Measuring pH (and pOH)

Measuring pH pH can be measured precisely using a pH meter or you could use an indicator

Bromothymol blue changes from yellow to blue as the pH rises from 6.00 to 7.60 (mid range = green)

Example Separate samples of a solution of unknown pH cause the following acid base indicator colours Orange IV = yellow Bromothymol blue = blue Phenolphthalein = colourless What is the solution pH? Hint: use the indicator chart at the back of your workbook!

Modified Arrhenius Acid = a substance that reacts with water to produce H3O+ Base = a substance that reacts to produce OH-

Example NH3(aq) + H2O  Test for acid  Test for base  More familiar ion?! BASE!

Example 2 CO2 + H2O  Test for acid  Test for base  More familiar ion = ACID!!

Example 3 HSO 4 -

Limitations In some cases, the modified theory cannot predict acid or base because both ions are familiar (i.e. HSO4-)

Neutralization Acids react with bases to form water and a salt (a neutral ionic compound) i.e. NaOH + HCl  H2O + NaCl

Show the reaction between sodium hydroxide and sulfuric acid

Ionic Neutralization H3O+ + OH-  2H2O

Strengths of Acids and Bases Defined in terms of how completely an acid ionizes in water to produce H+

Strong Acids weak bonds between H+ and the rest of the acid easily gives up its H+ completely

HClO 4 HI HBr HCl H 2 SO 4 HNO 3 H 3 O +

Weak Acids Stronger bond with its H+ only partially gives up its H+ example: Vinegar

Base strength is determined according to its OH- dissociation ease

Strong Bases Always contains OH- weak bonds between OH- and the rest of the base example: NaOH

Weak Bases Slightly dissociate into OH- <50% example: NH 3

Monoprotic Acids Mono form 1 H+ or 1OH- in solution Ex. Show the ionization for Hydogen fluoride: Ex. Show the dissociation of potassium hydroxide:

Polyprotic Acids Poly form more than 1 hydrogen or hydroxide through a series of steps

Ex. H3PO4