Balanced Equation Indicator Choice And Calculation In Oxalic Acid And Sodium Hydroxide Titration
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 for 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:
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Apparatus Required
Pipette
Burette
Burette stand
Conical flask
Stirrer
Measuring flask
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 take 10cm3 of oxalic acid solution in a titration flask. Fill the burette with sodium hydroxide solution and also remove the air gap if any.
In a 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 color 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
Calculations:
Mass of oxalic acid dissolved (100ml) in standard solution = x g
Estimation of sodium hydroxide
Strength of oxalic acid = X \[\times\] 10 g/L
Normality (N) of standard oxalic acid = Strength/ Equivalent weight = \[X \times \frac{10}{63.04}\]
Normality (N₁) of sodium hydroxide solution
\[N₁ x V₁ = N x V\]
\[N₁ = \frac{V}{V_1} \times N \]
Normality(N₂) of given oxalic acid solution
\[N₂ x V₂ = N₁ x V₁ \]
\[N_2 = \frac{V_1}{V_2} \times N_1 \]
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.
Properties of Sodium Hydroxide
Sodium Hydroxide is our main component in this titration process against oxalic acid. Let's understand some of the chemical properties of sodium hydroxide to understand the components used in the titration. Sodium hydroxide is an odorless and white crystalline substance that absorbs moisture from the air at the environmental or surrounding temperature. It's a synthetic chemical. When dissolved in water or neutralized with acid, it releases a significant amount of heat, which could ignite combustible objects. Sodium hydroxide is a highly corrosive substance. It's usually applied as a solid or a 50% solution. Caustic soda and lye are two more frequent names for this substance. Products like Dyestuffs, explosives, paper, rayon, Soaps, and petroleum are all made with the help of sodium hydroxide. Sodium hydroxide is also used in the processing of cotton and fabric, metal cleaning and processing, laundry and bleaching, electrolytic extraction, electroplating, and oxide coating, among other things. Commercial drain and oven cleansers frequently contain it.
Properties of Oxalic Acid
Another important component of titration is oxalic acid. Let's understand the properties of oxalic acid. The first member of the di-carboxylic acid group is oxalic acid. One molecule contains two carboxyl groups. Its potassium salt can be found in Rhubarb, Sorrel, and other oxalic group plants. Calcium oxalate is found in several plants and animals. It is created in the lab by oxidizing sugar cane sugar. It's created in a commercial setting by heating Sodium Formate. It comes in two forms: crystal and amorphous. Two molecules of Kelsan water make up one molecule of crystalline oxalic acid. The composition formula for amorphous oxalic acid is H2C2O4 and the molecular formula is H2C2O4.
Physical properties of Oxalic Acid
The physical properties of oxalic acid are also important to keep in mind from an exam point of view. The first thing to understand is that oxalic acid is present in a solid form that is colourless in its appearance and odourless in nature, that is there is no particular smell of it. Another form of oxalic acid is crystalline oxalic acid has a melting temperature of around 101.5°C, while anhydrous oxalic acid has a melting point of 189.5°C. Anhydrous oxalic acid is also soluble in alcohol and water and is unbreakable in ether.
FAQs on Titration Of Oxalic Acid Against Sodium Hydroxide Explained
1. What is the reaction between oxalic acid and sodium hydroxide in titration?
The reaction between oxalic acid and sodium hydroxide is a neutralization reaction: H2C2O4(aq) + 2NaOH(aq) → Na2C2O4(aq) + 2H2O(l).
- Oxalic acid is a diprotic acid (donates two H+ ions).
- Each mole of oxalic acid reacts with 2 moles of NaOH.
- The products are sodium oxalate and water.
2. Why is oxalic acid considered a primary standard in titration?
Oxalic acid (usually H2C2O4·2H2O) is considered a primary standard because it is pure, stable, and has a known molar mass.
- It is available in highly pure crystalline form.
- It is non-hygroscopic and stable in air.
- Its molar mass can be accurately calculated for precise standard solution preparation.
3. What indicator is used in the titration of oxalic acid against sodium hydroxide?
The commonly used indicator in this titration is phenolphthalein.
- Phenolphthalein is colorless in acidic medium.
- It turns pale pink in slightly basic solution.
- The end point is the first permanent light pink color.
4. How do you calculate the molarity in oxalic acid and sodium hydroxide titration?
The molarity is calculated using the relation M1V1n1 = M2V2n2, where n represents the number of moles of H+ or OH- exchanged.
- For oxalic acid, n = 2 (diprotic).
- For NaOH, n = 1 (monobasic).
- Alternatively, use N1V1 = N2V2 for normality calculations.
5. Why is oxalic acid called a diprotic acid?
Oxalic acid is called a diprotic acid because one molecule can donate two hydrogen ions (H+) in solution.
- Its formula is H2C2O4.
- It ionizes in two steps, releasing two acidic protons.
- This is why it reacts with 2 moles of NaOH per mole of acid.
6. What is the end point in the titration of oxalic acid against NaOH?
The end point is reached when the solution turns a permanent pale pink due to phenolphthalein.
- This indicates slight excess of NaOH.
- The color should persist for about 30 seconds.
- It closely matches the equivalence point of the reaction.
7. What is the balanced chemical equation for the neutralization of oxalic acid with NaOH?
The balanced neutralization equation is H2C2O4(aq) + 2NaOH(aq) → Na2C2O4(aq) + 2H2O(l).
- Two hydroxide ions neutralize two acidic protons.
- The salt formed is sodium oxalate.
- The reaction follows a 1:2 mole ratio (acid:base).
8. How do you prepare a standard solution of oxalic acid for titration?
A standard oxalic acid solution is prepared by accurately weighing a known mass of H2C2O4·2H2O and dissolving it in distilled water to a fixed volume.
- Weigh the required mass using an analytical balance.
- Dissolve it in a beaker with distilled water.
- Transfer to a volumetric flask and make up to the mark.
9. What precautions should be taken during the titration of oxalic acid and NaOH?
Key precautions include accurate measurement, proper indicator use, and careful observation of the end point.
- Rinse burette with NaOH and pipette with oxalic acid before use.
- Add phenolphthalein in small quantity (2–3 drops).
- Add NaOH slowly near the end point to avoid overshooting.
- Record readings at eye level to avoid parallax error.
10. What is the principle behind the titration of oxalic acid against sodium hydroxide?
The principle is based on a neutralization reaction between a strong base (NaOH) and a weak diprotic acid (oxalic acid).
- At equivalence point, moles of H+ equal moles of OH-.
- The reaction forms salt and water.
- The stoichiometric ratio is 1 mole oxalic acid : 2 moles NaOH.
