Experiment Name
Standardization of Sodium Hydroxide (NaOH) solution with standard Oxalic Acid solution.
Theory
In this experiment we shall determine the strength of NaOH solution by a standard solution of Oxalic Acid. This is done by means of Titration. The important matters that are related with the experiment are stated below:
Titration:— In presence of a suitable indicator, the volumetric analysis in which a standard solution is added to another solution (whose strength is not known) to reach its end point to determine the strength of that solution is called titration.
Standard Solution: — A solution of known concentration is called a standard solution.
Indicator: — In acid-base titration there is an important use of indicator. An indicator is a chemical substance that detects the equivalent point (i.e. the end point) of reaction by changing its color.
Equivalent Point: — The equivalent point is the point in a titration when a stoichiometric amount of reactant has been added.
Molarity: -In current practice, concentration is most often expressed as molarity.
Molarity (symbol M) is defined as the number of moles of solute per liter of solution. If n is the number of moles of solute and V liters the volume of solution,
Molarity= Moles of solute/ Volume in liters Or, M= n/V (in liters)
Here, n= x (in gm)/ Molecular weight
Normality: -The number of gram equivalent weight of a solute per liter of solution is called normality.
Normality (N)= gm equivalent of solute /liters per solution.
In this experiment the reaction we shall use is as follows:
HOOC-COOH + 2NaOH ——>NaOOC-COONa + 2H2O
The formula required to determine the strength of NaOH solution is: -
V base × S base = V acid × S acid
or, V b × S b = V a × Sa
Where, V represents volume and S represents strength.
The volume of Oxalic acid is measured by watching the Equivalent point. The point at which acid- base neutralizes each other is called Equilibrium point. This point is determined with the help of an indicator.
Why Phenolphthalein is used as indicator: In this experiment, Phenolphthalein is selected as indicator whose working pH range is 8.3-10.0 i.e. it is works when the environment is acid. This indicator gives pink color in basic solution and becomes colorless when the base is neutralized.
Data and calculation
|
No.
of Obs. |
Volume
of NaOH (mL) |
Burette
Reading (mL) |
Volume
of Oxalic-Acid (mL) |
Average
Reading (mL) |
|
|
Initial
Reading (mL) |
Final
Reading (mL) |
||||
|
1 |
10 |
0 |
5 |
5 |
5.3 |
|
2 |
10 |
0 |
5.2 |
5.2 |
|
|
3 |
10 |
0 |
5.5 |
5.5 |
|