Why Use a Universal Indicator in Strong Base Titration?
While performing any experiment, it is important to know the amount of substance present. This titration is the same process that lets you identify the amount of substance present and to know its proportion.
When we mix any other substance to an unknown amount of one substance, it is known as titration. You can quickly identify the unknown amount of one substance with the reaction taking place. The results gained are in the form of proportion in which the two substances mix. An experimental observation is made when titrant or titrating reagent is added in the definite amount using a burette having a stop cock.
Titration Experiment
Suppose you are given a substance or solution with an unknown amount, and your goal is to find the amount of substance available to you, the process of titration is used in such cases. In the experiment, you will be using the known amount of substance or solution and add to that unknown amount. When this universal indicator or titrating reagent brings a change in the solution’s colour, the point of equivalence is reached.
Initially, you will observe a slow change in the shade of the solution. However, be careful when you are about to reach the point of equivalence. The changes observed at that time are very rapid.
Example of Titration
Titration can be done with:
Strong Acid with universal Indicator.
Strong Acid with Strong Base.
Strong Base with Universal Indicator.
Below we will study the titration of a Strong Base using the Universal Indicator experiment.
Performing The Experiment
Aim of the Experiment:
To study the change in pH value with titration of a strong base using universal indicator experiment.
Things Required:
One burette, 2beakers of 250 ml each, a conical flask of 100 ml, 25 ml of Hydrochloric acid with 0.1 M, a dropper, a pH chart, 50 ml of sodium hydroxide solution of 0.1 M, and a universal indicator.
Setting Up Experiment Base:
In the above picture, a burette is set on a stand having a stop cock. A flash is kept at the base having a base or acidic indicator. Burette will be containing a base or acid to which you want to test.
Procedure to Follow:
In the conical flask kept at the base, take Hydrochloric acid with 0.1 M.
As you have taken acid in the flask, add a base to the burette. Add Sodium hydroxide with 0.1 M.
Now add two-three drops of universal indicator in the conical flask kept at the base.
Open the stop cock, and keep adding a base to acid drop by drop. Also, keep shaking the flask simultaneously.
Keep observing the flask and note down if colour change content is observed. Every time you keep adding solution from the burette, keep noting the colour and compare it with the pH value scale.
Note down your observation in the observation table.
Also, plot a final graph for pH V/s for the total volume of NaOH used from the burette.
Observations:
As you keep adding NaOH to HCl, you need to keep observing when it finally reaches its neutral point, with each observation made drop by drop.
The below table is used to note down your NaOH observations used in 25 ml of HCl with both 0.1 M.
Precautions to Take While Performing Titration Experiment:
The concentration of both strong acid and strong base must be the same.
Use the minimum indicator as possible.
Do not open the stop cock at once. Be sure to add a base to acid drop by drop.
What are The Different Viva Voice Questions for Reference?
How will you define titrate in your terms?
What is titrant according to you?
What should be the final pH value for the experiment performed?
What will happen if you perform the same experiment with a strong base and a weak acid?
FAQs on Titration of a Strong Base Using Universal Indicator: Step-by-Step Guide
1. What are the step-by-step instructions for performing the titration of a strong base with a strong acid?
The titration of a strong base (like NaOH) with a strong acid (like HCl) involves the following key steps:
- Preparation: Rinse the burette with the acid (the titrant) and the conical flask with the base (the analyte).
- Setup: Fill the burette with the standard acid solution and record the initial reading. Accurately pipette a known volume of the strong base solution into the conical flask.
- Indicator: Add 2-3 drops of a suitable indicator, such as phenolphthalein or a universal indicator, to the conical flask.
- Titration: Slowly add the acid from the burette to the base in the flask while constantly swirling the flask.
- Endpoint: Stop adding acid the moment you observe a permanent colour change in the solution. This is the endpoint.
- Reading: Record the final burette reading. The difference between the final and initial readings gives the volume of acid used.
- Repetition: Repeat the titration at least three times to get concordant readings (values that are very close to each other) for accuracy.
