Titration Lab Report

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Angelica Rodriguez 05/14/13 Period 4 Acid-Base Crime Scene Titration Introduction: Titration is a lab technique used to determine the exact concentration of an acid or base. In this laboratory experiment, the crime scene analyst will use their knowledge of acids and bases to determine the concentration of each acid found as evidence in a murder. The titration technique will be used in the investigation to neutralize each HCl acid; that of the crime scene and of the samples belonging to three suspects. In order to neutralize each acid, it must be known that when an acid and base react with one another, they neutralize and produce a solution that is not acidic or basic, but neutral. Thus, the crime scene analyst can use a known concentration of a base, 1.0 M NaOH, to neutralize the unknown concentrations of each acid found. The reaction of an acid and base is known as a neutralization reaction, where neutral water and salt are the products. Phenolphthalein indicator is a molecular substance that changes color when it comes into contact with acids and bases and will be used to show when the reaction has completely neutralized. Phenolphthalein is colorless when in an acidic solution and turns pink in a basic solution. Once enough base is added to neutralize the acid, the reaction reaches the equivalence point. The point at which the moles of base is equal to the moles of acid. The equivalence point can be used to determine the initial concentration of an acid. The goal of the titration is to get as close as possible to the equivalence point by careful addition of the base. This will ensure that the calculated acid concentration is as close to the true value as possible. Having the calculated acid concentration for each of the different acids found in the investigation will allow the crime scene analyst to identify who killed Mr. Meck by matching the molarity of the crime scene HCl acid sample to the molarity of the suspect’s acid sample.

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Procedures: 1. Goggles were put on. The following materials were obtained: · 50 mL graduated cylinder. · 50 mL burette, stand, and clamp. · 125 mL Erlenmeyer flask. · Phenolphthalein indicator. · Glass funnel. 2. The stopcock at the bottom of the burette was turned such that it was perpendicular to the tube of the burette in a closed position. 3. The burette was carefully filled near the top with the 1.0 M NaOH base. It was made sure to not go above the graduations. The initial volume of NaOH was recorded. 4. Exactly 20.0 mL from one of the acid samples was measured using a graduated cylinder. This was then poured into the Erlenmeyer flask. The flask was positioned on a white paper towel, directly beneath the burette so that when the color changed, it was easier to see. 5. 3 drops of phenolphthalein indicator was added to the acid (it stayed clear). 6. The unknown acid was titrated with the NaOH by having opened the stopcock until there was a slow stream of NaOH. 7. As the drops came out, the flask was gently swirled to make sure the coloring disappeared. Observations were recorded in the observations/notes section in Table 1. 8. It was evident when the solution was approaching neutralization because the solution became pink faster and took longer to swirl before it became clear again. 9. When this happened, the stopcock was turned very gently to the “partly open” position. Smaller, individual drops were coming from the burette one at a time instead of having a stream of NaOH. 10. As soon as the coloring did not go away and the solution stayed pink, the stopcock was immediately turned to the “closed” position. 11. The final volume of NaOH in the burette was recorded. 12. The “Total Volume (in mL) of NaOH Used” to neutralize the suspect’s acid sample was calculated and recorded in the data table. 13. The burette was refilled with NaOH and the procedure was repeated for the other 3 samples. Two trials were done for each sample. 2

Data: Table 1: Data obtained through various titration trials and the calculated molarity of HCl.

Trial Suspect