Question

This is from a Study of Buffer Solutions and pH of Salt Solutions Lab. I calculated...

This is from a Study of Buffer Solutions and pH of Salt Solutions Lab. I calculated Ka to be 3.2*10^-5. Why is my value larger than the standard value?

Procedure:
10. How does your calculated value of Ka compare with the standard value of Ka for acetic acid? Discuss why your value may be larger or smaller than the standard value. Caleutats Ka 3.2x 10-5) Cyato-s
Learning Objectives: 1. To test the acidic and basic properties of ionic compounds 2. To create a buffer solution and calculate its pH 3. To determine the acid dissociation constant of acetic acid using the Henderson-Hasselbach equation. 4. To test a buffer's capacity by reacting it with a strong acids and a strong base. Discussion: Buffers are solutions that resist changes in pH when small quantities of an acid or base are added to them. These solutions contain a weak acid and its conjugate base or a weak base and its conjugate acid. Because these mixtures contain both the acidic and basic species, they can easily neutralize small quantities of either H or OH. Buffers are also resistant to dilution effects, maintaining the same pH even when water is added to them Part A: Acidic and Basic Properties of lonic Compouds The first part of the experiment involves using a pH meter to determine the pH of several salt solutions A pH meter consists of a meter and two electrodes. The measurement of pH requires two electrodes, a sensing electrode that is sensitive to HaO concentration and a reference electrode This is because the pH meter is really a voltmeter that measures the electrical potential of a solution. The reference electrode is an electrode that develops a known potential that is essentially independent of the contents of the solution into which it is placed. The glass electrode is sensitive to the HiO* concentration of the solution into which it is placed Part B: Buffers A buffer system will be prepared from solutions of conjugate acid - base pairs. The pH of the buffer system will be determined using the pH meter. The Ka of the weak acid used in the buffer will be calculated using the pH data. The effect of adding an acid and a base to the system will be monitored For a weak acid, H,O wal HA (ag)H2O Reaction: +A (aal [H O1IA HA And K Knowing the experimentally determined pH of the solution the [HsO*] can be calculated from pH= -log[HaO ] The Ka of the buffer system can be calculated from the Henderson-Hasselbalch equation pH pka log [A] [HA +

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