Question

You are given two colorless solutions, one containing \(\mathrm{NaCl}\) and the other sucrose \(\left(\mathrm{C}_{12} \mathrm{H}_{22} \mathrm{O}_{11}\right) .\) Suggest a chemical and a physical test that would distinguish between these two solutions.

Short answer

Chemical test: Perform electrolysis. Only the NaCl solution will conduct electricity. Physical test: Add both solutions to ethanol. The NaCl solution will not dissolve while Sucrose will.

Step-by-step solution

Specify chemical properties of NaCl and Sucrose

Sodium Chloride (NaCl) is an ionic compound that dissolves in water to produce ions, whereas Sucrose, a type of sugar, forms covalent bonds and does not dissociate into ions when dissolved. Based on these properties, a chemical test for distinguishing these two substances can be proposed. For example, an electrolysis test can be used, since ionic compounds conduct electricity due to their dissociation into ions, and covalent substances do not.

Specify physical properties of NaCl and Sucrose

One physical property to exploit is the fact that these two substances have different solubilities in the solvent. Sodium chloride has a high solubility in water, while sucrose has a moderate solubility. By adding both solutions to a solvent like ethanol, and observing which one dissolves and which one doesn't, we can differentiate these two solutions.

Conclusion

In conclusion, in a chemical test, Sodium Chloride (NaCl) and Sucrose (\(C_{12}H_{22}O_{11}\)) can be differentiated by carrying out electrolysis since NaCl, being ionic, will conduct electricity; Sucrose, being covalently bonded, will not. In a physical test, their solubility can be compared in a solvent like ethanol where Sucrose is quite soluble while Sodium chloride is virtually insoluble.

Key concepts

Ionic Compounds

Ionic compounds are made up of positively and negatively charged ions. These ions are held together by strong electrostatic forces known as ionic bonds. A typical example of an ionic compound is Sodium Chloride (NaCl). When NaCl is dissolved in water, it dissociates into its constituent ions: sodium ions (\( \text{Na}^+ \)) and chloride ions (\( \text{Cl}^- \)).
This dissociation is an important property that allows ionic solutions to conduct electricity. When a voltage is applied, the free-moving ions carry electric current, making electrolytic processes possible.
Key characteristics of ionic compounds include:

• High melting and boiling points due to strong ionic bonds.
• Conductivity of electricity when in molten state or aqueous solution.
• Tendency to dissolve in polar solvents like water.

This makes ionic compounds quite distinct in both their chemical and physical properties from covalent compounds.

Covalent Compounds

Covalent compounds are formed when atoms share pairs of electrons. This type of chemical bond occurs most commonly between nonmetal atoms. A well-known example of a covalent compound is sucrose (\( \text{C}_{12}\text{H}_{22}\text{O}_{11} \)), a type of sugar.
In covalent bonds, the atoms involved achieve stable electron configurations by sharing electrons. As a result, covalent compounds do not form ions in solution and are typically poor conductors of electricity.
Characteristics of covalent compounds include:

• Lower melting and boiling points compared to ionic compounds.
• Poor electricity conductivity in any state.
• Often solubility in organic solvents over polar solvents like water.

The lack of ion formation is what primarily distinguishes covalent compounds from ionic ones, especially when considering chemical identification tests like electrolysis.

Solubility Differences

Solubility is a key factor when distinguishing between different compounds. It refers to the ability of a substance to dissolve in a solvent, and it can vary significantly depending on the type of compound and the solvent used.
For example, Sodium Chloride (NaCl) is highly soluble in water but insoluble in organic solvents like ethanol. In contrast, sucrose has moderate solubility in water. This difference in solubility offers a physical method to differentiate between ionic and covalent compounds.

Ways to explore solubility differences include:

• Testing solubility in water: Ionic compounds like NaCl are likely to dissolve well, while many covalent compounds like sucrose show limited solubility.
• Experimenting with other solvents: Ethanol can reveal substantial differences, where sucrose dissolves more easily compared to NaCl.

These differences contribute to a deeper understanding of the physical properties of compounds, beyond just their electrical conductivity or bonds.

Electrolysis

Electrolysis is a chemical process that uses electrical energy to induce a chemical change in a substance, often decomposing it into different elements or compounds.
This process is especially relevant for ionic compounds. When substances like Sodium Chloride (NaCl) dissolve in water, they form ions that can carry an electric current. During electrolysis, these ions move towards oppositely charged electrodes, facilitating the electric circuit process.
Electrolysis can be an effective identification test for:

• Ionic substances, which will conduct electricity and allow electrolysis to occur.
• Covalent substances, which usually do not conduct electricity and thus are not electrolyzed easily.

This principle is rooted in the very nature of ionic and covalent bonding, and it provides one of the most straightforward demonstrations of whether a solution contains an ionic or covalent compound.