272_Exp4BC

5 calculate the volume at which you anticipate

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Unformatted text preview: L of a ~0.500 M solution? Show your work. 5. Potassium hydrogen phthalate, KHC8H4O4, is a primary standard acid that reacts with sodium hydroxide on a 1:1 molar basis. A sample of the acid weighting 0.5893 g was titrated with NaOH, requiring 22.49 mL to reach the end point. Calculate the molar concentration of the NaOH solution. 6. Determine the pH of 25.0 mL of a 0.100 M H3PO4 solution. 7. In this experiment you will be titrating a 25.0 mL aliquot of ~0.100 M H3PO4. Assume that the titrant is 0.200 M NaOH. Use the example in the experiment background to help you calculate the volume of NaOH necessary to reach the first equivalence point. Calculate the pH of the solution at this point. 8. Repeat the calculations in problem 7 above for the second equivalence point. 9. Identify the species present at the 1st, 2nd, and 3rd equivalence points. 10. Why don’t we use phenolphthalein in this experiment? MATERIALS & METHODS Preparation of the NaOH titrant Among the gases dissolved in the water used in the lab is carbon dioxide (CO2). The stockroom has removed the CO2 from distilled water by displacing the gas with N2. There are labeled carboys in the lab filled with degassed, distilled water. Use this water to prepare both the titrant and analyte samples. Stock NaOH solutions will be prepared in these flasks from 30%, by mass, commercial concentrated NaOH. Work in teams of four 1. Make 250 mL of a ~0.200 M solution of NaOH starting with a 30% by weight NaOH solution. Use a 250 mL volumetric flask and the degassed,...
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