Question

How would you differentiate between a strong and a weak monoprotic acid from the results of the following procedures? (a) Electrical conductivity of an equimolar solution of cach acid is measured. (b) Equal molarities of each are tested with pH paper. (c) Zinc metal is added to solutions of equal concentration.

Short answer

Measure electrical conductivity, test with pH paper, and observe reactions with zinc metal. Higher conductivity, lower pH, and more vigorous zinc reaction indicate a strong monoprotic acid.

Step-by-step solution

- Measure Electrical Conductivity

A strong monoprotic acid fully ionizes in water, producing a high concentration of ions, resulting in high electrical conductivity. In contrast, a weak monoprotic acid only partially ionizes, leading to lower ion concentration and lower electrical conductivity. Measure and compare the electrical conductivities of equimolar solutions of the two acids to determine which has higher conductivity, indicating the stronger acid.

- Test with pH Paper

A strong monoprotic acid has a lower pH due to its complete ionization, releasing more hydrogen ions. A weak monoprotic acid, only partially ionizing, will result in a higher pH. Dip pH paper into equal molar solutions of both acids and compare the color changes. The solution that shows a lower pH (stronger acid) is the one that ionizes more completely.

- React with Zinc Metal

When zinc metal is added to an acid solution, hydrogen gas is produced. A strong monoprotic acid, which ionizes completely, will react more vigorously with zinc, producing hydrogen gas rapidly. A weak monoprotic acid will react less vigorously due to partial ionization. Add zinc metal to each acid solution of equal concentration and observe the rate and volume of hydrogen gas production; a stronger acid will result in faster and more gas.

Key concepts

Electrical Conductivity

Electrical conductivity is a key method to differentiate between strong and weak monoprotic acids. When we dissolve an acid in water, it ionizes, releasing charged particles that can carry electricity. A strong acid ionizes completely, producing a high concentration of ions, which in turn results in high electrical conductivity. In contrast, a weak monoprotic acid only partially ionizes, resulting in fewer ions in solution and lower electrical conductivity.

By measuring the electrical conductivity of equimolar solutions of each acid, we can observe the following:

• Strong acids will exhibit high electrical conductivity due to a greater number of free ions.
• Weak acids will show lower electrical conductivity because of partial ionization.

This method is a reliable way to determine the strength of different monoprotic acids. Make sure to use equimolar solutions for accurate comparison.

pH Measurement

pH measurement is another effective way to differentiate between strong and weak monoprotic acids. pH is a scale that indicates the acidity or basicity of a solution. It ranges from 0 to 14, with lower numbers representing stronger acids. When an acid ionizes, it releases hydrogen ions (H+), affecting the pH.

A strong monoprotic acid, which ionizes completely, will have a higher concentration of hydrogen ions and thus a lower pH. A weak monoprotic acid, on the other hand, only partially ionizes, yielding fewer hydrogen ions and a higher pH.

• Dip pH paper into equal molar solutions of each acid.
• Compare the color changes on the pH paper.

The solution that shows a lower pH is the stronger acid, as it ionizes more completely and produces more hydrogen ions.

Acid-Metal Reaction

Adding zinc metal to acid solutions is a practical way to observe the reactivity difference between strong and weak monoprotic acids. When zinc is added to an acid, it reacts with the hydrogen ions to produce hydrogen gas (H2).

In a strong monoprotic acid, which ionizes completely, the concentration of hydrogen ions is high, leading to a vigorous reaction and rapid production of hydrogen gas. Conversely, a weak acid, with fewer hydrogen ions due to partial ionization, reacts less vigorously, producing hydrogen gas more slowly.

• Add zinc metal to each equimolar acid solution.
• Observe the rate at which hydrogen bubbles form.
• Monitor the volume of hydrogen gas produced over a set period.

The acid that reacts more vigorously is the stronger acid. This straightforward experiment visually and quantitatively demonstrates the difference between strong and weak acids.