Question

Musical instruments like trumpets and trombones are made from an alloy called brass. Brass is composed of copper and zinc atoms and appears homogeneous under an optical mi-croscope. The approximate composition of most brass objects is a \(2 : 1\) ratio of copper to zinc atoms, but the exact ratio varies somewhat from one piece of brass to another.(a) Would you classify brass as an element, a compound, a homogeneous mixture, or a heterogeneous mixture? (b) Would it be correct to say that brass is a solution? [ Section 1.2\(]\)

Short answer

(a) Brass is a homogeneous mixture. (b) Yes, it would be correct to say that brass is a solution.

Step-by-step solution

Understanding Elements, Compounds, and Mixtures

An element is a pure substance made of only one type of atom. A compound is a pure substance made of two or more elements chemically bound together in a fixed proportion. A mixture is a combination of two or more substances that are not chemically bound together. A homogeneous mixture has a uniform composition throughout, while a heterogeneous mixture does not have a uniform composition and its components are easily distinguishable.

Classifying brass

Brass is composed of copper and zinc atoms, and its composition varies somewhat from one piece of brass to another. The approximate ratio of copper to zinc atoms is \(2:1\). Since brass is composed of two different types of atoms (copper and zinc) and its composition is not fixed, it cannot be considered an element or a compound. Brass appears homogeneous under an optical microscope, so it can be classified as a homogeneous mixture.

Determining if brass is a solution

A solution is a type of homogeneous mixture where one substance is uniformly distributed in another substance at the molecular or ionic level. In brass, copper and zinc atoms are uniformly distributed, making it a homogeneous mixture. Thus, it would be correct to say that brass is a solution. Answer: (a) Brass is a homogeneous mixture. (b) Yes, it would be correct to say that brass is a solution.

Key concepts

Homogeneous Mixture

A homogeneous mixture is a type of mixture where the composition is consistent and uniform throughout the entire substance. That means if you were to take samples from any part of the mixture, each sample would have the same number and types of components.

In the case of brass, it's made by combining copper and zinc. Once these metals are mixed, they form a consistent appearance even under a microscope. This even distribution of components is what makes brass a homogeneous mixture.

• Uniform appearance and texture
• Components cannot be distinguished even under a microscope
• Example: brass is made of copper and zinc evenly mixed

Homogeneous mixtures vary in form and can be found as solids, liquids, or gases. Other examples like air and saltwater also fall into this category.

Solution

A solution is a specific kind of homogeneous mixture where the solute is dissolved completely in the solvent, making it uniform at the molecular or ionic level. This means that in a solution, the components are so thoroughly mixed that they cannot be seen individually.

For brass, the main components, copper and zinc, are mixed at a molecular level, making brass an excellent example of a solid solution. Even though we often associate solutions with liquids, they can exist in all states of matter.

• Solutes are uniformly distributed in the solvent
• Mixtures are uniform at both macro and microscopic scales
• Brass acts as a solid solution with two metals mingled at the atomic level

Understanding that solutions can be solids too helps in recognizing that mixtures like brass fit comfortably in this category.

Element vs Compound vs Mixture

Elements, compounds, and mixtures are fundamental terms in chemistry that describe pure substances and combinations.

• Element: A pure substance consisting of only one type of atom, like oxygen or copper. They cannot be broken down into simpler substances.
• Compound: Made up of two or more elements chemically bonded together in a definite ratio, like water ( H_2O ), and have different properties from their constituent elements.
• Mixture: Consists of two or more substances that are mixed but not chemically bonded. Mixtures can be homogeneous or heterogeneous. Brass is a homogeneous mixture of copper and zinc, varying in proportions.

Brass, being a mixture, varies in its exact composition, unlike a compound which has a fixed ratio of elements. Understanding the differences between these allows us to classify materials correctly.