1a - archimedes principle

1b,1c - which formulas do i use

Problem 1. You are interested in using PLGA to make microparticles for controlled release applications. You find a bottle of PLGA (50:50) pellets in your lab that you are interested in using for a future experiment. The label has come off so you have no knowledge of the molecular weight (Mn, avg) or the mass density (p) of the polymer pellets. Nevertheless, you are interested in determining the rate constants of degradation of these polymer pellets. You set up two degradation experiments. The first degradation experiment consists of you incubating PLGA (50:50) pellets of known mass in buffer at pH = 7.4 for a given time. You continuously titrate the buffer solution with sodium hydroxide to ensure that the pH remains constant across the entire degradation experiment. You then remove the solid pellets, dissolve them in chloroform and run GPC to identify the Mn. The resulting data is shown below: t(week) 0 1 2 3 4 5 6 7 8 9 10 11 12 N Mnavg (g/mol) ??? 5000 3500 2600 2100 1800 1500 1300 1200 1000 950 900 800 a. Devise a simple method of calculating the mass density of the water-insoluble polymer. (use a combination of common sense and high school physics). b. Assume that you measure a density of 1.02 g/cm from part (a). What is the effective rate constant of degradation in this first experiment (Keff,1)? C. What is the initial molecular weight (Mn, avg,0) of the polymer