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# can someone help me answer these 5 questions and figire this graph out please? Acid-Base Titration...

can someone help me answer these 5 questions and figire this graph out please?

Acid-Base Titration of a Weak Acid with a Strong Base: Determination of K. Introduction: You will be titrating a solution of a weak acid with 0.100 M NaOH, while monitoring the reaction using a pH meter. Weak acids have characteristic acid-ionization constants, K. The purpose of this lab is to use the titration to determine the value of this constant for the weak acid called “benzoic acid” (HC-H502). The reaction equation is below: HC,H,O2 + NaOH NaC-H502 + H2O The pH curve for titration of acetic acid (a weak acid related to benzoic acid) is shown below. It differs from the pH curve for a strong acid in a few key ways. pH Curve for Titration of HC HO with NaOH 2 3 2 14.00 12.00 ocas 10.00 рн 3Fquivalence Pont 8.00 Haway Point foH = akaj 6.00 eeee 4.00 998 2.00 000 000 40 on 5000 2000 1000 Wu une ol Nai Because the titration involves the creation of a salt of a weak acid, the salt itself acts as a weak base. So, unlike the titration of a strong acid, the "neutralization point" in the titration occurs at a basic pH. (The term "equivalence point" is sometimes used since the salt solution will not have a neutral pH of 7.) The equivalence point (and equivalence pH) of the titration can be determined from the pH curve by finding the curve's point of inflection. This will always correspond to the equivalence point, just as it does for titration of a strong acid.
For titration of a weak acid, the pH curve also provides a way of determining the value of the acid ionization constant. At the point on the curve corresponding to one-half of the volume of base needed to reach the equivalence point, the pH of the solution will equal the pKa oft of the acid. The pK, is related to K, the way pH is related to hydrogen ion concentration: pKa = -log K OR K. =antilog(-pK) Example: If the p for a weak acid is 3.56, then K. - antilog (-3.56) - 2.8 x 10-4.
Procedure: 1. 2. 3. I Measure 25,0 mL of benzoic acid solution into a 250-ml beaker (not a flask) using a volumetric pipet. Add 25 mL of distilled water (from your squirt bottle). Fill a buret with 0.100 M NaOH solution, taking care to remove air bubbles from the tip by dispensing a few mL's into a waste container. Adjust the reading of the buret to the 0.0 mL line. If you wish, you may mix in a few drops of phenolphthalein indicator solution into the 250-ml beaker in order to enjoy the color change that the titration will produce. (However, we will not use the color change as a basis for calculating the neutralization point.) Set up your solution for titration as your instructor suggests. Rinse the tip of the electrode with distilled water and wipe it off before transferring it to your acid solution. You need to have the pH electrode completely immersed in your acid solution throughout the titration, but the electrode should not touch the bottom during the experiment. The tip of the electrode is very fragile. Record the initial pH of the acid solution before adding any base from the buret. The value should be within a few tenths of 2.5. Add base in 1-mL increments. After each 1-mL addition, swirl to stir, then obtain a stable reading on the pH meter and record the pH to the nearest 0.1 unit. Keep track of the pH values on the report sheet. When the pH begins to rise rapidly with addition of base, add the base in 0.1 mL increments (a drop or two at a time). When the pH levels off again, add base in 1-mL increments until the pH is above 11.5 or so. Plot your pH values (Y-axis) vs the volume of base added (X-axis). Draw a smooth curve through the points. Locate the equivalence point. What is the pH at this point? Find the volume of base that corresponds to the halfway point. Record the pH at this volume of basc, and calculate the value of K, for benzoic acid. Dispose of the solutions down the sink. Answer the questions on the report sheet, and turn it in along with your titration curve. 5. 6. 7 8 9.
Acid-Base PH Report Sheet1 Total volume of Base Added pH Total volume of Base Added pH 3.27 8.0 11.99 1 3.71 9.0 12.08 2 4.15 12.15 10.0 15.0 2.5 4.32 12.34 3 4.51 3.25 4.58 3.5 4.72 4.93 I 3.75 4.0 5.13 4.1 5.24 4.2 5.38 4.3 5.57 5.88 4.6 6.86 4.7 9.54 4.8 10.30 4.9 10.79 5.0 10.90 5.2 11.08 5.3 11.19 5.4 11.28 5.5 11.35 5.75 11.46 6.0 11.57 6.5 11.74 7.0 11.85
Acid-Base pH Titration of a Weak Acid with a Strong Base Report Sheet 2 Questions 1. What volume of base was required to reach the equivalence point? 2. What is the volume at the halfway point to equivalence? 3. What is the pH at the halfway point? I 4. The answer to question 3 is also the p. of benzoic acid. Calculate the value for K. 5. Salicylic acid (HC H:03) is closely related to benzoic acid in structure, and has a p. of 2.98. Considering your data for this experiment, which is the stronger acid, benzoic acid or salicylic acid? (Hint: Think about the relationship between acid strength and K.)
pH Titration Curve for Benzoic Acid/NaOH 140 130 100 B. pH 2 D 19 110 150 Volume of NaOH (mL)

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