Neutralization of Acids and Bases

In general, a titration involves the addition of either a strong acid, strong base or both (must go to completion) as follows: ACID + BASE  WATER + SALT Titrations do not always yield an equivalence point with a pH of 7. Why? Can further hydrolyze to form acidic or basic solutions

Titrations Standard Solution Sample Solution Burette Unknown [ ] Sample Solution Known [ ] Standard Solution Primary Standard with a precisely known [ ] 1st titration 2nd titration ?

Why a primary standard? If NaOH is the standard solution, it ’ s [ ] may not be accurate. Why? NaOH is hygroscopic (absorbs moisture in the air) which can affect its molar mass A primary standard is used to verify the [ ] of the “ known ” standard solution A primary standard must be: –Pure & stable –Non-hygroscopic –Have an accurately known molar mass

Choosing Indicators For Titrations will depend on the overall pH of the salt produced yellowblue

Strong Acids and Strong Base Titrations Example: HCl (strong acid) and NaOH (strong base) Formula Equation:__________________________________ Complete Ionic Equation: ____________________________ Net Ionic Equation:__________________________________ pH at equivalence point: _____________________________ Possible Indicators:__________________________________ HCl + NaOH  H 2 O + NaCl H + + Cl - + Na + + OH -  H 2 O + Na + + Cl - H + + OH -  H 2 O pH = 7 (neutral salt) Bromothymol blue

Titration Curve for Strong Acid & Strong Base pH of sample solution is very low  SA Base is the standard solution being added

Example: CH 3 COOH (weak acid) and NaOH (strong base) Formula Equation:__________________________________ Complete Ionic Equation: ____________________________ Net Ionic Equation:__________________________________ pH at equivalence point: _____________________________ Possible Indicators:__________________________________ Weak Acids and Strong Base Titrations

Weak Acid & Strong Base pH starts higher as CH 3 COOH is a weaker acid E.P > 7

Weak Base and Strong Acid Titrations Example: NH 3 (weak base) and HCl (strong acid) Formula Equation:__________________________________ Complete Ionic Equation: ____________________________ Net Ionic Equation:__________________________________ pH at equivalence point: _____________________________ Possible Indicators:__________________________________

Weak Base & Strong Acid Standard Acid is added Sample of Strong Base E.P < 7

Three types of Titrations:

Monoprotic Acids When the mole ratio of acid to bases is 1:1 in the balanced equation (assuming that the conc ns are the same), then they will require equal volumes to reach equivalence point Acid and Base strength is irrelevant!! strong acid weak base Example: A 0.2 M strong acid requires an equal volume of 0.2 M weak base to reach equivalence point if they have 1:1 ratio

Polyprotic Acids When an acid releases more than one proton, ie. H 2 SO 4, then they will require twice the volume of base to reach equivalence point

Titration of a polyprotic acid: one equivalence point per acidic hydrogen