2. Which indicators are suitable for a strong acid-strong base titration and why?
For a strong acid-strong base titration, the most suitable indicators are those whose pH range for colour change falls within the steep vertical portion of the titration curve, which is roughly between pH 3 and 11. The two most common choices are:
- Phenolphthalein: It changes colour in the pH range of 8.2–10. It is colourless in acidic solution and turns pink in basic solution, providing a very sharp and easily detectable endpoint.
- Methyl Orange: It changes colour in the pH range of 3.1–4.4. It is red in acidic solution and yellow in basic solution.
3. What is the purpose of using a universal indicator in a titration experiment?
While single indicators like phenolphthalein are preferred for precise endpoint detection in quantitative analysis, a universal indicator serves a different purpose. Its main function is to demonstrate the continuous change in pH throughout the titration process. As the titrant is added, a universal indicator will cycle through a spectrum of colours (e.g., red in strong acid, through orange, yellow, green at neutral, to blue and violet in strong base), visually representing the titration curve. It is an excellent educational tool for understanding the concept of neutralisation but is generally not used for accurate quantitative results because its colour change is gradual rather than sharp at the endpoint.
4. What is the fundamental chemical reaction that occurs during the titration of a strong acid and a strong base?
The fundamental chemical reaction is a neutralisation reaction. In this process, hydrogen ions (H⁺) from the strong acid react with hydroxide ions (OH⁻) from the strong base to form water (H₂O). The other ions, the cation from the base (e.g., Na⁺ from NaOH) and the anion from the acid (e.g., Cl⁻ from HCl), remain in the solution as spectator ions and form a salt. The net ionic equation, which represents the core process, is: H⁺(aq) + OH⁻(aq) → H₂O(l). This reaction continues until all the ions of the limiting reactant have been consumed at the equivalence point.
5. How do you interpret a titration curve for a strong acid-strong base reaction?
A titration curve for a strong acid-strong base reaction plots pH (on the y-axis) against the volume of titrant added (on the x-axis). You can interpret it by observing three key regions:
- Initial Slow Change: The pH changes slowly at the beginning as the titrant is added.
- Steep Vertical Section: Near the equivalence point, the pH changes very rapidly with the addition of just a small volume of titrant. The midpoint of this vertical section is the equivalence point.
- Final Slow Change: After the equivalence point, the pH again changes slowly as the solution becomes progressively more acidic or basic.
6. Why is the pH at the equivalence point of a strong acid-strong base titration exactly 7 (at 25°C)?
The pH at the equivalence point is exactly 7 because at this specific point, the moles of acid (H⁺ ions) are stoichiometrically equal to the moles of base (OH⁻ ions). They completely neutralise each other to form water. The resulting solution contains only water and a neutral salt (e.g., NaCl), which is formed from the cation of a strong base and the anion of a strong acid. Neither of these ions undergoes hydrolysis (reacts with water) to produce excess H⁺ or OH⁻ ions. Therefore, the solution is neutral, with a pH of 7.
7. How is the concentration of the unknown solution calculated after completing the titration?
The concentration of the unknown solution is calculated using the titration formula, which is derived from the stoichiometry of the neutralisation reaction. The formula is: M₁V₁ / n₁ = M₂V₂ / n₂. Where:
- M₁ and V₁ are the molarity and volume of the acid.
- M₂ and V₂ are the molarity and volume of the base.
- n₁ and n₂ are the stoichiometric coefficients (mole ratio) of the acid and base from the balanced chemical equation.
8. What are the most common sources of error in a titration experiment and how can they be minimized?
Common sources of error in titration can be systematic or random. Key examples include:
- Misreading the Burette: An error in reading the initial or final volume. This can be minimized by reading the volume at eye level from the bottom of the meniscus.
- Incorrect Endpoint Detection: Overshooting the endpoint by adding too much titrant. This is minimized by adding the titrant drop by drop near the endpoint and swirling continuously.
- Improperly Cleaned Glassware: Contaminants in the pipette or burette can alter concentrations. Ensure all glassware is rinsed with deionised water and then with the solution it will contain.
- Air Bubbles in the Burette: An air bubble in the burette tip can be dislodged during titration, leading to an inaccurate volume reading. Ensure all bubbles are removed before starting.
