CH118 ka from ph

# CH118 ka from ph - unknown acid 453 is 1.58 x 10-4 ± 0.06...

This preview shows pages 1–2. Sign up to view the full content.

Determination of Ka from pH I. Validity of the Method The general formula for Ka of a weak acid is Ka= [H 3 O + ][A - ] / [HA]. The Henderson- Hasselbach equation can be used to find pKa (and therefore Ka) from pH. The Henderson- Hasselbach equation is pH = pKa + log [A - ] / [HA]. At the half equivalence point, [HA] = [A - ] = [H + ] = ½ [HA] o ,which makes pKa = pH. pKa is the negative log of Ka. In this experiment, the pH of acetic acid at the half-equivalence point was 4.52 so pKa = 4.62. To get Ka calculate 10 -4.62 , which is 2.40 x 10 -5 . The Ka of acetic acid is 2.40 x 10 -5 ± 0.09. The percent error is 75%. II. The Ka of the Acid The pH at the half equivalence point of unknown #453 was 3.80. The pKa is 3.80. The Ka of

This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: unknown acid # 453 is 1.58 x 10-4 ± 0.06. III. Kb of a Weak Base The Kb of a weak base is [HA][OH-] / [A-]. To experimentally determine a Kb, I would titrate a strong acid such as HCl into a beaker with the weak base and an indicator that would change color at a low pH as opposed to a high one like phenolphthalein. The Henderson-Hasselbach equation would be pH = pKb + log [HA] / [A-] IV. Summary of the Data Acid pH at half equilibrium pH at equilibrium pKa Ka Acetic Acid 4.62 6.91 4.62 2.4 x 10-5 Unknown #453 3.8 5.22 3.8 1.58 x 10-4 V. Titration Curves...
View Full Document

## This note was uploaded on 06/15/2011 for the course CH 118 taught by Professor March during the Fall '09 term at University of Alabama at Birmingham.

### Page1 / 2

CH118 ka from ph - unknown acid 453 is 1.58 x 10-4 ± 0.06...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document
Ask a homework question - tutors are online