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Determination of Buffer Capacity

Determination of Buffer Capacity . Lab 5. Outline. Purpose Buffers Equilibrium Expression / Henderson-Hasselbalch Equation Things to Remember Buffer Capacity Safety Concerns Solutions and Waste Next Lab Reminder. Purpose .

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Determination of Buffer Capacity

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  1. Determination of Buffer Capacity Lab 5

  2. Outline • Purpose • Buffers • Equilibrium Expression / Henderson-Hasselbalch Equation • Things to Remember • Buffer Capacity • Safety Concerns • Solutions and Waste • Next Lab Reminder

  3. Purpose Students will determine the buffer capacity of several acetic acid / acetate buffer solutions using a pH probe.

  4. Buffers • A buffered solution is a solution that resists a change in pH. • In order to have a buffer, two components are essential: • a weak acid • a weak base • These two must have a common ion: called a conjugate acid-base pair

  5. Buffer Example • Acetic Acid / Acetate Ion: CH3COOH CH3COO-+ H+ • Weak acid neutralizes OH-: OH- + CH3COOH CH3COO-+ H2O • Weak base neutralizes H+: H+ + CH3COO- CH3COOH Thus, a change in pH is resisted.

  6. Equilibrium Expression and theHenderson-Hasselbalch Equation CH3COOH CH3COO-+ H+ Ka= pH = pKa + log

  7. Things to remember: • Buffers are most effective when the pH of the buffered system is equal to the pKa of the conjugate acid. • Buffers are only effective when the pH is within 1 unit from the pKa. pH = pKa ±1 • When this pH is exceeded, we have exceeded the buffer capacity.

  8. Buffer Capacity • The amount of acid or base that can be absorbed by a buffered system without changing the pH by more than one unit is called buffer capacity. Cb = • The concentrations of all your buffers for today were set at a 1:1 ratio. • We will titrate to a change in pH of exactly 1 unit.

  9. Safety Concerns • Reagents: • Acetic Acid (1 N) • Acetate Buffers • Sodium Hydroxide (0.1 N) / Potassium Hydroxide (0.1 N) • Eye Contact: • Irritation, tearing, redness, pain, impaired vision, severe burns and irreversible eye injury. • Skin Contact: • Severe skin irritation, soreness, redness, destruction of skin (penetrating ulcers) . May cause sensitization and / or allergic reaction. • Inhalation: • May cause coughing, serious burns, pneumonitis, pulmonary edema, and coma. • Ingestion: • Toxic. Corrosive to mucous membranes. May cause perforation of the esophagus and stomach, abdominal pain, nausea, vomiting, diarrhea, general gastro-intestinal upset.

  10. Solutions and Waste • Your solutions are located in the back of the lab. • Please conserve distilled water during cleanup. • Dispose of waste in the appropriate waste receptacles. • Acidic and basic solutions / waste need to be disposed in the acid/base waste container in the fume hood. • Solutions with a pH between 6 and 8 can be disposed down the drain.

  11. Lab 6 Reminder • Lab 6 next week.

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