Volumetric Analysis – Titrations. Volumetric Analysis a process of analysis accomplished by adding together particular volumes of 2 solutions the objective may be to determine the molar concentration of a solution of unknown strength, the percent purity of a sample, etc. Titration
E.g. A + 2B C + D
The way indicators like phenolphthalein, litmus, & bromthymol blue change colour is readily explained on the basis of equilibrium shifts.
Acid-base indicators are really just very weak acids or bases which are slightly dissociated and set up equilibrium between the molecular and ionic forms, which are different colours.
It is a weak acid which in water sets up this equilibrium:
HPh + H2O H3O+ + Ph-
Using bromthymol blue as an example we have:
Equilibrium: HIn + H2O H3O+ + In-
1) Acid titrated with a base.
At the equivilence or endpoint [H3O+] = [OH-]
This is where the indicator colour changes & pH changes rapidly.
At the top of the graph the [OH-] > [H3O+].
At the endpoint the concentrations are equal.
At the end of the graph [OH-] < [H3O+].
1. Find the concentration of an H2SO4 solution if 15.0 mL of it is needed to neutralize 40.0 mL of 0.60 M NaOH solution, according to the equation: 2NaOH + H2SO4 Na2SO4 + 2H2O
What volume of 3.00 M HCl can be neutralized by a reaction with 13.4 g of sodium carbonate?
Na2CO3 + 2HCl 2NaCl + H2O + CO2
Find the percent purity of a sample of Na2CO3 if 250.0 mL of 0.300 M HCl is required to react completely with a 5.0 g sample of the impure salt. Rxn: Na2CO3 + 2HCl 2NaCl + H2O + CO2