Problem 37 - Chemistry: The Central Science in SI Units, Global Edition

Question

Classify each of the following substances as a nonelectrolyte, weak electrolyte, or strong electrolyte in water: (a) HF, (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\) (benzoicacid), (c) \(\mathrm{C}_{6} \mathrm{H}_{6}\) (benzene), (d) \(\mathrm{CoCl}_{3}\) (e) \(\mathrm{AgNO}_{3}\)

Step-by-Step Solution

Answer

The classification of each substance in water is as follows: (a) HF: weak electrolyte (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\) (benzoic acid): weak electrolyte (c) \(\mathrm{C}_{6} \mathrm{H}_{6}\) (benzene): nonelectrolyte (d) \(\mathrm{CoCl}_{3}\): strong electrolyte (e) \(\mathrm{AgNO}_{3}\): strong electrolyte

Step 1: Classify HF

Hydrofluoric acid (HF) is a weak acid. When dissolved in water, it partially ionizes, producing a small amount of ions. Since it does not completely ionize, we can classify HF as a weak electrolyte.

Step 2: Classify \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\) (benzoic acid)

Benzoic acid (C6H5COOH) is a weak acid as well. When it is dissolved in water, it partially ionizes, forming a small amount of ions. So, we can classify benzoic acid as a weak electrolyte.

Step 3: Classify \(\mathrm{C}_{6} \mathrm{H}_{6}\) (benzene)

Benzene (C6H6) is a nonpolar compound, and it does not ionize when dissolved in water. Therefore, it does not conduct electricity, and we can classify benzene as a nonelectrolyte.

Step 4: Classify \(\mathrm{CoCl}_{3}\)

Cobalt(III) chloride (CoCl3) is an ionic compound that, when dissolved in water, dissociates completely into ions. Therefore, it conducts electricity, and we can classify CoCl3 as a strong electrolyte.

Step 5: Classify \(\mathrm{AgNO}_{3}\)

Silver nitrate (AgNO3) is an ionic compound. When dissolved in water, it dissociates completely into ions, conducting electricity. Thus, we can classify AgNO3 as a strong electrolyte. In conclusion, the classification of each substance in water is as follows: (a) HF: weak electrolyte (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\) (benzoic acid): weak electrolyte (c) \(\mathrm{C}_{6} \mathrm{H}_{6}\) (benzene): nonelectrolyte (d) \(\mathrm{CoCl}_{3}\): strong electrolyte (e) \(\mathrm{AgNO}_{3}\): strong electrolyte

Key Concepts

Weak Electrolytes

Weak electrolytes are substances that only partially ionize in water. This means that when they dissolve, only a small percentage of their molecules break apart into ions. Because they don’t produce many ions, they are weak conductors of electricity. Two common examples of weak electrolytes are weak acids and weak bases.
Weak acids, like hydrofluoric acid (HF) and benzoic acid (\(\mathrm{C}_{6}\mathrm{H}_{5}\mathrm{COOH}\)), are classic weak electrolytes. When you put them in water, they dissociate only slightly. This means you end up with a mix of ionized and non-ionized molecules.

• For instance, HF in water doesn’t completely break up into hydrogen (H\(^+\)) and fluoride (F\(^-\)) ions.
• Similarly, benzoic acid only partially ionizes to form ions.

These partial ionizations contribute to their weak electrolytic property.

Strong Electrolytes

Strong electrolytes are substances that completely dissociate into ions in water. This complete dissociation means that strong electrolytes conduct electricity very well. They usually consist of strong acids, strong bases, and most salts.Ionic compounds like cobalt(III) chloride (\(\mathrm{CoCl}_{3}\)) and silver nitrate (\(\mathrm{AgNO}_{3}\)) are typical examples of strong electrolytes. When they dissolve in water, they break entirely into their respective ions.

• Cobalt(III) chloride dissociates into cobalt (Co\(^{3+}\)) and chloride (\(\mathrm{Cl}^{-}\)) ions.
• Silver nitrate separates into silver (Ag\(^+\)) and nitrate (\(\mathrm{NO}_{3}^{-}\)) ions.

This complete ionization is why they effectively conduct electricity in solution.

Nonelectrolytes

Nonelectrolytes are substances that do not produce ions when dissolved in water. Consequently, they do not conduct electricity. Most covalent compounds that do not produce ions fall into this category. Benzene (\(\mathrm{C}_{6}\mathrm{H}_{6}\)) is a common example of a nonelectrolyte. Because it is nonpolar, it does not interact well with water, and therefore does not ionize or dissociate into ions at all.

• This means that no electrically charged particles are available to carry an electric current.
• As a result, solutions of nonelectrolytes like benzene remain nonconductive.

Understanding this helps us see why certain substances are used in particular applications where nonconductivity is required.

Chemical Ionization

Chemical ionization is the process by which a molecule acquires a charge by gaining or losing an electron, resulting in the formation of ions. It is a key concept in understanding how substances behave when they dissolve in water. The extent of ionization varies significantly among different substances:

• Strong electrolytes completely ionize, producing a high concentration of ions.
• Weak electrolytes only partially ionize, leading to a lower concentration of ions.
• Nonelectrolytes do not ionize at all.

Chemical ionization is central to phenomena such as conductivity in solutions. A solution's ability to conduct electricity is directly linked to the presence of free-moving ions generated through ionization. Appreciating this helps in predicting how a substance will behave in an aqueous environment and in designing solutions with desired electrical properties.