Question

 

Classify each titration curve as representing a strong acid titrated with a strong base, a strong base titrated with a strong acid, a weak acid titrated with a Strong base, a weak base titrated with a strong acid, or a polyprotic acid titrated with a strong base.

Answer 1

Concepts and reason

This problem is based on titration curves of acids and bases.

Titration curve is a plot of the pH of the analyte solution against the volume of added titrant. In a titration of an acid or base analyte against the titrant (base or acid),at a certain point called equivalence point the number of moles of hydrogen ions becomes equal to the number of moles of the hydroxide ions.

The hydrogen ions react with the hydroxide ions to produce water, which is neutral having a pH of seven.

Fundamentals

In case of strong acid-strong base titration when both the solution is of equal strength, the analyte solution at equivalence point contains no hydrogen or hydroxide ions and so the pH is always equal to 7.

However, in case of weak analyte or titrant, the pH at equivalence point is not equal to 7. In these cases, at equivalence point, the solution contains the salt of a weak acid or base which are conjugate base or acid. So, solution becomes basic or acidic, but not neutral.

Equivalence point is where the titration curve exhibits an inflection point.

In case of polyprotic acids, each molecule of acid release more than one hydrogen ion, so its titration curve with a strong base titrant shows an inflection point or equivalence point for each hydrogen ion released.

(1)

For the titration curve shown below:

Equivalence point is at also, titration starts at low pH and ends at high pH this indicates that titration is between strong acid and strong base.

(2)

For the titration curve shown below:

Equivalence point is at and titration curve begins at high pH and ends at low pH

this indicates that titration is between strong base and strong acid.

(3)

For the titration curve shown below:

At equivalence point pH is greater than 7 also, curve begins at low pH and ends at high pH therefore, this indicates the titration between weak acid and strong base. Since, pH is more than 7 that means analyte is base.

(4)

For the titration curve shown below:

At equivalence point pH is less than 7 also, curve begins at high pH and ends at low pH therefore, this indicates the titration between weak base and strong acid. Since, pH is less than 7 that means analyte is acid.

(5)

For the titration curve shown below:

There are two equivalent points also curve starts from low pH and ends at high pH. There must be a polyprotic acid (weak) because there are 2 equivalent points and starting point is low pH.

Therefore, this indicates titration of polyprotic acid and strong base.

Ans: Part 1

Titration curve is for strong acid and strong base titration.

Part 2

Titration curve is for strong base and strong acid titration.

Part 3

Titration curve is for weak acid and strong base titration.

Part 4

Titration curve is for weak base and strong acid titration.

Part 5

Titration curve is for polyprotic acid and strong base titration.