Question

Sketch molecular-level drawings to differentiate between two soluble compounds: one that is a strong electrolyte, and one that is not an electrolyte.

Short answer

A strong electrolyte, such as NaCl, dissociates completely into ions when dissolved in water. Sketch this by showing dissociated Na⁺ and Cl⁻ ions, each surrounded by water molecules with the oxygen atoms oriented towards Na⁺ and hydrogen atoms oriented towards Cl⁻. A non-electrolyte, such as sugar (C₁₂H₂₂O₁₁), does not dissociate when dissolved in water but forms hydrogen bonds with water molecules. Sketch this by showing sugar molecules surrounded by water molecules, with hydrogen bonding interactions between the water's hydrogen atoms and sugar's oxygen atoms.

Step-by-step solution

Definition of strong electrolytes and non-electrolytes

Strong electrolytes are substances that, when dissolved in water, dissociate completely into ions, resulting in a high electrical conductivity. Examples of strong electrolytes include strong acids (e.g., HCl, HNO₃), strong bases (e.g., KOH, NaOH), and soluble salts (e.g., NaCl, KBr). On the other hand, non-electrolytes are substances that do not dissociate at all, or do so poorly, when dissolved in water. As a result, they do not produce any significant change in electrical conductivity. Examples of non-electrolytes include molecular compounds with covalent bonds (e.g., sugar, urea, ethanol).

Sketch a strong electrolyte in solution

First, we will draw the molecular-level representation of a strong electrolyte in solution. Let's choose NaCl as our strong electrolyte example. When each NaCl molecule dissolves in water, it forms one Na⁺ cation and one Cl⁻ anion. In the sketch, illustrate the following: - A dissociated Na⁺ ion surrounded by water molecules with the oxygen atoms oriented towards the Na⁺ ion. - A dissociated Cl⁻ ion, also surrounded by water molecules, with the hydrogen atoms oriented towards the Cl⁻ ion. - Draw several water molecules between the Na⁺ and Cl⁻ ions to establish that they are separated from one another and fully dissociated.

Sketch a non-electrolyte in solution

Next, we will draw the molecular-level representation of a non-electrolyte in solution. Let's choose sugar (C₁₂H₂₂O₁₁) as our non-electrolyte example. When sugar dissolves in water, it does not dissociate into ions. Instead, the sugar molecules form hydrogen bonds with the water molecules. In the sketch, illustrate the following: - A sugar molecule with its hydrogen and oxygen atoms labeled. - Water molecules forming hydrogen bonds with the sugar molecule, with the hydrogen atoms of water interacting with the oxygen atoms of sugar. - Several water molecules surrounding the sugar molecule, indicating the formation of a hydration shell. With these two sketches, we can clearly differentiate between a strong electrolyte and a non-electrolyte at the molecular level. The strong electrolyte (NaCl) dissociates into ions, while the non-electrolyte (sugar) remains as a single molecule with hydrogen bonding interactions to the water molecules.

Key concepts

Strong Electrolytes

Strong electrolytes are fascinating because of their unique ability to conduct electricity efficiently in a solution. This property stems from their complete dissociation into ions. For instance, when substances like sodium chloride (NaCl) dissolve in water, they fully separate into Na⁺ and Cl⁻ ions. This is what makes strong electrolytes highly conductive.

• Strong acids like hydrochloric acid (HCl) break down into H⁺ and Cl⁻ ions.
• Strong bases, such as potassium hydroxide (KOH), dissociate into K⁺ and OH⁻ ions.
• Soluble salts, like NaCl, dissociate fully into their respective ions in water.

What's interesting is how water molecules surround these ions. The positive ion (cation) is typically surrounded by water molecules with the oxygen atom facing the ion, while the negative ion (anion) is surrounded by water molecules with the hydrogen atom facing the ion. This separation into cations and anions and the interaction with water molecules allow for the free flow of electric charge through the solution.

Non-electrolytes

Unlike strong electrolytes, non-electrolytes do not dissociate into ions in water. This means they don't contribute to electrical conductivity. Instead, non-electrolytes remain intact as molecules when dissolved. Common examples include sugar, urea, and ethanol.

• Sugar (C₁₂H₂₂O₁₁) dissolves by forming hydrogen bonds with water molecules rather than dissociating.
• Similarly, molecular compounds with covalent bonds, like ethanol, interact with water without forming ions.
• The result is a solution that does not conduct electricity.

These compounds usually engage in interactions like hydrogen bonding. When sugar dissolves in water, the sugar molecules become surrounded by water molecules forming a so-called 'hydration shell'. No ions are produced, which explains the lack of conductivity, distinguishing them from strong electrolytes.

Molecular-level Drawings

To visually distinguish strong electrolytes from non-electrolytes at the molecular level, molecular-level drawings can be an incredibly useful tool. When depicting a strong electrolyte like NaCl in water:

• Represent Na⁺ cations completely separated from Cl⁻ anions.
• Show these ions surrounded by water molecules.
• The orientation of water molecules should highlight their partial charges: oxygen atoms near Na⁺ and hydrogen atoms near Cl⁻.

For a non-electrolyte such as sugar, the picture shifts to show:

• Intact sugar molecules fully surrounded by water molecules.
• Hydrogen bonds formed between the hydrogen of water and the oxygen of sugar.
• Show a clear hydration shell with no evidence of ion formation.

These drawings not only visualize the molecular interactions but also highlight the fundamental differences in how substances behave when dissolved in water.