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Difference between homogeneous and heterogeneous mixtures

Homogeneous mixtures are uniform, that is, their composition is the same wherever you look at it; while heterogeneous mixtures are uneven, with a composition that varies from one point to another. In homogeneous mixtures, there seems to be only one component (solute and solvent), but in heterogeneous, we easily visualize more than two components.

Consider for example a bowl of cereal like the one in the image below. At first glance we can see donuts (or loops) of different colors. When milk is added, we have a heterogeneous mixture of milk and cereal, two different components that are immiscible with each other.

Cereals are notoriously heterogeneous breakfasts due to the visible variety of their components

They are said to be immiscible because they do not dissolve each other (unless the donuts are finely powdered). Milk, on the other hand, is a homogeneous mixture, since although it is composed of many nutrients, these cannot be seen without the use of a microscope.

Homogeneous mixtures

Heterogeneous mixtures

Composition

Uniforms

Not uniform or uneven.

Phases

A material phase.

More than two material phases.

Components (edit)

Its components cannot be seen with the naked eye.

Its components can be seen with the naked eye.

Miscibility

Solute and solvent mix.

There is no talk of solute or solvent, since they do not mix.

Examples

Examples: oil, sea water, alloys.

Examples: cereals with milk, ice in a drink, paella.

Homogeneous mixtures

features

Homogeneous mixtures, also called solutions or solutions, have the following characteristics:

-They are uniform in appearance, so in principle they have a single color.

-They have a single material phase. That is, they are completely gaseous, liquid or solid, without having more than one state of matter at the same time.

-Its components cannot be seen with the naked eye, because they are extremely small.

-They are composed of solutes and a solvent, which is usually found in a higher proportion.

-They are stable under certain temperatures and pressures. If these factors change, their homogeneity is likely to “break”.

-The solute and the solvent mutually dissolve, that is, they are miscible. Otherwise, we would see two perfectly recognizable phases (liquid-liquid, solid-liquid, liquid-gas, etc.).

Phases

Homogeneous mixtures are uniform thanks to the fact that they have a single phase, in which the solute and the solvent are interacting with each other. This interaction is so efficient that the solute particles become very small as a result of solvation; that is, the solvent molecules surround the solute and prevent its size from growing, making it difficult for it to precipitate or settle.

Generally, the solvent defines the phase of the homogeneous mixture. A liquid solvent will result in a liquid homogeneous mixture or solution. This is the case, for example, of water and its aqueous solutions. Meanwhile, if the solvent is solid, then the homogeneous mixture will be solid, whose components or solute will be dissolved as part of the same uniform solid.

Types of homogeneous mixtures

The phases give rise to three types of homogeneous mixtures:

-Liquids (solutions or solutions)

-Solid (solid solutions)

-Gaseous (carbonated solutions)

However, liquid homogeneous mixtures or solutions in turn are divided into the following classifications, according to the amount of solute they have dissolved:

-Saturated

-Unsaturated

-Oversaturated

These three types of solutions depend on the solubility of the solute.

In saturated, the solvent has reached the maximum amount of solute that it can dissolve, so it precipitates, and the liquid has a concentration rich in solute. Meanwhile, in unsaturated solutions there is still more room for more solute to dissolve, having a relatively low concentration of solute.

On the other hand, supersaturated solutions are those in which the solvent has a greater amount of dissolved solute than it can dissolve under normal conditions. They are metastable (temporarily stable) under certain temperatures, and they quickly transform into saturated solutions.

The higher the affinity between the solute and the solvent, the more difficult it will be to saturate or supersaturate the solutions.

Examples of homogeneous mixtures

Air

Air is a homogeneous mixture consisting of a gaseous solution. Nitrogen, being the main component (78% approximately), could be considered as the solvent of the air; while oxygen (21%), argon (0.9%) and the other gases are the solutes, the components with the lowest proportion.

Sea water

Sea water is a liquid homogeneous mixture or solution in which huge amounts of salts are dissolved.

Milk chocolate

Milk chocolate is a homogeneous mixture in which milk would be the solvent, and chocolate (along with sugar) the solute.

Colorful glasses

Oxides give glasses different colors

The colored glasses are solid homogeneous mixtures or solid solutions, in which the glass is the solvent, and the colored metal oxides the solutes.

