Problem 25 - Chemistry The Science in Context

Question

Which of the following is an example of a chemical property of formaldehyde (CH \(_{2} \mathrm{O}\) )? a. It has a characteristic acrid smell. b. It is soluble in water. c. It burns in air. d. It is a gas at room temperature. e. It is colorless.

Step-by-Step Solution

Answer

Answer: It burns in air.

Step 1: Identify Physical Properties

Physical properties can be observed or measured without changing the composition of a substance. We need to rule out these options first. a. It has a characteristic acrid smell: Physical property, because it describes a sensory perception and does not involve chemical reactions. b. It is soluble in water: Physical property, because solubility is based on the physical interactions of molecules and does not involve a composition change. d. It is a gas at room temperature: Physical property, because it is a characteristic of the substance that can be observed without a chemical reaction. e. It is colorless: Physical property, because color can be observed without a chemical reaction or change in the substance's composition.

Step 2: Identify Chemical Properties

Now, let's analyze the remaining option and determine if it corresponds to a chemical property of formaldehyde. c. It burns in air: Chemical property, because burning involves a chemical reaction between formaldehyde and oxygen in the air, resulting in the formation of new substances (such as CO\(_{2}\) and H\(_{2}\)O).

Step 3: Select the Correct Answer

Only one option corresponds to a chemical property of formaldehyde, as determined in Step 2: c. It burns in air.

Key Concepts

Physical Properties of Formaldehyde

Understanding the physical properties of formaldehyde is essential for students as these characteristics can be observed without altering the substance's chemical nature. Formaldehyde is a colorless gas that possesses a distinct, pungent odor. Its physical state at room temperature is gaseous, making it easy to detect in laboratory settings. Moreover, one of its most notable physical features is its solubility in water, which can be critical when considering storage and handling.

Its boiling point is -19 degrees Celsius, and it has a melting point of -92 degrees Celsius, facts that help us understand its behavior under different temperature conditions. In addition to being colorless and gas at room temperature, its density is another physical characteristic, helping predict how it will behave in mixtures with other substances.

Chemical Reactions Involving Formaldehyde

When discussing the chemical reactions of formaldehyde, we focus on how it interacts with other substances creating new compounds. A crucial chemical property of formaldehyde is its flammability; it burns in the presence of air, undergoing a chemical reaction with oxygen to produce carbon dioxide and water:
\[ CH_{2}O + O_{2} \rightarrow CO_{2} + H_{2}O \].

The ability to react with other chemicals also extends to its role in the synthesis of resins and as a crosslinking agent in the production of polymers. This reactivity is due to its aldehyde functional group, making it an important building block in organic synthesis and various industrial applications.

Solubility of Formaldehyde

The solubility of a substance profoundly affects how it can be used and handled, and for formaldehyde, this is no exception. It is highly soluble in water, which affects its storage methods; it's commonly stored as an aqueous solution called formalin, which is 37-40% formaldehyde by weight.

This water compatibility allows formaldehyde to be used in various aqueous environments, like as a preservative in biological laboratories. However, this physical property doesn't change the compound's identity, which is why it is distinguished from its chemical properties.

States of Matter and Formaldehyde

The states of matter—solid, liquid, and gas—are determined by temperature and pressure. Formaldehyde typically exists as a gas at room temperature and atmospheric pressure, fitting into one of these states. However, when discussing changes in states of matter like evaporation or condensation, it's crucial to note that these are physical changes. The substance doesn't become a different chemical; it only changes its form.

When cooled below its boiling point, formaldehyde gas condenses into liquid. It can also transition to a solid when frozen. This physical property is valuable in understanding how to store and manipulate the substance in practical applications, which directly ties into experimental design and safety procedures in the laboratory setting.