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Fundamentals of Chemistry pH (pH = power of Hydrogen (Definition of pH = A…
Fundamentals of Chemistry pH
pH = power of Hydrogen
The measure of acidity in the water
Pure water at 25 = the concentration of hydrogen ions = the concentration of hydroxide ions
Definition of pH = A measurement of the concentration of hydrogen ions in a solution
pH of a solution is defined as: pH = -log [H3O+]
pH of a solution is defined as: pH = -log [H+]
Acid = pH lower than 7.0
Alternative definition = Acid is a proton donor
Base = pH higher than 7.0
Alternative definition = Base is a proton acceptor
pH can be measured by:
a pH indicator into the solution
pH meter together with a pH selective electrodes
pH paper, indicator paper that turns different colour corresponding to a particular pH
pH logarithmic scale
The difference between each value is 10-fold
Strong acid fully dissociates in a solution
Weak acid partially dissociates in a solution (does not go to completion.)
Acidity constant Ka is not the same as pH
Higher Ka value the stronger the acid- because less of HX left
Weak acids have small Ka values - lots of HX left at equilibrium of dissociation
HX = concentration of acid present
Calculation of pH
It is assumed that the water does not provide any hydrogen ions
Neutralization
The reaction between and acid and a base
Will produce a salt and neutralised base
The basis of titration
Where a pH indicator shows when the equivalent number of moles of a base have been added to an acid
It will not always give a solution of pH 7.0
Only with acids and bases of similar strengths
A strong base is a base which hydrolyzes completely - Raising the pH of a solution towards 14
Strong base example = sodium hydroxide
Arrhenius bases are water-soluble and donate hydroxide ions
Alkalis are bases however not all bases are alkalis = Alkalis are Arrhenius bases and hydroxides of the alkali metals e.g sodium, potassium
Weak base example = ammonia
Buffer solution = an aqueous solution consisting of a mixture of a weak acid and its conjugate base or weak base and its conjugate acid
Resists large changes in pH when small volumes of acids or bases are added
used to keeping pH at a nearly constant value in biochemical applications