Effect of pH on Aspirin Dissolution Group 101-2B Aims/Objective & Hypotheses: To determine the optimal pH for dissolution for aspirin (acetylsalicylic acid) using gravimetric analysis. The pH levels of 1,2,3,5,6,7, and 8 chosen represent the pH levels of different regions along the digestive tract. It is hypothesized that aspirin will have optimal dissolution at pH of 1-3, which corresponds to that of the stomach.

Methods and Protocol: Equipment: Dissolve 200mg of aspirin powder in 100mL of buffer solution for 20min. Buffer solutions have pHs set at 1, 2, 3, 5, 6, 7, and 8 Separate the dissolved solution from the undissolved aspirin with filter paper and dry. Weigh the mass of undissolved aspirin and calculate the percentage mass dissolved. Equipment: Magnetic stirrer & stirring bar Filter paper Oven Electric beam balance Buffer solution Aspirin powder

Proposed Results/Findings/Deliverables: Solubility increases as pH decreases; and the optimal pH is in the range 1-3, which is the pH of the stomach. The amount of dissolved aspirin against the time will give the rate of dissolution at each pH. According Bayer HeathCare, dissolution occurs in the stomach, but absorbs in the small intestine. stomach pH: 1-3 small intestine: pH 6-8 For this reason we propose that the aspirin should take less time to completely dissolve (lower rate of dissolution) at a low pH level (stomach).

Potential Pitfalls: Time allowed for dissolution (20 min) is too short for enough aspirin to dissolve. This might show that there is no significant difference among the different pHs even if there may be. The effects of solutions with two different pHs cannot be compared if all 200 mg of aspirin dissolved completely in both. Optimal pH is out of the range that we test.

Materials and Budget & Justification: 500mL of buffer solution with pH 1,2,3,5,6,7, and 8 from Fischer Chemical: $162.84 1lb of aspirin powder from Vedco: $9.95 Fine porosity quantitative grade filter paper from Fischer Scientific: $8.85 Total: $181.64