Monday, January 9, 2012

Titration of a strong base with a strong acid(Determination of the concentration of sodium hydroxide using 0.10 M HCl)


All acid base titrations basically involve the following reaction

As the titration proceeds, initially the pH drops slowly, but nearer the end point, the pH of the solution drops rapidly. i.e. in the vicinity of the equivalence point the rate of change of pH of the solution is very rapid.

If you cant see the image clearly please click on it


(a)Prepare a 250.00 mL solution of 0.10M HCl using the concentrated HCl acid provided.
(b)Pipette out 25.00 mL of the given NaOH solution in to the titration flask, add few drops of phenolphthalein indicator. Titrate this solution with the HCl solution you prepared. Repeat the titration using methyl orange as the indicator. Obtain two
readings in each.
(c)Calculate the concentration of NaOH solution using your results.

The concentration of NaOH calculated when methyl orange is used as the indicator
will be slightly higher than the concentration when phenolphthalein is used.
Phenolphthalein is a weak base which has a pH range 8.0-10.0. Methyl orange is a
weak acid which have the pH range 3.0-5.0. More HCl is consumed when methyl orange
is used as the indicator because it shows the acidic color when the pH of the
medium fall to pH 3.

Total free energy for above neutralization reaction (Room temperature 30o C)

Δ G = - RT ln K
= 8.314Jmol-1 K-1 × 303K × 2.303 × log 10 ^14
= -8.1222 × 1014 J
Where Δ G = Free energy change
R= Universal gas constant
T= Absolute temperature
K= Equilibrium constant


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