Question

Classify each of the following as an element, a compound, a homogeneous mixture, or a heterogeneous mixture: (a) seawater, (b) helium gas, (c) sodium chloride (salt), (d) a bottle of soft drink, (e) a milkshake, (f) air in a bottle, \((\mathrm{g})\) concrete.

Short answer

(a) Homogeneous mixture, (b) Element, (c) Compound, (d) Heterogeneous mixture, (e) Heterogeneous mixture, (f) Homogeneous mixture, (g) Heterogeneous mixture.

Step-by-step solution

Understanding Elements

An element is a pure substance consisting of only one type of atom. It cannot be broken down into simpler substances by chemical means. For example, helium gas is an element because it consists solely of helium atoms.

Understanding Compounds

A compound is a substance formed when two or more chemical elements are chemically bonded together. Sodium chloride (salt) is a compound because it is composed of sodium and chlorine atoms bonded together in a fixed ratio.

Understanding Homogeneous Mixtures

A homogeneous mixture has a uniform composition and appearance throughout. For instance, air in a bottle is a homogeneous mixture because it's a mixture of gases that are evenly distributed.

Understanding Heterogeneous Mixtures

A heterogeneous mixture is one that has a non-uniform composition, where the individual substances remain distinct. Examples include a bottle of soft drink, which can contain differing concentrations of dissolved gases, and a milkshake, which has solid particles and liquid.

Classifying Seawater

Seawater is a homogeneous mixture. It consists of various salts, water, and other dissolved substances that are evenly distributed.

Classifying Helium Gas

Helium gas is an element because it contains only helium atoms with no mixture of other substances.

Classifying Sodium Chloride

Sodium chloride, or table salt, is a compound comprised of sodium and chloride ions in a fixed ratio.

Classifying a Bottle of Soft Drink

A bottle of soft drink is a heterogeneous mixture because, apart from the liquid, it typically contains visible bubbles of carbon dioxide gas and may have differing concentrations of flavorings.

Classifying a Milkshake

A milkshake is a heterogeneous mixture due to the presence of solid components like ice cream or fruit pieces mixed with liquid.

Classifying Air in a Bottle

Air in a bottle is a homogeneous mixture; it is primarily made up of nitrogen, oxygen, and other gases mixed uniformly.

Classifying Concrete

Concrete is a heterogeneous mixture as it consists of cement, water, and aggregate (like sand or gravel) that are not uniformly mixed.

Key concepts

Elements

Elements are the simplest pure substances and are made of only one type of atom. These atoms cannot be broken down into simpler substances through chemical reactions. Unlike compounds, elements do not contain multiple types of atoms. Instead, each element is unique and defined by the number of protons it has in its nucleus, also known as its atomic number. A well-known example of an element is helium gas, which is made entirely of helium atoms. Elements are the building blocks for all other types of matter and are represented on the periodic table.

Compounds

Compounds are formed when two or more elements chemically combine in a fixed ratio. The properties of a compound are different from the properties of the individual elements that form it. Compounds can only be separated by chemical reactions since their elements are bonded together. For instance, table salt or sodium chloride is a compound composed of sodium and chlorine atoms. When bonded, these elements form a new substance with unique properties, making it fundamentally different from either sodium or chlorine in their elemental forms. Compounds, like elements, are pure substances.

Homogeneous Mixtures

Homogeneous mixtures are uniform in composition and appearance throughout. The components in a homogeneous mixture are thoroughly mixed so that every portion of the mixture is the same as any other portion. They are also referred to as solutions. A classic example is air, where gases like nitrogen and oxygen are evenly distributed within the mixture. In a bottle of air or seawater, though different substances make up the mixture, they are dissolved fully and appear as a single phase. This even distribution means you cannot distinguish between the different components at a glance.

Heterogeneous Mixtures

Heterogeneous mixtures are made up of visibly different substances or phases. Unlike homogeneous mixtures, the components are not uniformly distributed and can often be seen with the naked eye. For example, a milkshake may contain pieces of fruit and ice cream, which are distinctly visible from the liquid. Similarly, a bottle of soft drink might show carbonation as bubbles, which differ from the liquid itself. Each part of a heterogeneous mixture remains separate, maintaining its own properties, and can often be separated through physical methods like filtration or decanting.