Problem 56 - Chemistry for Allied Health

Question

Based on the given information, identify each as a strong, weak, or non- electrolyte. a. \(\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(s) \rightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(a q)\) b. \(\mathrm{NaCl}\) is added to water and the conductivity increases dramatically. c. \(1.5\) moles of \(\mathrm{HCl}\) are added to a container of water. The resulting solution has \(1.5\) moles of \(\mathrm{H}^{+}\) ions and \(1.5\) moles of \(\mathrm{Cl}^{-}\) ions. d. Acetic acid (CH \(_{3}\) COOH) partially dissociates in water. e. An HCN solution contains \(0.50\) moles of HCN molecules and \(0.05\) moles of \(\mathrm{H}^{+}\) ions and \(0.05\) moles of \(\mathrm{Cl}^{-}\) ions. f. Acetone is added to water and the conductivity does not change.

Step-by-Step Solution

Answer

a. Non-electrolyte, b. Strong electrolyte, c. Strong electrolyte, d. Weak electrolyte, e. Weak electrolyte, f. Non-electrolyte.

Step 1: Analyze Substance A

For substance (a) \( \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(s) \rightarrow \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(aq) \), glucose dissolves but does not ionize or dissociate into ions in water. Therefore, it does not conduct electricity and is a non-electrolyte.

Step 2: Analyze Substance B

Substance (b) \( \mathrm{NaCl} \) is added to water. NaCl is an ionic compound that completely dissociates into \( \mathrm{Na}^{+} \) and \( \mathrm{Cl}^{-} \) ions in solution, hence increasing conductivity dramatically. Thus, NaCl is a strong electrolyte.

Step 3: Analyze Substance C

In (c), 1.5 moles of \( \mathrm{HCl} \) are added to water, forming 1.5 moles each of \( \mathrm{H}^{+} \) and \( \mathrm{Cl}^{-} \) ions. This complete dissociation into ions implies that HCl is a strong electrolyte.

Step 4: Analyze Substance D

For (d), acetic acid \( \text{CH}_3\text{COOH} \) only partially dissociates in water, forming fewer ions. This partial dissociation identifies acetic acid as a weak electrolyte.

Step 5: Analyze Substance E

In (e), the solution has 0.50 moles of HCN molecules, and only 0.05 moles each of \( \mathrm{H}^{+} \) and \( \mathrm{Cl}^{-} \) ions. Since only a small fraction dissociates, HCN is a weak electrolyte.

Step 6: Analyze Substance F

Substance (f) is acetone in water, and the conductivity does not change, suggesting that it doesn't dissociate into ions. Therefore, acetone is a non-electrolyte.

Key Concepts

strong electrolytes

Strong electrolytes are substances that completely dissociate into ions when dissolved in water. This means they produce a large number of ions in solution, which allows the solution to conduct electricity very effectively. **NaCl** and **HCl** are examples of strong electrolytes.

• NaCl (Sodium Chloride): When NaCl is added to a container of water, it dissociates fully into sodium ions (\(\mathrm{Na}^{+}\)) and chloride ions (\(\mathrm{Cl}^{-}\)). This full dissociation significantly increases the conductivity of the solution.
• HCl (Hydrochloric Acid): Similarly, when HCl is dissolved in water, it completely splits into hydrogen ions (\(\mathrm{H}^{+}\)) and chloride ions. For example, when 1.5 moles of HCl is added to water, it results in 1.5 moles of each ion, demonstrating complete ionization.

The high conductivity in these solutions is due to the free movement of these ions, making strong electrolytes very effective in conducting electricity.

weak electrolytes

Weak electrolytes only partially dissociate into ions in water. This partial dissociation means fewer ions are present, resulting in a weak ability to conduct electricity.

• Acetic Acid (CH\(_{3}\)COOH): Acetic acid is a classic example of a weak electrolyte. When dissolved, only a small portion of it dissociates into ions. Most of the acetic acid remains as complete molecules, with only a few ionized into \(\mathrm{H}^{+}\) and acetate ions.
• HCN (Hydrogen Cyanide): Another example is HCN, which mainly remains as molecules in water with very few ions formed. The presence of only 0.05 moles of ions in a situation involving 0.50 moles of HCN confirms its partial dissociation.

The lower number of free ions leads to minimal electrical conductivity, which is characteristic of weak electrolytes.

non-electrolytes

Non-electrolytes are substances that do not ionize at all in solution. This means they exist solely as neutral molecules in water and therefore do not conduct electricity. Examples like glucose and acetone fit this category.

• Glucose (C\(_6\)H\(_{12}\)O\(_{6}\)): When glucose is dissolved in water, it disperses as individual molecules without forming any ions.
• Acetone: Similarly, when acetone is added to water, its structure remains unchanged. It retains its molecular form and does not increase the solution's conductivity.

Non-electrolytes are essential in solutions where no electrical current needs to pass, making them very different from their electrolyte counterparts.

dissociation in water

Dissociation in water is a process that refers to the splitting of a compound into ions when it is mixed with water. This process is crucial in determining an electrolyte's ability to conduct electricity.

For strong electrolytes like \(\text{NaCl}\)and \(\text{HCl}\), dissociation in water is complete, meaning they split fully into free ions that can carry electrical current. On the other hand, weak electrolytes such as \(\text{CH}_3 ext{COOH}\)in water undergo partial dissociation, creating a lower concentration of ions and thus less conductivity.

Non-electrolytes, including substances like glucose, do not dissociate at all when dissolved in water. They remain as whole molecules and fully retain their chemical structure.

• A key factor affecting dissociation is the nature of the bonds in the compound; ionic bonds tend to dissociate more easily compared to covalent bonds.
• The degree of dissociation also influences the conductivity of the solution, with more ion formation equating to higher conductivity.

Understanding the concept of dissociation helps in predicting the electrical behavior of different substances in aqueous solutions.