Transcript Acid – Base Titrations

Acid – Base Titrations
A titration is a quantitative study of a neutralization reaction.
The parameters involved are:
1.moles of the acid (from M x V, or mass/molar mass if it’s a solid)
2.moles of the base (also from M x V)
3.the reaction mole ratio (from the balanced equation)
Example 1: In the reaction: Ca(OH)2 + 2 HCl  2 H2O + CaCl2,
an equivalence point is reached after 29.23 mL of 0.0725 M HCl
is added to 25.00 mL of Ca(OH)2. Find the [Ca(OH)2].
moles of HCl = M x V
= 0.0725 mol x 0.02923 L
L
= 2.12 x 10-3 mol
moles of Ca(OH)2 = moles of HCl x mole ratio
[Ca(OH)2] =
= 2.12 x 10-3 mol HCl x 1 mol Ca(OH)2
2 mol HCl
= 1.06 x 10-3 mol
moles
volume
= 1.06 x 10-3 mol
0.02500 L
= 4.24 x 10-2 M
Titrations can be used to determine the amount of pure acid
(or base) in a mixture, since only the acid (or base) is
neutralized.
Example:
The ASA (a monoprotic acid with a molar mass of 180.2 g/mol) in
a 325 mg Aspirin® tablet is neutralized by the addition of 22.25
mL of 0.0711 M NaOH. Find the percentage purity of the tablet.
moles of NaOH = M x V
= 0.0711 mol
x 0.02225 L
L
= 1.58 x 10-3 mol
moles of ASA = moles of NaOH (since acid is monoprotic, mole
ratio will be 1:1)
= 1.58 x 10-3 mol
mass of ASA = 1.58 x 10-3 mol x 180.2 g
mol
= 2.85 x 10-1 g
= 2.85 x 10-1 g x 1000 mg
1g
= 285 mg
% ASA in tablet = pure mass
x 100
total =mass
87.7 %
= 285 mg
325 mg
x 100
Read other examples, p.155-157
(including Experimental Note)
Exercises 94 – 96, 98, 100, 101, 103, 105, 106