Question

Which of the following statements describe physical properties and which describe chemical properties? (a) Iron has a tendency to rust. (b) Rainwater in industrialized regions tends to be acidic. (c) Hemoglobin molecules have a red color. (d) When a glass of water is left out in the sun, the water gradually disappears. (e) Carbon dioxide in air is converted to more complex molecules by plants during photosynthesis.

Short answer

(a) Chemical, (b) Chemical, (c) Physical, (d) Physical, (e) Chemical.

Step-by-step solution

Understanding Physical vs. Chemical Properties

Physical properties are characteristics of a substance that can be observed or measured without changing its composition, such as color, odor, melting point, boiling point, and density. Chemical properties describe the substance's ability to undergo a specific chemical change or reaction, forming new substances.

Analyzing Statement (a)

The statement 'Iron has a tendency to rust' describes a chemical property because rusting involves iron reacting with oxygen to form iron oxide, which is a new substance.

Analyzing Statement (b)

The statement 'Rainwater in industrialized regions tends to be acidic' refers to a chemical property since it involves chemical reactions between rainwater and industrial pollutants, producing acidic compounds.

Analyzing Statement (c)

The statement 'Hemoglobin molecules have a red color' is a description of a physical property because color is an observable characteristic that does not alter the hemoglobin molecule's chemical composition.

Analyzing Statement (d)

The statement 'When a glass of water is left out in the sun, the water gradually disappears' describes a physical property. This process is evaporation, a change of state from liquid to gas, which does not alter the chemical composition of water.

Analyzing Statement (e)

The statement 'Carbon dioxide in air is converted to more complex molecules by plants during photosynthesis' describes a chemical property. Photosynthesis involves chemical reactions that convert carbon dioxide and water into glucose and oxygen.

Key concepts

Physical Properties

Physical properties are observable or measurable traits of a substance that do not change its internal composition. These properties include aspects like color, mass, volume, and the state of matter. For instance, the statement that 'Hemoglobin has a red color' reflects a physical property. It's an aspect you can see that doesn't alter the hemoglobin itself. Similarly, evaporation, which is a common process occurring when water is left out in the sun, is another example of a physical property. Water transitions from a liquid to a gas, but its molecular structure remains the same as H₂O throughout this process.

• Color
• Odor
• Melting and boiling points
• Density

Recognizing these properties helps differentiate them from chemical properties, which involve altering the substance’s composition.

Chemical Properties

Chemical properties of a substance are those that require a chemical change to observe. This involves forming new substances through reactions. An example of a chemical property is the tendency of iron to rust. Rusting involves iron reacting with oxygen to form iron oxide, a process that changes the composition of the original material.
The acidity of rainwater in industrialized regions also showcases chemical properties, as industrial pollutants chemically react with rainwater to form new acidic compounds.

• Reactivity with other chemicals
• Combustibility
• Corrosiveness
• pH levels

Understanding these properties sheds light on how substances interact with each other and under what conditions new materials can be created.

Examples of Chemical Reactions

Chemical reactions involve breaking and forming bonds between atoms to create new substances. Knowing examples helps in identifying chemical properties in practice. Rusting of iron is a straightforward example, where iron reacts with oxygen to form iron oxide.
Another example is the acidification of rainwater due to industrial pollutants, where sulfur dioxide and nitrogen oxides undergo reactions with water vapor to produce acids. The process of photosynthesis is a classic example of a complex chemical reaction, converting carbon dioxide and water into glucose and oxygen in the presence of sunlight and chlorophyll.

• Combustion - burning fuel produces energy, carbon dioxide, and water.
• Oxidation - iron rusts when exposed to moisture and oxygen.
• Neutralization - acid reacts with a base to form water and salt.

These examples emphasize the chemical changes that occur in various contexts in nature and industry.

Evaporation Process

Evaporation is a type of phase change where a liquid transforms into a gas or vapor. This occurs regularly, like when water gradually disappears from a glass left in the sun. Although the state changes from liquid to vapor, the chemical identity of water as H₂O remains constant.
The rate of evaporation depends on several factors such as temperature, surface area, and humidity. Higher temperatures increase the speed of evaporation. Similarly, increased surface area allows more water molecules to escape into the air.

• Non-boiling transition from liquid to vapor
• Maintains chemical composition
• Influenced by environmental factors

Understanding evaporation reveals insight into the physical changes substances can undergo without chemical alterations.

Photosynthesis Reaction

Photosynthesis is a vital chemical process performed by plants, algae, and some bacteria, converting light energy, usually from the sun, into chemical energy stored in glucose. This process transforms carbon dioxide and water into glucose and oxygen using sunlight.
It consists of complex reactions facilitated by chlorophyll, which absorbs light, primarily in the blue and red wavelengths, while reflecting green, which is why plants appear green. The overall chemical equation for photosynthesis can be represented as: \[ 6CO_2 + 6H_2O + light \rightarrow C_6H_{12}O_6 + 6O_2 \] This reaction is essential for life on Earth as it provides oxygen for animals and humans to breathe, and forms the foundation of the food chain by providing energy-rich compounds.