Problem 48 - Chemistry The Molecular Science

Question

Identify each substance as a strong electrolyte, weak electrolyte, or nonelectrolyte. (a) \(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}\) (b) \(\mathrm{HCOOH}\) (c) \(\mathrm{NH}_{3}\) (d) HI

Step-by-Step Solution

Answer

(a) Strong electrolyte, (b) Weak electrolyte, (c) Weak electrolyte, (d) Strong electrolyte.

Step 1: Understanding Electrolytes

Electrolytes are substances that dissolve in water to produce a solution that conducts electricity. Strong electrolytes completely dissociate into ions when dissolved in water, weak electrolytes partially dissociate, and nonelectrolytes do not dissociate into ions.

Step 2: Analyzing Potassium Dichromate ( \oldsymbol{\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7}} )

Potassium dichromate is a salt composed of metal cations (K^+) and a polyatomic anion (Cr2O7^2−). It completely dissociates into ions in solution, thus it is classified as a strong electrolyte.

Step 3: Analyzing Formic Acid ( \oldsymbol{\mathrm{HCOOH}} )

Formic acid is an organic compound known to partially dissociate in solution, producing a moderate concentration of ions. This partial ionization characterizes it as a weak electrolyte.

Step 4: Analyzing Ammonia ( \oldsymbol{\mathrm{NH}_{3}} )

Ammonia, when dissolved in water, slightly ionizes to form \(\text{NH}_4^+\)and \(\text{OH}^-\) ions. It does not completely ionize, which classifies it as a weak electrolyte.

Step 5: Analyzing Hydroiodic Acid ( \oldsymbol{\mathrm{HI}} )

Hydroiodic acid is a strong acid that fully dissociates into ions in solution: \(\text{H}^+\)and \(\text{I}^-\). Therefore, it is a strong electrolyte.

Key Concepts

Strong Electrolytes

Strong electrolytes are substances that completely dissociate into ions when dissolved in water. This full dissociation allows the solution to conduct electricity very well.
For example, potassium dichromate (\(\mathrm{K}_{2} \mathrm{Cr}_{2} \mathrm{O}_{7} \)) is a compound made up of potassium ions (\(\text{K}^+ \)) and dichromate ions (\(\text{Cr}_2\text{O}_7^{2-} \)). When it dissolves in water, it separates completely into these ions.
Likewise, hydroiodic acid (\(\text{HI} \)) dissociates fully into hydrogen ions (\(\text{H}^+ \)) and iodide ions (\(\text{I}^- \)). Because of the complete ionization in the solution, both of these substances are strong electrolytes and highly conductive.

• Examples: Potassium dichromate, Hydroiodic acid.
• Properties: Fully dissociates in water, strong conductor of electricity.
• Applications: Commonly found in batteries and various chemical reactions.

Weak Electrolytes

Weak electrolytes are characterized by their partial ionization in water. This means only a small fraction of their molecules separate into ions, resulting in limited conductivity.
Formic acid (\(\text{HCOOH} \)) serves as a prime example of a weak electrolyte. When formic acid dissolves in water, only some of its molecules ionize, producing a few hydrogen ions (\(\text{H}^+ \)) and formate ions (\(\text{HCOO}^- \)).
Similarly, ammonia (\(\text{NH}_3 \)) also partially ionizes in water, forming ammonium ions (\(\text{NH}_4^+ \)) and hydroxide ions (\(\text{OH}^- \)). However, this ionization is not complete, which limits its ability to conduct electricity.

• Examples: Formic acid, Ammonia.
• Properties: Partially dissociates in water, weak conductor of electricity.
• Applications: Often used in pharmaceuticals and cleaning products.

Nonelectrolytes

Nonelectrolytes are substances that do not ionize at all in water, meaning they produce no ions in solution. As a result, solutions containing nonelectrolytes do not conduct electricity.
Such substances are often covalent compounds, which are mainly composed of nonmetals. For instance, substances like glucose and urea do not separate into ions when dissolved.
Due to their inability to conduct electricity, nonelectrolytes do not play a part in electrical processes but are mainly used for other purposes such as in food and skincare products.

• Examples: Glucose, Urea.
• Properties: Do not dissociate in water, non-conductor of electricity.
• Applications: Widely used in the food industry, cosmetics, and medical applications.