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AimThe objective of this experiment is to find out the potency of a given solution of sodium hydroxide by conducting a titration using a standardized solution of oxalic acid.
Apparatus RequiredBurette
Conical flask
Burette stand
White glazed tile
Measuring flask
Oxalic acid (solid)
Oxalic acid (as per needed)
Sodium hydroxide solution (as per needed)
Phenolphthalein indicator (as per needed)
TheoryThe process of estimation involves the use of phenolphthalein as the preferred indicator to conduct a titration of a weak acid, namely oxalic acid, against a strong base, sodium hydroxide. The chemical reaction between oxalic acid and sodium hydroxide can be represented as:
(COOH)2 + 2NaOH → (COONa)2 + 2H2O
Since sodium hydroxide is not considered a primary standard, a standardized solution of oxalic acid is prepared and utilized for standardizing the sodium hydroxide.
In acid-base titration, the amount of acid becomes chemically equivalent to the amount of base present at the end point. In the case of strong acid and strong base titration, the solution reaches the end point when the solution becomes chemically neutral.
Procedure(a) Preparation of 0.1M Standard Oxalic Acid Solution
Take a watch glass, clean it using distilled water, and dry it properly.
Weigh the watch glass accurately and record its weight in a notebook.
Weigh 3.15 g of oxalic acid on the watch glass and record this weight in the notebook.
Using a funnel, carefully transfer the oxalic acid into a clean and dry measuring flask.
To remove any particles stuck on the watch glass, wash it with distilled water. Use a wash bottle and make sure that the volume of distilled water does not exceed 50 ml.
Wash the funnel multiple times with distilled water to move the particles into the measuring flask. Use a wash bottle and add water in small quantities, ensuring that the total volume of distilled water used does not exceed 50 mL.
Carefully wash the funnel using distilled water to transfer the solution from the funnel into the measuring flask.
Turn the measuring flask to dissolve the oxalic acid.
Using a wash bottle, add distilled water to the measuring flask until the volume is just below the etched mark.
Add the last few drops of distilled water carefully into the measuring flask until the meniscus level just touches the mark.
Place the stopper on the measuring flask’s mouth and shake it gently to make the solution uniform.
Calculate the solution of oxalic acid as M/10.
(b) Titration of Sodium Hydroxide and Oxalic Acid Solution
First, rinse the burette with standard oxalic acid solution.
Take 10 ml of the oxalic acid solution in a titration flask and fill the burette with sodium hydroxide solution.
Remove any air bubbles from the burette by forcefully running the solution out of the burette nozzle, and then note the initial reading.
Pipette out 20 ml of the NaOH solution into a conical flask and add 2-3 drops of phenolphthalein indicator to it.
Titrate the base with the oxalic acid solution until the pink color disappears.
Repeat the titration process until three concordant readings are obtained.
Observation and ResultObservations:
Initial reading of the burette: 0 ml
Final reading of the burette: 21.5 ml
Volume of NaOH solution used: 21.5 – 0 = 21.5 ml
Volume of oxalic acid solution used: 10 ml
Indicator used: Phenolphthalein
The endpoint of the titration was reached when the pink color disappeared.
Calculations: The balanced chemical equation for the reaction between sodium hydroxide and oxalic acid is: (COOH)2 + 2NaOH → (COONa)2 + 2H2O
From the equation, we can see that 1 mole of oxalic acid reacts with 2 moles of NaOH.
The concentration of oxalic acid solution can be calculated as follows:
Number of moles of NaOH used = (concentration of NaOH solution in M) x (volume of NaOH solution used in L)
Number of moles of oxalic acid used = (number of moles of NaOH used) / 2 (from the balanced equation)
Concentration of oxalic acid solution in M = (number of moles of oxalic acid used) / (volume of oxalic acid solution used in L)
Let’s assume that the concentration of oxalic acid solution used for standardization is 0.1 M.
Using the above formulae, we can calculate the concentration of NaOH solution:
Number of moles of NaOH used = (0.1 M) x (21.5 / 1000 L) = 0.00215 moles
Number of moles of oxalic acid used = 0.00215 / 2 = 0.001075 moles
Concentration of NaOH solution in M = (0.1 M) x (10 / 21.5) x (1 / 0.001075) = 4.65 M
Therefore, the concentration of the given solution of NaOH is 4.65 M.