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biochemlab1 - 1 pH AND BUFFERS Julia Quartermain Date Jan...

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pH AND BUFFERS Julia Quartermain Date: Jan. 21, 2010 Date performed: Jan. 14, 2010 Introduction: The purpose of this lab was to familiarize our selves with the pH of some common liquids and to observe a buffer in action. The preparation of a buffer and what effects buffers have on acidic and basic solutions will be studied. A buffers aim is to resist the changes in pH, which is the negative log of the hydrogen ion concentration. By using a pH meter and a variety of different pH papers we will be able to determine the pH of several common solutions. Experimental: The first part of the lab consists of several measurements of the pH of different solutions using two varieties of pH paper and a pH meter. First wide range pH paper was used to indicate the range in which the pHs of the following solutions fit; tap water; deionised water; 0.1M HCl; 0.1M NaOH; 1% Na 2 CO 3 in water; and 1% NaHCO 3 in water. The six solutions were used in 10mL aliquots and a glass-stirring rod was used to dab a drop of each onto six pieces of wide range pH paper. These six pH measurements were then used to select the appropriate narrow range pH paper based the their pH values. A more accurate measurement of the pH was then taken for each of the six solutions. Finally the pH of each of the six solutions was measured using a pH meter. In the second part of lab a buffer solution was prepared from one mL of 0.1M sodium acetate; one mL of 0.1M acetic acid; and eight mL of deionised water. The pH of this acetate buffer solution was measured using wide and narrow pH paper. Approximately 20 mL of 0.1M HCl was added to a buret set up in a stand. Bromophenol blue was added to 10 mL of deionised water as and indicator and was titrated with the 0.1M HCl in the buret drop by drop until the blue solution turned yellow. The initial and final volumes of HCl used were recorded. Next, the HCl was then used to titrate the acetate buffer solution containing the bromophenol blue indicator. This 1
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