Chem Labs

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INVESTIGATION 15.4: BUFFERS Background Information Please refer to pages 484-486 in the Nelson Chemistry textbook.

Problem What effect does the addition of acids and bases have on a buffer? Prediction According the background information, acetic acid will act as a buffer and will prevent any drastic change in pH. Water, on the other hand, is unbuffered and therefore its pH will change proportionally to the volume of acid or base added.

Materials Ø pH meter Ø acetic acid solution Ø distilled water Ø beakers Ø hydrochloric acid solution Ø sodium hydroxide solution Procedure 1. Prepare a 0.10mol/L buffer solution using acetic acid. Use 50mL of this solution.

2. Add a moderate quantity of sodium hydroxide solution and observe changes.

3. Add a moderate quantity of hydrochloric acid solution and observe changes.

4. Repeat steps two and three with 50mL and use results as a control.

Evidence Sample Initial pH PH after addition of NaOH(aq) PH after addition of HCl(aq) Buffer 4.75

4.75 4.75 Water 6.40 9.10 N/A Analysis It was observed that the buffer experienced no notable pH change after the addition of strong acids and bases. The following equations explain the results.

Na+(aq), OH-(aq) (SB), CH3COOH(aq) (SA), CH3COO-(aq), H2O(l) OH-(aq) + CH3COOH(aq) Ã H2O(l) + CH3COO-(aq) H3O+(aq), Cl-(aq), CH3COOH(aq), CH3COO-(aq), H2O(l) H3O+(aq) + CH3COOH(aq) Ã H2O(l) + CH3COOH(aq) Evaluation This experiment can be considered adequate for answering the problem. Little could have been confused in this investigation's procedure. In the future, other buffers could be experimented with. Furthermore, substances used could be measure more precisely.

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