Question

When a strong acid is titrated against a strong base, the end point is the point of (a) zero conductance (b) maximum conductance (c) minimum conductance (d) none of these.

Short answer

The end point of a strong acid-strong base titration corresponds to minimum conductance.

Step-by-step solution

Understanding Titration

Understand that titration is a controlled chemical reaction between a chemical solution of known concentration (titrant) and a solution of unknown concentration (analyte). In this case, a strong acid is being titrated with a strong base.

Understanding Conductance

Recognize that conductance is the measure of a solution's ability to conduct electricity. It is proportional to the ion concentration in a solution – the greater the concentration of ions, the higher the conductance.

Identifying the End Point

Understand that the end point of a titration is the point at which the reaction between the titrant and the analyte is complete. In the case of titrating a strong acid with a strong base, the end point is achieved when the acid has been completely neutralized by the base.

Determining the Conductance at the End Point

In this titration where a strong acid is being neutralized by a strong base, at the end point or point of neutralization, water is formed along with a salt. As water minimally conducts electricity, the conductance at the end point should be at its minimum. Therefore, the correct answer is (c) minimum conductance.

Key concepts

Understanding Strong Acids

To grasp titrations involving a strong acid, we need to start by defining what a strong acid is. A strong acid is one that completely dissociates in water. This means every molecule of the acid breaks down into hydrogen ions, boosting the ion concentration. Some common examples of strong acids include:

• Hydrochloric acid (HCl)
• Sulfuric acid (H₂SO₄)
• Nitric acid (HNO₃)

Because strong acids fully dissociate, they have high initial conductance in solution. This feature allows them to significantly influence the conductivity of the solution as the titration begins. It is important to remember that the behavior of strong acids is vastly different from weak acids, which do not fully dissociate in solution.

Exploring Strong Bases

Just like strong acids, strong bases are substances that completely dissociate in water, releasing hydroxide ions. This complete dissociation is what earns them the 'strong' label, indicating their ability to dramatically alter the solution's properties. Some common strong bases are:

• Sodium hydroxide (NaOH)
• Potassium hydroxide (KOH)
• Barium hydroxide (Ba(OH)₂)

When a strong base is added to a solution during titration, it increases the number of hydroxide ions in the solution. This, in turn, affects the conductivity and pH of the solution. The complete dissociation of a strong base is crucial in a titration because it ensures a predictable and uniform reaction with a strong acid, leading to an accurate end point at neutralization.

Understanding Conductance in Solutions

Conductance in a solution measures how well the solution carries electricity. This electrical conductance arises from the movement of ions in the solution. The factors affecting conductance include:

• Number of ions: More ions mean better conductance.
• Mobility of ions: Smaller ions usually move faster.
• Charge of ions: Ions with more charge carry more current.

In the context of titration, the conductance changes as the reaction between the acid and base proceeds. Initially, as strong acid dissociation leads to high conductance due to lots of ions. However, as titration progresses and approaches the end point, hydrogen ions from the acid react with hydroxide ions from the base to form water, which doesn't conduct electricity well.

Neutralization in Titration

Neutralization is a core component in titration involving a strong acid and strong base. This chemical reaction involves the combination of hydrogen ions from the acid with hydroxide ions from the base to form water. The equation for this reaction is:\[ H^+ + OH^- ightarrow H_2O \]Through this process, the acidic and basic properties of the solutions are nullified. The objective of a titration is to reach the neutralization point where the amounts of the acid and base are exactly balanced. At neutralization in a titration, conductance is notably low because water and the neutral salt produced do not conduct electricity as well as the original acids and bases. This is why minimum conductance is observed at the end point of titration. It is a critical signifier of the titration's completion.