Jul 30, 2015 - Viva Questions 1. What is a weak acid? Weak acid is a weak electrolyte, which ionises incompletely in aqueous solution. 2. What is PKa of a weak acid? PKa is a modern method of expressing the strength of weak of acids. It is mathematic
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Idea Transcript
Bronsted-Lowry acid-base theory
- strength of an acid is related to its ability to donate protons
weak acid dissociation
- weak acids partially dissociate - HA + H O H O + A
dissociation constant
K = [H O ][A ] / [HA]
pH
- log [H O ] = pH
pK
pK = -log K
titrating weak acid w/ base
- there will be a point in titration at which the number of moles of base added is half the number of moles of acid initially present - 50% of acid has been titrated to produce A and 50% remains as HA - pH = pK
titration curve
- used to determine ionization constant of weak acid
pH meter
- electronic instrument to measure pH through course of titration
parallax error
- consists of a meter and electrode assembly - sensing electrode: sensitive to H O concentrations - reference electrode: develops a known potential that is essentially independent of the contents of the solution into which it is placed - displacement or difference in the apparent position of an object viewed along two different lines of sight - to avoid error, read meniscus at eye level