# Titration of Oxalic Acid against Sodium Hydroxide

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## Titration Practical

This technique is used to determine the unknown concentration of an acid or a base by neutralizing it with an acid or base of known concentration. The process of determination of the strength of a solution of acid by titration with a standard solution of a base is termed acidimetry, on the other hand when the strength of a solution of an alkali is determined using titration with a standard solution of an acid it is called as alkalimetry. Now we will learn about the titration practical or titration of oxalic acid for the estimation of Sodium Hydroxide.

### Aim

To determine the strength of the sodium hydroxide solution by titrating it against a standard solution of oxalic acid.

### Theory

Here, the sodium hydroxide solution is not a primary standard and is taken in a burette and a known volume of the oxalic acid (a standard solution) is taken in the titration flask. The titration is carried out using phenolphthalein as an indicator. In an acid-base titration, the amount of acid becomes chemically equivalent to the amount of base present in the end. In the case of strong acid and strong base titration, the solution becomes neutral at the endpoint of the solution.

The reaction involved in the titration:

### Apparatus Required

• Pipette

• Burette

• Burette stand

• Stirrer

• Oxalic acid NaOH

• Sodium hydroxide solution

• Phenolphthalein indicator

### Procedure:

• Take a burette and wash it thoroughly with clean water and dry it.

• Weigh the exact amount of dried watch glass and record its weight.

• Using a funnel shift oxalic acid carefully from the watch glass into a dried measuring flask.

• Wash the watch glass with distilled water, the volume of distilled water should not be more than 50 ml.

• Wash the funnel carefully using a wash bottle with distilled water, turn the flask of measurement until the oxalic acid dissolves.

• Thoroughly add enough distilled water to the measuring flask just below the mark.

• Add the last few drops of distilled water into the measuring flask until the reduced meniscus level just touches the mark.

• Put the stopper on the mouth of the flask and shake it gently to make the entire solution uniform. Calculate the solution of oxalic acid M/20.

### Estimation of Oxalic Acid by Titrating it with NaOH

• Rinse the burette with the standard oxalic acid solution and take10cm3 of oxalic acid solution in a titration flask. Fill the burette with sodium hydroxide solution and also remove the air gap if any.

• In pipette, take out 20ml of NaOH solution in a conical flask. Add two drops of phenolphthalein indicator into it and place it below the nozzle of the burette.

• Now run the sodium hydroxide solution slowly and dropwise into the flask until a very faint permanent pink colour is just obtained. Read the lower meniscus of the solution again in the burette and record it as the final burette reading. Repeat this procedure two to three times.

### Observations

Molarity of oxalic acid solution = $\frac{M}{20}$

Molarity of sodium hydroxide solution = m

The volume of oxalic acid solution = 10cm³

The indicator used = Phenolphthalein

Endpoint indication = Light pink colour

 Initial Reading Final Reading The volume of NaOH used Readings x  cm³ y cm³ (y - x)cm³ V cm³ y cm³ z cm³ (z - y)cm³ V cm³ z cm³ w cm³ (w - z)cm³ V cm³

### Calculations:

Mass of oxalic acid dissolved (100ml) in standard solution = x g

Estimation of sodium hydroxide

Strength of oxalic acid = X x 10 g/L

Normality (N) of standard oxalic acid = Strength/ Equivalent weight = X x $\frac{10}{63.04}$

Normality (N₁) of sodium hydroxide solution

N₁  x  V₁  =  N  x  V

N₁  =  $\frac{V}{V_{1}}$ x N

Normality(N₂) of given oxalic acid solution

N₂  x  V₂  =  N₁  x  V₁

N₂  =  N₁  x  $\frac{V_{1}}{V_{2}}$

Strength of given oxalic acid = N₂  x  63.04 g/L

Result: The strength of the given solution(NaOH) is _______ g/L.

### Precautions

• Wash the burette with water before and after titration is over.

• Wash the watch glass carefully so that there is no crystal left on the watch glass.

• The last few drops should be added using a pipette to avoid any extra addition of distilled water above the mark on the neck.