Which compound, when dissolved in water, conducts electricity and forms a basic solution?
NaOH
Understanding Conductivity and Basic Solutions
The question asks us to identify a compound that meets two criteria when dissolved in water:
- It conducts electricity.
- It forms a basic solution.
Let's break down what these criteria mean in the context of chemistry.
Electrical Conductivity in Aqueous Solutions
For a solution to conduct electricity, it must contain mobile charge carriers, which are typically ions. When ionic compounds or certain polar covalent compounds dissolve in water, they can dissociate or ionize, forming positive and negative ions. Substances that produce ions in solution and thus conduct electricity are called electrolytes. Strong electrolytes dissociate almost completely, weak electrolytes only partially, and non-electrolytes do not produce significant ions.
Formation of Basic Solutions
A solution is considered basic (or alkaline) if it has a pH greater than 7. Basic solutions are typically formed when a substance produces hydroxide ions ($\text{OH}^-$) when dissolved in water, or removes hydrogen ions ($\text{H}^+$ or $\text{H}_3\text{O}^+$) from the solution.
Analyzing the Options
Let's examine each given compound:
| Compound | Type | Behavior in Water | Electrical Conductivity | Solution Nature |
|---|---|---|---|---|
| HCl (Hydrochloric Acid) | Strong Acid | Ionizes: $\text{HCl(aq)} \rightarrow \text{H}^+\text{(aq)} + \text{Cl}^-\text{(aq)}$ | Conducts (Strong Electrolyte) | Acidic (forms $\text{H}^+$) |
| CH3COOH (Acetic Acid) | Weak Acid | Partially ionizes: $\text{CH}_3\text{COOH(aq)} \rightleftharpoons \text{H}^+\text{(aq)} + \text{CH}_3\text{COO}^-\text{(aq)}$ | Conducts (Weak Electrolyte) | Acidic (forms $\text{H}^+$) |
| CH3OH (Methanol) | Alcohol | Dissolves but does not significantly ionize. | Does not conduct (Non-electrolyte) | Neutral |
| NaOH (Sodium Hydroxide) | Strong Base | Dissociates: $\text{NaOH(s)} \rightarrow \text{Na}^+\text{(aq)} + \text{OH}^-\text{(aq)}$ | Conducts (Strong Electrolyte) | Basic (forms $\text{OH}^-$) |
Based on this analysis:
- HCl conducts electricity but forms an acidic solution.
- CH3COOH conducts electricity but forms an acidic solution.
- CH3OH does not conduct electricity and forms a neutral solution.
- NaOH conducts electricity and forms a basic solution.
Therefore, Sodium Hydroxide (NaOH) is the compound that satisfies both conditions specified in the question.
Conclusion
The compound that conducts electricity when dissolved in water and forms a basic solution is NaOH.
Revision Table: Key Concepts
| Term | Definition | Relevance to Question |
|---|---|---|
| Electrolyte | Substance that produces ions when dissolved in a solvent, making the solution electrically conductive. | Required for electrical conductivity criterion. |
| Strong Electrolyte | Substance that dissociates or ionizes almost completely in solution. | Results in high conductivity. NaOH and HCl are strong electrolytes. |
| Weak Electrolyte | Substance that only partially dissociates or ionizes in solution. | Results in lower conductivity than strong electrolytes. CH3COOH is a weak electrolyte. |
| Non-electrolyte | Substance that does not produce significant ions when dissolved in a solvent. | Does not conduct electricity. CH3OH is a non-electrolyte. |
| Acidic Solution | Aqueous solution with pH < 7, typically due to excess $\text{H}^+$ or $\text{H}_3\text{O}^+$ ions. | Formed by HCl and CH3COOH. |
| Basic Solution | Aqueous solution with pH > 7, typically due to excess $\text{OH}^-$ ions. | Formed by NaOH. |
Additional Information: Ionization and Dissociation
When ionic compounds like NaOH dissolve in water, their crystal lattice breaks apart, and the pre-existing ions ($\text{Na}^+$ and $\text{OH}^-$) separate and become surrounded by water molecules (hydration). This process is called dissociation:
\(\text{NaOH(s)} \xrightarrow{\text{H}_2\text{O}} \text{Na}^+\text{(aq)} + \text{OH}^-\text{(aq)}\)
When certain polar covalent compounds, like acids such as HCl and CH3COOH, dissolve in water, they react with water molecules to form ions. This process is called ionization:
\(\text{HCl(g)} + \text{H}_2\text{O(l)} \rightarrow \text{H}_3\text{O}^+\text{(aq)} + \text{Cl}^-\text{(aq)}\)
\(\text{CH}_3\text{COOH(l)} + \text{H}_2\text{O(l)} \rightleftharpoons \text{H}_3\text{O}^+\text{(aq)} + \text{CH}_3\text{COO}^-\text{(aq)}\)
Non-electrolytes like methanol (CH3OH) dissolve by forming intermolecular forces (like hydrogen bonds) with water but do not break apart into ions or react to form ions to a significant extent. Therefore, their solutions do not conduct electricity.
Understanding the difference between dissociation, ionization, and simple dissolution is crucial for predicting the conductivity and acid-base properties of aqueous solutions.
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