the bottle containing the KHP to the desiccator. Clean three 250-mL Erlenmeyer flasks with soap and water. Rinse the Erlenmeyer flasks with 5-10 mL portions of distilled water. Label the Erlenmeyer flasks as 1, 2, and 3. Weigh three samples of KHP between 0.6 and 0.8 g using the analytical balance in the back of the laboratory room, one for each of the Erlenmeyer flasks. Record the exact weight of each KHP sample to the nearest 0.0001 g. Add 100 mL of distilled water to KHP sample 1. Add 2-3 drops of phenolphthalein indicator solution. Swirl to dissolve the KHP sample completely. Record the initial reading of the NaOH solution in the buret to the nearest 0.01 mL, remembering to read across the bottom of the curved solution surface (meniscus). Begin adding NaOH solution from the buret to the sample in the Erlenmeyer flask, swirling the flask constantly during the addition. If your solution was prepared correctly, and if your KHP samples are of the correct size, the titration should require at least 20 mL of NaOH solution. As the NaOH solution enters the solution in the Erlenmeyer flask, streaks of red or pink will be visible. They will fade as the flask is swirled. Eventually the red streaks will persist for a longer and longer time. This indicates the approach of the endpoint of the titration. Begin adding NaOH one drop at a time, with constant swirling, until one single drop of NaOH causes a permanent pale pink color that does not fade on swirling. Record the reading of the buret to the nearest 0.01 mL. Repeat the titration of the remaining two KHP samples. Record both initial and final readings of the buret to the nearest 0.01 mL. Given the molecular weight of potassium hydrogen phthalate is 204.2 g/mol, calculate in your results the number of moles of KHP in samples 1, 2, and 3. From the number of moles of KHP present in each sample, and from the volume of NaOH solution used to titrate the sample, calculate the concentration of NaOH in the titrant solution in moles per liter. The reaction between NaOH and KHP is of 1:1 stoichiometry. If your three values for the concentration differ by more than 1%, weigh out an additional sample of KHP and repeat the titration. This part of the experiment must be completed before you can continue. Use the average concentration of the NaOH solution for subsequent calculations for the unknowns.
Analysis of a Vinegar Solution Vinegar is a dilute solution of acetic acid and can be effectively titrated with NaOH using the phenolphthalein endpoint. Clean and dry a small beaker, and obtain 25-30 mL of the vinegar solution. Cover the vinegar solution with a watchglass to prevent evaporation. Clean three 250 mL Erlenmeyer flasks, and label as samples 1, 2, and 3. Rinse the flasks with small portions of distilled water. Rinse a 5 mL pipet with a sample of the vinegar solution and discard the rinse. Pipet a
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- Spring '17
- Chemistry, Sodium hydroxide, Erlenmeyer flask, KHP, sodium hydroxide solution