Question

I Classify the following compounds as acids or bases, weak or strong. (a) perchloric acid (b) cesium hydroxide (c) carbonic acid, \(\mathrm{H}_{2} \mathrm{CO}_{3}\) (d) ethylamine, \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{NH}_{2}\)

Short answer

Question: Classify the following compounds as acids or bases, and as weak or strong: (a) perchloric acid, (b) cesium hydroxide, (c) carbonic acid, and (d) ethylamine. Answer: (a) perchloric acid is a strong acid, (b) cesium hydroxide is a strong base, (c) carbonic acid is a weak acid, and (d) ethylamine is a weak base.

Step-by-step solution

Identify the compounds as acids or bases

First, let's look at the formula for each compound and determine if it is an acid or a base. (a) perchloric acid: The formula is \(\mathrm{HClO}_{4}\). Since it has an H+ ion in its formula, it is an acid. (b) cesium hydroxide: The formula is \(\mathrm{CsOH}\). Since it has an \(\mathrm{OH}^{-}\) ion in its formula, it is a base. (c) carbonic acid: The formula is \(\mathrm{H}_{2}\mathrm{CO}_{3}\). Since it has H+ ions in its formula, it is an acid. (d) ethylamine: The formula is \(\mathrm{C}_{2}\mathrm{H}_{5}\mathrm{NH}_{2}\). Since it has an amine group (\(\mathrm{NH}_{2}\)), which can accept an H+ ion, it is a base.

Classify the acids as weak or strong

Next, let's classify the identified acids as weak or strong. There are a few common strong acids, including perchloric acid, which ionizes completely in water. Other acids are generally weak. (a) perchloric acid: It is one of the strong acids. (c) carbonic acid: It is not a strong acid, so it is a weak acid.

Classify the bases as weak or strong

Lastly, let's classify the identified bases as weak or strong. Hydroxides of alkali metals (Group 1 on the periodic table) are generally strong bases. Additionally, amines are considered weak bases. (b) cesium hydroxide: Cesium is an alkali metal, so its hydroxide is a strong base. (d) ethylamine: It is an amine, a type of weak base.

Final Classifications

Here are all the classifications for the given compounds: (a) perchloric acid: strong acid (b) cesium hydroxide: strong base (c) carbonic acid: weak acid (d) ethylamine: weak base

Key concepts

Strong Acids

Strong acids are special because they completely dissociate in water. This means they separate fully into their ions.
When you encounter a strong acid, it will release its hydrogen ions ( H^+ ) into the solution. This makes the solution very acidic. Common strong acids include:

• Hydrochloric acid ( HCl )
• Nitric acid ( HNO_3 )
• Perchloric acid ( HClO_4 ) which was featured in your exercise
• Sulfuric acid ( H_2SO_4 ) - but note, only the first hydrogen ion dissociates strongly

In the original exercise, perchloric acid ( HClO_4 ) was a strong acid. This is because it completely ionizes in water, contributing high acidity to the solution.

Weak Acids

Weak acids are different from strong acids because they do not fully dissociate in water.
Instead, only a small fraction of the acid molecules release hydrogen ions ( H^+ ). The rest remains intact, making the solution less acidic compared to strong acids. Examples include:

• Acetic acid ( CH_3COOH ), found in vinegar
• Formic acid ( HCOOH ), found in ant venom
• Carbonic acid ( H_2CO_3 ) - which you saw in your exercise

Carbonic acid is a weak acid because it only partially ionizes in water. It forms from the dissolution of CO_2 in water and is key in maintaining the pH balance in blood and Earth's oceans.

Strong Bases

Strong bases are compounds that fully dissociate into hydroxide ions ( OH^- ) in water.
This makes them highly effective at increasing the pH of a solution, making it more basic. Most strong bases are hydroxides of alkali and alkaline earth metals. They include:

• Sodium hydroxide ( NaOH )
• Potassium hydroxide ( KOH )
• Cesium hydroxide ( CsOH ) which appeared in your task

In the exercise, cesium hydroxide ( CsOH ) was classified as a strong base because it completely dissociates in water. Being an alkali metal hydroxide, it contributes significantly to the alkalinity of any solution it is mixed with.

Weak Bases

Weak bases do not fully dissociate in solution.
Instead, they only partially ionize, accepting hydrogen ions or donating hydroxide ions to a limited extent. This results in a solution that is less basic compared to one with strong bases. Common examples are:

• Ammonia ( NH_3 )
• Ethylamine ( C_2H_5NH_2 ), one of your exercise compounds
• Other organic amines

Ethylamine is a weak base due to its amine group, which can accept a hydrogen ion but does so weakly. As a weak base, it participates in reactions that result in a moderate increase in solution pH, unlike strong bases that create a significant change.