lab 3 write up

lab 3 write up - Atinuke Omolara Biology 2112 Lab 5:10-8:00...

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Atinuke Omolara Biology 2112 Lab 5:10-8:00 pm Instructor: Erin Walsh Due: October 8, 2008 Title: Buffering capacity and pH Introduction: Chemists and biologist use the pH scale to measure the acidity of a solution but specifically, the concentration of [H + ] or hydrogen ions in a solution. As an equation, the pH can be expressed as -log [H + ] . Since concentrations of hydrogen ions are very small, the pH scale was designed to make comparisons of [H + ] easier by using a logarithmic scale. With pH values one can define a solution acidic, basic or neutral. A neutral solution is one with the pH of 7, a solution with a pH less than 7 is considered acidic and one with a pH greater than 7 is considered basic. The concept to remember here is that as the pH decreases the acidity increases and as the pH increases, acidity decreases. The stability of pH is very important in plants and animals. To regulate the pH a buffer is used, which regulates a system against the change in pH. A buffer is a mixture made of a weak acid and its conjugate base so that it can neutralize a strong acid or base by acting as both. In this lab monobasic potassium phosphate (KH 2 PO 4 ) and dibasic potassium phosphate (K 2 HPO 4 ) as our salt and acid will be used, respectively, to make a buffer. An ideal buffer would be a mixture of KH 2 PO 4 and K 2 HPO 4 because it satisfies the criteria of a buffer as the salt will react with the acid and the acid with the base, neutralizing the system. This hypothesis will be proven by using an instrument used to measure the pH of a solution is called a pH meter . The electrode on the meter is sensitive to hydrogen ions, so if [H + ] are present, it turns the voltage energy into a pH. Several solutions will be made and titrated with an acid or a
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base in order to determine the buffer range and capacity. The pH meter will be used throughout this experiment to measure the pH change over a period of acid/base additions to the solutions. Materials and Methods: In order to test the task at hand, the following materials and methods were used: -Dipotassium phosphate (K 2 HPO 4 ) -Potassium phosphate (KH 2 PO 4 ) -Distilled water -0.1M HCl -0.1M NaOH -pH meter -stir plate and magnetic stir bar -two burettes and stand Through the calculations done before the lab, it was concluded that 3.48 g of K 2 HPO 4 and 2.72 g of KH 2 PO 4 needed to be weighed out. Using our solution and measurement technique, 100 mL of 0.2M K 2 HPO 4 and KH 2 PO 4 stock solution was prepared in order to make 40 mL of the following dilutions:
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a) 0.02M K 2 HPO 4 e) 0.02M K 2 HPO 4 / 0.02M KH 2 PO 4 b) 0.02M K 2 HPO 4 f) 0.02M K 2 HPO 4 / 0.02M KH 2 PO 4 c) 0.02M KH 2 PO 4 g) H 2 O d) 0.02M KH 2 PO 4 h) H 2 O Solutions a, c, e, and g were titrated with HCL and solutions b, d, f and h were titrated with NaOH. The titration setup consisted of the stir plate resting on the base of the stand. A magnetic
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This note was uploaded on 04/12/2009 for the course BIOLOGY 1111 taught by Professor Tanaka during the Fall '09 term at Temple.

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lab 3 write up - Atinuke Omolara Biology 2112 Lab 5:10-8:00...

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