Neutralisation Titration - GCSE Science Required Practical (Triple)

Summary

This video explains a titration experiment used to determine the concentration of an unknown solution. The instructor walks through the process of reacting sodium hydroxide of known concentration with sulfuric acid of unknown concentration. Key tools like the pipette and burette are introduced, with safety precautions emphasized. The procedure includes measuring volumes accurately, adding indicators, and conducting both rough and accurate titrations. The video concludes with calculations derived from the balanced equation to find the exact concentration of sulfuric acid, revealing it to be stronger than initially estimated.

Takeaways

• 🔬 A titration is used to determine the concentration of an unknown solution by reacting it with a solution of known concentration.
• 🧪 In this experiment, the sodium hydroxide solution has a concentration of 0.1 mol/dm³, and the sulfuric acid solution's concentration is unknown but estimated at around 0.05 mol/dm³.
• 👩‍🔬 A pipette is used to measure an exact volume of sodium hydroxide (25 cm³), and it's crucial to use a safety filler to avoid health risks.
• 📏 The meniscus, the curved surface of the liquid in a pipette, must be aligned with the measurement line to ensure accuracy.
• ⚗️ The burette is used to measure the volume of sulfuric acid added, with the level set to zero at the start of the titration.
• 🔍 Methyl orange is the chosen pH indicator, changing from yellow to pink as sulfuric acid is added to sodium hydroxide during titration.
• 🔄 The first titration is a rough estimate to determine an approximate volume of acid needed; subsequent titrations are done more accurately.
• 💧 Adding the sulfuric acid drop by drop near the endpoint ensures precision when identifying the color change for neutralization.
• 📊 After determining the exact volume of acid, the concentration of the sulfuric acid can be calculated using the balanced equation and mole ratio.
• 📉 The calculated concentration of the sulfuric acid turned out to be 0.095 mol/dm³, almost twice the expected concentration of 0.05 mol/dm³.

Q & A

What is the purpose of performing a titration in this experiment?

The purpose of the titration is to determine the concentration of an unknown sulfuric acid solution by reacting it with a sodium hydroxide solution of known concentration.

What piece of equipment is used to measure out an exact volume of the sodium hydroxide solution?

A pipette is used to measure out an exact volume of 25 cm³ of sodium hydroxide solution.

Why is it important not to blow out the small amount of solution left in the tip of the pipette?

The small amount left in the tip is accounted for in the design of the pipette. Blowing it out would result in more than the intended 25 cm³ being transferred, which would affect the accuracy of the experiment.

What is a meniscus, and how does it affect measurements in this experiment?

A meniscus is the curved surface of a liquid in a container. When measuring the sodium hydroxide and sulfuric acid, the bottom of the meniscus should be aligned with the calibration line for an accurate measurement.

What is the role of the burette in the titration process?

The burette is used to gradually add the sulfuric acid to the sodium hydroxide solution, allowing precise control over the volume of acid being added during the titration.

Why is methyl orange used in this titration, and what does the color change indicate?

Methyl orange is used as a pH indicator in this titration because it works well for the reaction between sodium hydroxide and sulfuric acid. The color change from yellow to pink indicates the endpoint of the titration, where neutralization occurs.

What is the difference between a rough titration and an accurate titration?

A rough titration is done quickly to get an approximate idea of the volume of acid needed. In an accurate titration, the acid is added slowly, drop by drop, to precisely determine the endpoint.

What is the balanced chemical equation for the reaction between sodium hydroxide and sulfuric acid?

The balanced chemical equation is: 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O. Two moles of sodium hydroxide react with one mole of sulfuric acid.

How is the number of moles of sodium hydroxide calculated from the known concentration and volume?

The number of moles is calculated using the formula: moles = concentration × volume. In this experiment, the concentration is 0.1 mol/dm³ and the volume is 25 cm³, which is converted to 0.025 dm³. The moles of sodium hydroxide = 0.1 × 0.025 = 0.0025 moles.

How is the concentration of sulfuric acid determined after the titration?

The concentration of sulfuric acid is determined using the ratio from the balanced equation. Since 2 moles of NaOH react with 1 mole of H₂SO₄, the number of moles of H₂SO₄ is half that of NaOH. The concentration is then calculated using the formula: concentration = moles/volume.