A mixture is a combination of two or more substances that do not chemically react. As we explain later on, mixtures can either be heterogeneous or homogeneous.
Mixtures are defined based on how the constituents are combined. They could be a combination of various states of matter, for example, air dissolved in water, or a combination of solids such as the mixture of cement, sand, and aggregate.
The proportion of the constituents often determines the type and physical properties of a mixture. In other cases, however, the proportion is not very important, and it may only be incidental.
Mixtures occur naturally, such as in the case of air, which is a mixture of 78% nitrogen, 21% oxygen, and 1% other gases. Mixtures can also be artificially created at very precise proportions for specific purposes. For example, steel is a mixture of carbon, iron, and other metals.
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What is a Mixture in Chemistry?
In chemistry, a mixture is defined as a physical combination of two or more substances that do not produce a chemical reaction.
This means that chemical bonds are neither created nor broken between atoms. The individual constituents therefore retain their unique chemical properties. 
Nonetheless, the molecules of the constituent substances of a mixture may form static electrical attractions. Ions may also be formed in the process, such as in the case of salt being dissolved in water. In this type of mixture the constituents are a bit harder to separate.
Classifying Mixtures
Mixtures can be classified into two general categories (homogenous and heterogenous – more on those below) and several specific groups.
A mixture can be either both solids, both gases, or both liquids. They can also be a combination of various states of matter Examples of this include:
- A gas and a liquid, such as carbonated water
- A solid and a liquid, such as milk, which is a combination of fat globules in colloidal mixture with water
- A gas and a solid, such as suspended dust in the air.
Mixtures can have multiple components and states of matter, like air, which is a mixture of nitrogen, oxygen, other gases, and particulates.
Types of Mixtures
A mixture has at least two different constituents. These constituents can be so thoroughly mixed together that they are indistinguishable from each other, and they cannot be separated under standard conditions. Generally, mixtures can be categorised into two main groups – heterogeneous and homogeneous.
Special processes, such as distillation, are needed to separate such mixtures. This type of mixture is a homogeneous mixture. An example of a homogenous mixture is table salt dissolved in water.
A mixture can also have constituents that can easily be separated from each other under standard conditions without a need for special processes. This is a heterogeneous mixture.
An example of a heterogeneous mixture is a suspension, where solid particles are mixed with a liquid, but the solid particles don’t dissolve. Suspensions easily separate once the mixture is allowed to settle.
- Heterogeneous mixtures have distinct or easily identifiable constituents. Mixtures of this type are also easy to separate. Some may not even require any active effort or energy to be separated.
- Homogeneous mixtures have constituents that are virtually indistinguishable from each other. They tend to be harder to separate and require more effort and energy.
These are some examples of different types of mixtures:
- Solutions – these are homogeneous mixtures that contain two main components – the solvent and the solute(s). The solvent dissolves the solute. Generally speaking, the solvent is proportionally greater than the solute(s).
- Alloys – an example of a homogeneous mixture, alloys are characterised by two or more solid elements (at least one of which is a metal) that are mixed together. This is done to either strengthen the alloy or produce other desirable characteristics, for example, tarnish resistance. Much like a solution, one component (the metal) is proportionally greater than the other constituents.
- Suspensions – in this type of heterogeneous mixture, solid particles are mixed with a liquid but the particles do not dissolve. Suspensions easily separate once the mixture is allowed to settle.
- Colloids – these are heterogeneous mixtures with small particles that are evenly distributed in the liquid medium. Colloids are similar to a solution, but the particles aren’t dissolved.
Examples of Mixtures in Chemistry
Mixtures are either intentionally mixed or they are naturally-occurring. As we mentioned before, they can also be homogeneous or heterogeneous. Here are some examples of mixtures in chemistry:
- Sand and water – on a beach, the water and sand exist as a heterogeneous mixture. The water can be easily separated from the sand.
- Salt and water – the marine ecosystem is distinguished by its high salt content. The entire ocean is a homogeneous mixture of water, salt, other minerals, and organic substances.
- Sugar and salt – if you combine sugar and salt and mix them well, it becomes a heterogeneous mixture. Although the two crystalline substances are the same colour, they are still distinguishable from each other.
- Ethanol in water – wine, gin, whisky, and other alcoholic beverages are basically a homogenous mixture of ethanol and water. Ethanol is the only alcohol that can be consumed by humans without killing them.
Wine is a homogeneous mixture of ethanol and water
The Difference Between Mixtures and Solutions
Solutions are a homogeneous type of mixture. Mixtures, however, is a more general term that encompasses other types such as colloids and suspensions.
The distinguishing characteristic of solutions as mixtures is the fact the solutes are dissolved in the solvent. This means the solutes have become incorporated with the solvent and evenly distributed, either as molecules or ions.
The Significance of Mixtures in Chemistry
Chemistry is a scientific discipline focused on how substances (elements, compounds, mixtures, complexes, and ions) react with other substances and how they behave under certain conditions.
Chemistry is interested in the properties and structures of substances. Mixtures are a category of substances that aren’t chemically bonded together, but can behave in certain ways. For example, hydrochloric acid is an aqueous solution of the gaseous hydrogen chloride, and it can only act as an acid when dissolved in water.
Chemistry works with substances to either repurpose them, synthesising new substances, or use them for analytical purposes. Mixtures are used for these two major purposes.
Mixtures can be used as reagents to rule out or detect the presence of certain substances. For example, Fehling’s solution is a reagent used to differentiate between carbohydrate molecules and ketone functional groups. It’s also used for detecting reducing sugars and non-reducing sugars.
Applications and Importance
Mixtures are ubiquitous, from the air that we breathe to the products we use every day. Most of our drinks and food are mixtures – it really is difficult to underestimate how important mixtures are.
From our handheld gadgets to large structures, mixtures are present everywhere. For example, the concrete used in building skyscrapers, roads, and other structures are mixtures of cement, air, water, sand, and gravel.
Summary
In chemistry, mixtures are classified into general and specific categories. Each one has characteristics that are unique to that particular category. Mixtures exist naturally but some are made intentionally for a specific purpose. Although the substances in a mixture physically merge, their unique chemical properties do not change.
