## Question

###### Discussion: 1. Compare the molarities of the three samples of vinegar that you analyzed. The "precision"...

Discussion: 1. Compare the molarities of the three samples of vinegar that you analyzed. The "precision" of your titration technique is how similar the three values are (the closer the values, the better your precision). 2. Compare the average molarity you obtained to the molarity of the acetic acid in the vinegar as listed on the vinegar bottle. What could account for any differences between these values? 3. How do your pH values compare to the pH determined using the pH paper? There will probably be a difference between these 2 pH values. What could account for this difference? rgn phth late ACy Hy O,-H+NaoH + Nat+ H20 Potasium KHP PhendPiyla le acidolerles PH=7-5pnk Base Reed lalakons Vinegeracchie add males KHP= moles NaoH Amde Valuun CL) &wlet NADA Ganvect toll)

ladi da s ni bobulani ad bluod 2-1eqala o (hog CHM 1100 Experiment #7-Titration of Vinegar Week #2- Titration of Vinegar Introduction: Vinegar is an aqueous solution of acetic acid, HC H3O2, which is a weak acid. In water, acetic acid can dissociate into a proton (H) and the acetate ion (C2H302) according to the following equation: Equation A HC H3O2 H2O H0 C2H3O2 In this experiment we want to determine the exact concentration of acid (H) in vinegar. To do this, we will neutralize every H with an equal amount of hydroxide ions (OH) according to the equation: Equation B Но +OH 2H,0 Thus, we will titrate the unknown number of protons in the vinegar with a known number of hydroxide ions. We will use an indicator solution, bromothymol blue, to tell us when we have neutralized every proton. Bromothymol blue changes color as the pH of the solution changes. Bromothymol blue is yellow in acid (pH <7), green at neutral pH (pH- 7), and blue in basic solution (pH> 7). Suggested Procedure: 1. Using a 10 mL graduated cylinder, measure out exactly 5.0 mL of vinegar and put this volume into an Erylenmeyer flask. Record the precise volume in your notebook. Estimate the pH of the vinegar using pH paper. 2. Add about 4 drops of bromothymol blue to the vinegar. 3. Put 25.0 mL of your NaOH solution into a 25 mL graduated cylinder. Record the initial volume (with the proper number of significant figures) in your notebook. 4. Using a Pasteur pipette, slowly add the NaOH dropwise to the vinegar until the vinegar solution turns green and stays green 30 seconds. Be sure to continuously swirl the flask to mix the vinegar and the NaOH. If you perform this experiment on a piece of white paper, it will be easier to see the color change. Return any NaOH in your Pasteur pipette to the graduated cylinder. Record the precise final volume of NaOH remaining in the graduated cylinder in your notebook. 5. Determine how many mL of your NaOH that it took to reach the green end point. 6. Repeat steps 1-5 with two additional 5.0 mL samples of vinegar. 7. Store your NaOH. All other solutions may be poured down the drain.

## Answers

Let vinegar contains 5% acetic acid (according to commercial one).

i.e. The molarity of acetic acid = 5 g/(60 g/mol) = 0.083333 mol or 83.333 mmol (in 100 mL)

Now, the millimoles of acetic acid in 5 mL vinegar = 5 mL * 83.333 mmol/100 mL = 4.167 mmol

Now, the volume of NaOH (let's say 1 M) required to reach the green end point = 4.167 mmol/(1 mmol/mL) = 4.167 mL

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