Exercise 1:
A solution of aspirin C H O (s)is prepared by dissolving a tablet in distilled water.
The conductimetric titration of a volume = 100 mL of the solution with a solution of
sodium hydroxide Na( ) + HO( ), of concentration = 1.0 × 10 mol ⋅ L , makes it possible
to plot the curve = ( ),
shown opposite.
The reaction equation for the titration is: C H O (aq) + HO (aq) → C H O (aq) + H O(l)
1. Determine the equivalence volume .
2. Give the expression for the concentration of hydrochloric acid in solution ,then
calculate it.
3. Deduce the mass of aspirin in the tablet.
Exercise 2
To determine the concentration of an iodine solution ( ), 20.0 mL of this solution is placed in a
beaker with starch solution. A dark blue solution is then obtained (starch is a color indicator that
allows visualization of the equivalence point: before equivalence the solution is blue; after
equivalence the solution is colorless).
In a graduated burette, a sodium thiosulfate solution is introduced, in which the
concentration of thiosulfate ions ( )is 0.20 mol.L .
This solution is added into the beaker until the dark blue color disappears; at that point, 24.2 mL of
titrant solution has been added. The disappearance of the dark blue color indicates the complete
disappearance of iodine ( ).
1. Write the equation of the titration reaction, knowing that the redox couples involved are
( )/ ( )and ( )/ ( ).
Specify, in this chemical reaction, which species is the oxidizing agent and which is the
reducing agent.
2. Define the equivalence point of a titration.
3. Using an advancement table (stoichiometric table) or another method, determine the reaction
that can be written at the equivalence point.
4. Calculate the concentration of diiodine in the titrated solution.
Deduce the mass of diiodine dissolved in a volume = 200 mL of solution.
Given: molar mass of diiodine : ( ) = 253.8 g.mol
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