Problem 18 - 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

(a) Physical: white solid, density; Chemical: reacts with acid. (b) Physical: gray, powdered; Chemical: reacts with iodine.

Step 1: Identify Physical Properties

Physical properties are characteristics that can be observed without changing the substance into another substance. In (a), 'Calcium carbonate is a white solid with a density of 2.71 g/cm^3' refers to the physical properties because these describe the appearance and density of calcium carbonate, which can be observed without altering the substance itself. In (b), 'Gray, powdered zinc metal' describes physical properties such as color and form.

Step 2: Identify Chemical Properties

Chemical properties describe how a substance reacts with other substances, resulting in a change in composition. In (a), 'It reacts readily with an acid to produce gaseous carbon dioxide' refers to chemical properties as this statement describes how calcium carbonate changes upon reacting with an acid. In (b), 'reacts with purple iodine to give a white compound' indicates chemical properties since this describes a reaction resulting in the formation of a new compound.

Key Concepts

Calcium Carbonate

Calcium carbonate is a fascinating and widely used chemical compound found in many everyday products. This white solid is known for its distinct physical and chemical properties. Physically, it presents as a white powder with a density of \(2.71 \text{ g/cm}^3\). These traits are easily observable without changing the substance itself, allowing us to classify them as physical properties.

Chemically, calcium carbonate plays a significant role in various reactions. A well-known chemical property is its ability to react with acids such as hydrochloric acid. This reaction produces carbon dioxide gas, a clear indicator of its transformation into new substances. The balancing chemical equation for this reaction is: \[\text{CaCO}_3 + 2\text{HCl} \rightarrow \text{CaCl}_2 + \text{CO}_2 + \text{H}_2\text{O}\]
Calcium carbonate is used in construction, as a dietary calcium supplement, and in agriculture. Recognizing its properties is essential for understanding its functionality in these diverse fields.

Zinc Metal

Zinc metal is an element characterized by its distinctive appearance and active chemical nature. This metal typically appears as a gray, powdered form, emphasizing its physical properties. Its metallic luster and ability to form fine particles without altering its composition exemplify such attributes.

Chemically, zinc is quite reactive. One common chemical property is its reaction with iodine, a non-metal, to produce a white compound. This reaction alters the chemical structure of zinc, forming zinc iodide (\(\text{ZnI}_2\)). This transformation from elemental zinc and iodine to a compound showcases zinc's chemical nature. The equation for this reaction is: \[\text{Zn} + \text{I}_2 \rightarrow \text{ZnI}_2\]
Zinc is not just limited to reactions and metal form; it is also crucial in applications like galvanizing, where it helps protect iron and steel from corrosion. Understanding zinc's properties is vital for utilizing it effectively in industrial and chemical processes.

Chemical Reactions

Chemical reactions are processes where substances, known as reactants, change into new substances, referred to as products. These reactions are central to both calcium carbonate and zinc metal's chemical properties. By illustrating how both substances interact with others (like acids for calcium carbonate and iodine for zinc), we see how their chemical properties allow them to transform into new products.

A key aspect of chemical reactions is the conservation of mass and the transformation of energy. This means the mass of reactants is equal to the mass of products, even when the substances undergo changes at the molecular level. For instance, when calcium carbonate reacts with hydrochloric acid, gaseous carbon dioxide is released, yet the total mass remains constant.

• Understanding chemical equations and their balancing is critical; these equations symbolically represent the reactions, showing the relationship between reactants and products.
• Reactions can be endothermic or exothermic, absorbing or releasing energy, respectively.

This foundational knowledge of chemical reactions helps in grasping how substances chemically transform and how new materials can be synthesized, making it pivotal for learning about chemistry.