Question

You are presented with three white solids, \(\mathrm{A}, \mathrm{B}\), and \(\mathrm{C}\), which are glucose (a sugar substance), \(\mathrm{NaOH}\), and AgBr. Solid A dissolves in water to form a conducting solution. B is not soluble in water. C dissolves in water to form a nonconducting solution. Identify \(\mathrm{A}, \mathrm{B}\), and \(\mathrm{C}\). [Section 4.2]

Short answer

Solid A is NaOH, as it dissolves in water and conducts electricity. Solid B is AgBr because it doesn't dissolve in water. Solid C is glucose, as it dissolves in water but doesn't conduct electricity.

Step-by-step solution

Analyze the solubility of each substance in water

Based on the information provided, we know that glucose and NaOH can dissolve in water, while AgBr is not soluble in water. This means that solid B is AgBr. Now we need to determine which of the remaining substances, glucose, and NaOH, is A and which one is C.

Analyze the conductivity of each substance in water

We are told that solid A dissolves in water and forms a conducting solution. This means that solid A forms ions when dissolved in water. NaOH is a strong base and dissociates completely in water to form \(\mathrm{Na}^{+}\) and \(\mathrm{OH}^{-}\) ions, which are charged particles and thus can conduct electricity. Therefore, solid A is NaOH. On the other hand, glucose dissolves in water to form a non-conducting solution, which means it does not form ions when dissolved in water. This allows us to identify solid C as glucose.

Provide the final identification of the solids

Based on our analysis: Solid A: NaOH (dissolves in water and conducts electricity) Solid B: AgBr (does not dissolve in water) Solid C: Glucose (dissolves in water but does not conduct electricity)

Key concepts

Conductivity

Conductivity is the ability of a substance to conduct electricity. Not all substances have this ability when they dissolve in water. Solutions that conduct electricity do so because they have free ions that can move and carry electric charge. In the case of solutions, these ions come from substances dissociating into positive and negative ions when they dissolve.

• For instance, when a substance like NaOH dissolves in water, it separates into sodium (Na⁺) and hydroxide (OH^-) ions.
• These ions are free to move in the solution, allowing it to conduct electricity effectively.

Solutions that do not conduct electricity are typically comprised of molecules that do not yield ions when they dissolve in water. Remember, for a solution to conduct current, such as with NaOH, it must have free-moving charged particles.

Ionic Compounds

Ionic compounds are composed of positive and negative ions. These ions are held together by strong electrostatic forces known as ionic bonds. Many ionic compounds are capable of dissolving in water, a property that often links them to conductivity. When ionic compounds dissolve, they dissociate into their constituent ions.

• For example, NaOH is an ionic compound that dissociates in water to create Na⁺ and OH^- ions.
• This dissociation results in a solution that can conduct electricity because of the free motion of ions.

Not all ionic compounds are soluble, though. For example, AgBr is an ionic compound, but it is known for its low solubility in water. This means it does not dissolve much and thus doesn't contribute free ions for conduction. The insolubility of compounds like AgBr is due to the strong forces between its ions.

Non-Ionic Compounds

Non-ionic compounds do not break into ions when they dissolve in water. One classic example of a non-ionic compound is glucose. When glucose dissolves, it maintains its molecular form in the solution. This means glucose solutions do not have free ions moving around, which is why they do not conduct electricity.

• Although glucose dissolves well in water, adding it to water doesn't increase the number of ions that can move freely.
• This property is due to glucose's covalent bonds, where electrons are shared between atoms rather than forming ions.

Thus, non-ionic compounds like glucose can still be very soluble in water, but they won't enable the solution to conduct electricity because no ions are present.