Potentiometric Titration of Strong Acid and Vinegar

Potentiometric Titration of Strong Acid and Vinegar

CHEM 1021-03

Professor Dr. Heather B. Miller

Petru A. Hadarau

April 10, 2017

Purpose

The purpose of this experiment was to monitor and determine the equivalence points of acid-base titrations. From the resulting graphs we will be able to determine the concentration of acidic solutions as well as the acid-ionization constant. It is Hypothesis that the titration curve will be very visible and obvious.

Materials and Methods

Part 1- Calculate how many grams of NaOH are needed to make 500mL of a .15 M solution of NaOH. Add 3.0-3.5 g of solid NaOH into 500 mL of deionized water, and stir until it dissolves. Weight 0.65-0.75 of solid KHP, add 100 mL of D.I water stir until is dissolved, add 3 drops of phenolphthalein indicator. Use NaOH to titrate the KHP solution.

Part 2- Add 25 mL of unknown HCl, add 75 mL of distilled water and stir. Add 1-2 mL of the titrant and record the pH using pH meter, keep adding until pH is 2.5, then add until you reach a pH of 12. Repeat the titration one more time.

Refill the buret with standardized NaOH, dispense 5.00 mL  aliquot of vinegar into a clean and dilute with 100 mL of D.I water, Add 1-2 mL of your titrant and allow solution to stabilize, record your pH. Keep adding until the pH reaches 6.8, then add 0.2-05 until ph level is 12. Repeat this titration one more time.

Results

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As shown in table 1.0 the results of our titration curve for the strong acid, the first trial the reaction hit its equivalent point between 24-27 mL while during the second trial the equivalent point was at 27-29 mL. The average of our first trials and the total average is also shown in table 1.0. [pic 4]

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As shown in table 1.1 the results of our titration curve for the vinegar, the first trial the reaction hit its equivalent point between 18.5-19 mL while during the second trial the equivalent point was at 18.5-19 mL. The average of our first trials and the total average is also shown in table 1.1.

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Discussion

The purpose of this this lab was to titrate a strong acid and vinegar, collect the data and graph in order to create a good titration curve. By analyzing the graph from the experiment we can determine where the equivalence point, the moles of the titrant and analyze are equal to one another. At the midpoint of the solution, the pKa value is equal to the pH value. Our pKa for the strong acid was 4.2 while our Ka was 5.01*10^-5. For our vinegar our pKa was 1.9 and our Ka was .0125. The hypothesis was that the strong acid will be more acidic than vinegar and as we can analyze from the data above it was proven to be right.The Ka value is a quantitative measure of the strength of an acid in solution. According to this lab the Ka of the strong acid was way smaller than the Ka of the vinegar therefore, the HCl seems to be a stronger acid than vinegar was, also if we examine the graph, the equivalent points for the strong acid was 26 mL while the vinegar was only 18.5 mL of titrant. Even so if we only physically analyze the graph without going in depth we can observe that the vinegar curve reacted faster and quicker to reach its equivalent point while the strong acid took more time to reach its equivalent point.