Buffer Lab[1] - Christina Wong AP Chemistry, 4th Hour...

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Christina Wong AP Chemistry, 4 th Hour 2/17/2010 Buffers Keep The Balance Lab I. Purpose Our purpose in this lab was to investigate what buffers are made of, and how they maintain the delicate pH balance needed for life and health. This lab consists of two parts. In the first part, we used carbonated seltzer water as a source of carbonic acid to prepare a model biological carbonic acid-bicarbonate buffer that is useful as the neutral pH solution. The effects of added acid or base on the pH and buffer capacity would be examined. In the second part, we used two phosphate buffers that reflected the psychological role of buffers within cells. The pH of the buffer solutions and the pH range over which phosphate buffers are effective will be measured. II. Procedure Part A: Model Carbonate Blood Buffer We began by setting up six medium-size test tubes in a rack and labeled them 1-6. We then used this table to measure and add up indicated volumes of solutions into each test tube: Table 1 Test Tube Number 1 2 3 4 5 6 Solution Carbonic Acid (Reference) Model Carbonate Blood Buffer Water (Control) Model Carbonate Blood Buffer Water (Control) Sodium Bicarbonate (Reference) Seltzer water (mL) 4 2 0 2 0 0 0.1 M Sodium bicarbonate (mL) 0 2 0 2 0 4 Distilled water (mL) 0 0 4 0 4 0 After this, we added 5 drops of bromthymol blue indicator solution to each test tube 1-6. We mixed and then recorded the initial color of each solution, and then measured the initial pH of each solution, using a narrow-range pH paper, pH 6.0-8.0. Then, we used a Beral-type pipet to add 0.1 M hydrochloric acid solution dropwise to the biological buffer
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solutions in test tubes 2 and 3. With that, we counted the number of drops of HCl required to change their colors to the same shade of yellow as the carbonic acid reference solution we used, and recorded this data. Next, we used a pipet to add 0.1 M sodium hydroxide solution dropwise to the biological buffer solution in test tubes 4 and 5, and counted the number of drops of NaOH required to change their colors to the same shade of blue as the sodium bicarbonate reference solution in test tube 6, and recorded this data. Part B: Biological Phosphate Buffers We obtained two large test tubes and labeled them A and B. Using clean graduated cylinders, we added 12 mL of NaH 2 PO 4 solution and 3 mL of Na 2 HPO 4 solution to test tube A (this was “Buffer A”), and 8 mL of NaH 2 PO 4 solution and 8 mL of Na 2 HPO 4 solution to test tube B (this was “Buffer B”). With that done, we took a microscale 24- well reaction plate, and filled selected wells of it with 1.5 mL of distilled water (the control), phosphate buffer A, or phosphate buffer B, according to a layout plan. For each filled well we added three drops of universal indicator solution, and then recorded the colors that resulted from this, for the water control and buffer solutions A and B. Using a piece of narrow-range 6.0-8.0 pH paper, we estimated the initial pH of each
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Buffer Lab[1] - Christina Wong AP Chemistry, 4th Hour...

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