Analytical balanceCabrillo College Chemistry 1B Buffer Problem Worksheet Due: Name:______________________ Score:_____________/10pts Please circle appropriate laboratory section: (1) TTH 8:00am (2) TTH 2:30pm Please attach additional sheets to show all your work. 1. A microbiologist desires to study the effect of pH on the growth of E. coli bacteria. She plans to do the research by preparing culture medium that is buffered at three distinctly different pH values. Therefore, she decides to use the triprotic acid phosphoric acid (H3PO4), potassium dihydrogen phosphate (KH2PO4), and potassium hydrogen phosphate (K2HPO4) to prepare the buffers. H3PO4 + H2O ÍÎ H2PO4- + H3O+ Ka1 = 7.11 x 10-3 H2PO4- + H2O ÍÎ HPO42- + H3O+ Ka2 = 6.32 x 10-8 H PO42- + H2O ÍÎ PO43- + H3O+ Ka3 = 7.11 x 10-13 Materials available: Standardized solutions: 1.00M H3PO4, 1.00 M KH2PO4, 1.00M K2HPO4, 1.00 M HCl, 1.00 M KOH Solids: KH2PO4, K2HPO4, K3PO4 Volumetric Glassware: Pipets 1.0, 5.0,10.0, 25.0, 50.0 mL buret 50.0 mL volumetric flask 100.0 mL Analytical balance A. The acidic buffer she decides to prepare will have a pH of 2.000. She will use the phosphoric acid (1.00M H3PO4) and the solid potassium dihydrogen phosphate (KH2PO4) to prepare 100.0 mL of pH 2.000. She knows that a greater buffer capacity is obtained from higher concentrated materials and that for most laboratory-scale applications 0.500M solutions is an acceptable level of concentration. Therefore, she decides to make the buffer 0.500M in phosphoric acid. She must calculate the volume of 1.00 M H3PO4 and the mass of KH2PO4 solid to be used to prepare 100.0 mL of the pH 2.000 buffer. Write a brief description of how you would prepare the required buffer. B. The second experiment, she buffers the medium at a neutral pH 7.00 to minimize the effect of acid-producing fermentation. What volumes of equimolar (1.00 M) aqueous solutions of KH2PO4 and K2HPO4 must she combine to make 100.0 mL of the pH 7.000 buffer that is 0.500 M in KH2PO4? C. In the third experiment, she buffers the medium at a basic pH 12.000. What is the molar concentration of the K2HPO4 if the desired molar concentration of the PO43- is 0.500M? D. What would the pH and pH change (∆pH) be if 1.0mL of 1.00M NaOH was added to 50.0mL of deionized water (pH 7.00)? Now, what are the pH and pH change (∆pH) that result from the addition of 1.0 mL of 1.00 M NaOH to 50.0 mL of the buffer prepared in part B above. E. What would the pH and pH change (∆pH) be if 10.0mL of 1.00 M HCl was added to 50.0 mL of deionized water pH 7.00? Now, what are the pH and pH change (∆pH) that results from the addition of 10.0mL of 1.00 M HCl to 50.0 mL of the buffer prepared in part B