Homogeneous and Heterogeneous Substances


This is part of HSC Chemistry course under the topic of Properties of Matter 

HSC Chemistry Syllabus

  • Explore homogeneous mixtures and heterogeneous mixtures through investigations

Homogeneous and Heterogeneous Substances

This video will explain how mixtures can be classified as homogeneous or heterogeneous and what those classifications mean. 


Pure Substances and Mixtures

When classifying matter, the classifications of pure substance or mixture can also be used to group elements and compounds, and mixtures. 

A pure substances is a substance which has a uniform and unchanging composition. This means that the chemical makeup of the substance is the same throughout. Elements and compounds are examples of pure substances.

Mixtures are examples of non-pure substances as they are formed from two or more elements and/or compounds being combined. This combination leads to the formation of a wide array of mixtures with varying properties and compositions.

Beyond this, mixtures can be further classified into two categories: homogeneous and heterogeneous mixtures. 

1. Homogeneous Mixtures

  • Definition:
    Homogeneous mixtures have a consistent and uniform distribution of components throughout. The composition appears consistent, no matter which portion of the mixture is examined.

  • Characteristics:
    Homogeneous mixtures typically exist in one phase of matter, be it liquid, gas, or solid. The individual substances in a homogeneous mixture are not easily distinguishable.

  • Examples:
    • Air: A classic example of a homogeneous mixture. It is a blend of nitrogen, oxygen, argon, carbon dioxide, and trace amounts of other gases. Its composition is consistent regardless of the sampling location.
    • Sugar solution: When sugar is dissolved in water, it forms a clear, uniform solution, where sugar molecules are evenly distributed throughout the water.

    Figure 1: Sugar Syrup is a homogeneous mixture as it has a uniform composition throughout its structure. 


    2. Heterogeneous Mixtures

    • Definition:
      Heterogeneous mixtures have a non-uniform distribution of components, leading to varying compositions in different parts of the mixture.

    • Characteristics:
      These mixtures may exhibit more than one phase (solid, liquid, gas).The different components are often visible and can be distinguished from each other.

    • Examples:
      • Soda with Ice Cubes: The ice cubes floating in soda create a visible separation between the solid ice and the liquid soda, exemplifying a heterogeneous mixture.
      • Granite: A common example from geology, granite is composed of different minerals like quartz, feldspar, and mica, each visible as separate entities. Different portions of a granite block may have different compositions of each type of mineral. In other words, the percentage of composition is not uniform in a black of granite.


    Figure 2: Granite is a heterogeneous mixture as it has a mixed proportion of components throughout its structure. Its components are distinguishable.



    Pure Substance

    A mixture can be physically separated into two or more pure substances by physical or mechanical means such as filtering, boiling or decanting

    A pure substance cannot be separated into two or more substances by physical means. A compound can however be separated into elements using chemical reactions such as electrolysis

    A mixture may be both homogeneous or heterogenous

    A pure substance can only exist in homogeneous form

    A mixture will display the properties of all of the individual pure substance components which make it up. If a mixture is homogeneous, different parts of it may show different properties

    A pure substance has constant properties such as appearance, colour, density, melting point, and boiling point

    The composition of a mixture is variable

    The composition of a pure substance is fixed

      Previous Section: Types of Matter 

      Next Section: Separation Techniques