What is Equivalence Point (acid-base titrations)?

Summary

This video explains the process of titration, where the pH of a solution changes as a base is added to an acid. The key moment in the titration is the equivalence point, where the amount of acid and base perfectly neutralize each other, causing a sharp change in pH. The equivalence point is compared to the pivot of a seesaw, where both sides are balanced. The titration’s endpoint is identified through an indicator, marking the point when no acid or base is left to react. This process reveals the crucial moment when the acid-base reaction is complete.

Takeaways

• 😀 pH changes during titration as a base is added to an acid.
• 😀 A graph of pH changes forms a pH curve, showing a significant rise in pH when a strong base like sodium hydroxide is added to a strong acid like hydrochloric acid.
• 😀 The pH curve has a sharp rise, indicating the transition from acidic to alkaline.
• 😀 The point of rapid pH change is called the equivalence point, where all the acid has reacted with the base.
• 😀 At the equivalence point, only salt and water remain in the solution.
• 😀 After the equivalence point, any extra base added will not react and will make the solution more alkaline.
• 😀 The equivalence point marks the moment when there is no excess acid or base present.
• 😀 The equivalence point is like the balancing moment on a seesaw, where the amounts of acid and base are equal.
• 😀 The sharp transition on the pH curve corresponds to this rapid change in pH at the equivalence point.
• 😀 We use an indicator to identify the end point of the titration, which occurs when the indicator changes color, signaling the equivalence point.

Q & A

What happens during a titration when a base is added to an acid?

During a titration, as a base is added to an acid, the pH of the solution in the flask or beaker changes. The pH increases, moving from acidic towards alkaline.

What is a pH curve and how does it relate to titration?

A pH curve is a graph showing how the pH of a solution changes as a titrant is added. In a titration, it helps visualize the transition of the solution from acidic to alkaline, highlighting the equivalence point where all the acid reacts with the base.

What does the pH curve look like when a strong base like sodium hydroxide is added to a strong acid like hydrochloric acid?

The pH curve of a titration between sodium hydroxide (strong base) and hydrochloric acid (strong acid) shows a sharp, sudden increase in pH. This rapid change occurs at the equivalence point.

What is the equivalence point in a titration?

The equivalence point in a titration is the moment when all the acid has reacted with the base, and neither acid nor excess base remains in the solution. At this point, only salt and water are present.

Why is the rapid pH change at the equivalence point significant?

The rapid pH change at the equivalence point is significant because it marks the transition from an acidic to an alkaline solution. This is the key moment in a titration where the amounts of acid and base are perfectly balanced.

How does the concept of a seesaw help explain the equivalence point?

The seesaw analogy helps explain the equivalence point by visualizing the balance between acid and base. As one is added, the seesaw tips until it suddenly pivots when both are perfectly balanced, just like the sharp change in the pH curve at the equivalence point.

What does the sharp line in a pH curve represent?

The sharp line in a pH curve represents the rapid change in pH as the titration nears the equivalence point. It shows the moment when the solution shifts dramatically from acidic to alkaline.

Why can’t we directly observe the equivalence point during a titration?

We can’t directly observe the equivalence point because it occurs very suddenly and is a brief moment in time. However, we can identify it using an indicator, which changes color when the equivalence point is reached.

What role does an indicator play in a titration?

An indicator is used to signal the end of the titration by changing color when the equivalence point is reached. This helps stop the titration at the correct moment.

What happens if extra base is added after the equivalence point?

If extra base is added after the equivalence point, the solution becomes alkaline, as there is no more acid to react with. This leads to a rapid increase in pH.