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Solutions and colloids

Middle School Chemistry

Solutions, Colloids, and Suspensions

Chemistry is the study of matter and the changes that matter undergoes. There are simple mixtures when you pour a cup of water, when you shake a bottle of milk, and when you mix soil with water. What you cannot see, and is true of all of these mixtures, is that the particles in these mixtures behave in very different ways.

Chemistry studies the reasons behind the separation of some liquids and the clarity of some compared to others. These differences can be due to the size, distribution, and stability of the particles that make up the liquid. For that, liquids are classified into solutions, colloids, and suspensions. These classes allow us to characterize the diverse materials we encounter in our lives and environment.

What is a Mixture?

A mixture is a combination of two or more substances that occurs without a chemical reaction, and the mixture retains the individual properties of each substance. The components of a mixture can be separated using physical means.

In a mixture:

  • There are two or more substances
  • The substances are not bonded chemically
  • Each substance retains its original properties
  • The substance can be altered
  • Separation can often be done using basic methods

Some examples of mixtures are:

  • Water and salt
  • Sand and iron filings
  • Air
  • Oil and water

Mixtures are found everywhere, whether in nature, at home or in the laboratory. Before understanding solutions, colloids, and suspensions, understanding mixtures is essential.

What are Solutions?

Solutions are a type of mixture where the ingredients combine equally, and they look the same from any ratio or angle. One ingredient has completely dissolved the other. Solutions have two components:

  • Solvent: the component that dissolves other component(s). The solvent is usually water.
  • Solute: is the dissolved component.

Consider dissolving salt in water:

  • Salt dissolves.
  • Salt is evenly dispersed in the water.
  • The mixture is clear and stable.

Solutions possess several characteristics:

  • The dissolved components are too small to be seen.
  • The mixture is clear, and light can pass through it.
  • The dissolved components do not settle down to the bottom.
  • The dissolved component can not be separated from the solvent by the process of filtration.

Several examples of solutions from daily life include:

  • Sugar in tea.
  • Saltwater.
  • Lemonade.
  • Vinegar.
  • Air

Solutions are vital in chemistry as reactions occur mostly in solutions, especially in biological and industrial interactions.

Solubility and Dissolving

Solubility is the capability of a chemical to be completely dissolved in a solvent. The rate of solubility is also dependent on other substances that are dissolved. Some of the factors that influence the dissolving capability are:

  • Chemical nature of the solute and solvent: In general, solutes and solvents of similar classes tend to dissolve in each other
  • Temperature: The majority of solid substances increase their solubility in warm water.
  • Stirring: In general, stirring accelerates the dissolving process.
  • Surface area: The smaller the particle size, the faster the dissolution.

When a solution reaches a point where no more solute can be dissolved, the solution is said to be saturated. The degree of solubility is of great importance in the formulation of drugs, beverages, and detergents.

What Is a Colloid?

A colloid is a heterogeneous mixture in which the size of the dispersed phase is between that of a true solution and that of a suspension. Colloids generally have a milky or hazy appearance.

In a colloid:

  • One substance is dispersed in the other.
  • The solvent is not homogeneous.
  • The dispersed phase is particles that are covered.
  • The particles correlate with particles and liquids and possess an unique property. The particle structure of the product acts as a liquid binding agent and gives the product unique properties.
  • Emulsifiers are a key factor in helping to improve the stability of colloidal emulsions.
  • Particles are typically in the range of 1 nm to 1 micron. Colloids are distributed within a liquid.
  • Colloids are also used in the paint and gel industries as well as other industrial sectors, and the environmental and medical sectors of the world.

The Tyndall Effect

Colloidal Dispersions Scattering Effect: The centered beam light reflects the beam. The other particles in the colloidal dispersion beam feel light.

The Tyndall Effect explains the following scenarios:

  • Headlights in fog
  • Sunbeam in a dusty room
  • Torch beam in smoke

Light Scattering Effect is not seen in solutions because the particles of the light-scattering sample are too small to scatter light.

Forms of Colloids

When assessing the form of a colloid, the state of the medium and the dispersed particles are taken into consideration.

Types of Colloids. At least four states of matter are represented in the above examples of colloids. Their use in food, medicine, and household products is explained by the various forms of colloids.

The following are examples of colloids in each state:

  • Aerosols - Fog, smoke
  • Emulsions - Milk, butter
  • Foams - Whipped cream, shaving foam
  • Gels - Jelly, toothpaste

What is a Suspension?

A suspension is a form of mixture that is heterogeneous in nature. A suspension is characterized by a mixture of solid particles that can be seen clearly and which do not dissolve. These solid particles in a suspension mixture will settle down and form a layer at the bottom of the suspension if the suspension is left undisturbed.

The following is a description of the major characteristics of suspension:

  • Particle size is the largest
  • The mixture will be heterogeneous
  • Sedimentation will occur due to the action of gravity
  • Components can be separated by filtration
  • The mixture is poorly defined

Examples of suspensions include muddy water, chalk and water mixture, and flour and water mixture.

When a suspension is stirred, a mixture of particles will settle out. This process is called sedimentation.

Types of mixtures: Solutions, Colloids, and Suspensions

These three categories of mixtures can be distinguished from one another by three properties:

Solutions

Particle Size
Extremely small
Appearance
Clear
Stability
Stable
Separation by Filtration
Not Possible
Light Scattering
No Scattering

Colloids

Particle Size
Medium (1 nm – 1 µm)
Appearance
Cloudy
Stability
Fairly Stable
Separation by Filtration
Not by Simple Filtration
Light Scattering
Shows Tyndall Effect

Suspensions

Particle Size
Large
Appearance
Cloudy and have visible particles
Stability
Unstable
Separation by Filtration
Possible
Light Scattering
Strong Scattering

These have been helpful to describe mixtures we see/ use in everyday occurrences.

Separation Methods

The physical processing methods to separate each of these mixtures are:

  • Suspensions - filtration, sedimentation, and decantation.
  • Colloids - special membrane filtration and centrifugation.
  • Solutions - evaporation, crystallization, and distillation.

These methods are commonly used in labs and for water purification and food processing.

Importance in everyday life and science

Solutions, colloids, and suspensions help to understand the world around the following examples:

In food and drinks:

  • Solutions: Soft drinks
  • Colloids: Milk

In medicine:

  • Solutions: Syrups
  • Suspensions: Some medicines

In the environment:

  • Colloids: Fog and smoke
  • Suspension: Dirty water

Understanding these examples will help you deal with various branches of chemistry, like reaction rates, solubility, separation techniques and materials science. Knowing how particles behave in a mixture helps to embrace the chemical processes in nature and technology.