Problem 10 - Chemistry and Chemical Reactivity

Question

Which part of the description of a compound or element refers to its physical properties and which to its chemical properties? (a) Calcium carbonate is a white solid with a density of \(2.71 \mathrm{g} / \mathrm{cm}^{3} .\) It reacts readily with an acid to produce gaseous carbon dioxide. (b) Gray, powdered zinc metal reacts with purple iodine to give a white compound.

Step-by-Step Solution

Answer

Physical properties: Color, physical state, density; Chemical properties: Reactivity with other substances.

Step 1: Identify Physical Properties

Physical properties are characteristics that can be observed or measured without changing the identity of the substance. In (a), the phrase "white solid with a density of 2.71 g/cm³" describes the physical properties of calcium carbonate. Similarly, in (b), "gray, powdered" describes the physical properties of zinc metal.

Step 2: Identify Chemical Properties

Chemical properties describe a substance's ability to undergo changes that transform it into different substances. In (a), "reacts readily with an acid to produce gaseous carbon dioxide" indicates the chemical properties of calcium carbonate. In (b), "reacts with purple iodine to give a white compound" describes the chemical properties of zinc.

Key Concepts

Physical Properties

Physical properties are the aspects of a substance that can be perceived or measured without altering the substance's chemical structure. These properties are visible and can be determined without conducting a chemical reaction. Common physical properties include:

• Color
• Density
• Mass
• Volume
• State (solid, liquid, gas)

For instance, in the case of calcium carbonate, its description as a "white solid with a density of \(2.71 \mathrm{g/cm^3}\)" is a perfect example of its physical properties. This describes how calcium carbonate appears and is quantified in physical form. Similarly, zinc metal being described as "gray, powdered" outlines its physical characteristics without involving a chemical change.

Calcium Carbonate

Calcium carbonate is a common chemical compound with the formula \(CaCO_3\). It is frequently found in rocks like limestone and is the main component of shells of marine organisms and snails. This compound can vary in appearance but is often a white, powdery substance.
You can observe several physical properties of calcium carbonate:

• White color
• Solid state at room temperature
• Specific density of \(2.71 \mathrm{g/cm^3}\)

Its chemical properties are also interesting. When calcium carbonate reacts with acids such as hydrochloric acid, it releases carbon dioxide gas. This is an example of a chemical property, demonstrating how it can transform into new substances during reactions.

Zinc Metal

Zinc is a chemical element with the symbol Zn and atomic number 30. It appears as a lustrous, bluish-gray metal in solid form and becomes dull when powdered. This is due to oxidation, which is a chemical change.
The physical properties of zinc include:

• Gray color in powdered form
• Metallic luster when solid
• Density of \(7.14 \mathrm{g/cm^3}\)

Zinc is flexible in terms of chemical reactions. One notable chemical property of zinc is its ability to react with iodine, a nonmetal. When they react, they form a new white compound, highlighting a change in the substance at a chemical level.

Chemical Reaction

Chemical reactions are processes where substances, known as reactants, are transformed into different substances, called products. Each reaction involves changes in chemical bonds and is usually accompanied by energy release or absorption.
Some key points about chemical reactions include:

• Substances change form and chemical properties.
• They may release gases or emit heat/light.
• The reactants are rearranged to form products.

The reaction between calcium carbonate and an acid is a typical example. Calcium carbonate reacts with the acid, forming carbon dioxide gas and a new solution. The chemical reaction between zinc and iodine also highlights a transformation, resulting in a white compound. This change signifies that chemical properties have been altered, proving that new substances with different properties are produced.