Acid Base Titration Calculations

STANDARDIZATION

The stockroom will provide 0.2 M NaOH solution. You will have to standardize this, that is find its exact concentration. You will do this by weighing out some pure Potassium Hydrogen Phthalate, (KHP) MW = 204.23, a monoprotic acid. You will neutralize this with the NaOH using the process of titration. These data will allow you to calculate the Molarity of the NaOH solution. A second titration of a new sample of "KHP" which gives the same Molarity to less than 1% error, is needed to support the accuracy of your work.

The amounts of "KHP" you use in each trial need not and in fact should not be the same. The more "KHP" you weigh out, the more NaOH solution it will take to neutralize it. While the weights and volumes for the two (or more) trials will not be the same, the calculated Molarities should be.

CALCULATING MOLARITY

Molarity = moles of solute per liter of solution

NaOH + KHC8H4O4 -------> H2O + KNaC8H4O4

Moles of KHP = g KHP/MW KHP

1 mol of KHP is neutralized by 1 mol of NaOH therefore

moles of "KHP" = moles of NaOH

Molarity of NaOH = mol NaOH/L of NaOH

ANALYSIS of VINEGAR

The stockroom will provide you with an UNKNOWN Vinegar sample. You will determine its Acetic Acid concentration using your standardized NaOH solution. You will pipet out 5.00 mL of the vinegar and titrate it with your NaOH to the phenolphthalein end point.

You will do this at least twice. Since the two volumes of the vinegar used are exactly the same, the volume of NaOH used to titrate these should also be the same. Maximum experimental error is two drops, 0.10 mL.

CALCULATING ACETIC ACID CONCENTRATION

CH3COOH + NaOH -----> CH3COONa + H2O

From the equation: 1 mol of NaOH will neutralize 1 mol of Acetic Acid

mmol of NaOH used = (ml NaOH)(MNaOH) = mmol of acetic acid

Molarity of UNKNOWN = mmol acetic acid/ Volume (mL)of vinegar titrated

Molarity = mol/Liter

w/v Per Cent = g/100 mL or grams per deciliter
Remember: g = (mol)(Mol Wt)
You want only 100 mL or 0.100 L

ANALYSIS of a VITAMIN C TABLET

Weigh the Vitamim C Tablet. Break it into small pieces after soaking so that only small fluffy or powdery solid remains. No chunks. Be careful, do not lose any. Titrate to the phenolphthalein end point.

Calculating mg Ascorbic Acid

C6H8O6 + NaOH ----> NaC6H7O6 + H2O

1 mol of NaOH reacts with 1 mol Ascorbic Acid

LOGIC of Calculation:

mmol NaOH > mmol Ascorbic Acid > mg Ascorbic Acid

 

RWK 1997