Question

Classify each of the following aqueous solutions as a strong or weak electrolyte: (a) \(\mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{3}(a q)\) (b) \(\mathrm{AlPO}_{4}(\mathrm{~s})\) (c) \(\mathrm{Ag}_{2} \mathrm{CrO}_{4}(\mathrm{~s})\) (d) \(\mathrm{CdSO}_{4}(a q)\)

Short answer

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

Step-by-step solution

Understand Strong vs. Weak Electrolytes

An electrolyte is classified as strong if it completely dissociates into ions in solution. Conversely, an electrolyte that only partially dissociates is considered weak. Generally, soluble ionic compounds and strong acids/bases are strong electrolytes, while weak acids/bases and slightly soluble ionic compounds are weak electrolytes.

Examine Solution (a)

The compound \(\mathrm{Fe}\left(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}\right)_{3}(aq)\) is considered. This is iron(III) acetate, a generally soluble compound in water, as acetates are typically soluble salts. Therefore, it behaves as a strong electrolyte because it dissociates completely into \(\mathrm{Fe}^{3+}\) and \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{O}_{2}^{-}\) ions.

Examine Solution (b)

This compound, \(\mathrm{AlPO}_{4}(s)\), is aluminum phosphate. It is a solid and is poorly soluble in water. As it does not dissociate significantly, it is classified as a weak electrolyte in its solid state.

Examine Solution (c)

The compound \(\mathrm{Ag}_{2} \mathrm{CrO}_{4}(s)\) is silver chromate, a solid with low solubility in water. Similar to aluminum phosphate, because it does not dissociate extensively in solution, it is considered a weak electrolyte.

Examine Solution (d)

Consider the compound \(\mathrm{CdSO}_{4}(aq)\), cadmium sulfate. This substance is soluble in water, and consequently dissociates completely into \(\mathrm{Cd}^{2+}\) and \(\mathrm{SO}_{4}^{2-}\) ions. Thus, it behaves as a strong electrolyte.

Key concepts

Understanding Strong Electrolytes

Strong electrolytes are substances that fully dissociate into ions when dissolved in water. This means that if you dissolve a compound like table salt ( NaCl) in water, it splits entirely into Na⁺ and Cl^- ions. This complete dissociation allows strong electrolytes to conduct electricity efficiently, much like turning on a light switch. Metals and many mineral salts fall into this category due to their high solubility.

Common examples of strong electrolytes include:

• Soluble ionic compounds, like sodium chloride (NaCl) and potassium nitrate (KNO₃).
• Strong acids, such as hydrochloric acid (HCl) and sulfuric acid (H₂SO₄).
• Strong bases like sodium hydroxide (NaOH).

When looking at a chemical formula, to determine if a compound is a strong electrolyte, consider its solubility and the strength of any acids or bases it contains. If it dissolves and dissociates fully, it's a strong electrolyte.

Exploring Weak Electrolytes

Weak electrolytes only partially dissociate into ions when dissolved in water. This means they don't break up completely, leaving a good portion of the compound intact. While they do conduct electricity, it's much weaker compared to strong electrolytes, similar to a dim light bulb.

Here's what you might find as weak electrolytes:

• Weak acids, like acetic acid (CH₃COOH).
• Weak bases, including ammonia (NH₃).
• Slightly soluble ionic compounds that don't fully dissociate, such as calcium sulfate (CaSO₄).

Take aluminum phosphate ( AlPO₄), for example. It's poorly soluble, and much of it remains in the solid form when mixed with water, making it a weak electrolyte by default. Weak electrolytes demonstrate the delicate balance between solubility and the tendency to form ions, affecting their electrical conductivity sharply.

The Concept of Solubility

Solubility is a measure of how well a substance dissolves in water or another solvent. It determines whether a compound is a strong or weak electrolyte. Highly soluble substances, like sugar in water, dissolve readily, resulting in more ions and greater electrical conductivity.

The solubility of a substance depends on various factors:

• Temperature: Generally, solubility increases with temperature for solids.
• Pressure: Solubility of gases increases under higher pressure.
• Nature of the solute and solvent: Like dissolves like, meaning polar solvents dissolve polar solutes well.

Taking cadmium sulfate ( CdSO₄) as an example, it dissolves completely in water, behaving as a strong electrolyte. In contrast, compounds like silver chromate ( Ag₂CrO₄) don't dissolve fully, thereby being classified as weak electrolytes. Understanding solubility helps explain why some substances conduct electricity better than others, making it crucial in chemistry.