Keywords: Acid-Base Titration, Hydrochloric Acid, Concentration, IGCSE, Prescribed Practical, pH, Indicator, Burette, Pipette, Titration

Introduction: Acid-base titration is a widely used technique in chemistry to determine the concentration of an unknown acid or base solution. In this practical investigation, we will be using acid-base titration to determine the concentration of a hydrochloric acid solution. The method involves reacting a known volume of the acid solution with a standard solution of a base, using an indicator to determine the endpoint of the reaction. The amount of base needed to neutralize the acid can be used to calculate the concentration of the acid solution.

Equipment:

Burette Pipette 250 ml Erlenmeyer flask 50 ml of hydrochloric acid solution 100 ml of sodium hydroxide solution (0.1M) Phenolphthalein indicator Distilled water

Method:

1. Clean and rinse the burette and pipette with distilled water.
2. Fill the burette with the sodium hydroxide solution.
3. Use the pipette to transfer 25 ml of hydrochloric acid solution to the Erlenmeyer flask.
4. Add 2-3 drops of phenolphthalein indicator to the acid solution.
5. Titrate the hydrochloric acid solution with the sodium hydroxide solution, swirling the flask continuously.
6. The endpoint of the titration is reached when the pink color of the indicator changes to colorless.
7. Record the volume of the sodium hydroxide solution used.
8. Repeat steps 3-7 two more times.
9. Calculate the average volume of sodium hydroxide solution used to neutralize the hydrochloric acid solution.
10. Calculate the concentration of the hydrochloric acid solution using the formula: concentration = (volume of sodium hydroxide solution used x concentration of sodium hydroxide solution) / volume of hydrochloric acid solution used.

Calculations and Expected Findings: The expected findings from this investigation are that the concentration of the hydrochloric acid solution can be calculated using the volume of the sodium hydroxide solution used to neutralize the acid. The concentration of the sodium hydroxide solution is known, and the volume of the hydrochloric acid solution used is also known. Using the formula, the concentration of the hydrochloric acid solution can be calculated.

Balanced equation for the reaction: HCl (aq) + NaOH (aq) → NaCl (aq) + H₂O (l)

Model Calculation: Moles of NaOH used = concentration × volume = 0.1 mol/dm³ × 0.025 dm³ = 0.0025 mol

From the balanced equation, we can see that the mole ratio of NaOH to HCl is 1:1. Therefore, the number of moles of HCl is also 0.0025 mol. The volume of HCl used is not given in the question, but let’s say it is 30 cm³.

We need to convert this to dm³, so: Volume of HCl used = 30 ÷ 1000 = 0.03 dm³ Now we can calculate the concentration of the HCl solution: Concentration of HCl = moles ÷ volume = 0.0025 mol ÷ 0.03 dm³ = 0.083 mol/dm³

Therefore, the concentration of the unknown hydrochloric acid solution is 0.083 mol/dm³.

Conclusion: The results of this investigation demonstrate that acid-base titration is a simple and effective method for determining the concentration of an unknown acid or base solution. By reacting a known volume of the unknown solution with a standard solution of a base, the concentration of the unknown solution can be calculated. This technique has important applications in many areas of chemistry.

Questions:

1. What is acid-base titration?
2. What is the purpose of using an indicator in acid-base titration?
3. How can the concentration of an unknown acid or base solution be determined using acid-base titration?
4. What is the standard solution used in this practical investigation?
5. What is the expected endpoint of the titration reaction?

Answers:

1. Acid-base titration is a technique used to determine the concentration of an unknown acid or base solution by reacting it with a known standard solution of the opposite type.
2. The purpose of using an indicator in acid-base titration is to signal the endpoint of the reaction, which is when the acid and base have reacted completely and the solution is neutral.
3. The concentration of an unknown acid or base solution can be determined using acid-base titration by adding a standardized solution of known concentration to the unknown solution until the reaction is complete. The point at which the reaction is complete is called the endpoint, which is determined by the color change of an indicator or by using a pH meter. By knowing the volume and concentration of the standardized solution added to the unknown solution, the concentration of the unknown solution can be calculated using stoichiometry.
4. The standard solution used in this practical investigation is sodium hydroxide (NaOH), which is a strong base of known concentration.
5. The expected endpoint of the titration reaction is when the amount of acid in the solution being titrated has reacted completely with the added base. At this point, the solution will be neutralized, and the pH of the solution will be around 7. This endpoint can be detected by the color change of the indicator used in the titration or by using a pH meter.

• Practical Chemistry