Experiment 8 - Chapa 1 Christine Chapa Olivia Naworol TA...

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Christine ChapaOlivia NaworolTA: Jessica StokesApril 11, 2016Weak Acids and BuffersIntroductionIn chemistry, a buffer is described as the capacity of a system to resist chemical change, and it is mostly in reference to the ability to resist change in pH to indicate the acidity of alkalinity of a solution.1When the buffer reaches a certain point in the solution and resists attempts to change its pH, it is commonly known as the buffering capacity.2The analytical techniques that were involved in this experiment required the distinguishing of the buffering capacities of the strong base and strong acid added to the buffer solutions, as well as identifying the equivalence and half-equivalence points for each separate trial. The Henderson-Hasselbach equation was used to find the theoretical pH of the buffer solution by taking the theoretical value of Kafor acetic acid and adding it by the log of each concentration component. In addition, the percentage error for acetic acid and buffered solution were calculated independently. For acetic acid, the percent error was identified by subtracting the measured Kafor acetic acid from the theoretical value, and then divided by the theoretical value of acetic acid. The percentage error for the buffered solution was calculated using the same method, except using its own measured Kavalue. The following experiment will involve the titration of a weak acid and buffer. Sodium hydroxide will be titrated with an acetic acid solution to identify the equivalence and half-equivalence points of the titration, followed by the titration of NaOH and HCl with a buffered acetic acid solution.ExperimentalIn part A of the experiment, acetic acid was titrated with NaOH. The first step in this process involved the preparation of a 0.05M acetic acid solution from a 0.5M acetic acid stock solution. Using a 50 mL graduated cylinder, 45 mL of deionized water was added to a 150 mL beaker and labeled as “0.05M acetic acid”. Five milliliters of the 0.5M acetic acid was added to the labeled beaker using a 10 mL graduated cylinder and then stirred with a glass-stirring rod. Afterwards, a 0.05M NaOH solution was prepared from a 0.5M NaOH stock solution. In a clean 250 mL beaker, 90 mL of deionized water was added, along with 10 mL of the 0.5M NaOH. Before titration began, the burette was conditioned with two portions of 10 mL of deionized water, followed by two portions of 5-10 mL of the prepared NaOH solution. After the burette was conditioned, a plastic funnel was placed on top of the burette and filled with the remaining NaOH solution that was previously prepared. The burette was secured to the clamp above the magnetic stir plate and the initial volume of the burette was recorded. In a clean 250 mL beaker, 50 mL of deionized water was added as well as a stir bar. A 10 mL volumetric pipette was used to obtain 10 mL of the prepared acetic acid solution. The beaker was then placed on top of the magnetic stir plate, beneath the tip of the burette, and gently

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