Titration of Oxalic Acid against Sodium Hydroxide
1.Aim:-To determine the molarity strength of a given solution of sodium hydroxide solution by titrating it against a standard solution of oxalic acid.
2.Materials Required:-Burette, Pipette, Conical flask, Burette stand, Funnel, Stirrer, White glazed tile, Measuring flask, Oxalic acid (solid) Sodium hydroxide solution, Phenolphthalein indicator
3.Theory:-This estimation involves titration of a weak acid that is oxalic acid against a strong base sodium hydroxide and phenolphthalein is the indicator of choice. The reaction between oxalic acid and sodium hydroxide is
(COOH)2 + 2NaOH → (COONa)2 + 2H2O
Since sodium hydroxide is not a primary standard a standard solution of oxalic acid is prepared and used for standardisation of sodium hydroxide.In acid-base titration at the end point the amount of acid becomes chemically equivalent to the amount of base present. In case of strong acid and strong base titration at the end point of solution the solution becomes neutral.
4.Procedure:-
(a) Preparation of 0.1M Standard Oxalic Acid Solution:-
M = Wb x 1000
GMM(b) x V1 (in ml)
W(b) = M x GMM (b) x V1 (in ml)
1000
W(b) = 1 x 126 x 250 ml = 1.575 g
20 1000
Take a watch glass, wash it with distilled water and dry it. Weigh the exact amount of clean and dried watch glass and record its weight in the notebook. Weigh 1.575 g of oxalic acid on the watch glass correctly and record this weight in the notebook. Using a funnel, transfer oxalic acid softly and carefully from the watch glass into a clean and dry 250ml measuring flask. Wash the watch glass with distilled water to move the particles that stick to it into the foam with the assistance of a wash bottle. For this purpose, the volume of distilled water should not exceed 50 ml. Wash the funnel several times with distilled water to move the sticking particles into the measuring flask using a wash bottle. Add water in tiny quantities while washing the funnel. The distilled water quantity used for this purpose should not exceed 50 ml. Using a wash bottle, wash the funnel carefully with distilled water to pass the solution attached to the funnel into the measuring flask Turn the flask of measurement until the oxalic acid dissolves. Using a wash bottle, thoroughly add enough distilled water to the measuring flask just below the etched mark on it. Add the last few mL of distilled water drop into the measuring flask until the reduced meniscus level just touches the mark. Put the stopper on the mouth of the flask and shake softly to make the entire solution uniform. Calculate it as a solution of oxalic acid M/20.
(b) Titration of Sodium Hydroxide and Oxalic Acid Solution:-
Rinse the burette with the sodium hydroxide solution. Take 25 ml of oxalic acid standard solution in a titration flask. Fill the burette with oxalic acid standard solution. Remove the air gap if any, from the burette by running the solution forcefully from the burette nozzle and note the initial reading. Pipette out 20ml of oxalic acid solution is a conical flask. Add 2-3 drops of phenolphthalein indicator to it. Titrate the oxalic acid solution with hydroxide solution until the pink colour disappears. Repeat the titration till three concordant readings are obtained.
5.Observations
Molarity of sodium hydroxide solution = M1
Indicator = Phenolphthalein
End point = Light pink colour
| S.N. | Volume of pipette (Volume of Oxalic acid) in ml | Volume of burette in ml | Volume of NaOH used | Concordant reading | |
| Initial | Final | ||||
| 1 | 25 ml | 0.0 ml | 20 ml | 25.4ml | 25.0 ml |
| 2 | 25 ml | 0.0 ml | 19.5 ml | 25.0 ml | |
| 3 | 25 ml | 0.0 ml | 19.5 ml | 25.0 ml | |
| 4 | 25 ml | 0.0 ml | 19.5 ml | 25.0 ml | |
6.Calculations:- Calculate the strength of HCl solution by using the equation
(COOH)2 + 2NaOH → (COONa)2 + 2H2O
NaOH solution (COOH)2 solution
a1 x M1 x V1 = a2 x M2 x V2
M 1= molarity of NaOH = ?
V1 = volume of NaOH solution = 20 ml
a1 = the acidity of the NaOH solution) = 1
M2= molarity of (COOH)2 = 1/20
V2 = volume of (COOH)2 solution =25 ml
a2 = the basicity of (COOH)2) = 2
1 x M1V1 = 2 x M2V2
M1 = 2 x M2 x V2
V1
M1 = 2 x 1 x 25 = 1 . =0.1 mol/L
20 x 25 10.
Concentration (strength) in g/L = Molarity×Molar mass
The strength of the given sodium hydroxide solution= 1 . X 40 g/mol = 4 g/lit
Results:- (1) Molarity of NaOH is 1 . or 0.1 mol/lit
10
(2) The strength of the given sodium hydroxide solution is 4 g/L.
Precautions:-
- While weighing, do not spill the substance on the balance pan.
- Rotate the knob of balance gently.
- Keep the weights in the weights box at the proper places after weighing
- Wash the watch glass carefully so that even a single crystal is not left on the watch glass.
- Bring the watch glass close to the funnel while transferring weighed substance and transfer it gently. Wash it repeatedly with distilled water.
- Wash the burette with water after titration is over.
- The last few drops should be added using a pipette to avoid extra addition of distilled water above the mark on the neck of the measuring cylinder.
CHEMIGOD 