Alloys

Alloys, such as bronze and brass, are also solid homogeneous mixtures, in which both the solvent and the solutes are metals.

Others

  • Coffee.
  • Tomato soup.
  • Orange juice.

Heterogeneous mixtures

features

Heterogeneous mixtures, unlike homogeneous mixtures, have the following characteristics:

-They are uneven or non-uniform in appearance, so they can show various colors or reliefs.

-They have more than two material phases. That is, there can be more than two solids, liquids, or gases at the same time.

-Its components can be seen and differentiated with the naked eye.

-We do not speak of solute or solvent, but simply of components or solutes, since these are not miscible. Consequently, each component is physically separated from the other, thus retaining its original properties.

For example, in the cereal bowl the sugary donuts, even when wet and softened in the milk, have not undergone any noticeable chemical change. The same is true of milk.

Phases

Heterogeneous mixtures have more than one material phase. Therefore, in it we will see more than one physical state, or more than two perfectly recognizable and differentiable liquids, solids or gases. Each phase retains its original properties because the interactions between the components of the mixture are not as intimate as in the case of homogeneous mixtures.

For example, in the cereal plate the donuts represent a solid phase, while the milk a liquid phase. It is therefore said that it is a liquid-solid or solid-liquid mixture, depending on the proportion of milk and donuts.

In the case of the oil-water mixture, we will have two immiscible liquids that form a liquid-liquid mixture. There are thus two phases: one of oil and the other of water, each with its original chemical properties.

A mixture of black pepper and salt would become a solid-solid heterogeneous mixture, where both components are distinguished by the difference in their colors.

Types of heterogeneous mixtures

Like homogeneous mixtures, phases define the types of heterogeneous mixtures that exist. There are of the following types:

-Liquid-solid

-Liquid-liquid

-Solid-solid

-Liquid-gas

-Solid-gas

-Gas-gas

And there may even be mixtures where we see the three states of matter, or many material phases (as in the case of multicolored or multilayer gelatin).

However, of the types of heterogeneous mixtures the most important are suspensions (liquid-solid) and colloids.

Suspensions

In suspensions we have solid particles temporarily suspended in the liquid. Its fragments are visible to the naked eye as turbidity. As time passes, gravity ends up settling the solid and the suspension is “cut”, leaving the liquid on top as a supernatant.

Examples of suspensions are the water-sand mixture and mud.

Colloids

Colloids are a particular type of heterogeneous mixture. They do not speak of liquid, solid or gaseous phases, but of dispersed (“solute”) and dispersant (“solvent”) phases. The dispersed phase is in a lower proportion, while the dispersant is in a greater proportion.

Each of the phases of the colloids can be in any state of matter. Thus, there are several types of colloids. The most characteristic of this type of heterogeneous mixture is that they are macroscopically homogeneous, that is, uniform. However, when viewed under the microscope, they are heterogeneous.

Why? Because the scattered particles, although small, are large enough to scatter the light that falls on them. They remain stable, do not sediment, and therefore behave very differently from suspensions.

Milk, for example, is a colloid, more specifically an emulsion (fat-water). Therefore, it is a heterogeneous mixture, even though it appears homogeneous to our eyes.

Examples of heterogeneous mixtures

Paella

Paella is a particularly heterogeneous dish among so many. Source: Pixabay.

In paella we have a solid heterogeneous mixture, made up of rice, seafood and fish, as well as other dressings.

Pickles

In the pickle jars we see many cut vegetables (olives, pickles, carrots, etc.), which together with vinegar or in a saline solution make up a solid-liquid heterogeneous mixture.

Plasticine

When different colored plasticine is kneaded, a heterogeneous mixture is obtained at first, until its colors are completely mixed and dark.

Clouds

Clouds are gaseous colloids. In them, microscopic drops of water, surrounded by dust and other particles, are suspended in the air, with enough density to scatter the sunlight in its characteristic whiteness.

Fizzy drinks

Soft drinks have all three states of matter: the drink itself (liquid), the ice cubes (solid), and the bubbles (gas).

Mosaics

The mosaics make up a kind of artistic work that stands out for the difference in the colors of its pieces or stones.

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