Problem 24 - Chemistry: An Atoms-Focused Approach

Question

Give three properties that enable a person to distinguish between table salt, sand, and copper.

Step-by-Step Solution

Answer

Briefly describe how each property can be used to differentiate these substances. Answer: Property 1: Color - Table salt is white, sand is usually light brown or yellow, and copper is reddish-brown and metallic. By comparing colors, we can differentiate between these substances. Property 2: Solubility - Table salt is soluble in water, while sand and copper are insoluble. Testing solubility in water can help distinguish between these materials. Property 3: Conductivity - Copper is an excellent conductor of electricity, table salt conducts electricity when dissolved in water, and sand does not conduct. Testing conductivity with a simple electric circuit can differentiate between these substances. Explanation: Each property can be observed or measured to easily distinguish one substance from the other. The color of the substances allows for visual differentiation, while solubility and conductivity provide ways to test the physical and chemical characteristics of each material in order to identify them.

Step 1: Property 1: Color

The color of a substance can be a helpful property in determining its identity. Table salt is typically white, sand can have different colors such as light brown or yellow, and copper has a reddish-brown metallic appearance. By comparing their colors, one can differentiate between these three substances.

Step 2: Property 2: Solubility

Solubility refers to the ability of a substance to dissolve in a solvent like water. Table salt (sodium chloride) is soluble in water, which means it can dissolve when mixed with water. Sand (silicon dioxide), on the other hand, does not dissolve in water, while copper, being a metal, is insoluble in water as well. To test for solubility, we can place a small amount of each substance in separate containers with water, shake or stir it, and observe which substances dissolve.

Step 3: Property 3: Conductivity

Conductivity is the measure of a material's ability to conduct electricity. Copper is an excellent conductor of electricity which is why it is commonly used in electrical wirings. Table salt, in its solid-state, is a poor conductor of electricity, but when it dissolves in water, the resulting solution conducts electricity due to the presence of free ions. Sand, however, does not conduct electricity. To test for conductivity, we can use a simple electric circuit with a battery, a bulb, and two electrodes. Attach the substance between the electrodes and observe if the bulb lights up. A bright light indicates high conductivity, while no light indicates low conductivity.

Key Concepts

Color in Chemistry

Color is one of the most apparent properties of substances in chemistry. It's a feature we can observe with our eyes, making it a practical tool for identifying materials.
Colors arise from how materials absorb, reflect, or emit light. For example, table salt, made primarily of sodium chloride, is usually white. This uniform color can help to identify it in a mixture.
Sand varies greatly in color because it's composed of different minerals and particles, such as quartz or iron oxide, which give it shades ranging from tan to yellow. These diverse colors can provide clues about its source and composition.
Copper, being a metal, has a distinct reddish-brown color. Its metallic luster and unique color make it easy to identify. This characteristic is not just important for visual identification but also plays a role in its applications, such as roofing and electrical fittings because it doesn't tarnish easily.

Solubility

Solubility refers to the capability of a substance to dissolve in a liquid, largely affecting its use and behavior in solutions. In general, solubility is determined by the interaction between the molecules of the solute and the solvent.
When a substance dissolves, its molecules disperse uniformly in a solvent, such as water. Table salt, for example, is highly soluble in water. It dissociates into sodium and chloride ions when it dissolves, readily mixing with the solvent to form a solution.
Sand, mainly composed of silicon dioxide, is insoluble in water. Its rigid molecular structure does not interact favorably with water molecules, preventing it from dissolving.
Copper, as a metal, also does not dissolve in water. Unlike ionic compounds, metals do not generally interact at the molecular level with water, hence they maintain their solid form. To observe solubility, one can mix the substance in water and see if it forms a homogeneous solution or remains undisturbed at the bottom.

Electrical Conductivity

Electrical conductivity measures a substance's ability to allow the flow of electric current. This property is crucial in identifying materials for electrical applications.
Copper is renowned for its excellent conductivity. This is because of the free electrons in its metallic bonds, which allow electricity to flow easily. It's commonly used in wiring owing to this property.
Table salt, when dissolved in water, can also conduct electricity. This happens due to the dissociation of salt into free ions, which move within the solution and carry electric charges. Solid salt, however, does not have free-moving ions or electrons to conduct electricity.
Sand is a different story; it is a poor conductor of electricity. Its structure does not support the movement of electrons or ions. This inertness is why sand is often used as an insulating material in various electrical applications. To test conductivity, one may complete an electric circuit through the substance and observe if an attached bulb lights up. A bright bulb indicates good conductivity, while no light suggests low conductivity.