Experiment No. 2a-b
Preparation and standardization of NaOH Solution
When solution of NaOH is to be prepared, it is recommended to use pre-boiled
and cooled distilled water in order to eliminate the dissolved CO2 .
An appropriate amount of solid NaOH is weighed and dissolved in appropriate
amount of distilled water to have the approximate desired concentration..
In order to prepare a known concentration of NaOH Solution the following is
needed for calculation of the NaOH amount needed tobe dissolved:
-
the molecular weight of NaOH = 40g per mol
-
the concentration of the prepared solution (0.1M)
-
the volume of the solution (250ml)
For the preparation of 250ml of 0.1 M NaOH Solution we need to have the
grams of NaOH
Weight = Concentration needed (in M) x M.Wt x Volume needed (in L)
Weight needed (in g) = 0.1 x 40 x 0.25= 1 g
Therefore 1g NaOH is dissolved in 250 mL to yeild a 0.1 M solution.
Standardization of the NaOH Solution Against Standardized HCl
Solid NaOH is hygroscopic where significant amounts of water vapor can be
absorbed. Also, as NaOH is a strong base, significant amounts of atmospheric
carbon dioxide can be absorbed. It is also clear that NaOH can not serve as a
primary standard and thus needs standardization by a primary or secondary
standard.
NaOH solutions can be directly titrated versus standardized HCl using
phenolphthalein or methyl orange indicator. If reasonable concentrations of the
acid and base are used, very sharp end points can be achieved. The concentration
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of NaOH solution can be calculated directly. The equation which shows the
reaction can be written as:
NaOH + HCl → NaCl + H2O
Procedure: preparation of 0.1M NaOH Solution
1- weigh 1g of solid NaOH
2- Dissolve in 250 ml a pre-boiled distilled water
3- Cool the solution and keep it in polyethylene bottle.
Procedure: Standardization of 0.1M NaOH Solution against Standardized
HCl
1. Transfer exactly 20 mL of the prepared NaOH Solution into a 100 mL
conical flask.
2. Add 4 drops of Phenolphthalene indicator.
3. Titrate against the standard 0. 1M HCl solution and record the volume .
Observations
Volume of NaOH
Volume of HCl
Molarity of NaOH
Calculations and Results:
Make averaging for the calculated NaOH concentration from the equation:
M1 x V1 = M2 x V2
1= HCl
2= NaOH
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