiment 27 100 ml. volumetric flask - pipets pipet bulb PRE-LAB 1. Write the equilibrium constant expression, Ka. for the dissociat en of acetic acid, HC₂H₂O₂. (Use Space 3 in the Data and Calculations table of this experim: st.) Figure 1 2. You have been assigned two different HC,H,O, solution concerations by your teacher. Determine the volume, in ml, of 2,00 M HC,H,O, required to separe cach. (Show your calculations and answers in Space 4 of the Data and Calculation table.) 27-1
Experiment 27 PROCEDURE 1. Obtain and wear safety goggles. 2. Put approximately 50 mL of distilled water into a 100 ml. volumetric flask. 3. Use a pipet bulb (or pipet pump) to pipet the required volan e of 2.00 M acetic acid (calculated in Pre-Lab Step 2) into the volumetric flask. CAUTION: Use care when handling the acetic acid. I can cause painful burns if it comes in contact with your skin or gets into your eyes. Fill the flask with distilled water to the 100 mL mark. To prevent overshooting the mark, use a wash bottle filled with distil od water for the last few ml. Mix thoroughly. 4. Use a utility clamp to secure a pH Sensor to a ring stand as shown in Figure 1. 5. Connect the probe to the computer interface. Prepare the computer for data collection by opening the file "27 Acid Dissociation Ka" from the Chenistry with Computers folder of Logger Pro. 6. Determine the pH of your solution as follows: • Use about 40 ml. of distilled water in a 100 ml. beaker to inse the pH Sensor. Pour about 30 ml. of your solution into a clean 100 ml. be sker and use it to thoroughly rinse the sensor. • Repeat the previous step by rinsing with a second 30 ml. portion of your solution. . Use the remaining 40 ml. portion to determine pH. Swirl the solution vigorously. (Note: Readings may drift without proper swirling!) Record the n easured pH reading in your data table. . When done, place the pH Sensor in distilled water. 7. Repeat the procedure for your second assigned solution. PROCESSING THE DATA 1. Use a scientific calculator to determine the [H'Jeg from the H values for each solution. 2. Use the obtained value for [H'leq and the equation: HC,H,O_(aq) →H(aq) + C₂H₂ (aq) to determine [C₂H₂O₂ leq and [HC₂H₂Oleq 3. Substitute these calculated concentrations into the K, expression you wrote in Step 1 of the Pre-Lab. 4. Compare your results with those of other students. What effe at does initial HC₂H₂O₂ concentration seem to have on Ka? OBSERVATIONS 27-2 Chemistry with Computers
DATA TABLE 1. Assigned concentration 2. Measured pH 3. K, expression 4. Volume of 2 M acetic acid 5. [Ha 6. [C₂H₂O₂ Jaq 7. [HC₂H₂O₂lea 8. K calculation 0.50 2.47 [CH₂ coo] [H] [CH₂COOH] + 100ML V₂ = ? Ka MI.5. [CH₂ COD Jea M₂. ZM ml. V₂= 25ml V₂ = 5ml mL PH = -log [HH] =2.47 PH = -loy [4²] =2.78 [H*Jeq = 5.39 × 10 ™M] [H+] eq=1.66×10 ³M M M (3.34 x 10-32 (6.5-3.39x10³) Ku=2-314x10 0.10 2.78 [CH3COO-][+] [CH3COOH] -5 M V₁ z 100ml M +3.39 × 10 m [clt₂000]eq=1.667151 M mir.f m2=2w M M M Ka - (1166×10-3)= 10.1-1..66×10 Ka-2.80210-5M
PROCESSING THE DATA 1. Use a scientific calculator to determine the [H'Jeq from the H values for each solution. 2. Use the obtained value for [H*]eq and the equation: HC,H,O,(aq) H(aq) + C₂H30, (aq) to determine [C₂H₂O₂ leq and [HC₂H₂O₂leq - 3. Substitute these calculated concentrations into the Ka expression you wrote in Step 1 of the Pre-Lab. 4. Compare your results with those of other students. What effe ct does initial HC₂H₂O₂ concentration seem to have on Ka?