pH

In the LaboratorySeidman & Moore pp. 380-383Problems 1-5 page 400

Ionization of Water

OHHOH 2

Equllibrium Constant, Keq

][]][[

2OHOHHKeq

]6.55[]10][10[ 77

MMMKeq

MKeq16108.1

Ion Product of Water, KW

]][[ OHHKW

1477 10]10][10[ MMKW

pH

]log[ HpH

14 pOHpHpKW

Acidity

Measuring pH

Indicater Dyes; Methyl Red, Phenol Red, etc.

pH Paper (Litmus Paper)

pH Meter

pH Meter

Voltmeter with electrode

Measures electrical potential difference across electrode due to protons

1 pH unit = 60 mV pH also dependent

on temperature

pH Electrode

Filled with reference solution (4 M KCl, sat. AgCl)

Glass semi permable (protons cannot cross)

Glass protected by plastic sleeve

Some are sensitive to Tris buffer

pH Standards Color coded 4, 7,

and 10 Potassium

Hydrogen Pthalate Standardize

everyday Bracket pH range

pH of Strong Acids

HCl <-> H+ + Cl- Assume complete dissociation 1 M HCl, pH = -log [H+] = -log 1 = ? 0.5 M HCl, pH = -log 0.5 = ? 6 M HCl, pH = -log 6 = ?

pH of Strong Bases

NaOH <-> Na+ + OH-

Assume complete dissociation pKW = pH + pOH = 14 pH = 14 – (-log [OH-]) 1 M NaOH, pH = 14 – (-log 1) = ? 0.01 M NaOH, pH = 14 – (-log 0.01) = ? 6 M NaOH, pH = 14 – (-log 6) = ?

pH of a Weak Acid