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Unknown KHP Determination 

Diego J. Gavia

Chemistry 116AL – W06

Tuesday-Thursday 6-10 PM

Sample ID:  KHP ??

Group Members: Jannice

Experimental Methods: 

            The unknown KHP sample and 3.0599 grams of KHP standard were added to individual weighing bottles. Both weighing bottles containing the samples were placed in an oven at a temperature of 110 ºC for two hours to completely dry the samples. After two hours, the unknown KHP sample and KHP standard were place in the desiccator to prevent the sample from absorbing moisture. Two liters of distilled water were boiled for 10 minutes to remove any carbon dioxide. To speed up the cooling process, the boiled distilled water was place in a bath consisting of cold water and ice. Once the distilled water was cooled to room temperature, 3.59 mL of 50% NaOH were carefully added to 960 mL of distilled water by not disturbing the precipitates at the bottom of the bottle, which resulted in a solution of ~0.1 M NaOH. The resulting solution was transferred to a polyethylene bottle. The other liter of water was added to a glass labeled bottled. A 50 mL burette was clean and filled the ~0.1 M NaOH solution. Three titration blanks were prepared in Erlenmeyer flasks by adding two drops of phenolphthalein as an indicator and 100 mL of distilled water to each. The blanks were titrated until the solutions turned pale pink by the ~0.1 M NaOH solution. Three standard KHP solutions were prepared by adding .7301g KHP, .7101g KHP and .7310g KHP accordingly along with two drops of phenolphthalein and 50 mL of distilled water. The standard KHP solutions were titrated until the solutions turned pale pink by the ~0.1 M NaOH solution. Finally, three unknown KHP solutions were prepared by adding 1.0263g unknown, .6084g unknown and .8116g unknown accordingly along with two drops of phenolphthalein and 50 mL of distilled water. The unknown KHP solutions were titrated until the solutions turned pale pink by the ~0.1 M NaOH solution.

Results: 

Table 1. Blank titration results.

                        Volume of Water        Total Volume of NaOH solution

Trial 1                      100 mL                                            .60 mL

Trial 2                      100 mL                                            .40 mL

Trial 3                      100 mL                                            .60 mL
 

Final Result

(.533 mL of NaOH solution)
 

Table 2. KHP standard titration results. 

                        Volume of Water        Mass      Total Volume of NaOH solution

Trial 1                      50 mL                .7301g                   48.95 mL

Trial 2                      49 mL                .7101g                   47.73 mL

Trial 3                   48.7 mL                .7310g                   49.21 mL
 

Final Result

(.07367 ± .002113732 M NaOH )

 
Table 3. KHP unknown titration results.

                         Volume of Water        Mass      Total Volume of NaOH solution

Trial 1                      50 mL               1.0263g                   41.13 mL

Trial 2                   46.5 mL                 .6084g                   24.64 mL

Trial 3                      50 mL                 .8116g                   32.99 mL

Final Result

(59.41 ± 2.02 % wt KHP)

Discussion: 

            To determining the mass percentage of an unknown KHP sample, several steps as well as calculations were required. Boiling distilled water for this experiment was crucial, since carbon dioxide had to be removed. Nonetheless, while the distilled water was cooling in the ice bath, carbon dioxide could have tainted the water sample. The KHP samples had to be dried at 110 ºC to remove all the moisture but in reality the KHP samples were exposed to moisture while weighing them. The titration process was difficult and decisive. Since NaOH reacts with glass, solutions of NaOH stored in glass equipment such as burettes and beakers for long periods of time were not dependable and had to be disposed of. Therefore, working quickly and working carefully were key in this experiment.