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Buffer Solutions

Buffer Solutions. A buffer solution is a solution that changes pH only slightly when small amounts of a strong acid or a strong base are added. A buffer contains significant concentrations of both a weak acid and its conjugate base, or a weak base and its conjugate acid.

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Buffer Solutions

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  1. Buffer Solutions • A buffer solution is a solution that changes pH only slightly when small amounts of a strong acid or a strong base are added. • A buffer contains significant concentrations of both • a weak acid and its conjugate base, or • a weak base and its conjugate acid.

  2. Sodium Acetate Buffer • This buffer relies on the dissociation reaction of acetic acid. CH3COOH CH3COO- + H+ Buffer animation

  3. Importance of Buffers • Our blood is buffered to a pH of 7.4 • Buffers are used when pH must be controlled in experiments. • Proteins • Enzymes

  4. Pure water increases in pH by about 5 pH units when the OH– is added, and decreases by about 5 pH units when the H3O+ is added. In contrast, the same amounts of OH– and H3O+ added to a buffer solution barely change the pH.

  5. Buffer Capacity andBuffer Range • There is a limit to the ability of a buffer solution to neutralize added acid or base. • This buffer capacity is reached before either buffer component has been consumed. • As a rule, a buffer is most effective if the concentrations of the buffer acid and its conjugate base are equal or nearly so.

  6. Buffer Capacity

  7. Purpose • Determine the buffer capacity of 3 different concentrations of sodium acetate buffer using an acid and a base.

  8. Safety • We will be using HCl and NaOH so you must wear lab coat, goggles, and gloves at all times!

  9. Procedure • Label one 250 mL beaker acid and the other one base. • Pour 50 mL of 1.0 M acetic acid buffer into each of the beakers. • In the beaker labeled base, add 1 mL of Universal Indicator. In the beaker labeled acid, add 1 mL methyl orange. • Measure and record the pH of each solution.

  10. Procedure cont. • Using a disposable pipet, add 1 mL of 1.0 M HCl to the beaker labeled acid. Mix well. Measure and record the pH. • Continue adding HCl 1 mL at a time until the pH and the color of solution changes. • Repeat steps 5-6 using the NaOH and the base beaker. • Rinse both beakers out and repeat steps 3-7 using the 0.1 M buffer and then the 0.01 buffer.

  11. Data • Make a Data Table to record your pH values.

  12. Graph • Graph your data with pH on the y-axis and volume of acid/base on the x-axis. • Don’t forget to include the units and titles for each axis. Your graph should also have a main title and a legend.

  13. Conclusion • How does the concentration of the buffer affect the buffer capacity? • How is the HCl graph different from the NaOH graph? • Write reaction equations to explain how your acetic acid-acetate buffer reacts with an acid and reacts with a base. • What is the buffer capacity of each buffer used (for both HCl and NaOH)?

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