Neutralization of Acids and Bases

Primary Standard with a Titrations Primary Standard with a precisely known [ ] Burette 1st titration Standard Solution Known [ ] Standard Solution 2nd titration How do we accurately know the [ ] of a standard solution? Ie. NaOH is hygroscopic and we are unable to accurately determine its concentration in order to make a standard solution. So, we use a primary standard which has the following characteristics: pure & stable non-hygroscopic accurately known molar mass Examples: Na2CO3 KHC8H4O4 (pottasium hydrogen phthalate) C6H5COOH (benzoic acid) Which one to use? Depends if your standard is an acid or a base - must use the opposite one to do a preliminary titration. Sample Solution Unknown [ ] Sample Solution

ACID + BASE WATER + SALT 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? The salts produced may further hydrolyze to change the equivalence to either acidic or basic

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

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:__________________________________

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

Strong Acid & Strong Base 4 3 2 1

How are the pH’s calculated at the various stages. Eg. 40. 0 mL of 0 How are the pH’s calculated at the various stages? Eg. 40.0 mL of 0.100 M HCl is titrated with 0.100 M NaOH. The initial acid concentration? 1 NaOH is added (eg. 30.0 mL) but acid is in excess? 2 Equivalence point? 3 Base is in excess (eg. 50.0 mL added)? 4

Weak Acids and Strong Base Titrations Example: CH3COOH (weak acid) and NaOH (strong base) Formula Equation:__________________________________ Complete Ionic Equation: ____________________________ Net Ionic Equation:__________________________________ pH at equivalence point: _____________________________ Possible Indicators:__________________________________

Weak Acid & Strong Base E.P > 7 pH starts higher as CH3COOH is a weaker acid

Weak Base and Strong Acid Titrations Example: NH3 (weak base) and HCl (strong acid) Formula Equation:__________________________________ Complete Ionic Equation: ____________________________ Net Ionic Equation:__________________________________ pH at equivalence point: _____________________________ Possible Indicators:__________________________________

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

Three types of Titrations:

Choosing an Indicator:

Monoprotic Acids When the mole ratio of acid to bases is 1:1, then they will require equal volumes to reach equivalence point Acid and Base strength is irrelevant Example: A strong acid requires an equal volume of weak base to reach equivalence point if they each have a coefficient of 1

Polyprotic Acids When an acid releases more than one proton, ie. H2SO4, then they will require twice the volume of base to reach equivalence point

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