Question

Which of these statements about alloys and intermetallic compounds is false? (a) Bronze is an example of an alloy. (b) "Alloy" is just another word for "a chemical compound of fixed composition that is made of two or more metals." (c) Intermetallics are compounds of two or more metals that have a definite composition and are not considered alloys. (d) If you mix two metals together and, at the atomic level, they separate into two or more different compositional phases, you have created a heterogeneous alloy.(e) Alloys can be formed even if the atoms that comprise them are rather different in size.

Short answer

Statement (b) is false because an alloy is not a chemical compound of fixed composition. Instead, it is a mixture of metals or a metal with other elements.

Step-by-step solution

Statement (a) Analysis

Bronze, an alloy consisting primarily of copper and tin, is indeed an example of an alloy. As alloys are mixtures of metals or metals with other elements, this statement is correct.

Statement (b) Analysis

An alloy is a mixture of metals or a metal with other elements, but it is not a chemical compound with a fixed composition. This definition does not fit with what an alloy is. Therefore, this statement is false.

Statement (c) Analysis

Intermetallic compounds are compounds of two or more metals with a definite composition. They do have distinct properties from their constituent metals and are not considered alloys. This statement is correct.

Statement (d) Analysis

When you mix two metals together and they separate into different compositional phases at the atomic level, it is indeed a heterogeneous alloy. These alloys have multiple distinct phases that do not mix uniformly, which means this statement is correct.

Statement (e) Analysis

Alloys can be formed even if the atoms that comprise them are different in size. The differences in atomic size can result in various properties in the alloy depending on their arrangement. This statement is correct.

Conclusion

After analyzing each statement, we find that statement (b), "Alloy" is just another word for "a chemical compound of fixed composition that is made of two or more metals." is the false statement.

Key concepts

Intermetallic Compounds

Intermetallic compounds are unique because they are made up of two or more metals that combine to form a distinct compound with a precise composition. Unlike alloys, intermetallic compounds have a fixed ratio of the constituent metals, meaning their chemical makeup is specific and often leads to unique properties, such as high temperature stability or excellent electrical conductivity.
For example, compounds like CuAl (Copper-Aluminum) or NiAl (Nickel-Aluminum) display these properties. Intermetallics are not just simple mixtures; they exhibit specific crystallographic structures due to the fixed arrangement of their atoms.
This characteristic differentiates them substantially from alloys, which can have a range of compositions.

Heterogeneous Alloy

A heterogeneous alloy is a type of metal mixture where the components do not mix uniformly. When different metals are combined, they sometimes separate on an atomic level into distinct phases. This means that the different metals remain somewhat separate, forming a structure that is not uniform throughout.
This can create differing regions within the material that have unique properties or characteristics. For example, in a heterogeneous alloy, you might observe clusters of one type of metal isolated from another.
This property can be beneficial in certain applications where multiple material properties are needed within a single piece.

Atomic Composition

Atomic composition refers to the specific types and numbers of atoms that make up a substance. In the context of alloys and intermetallic compounds, understanding the atomic composition is crucial, as it determines the physical and chemical properties of the material.
For alloys, the atomic composition can vary, leading to a wide array of potential properties and applications. In contrast, intermetallic compounds have a defined atomic composition, which contributes to their stability and distinct features.
Knowing the atomic composition helps in predicting attributes like strength, malleability, or electrical conductivity, which are essential for industrial applications.

Metal Mixtures

Metal mixtures, commonly referred to as alloys, are formed when two or more metals (or metals and other elements) are combined. The resulting mixture can exhibit properties different from the original components, such as increased strength, resistance to corrosion, or improved ductility.
Examples include steel, which is primarily iron mixed with carbon, or bronze, a combination of copper and tin. The advantage of creating metal mixtures is the ability to tailor their properties to suit specific needs. This adaptability makes alloys a staple in manufacturing and engineering.
By altering the ratios and types of metals, manufacturers can create materials suitable for a wide range of applications, from aerospace components to everyday kitchen utensils.