Understanding Homogeneous Mixtures and Solutions

Posted on Dec 20, 2024 in Chemistry

Homogeneous mixtures are uniform; that is, any portion has the same composition and properties. The blended components cannot be distinguished even with the aid of an electron microscope, which is the most powerful.

Homogeneous mixtures are also called solutions. Depending on the physical state of the mixture, solutions can be gaseous, liquid, or solid.

• Gaseous Solutions

  A set consisting of gases, such as the atmosphere, is made of 71% nitrogen, 21% oxygen, and 1% other gases.

• Solid Solutions or Alloys

  Alloys are mixtures of two or more metals in different proportions. The preparation of these alloys is carried out by melting the metals. After mixing in the appropriate proportion, they are allowed to solidify. Types of alloys:

  • Bronze

    Bronze has been known since prehistoric times. It is a mixture of copper and tin. In ancient times, it was used to produce domestic objects, weapons, and sculptures.

  • Brass

    This is a mixture of copper alloyed with zinc. It is used in decorative objects and has great resistance to corrosion (slow wear of the material).

  • Steel

    Steel is an alloy with extensive use today. It is a mixture of iron with a small proportion of carbon. It is used in all types of machinery and instruments (turbines, bodywork, cutlery, etc.). One well-known type is stainless steel, which is made by adding chromium and nickel to the iron and carbon.

    Another type of iron and carbon alloy is cast iron, which has a higher proportion of carbon. Cast iron is used to design complicated pieces.

• Liquid Solutions

  The best-known liquid solutions are those that mix with water, known as aqueous solutions. Water can be mixed with gases (like oxygen), liquids (like alcohol), and solids (like salt).

  In a liquid solution, the major component is called the solvent, and the minor component is called the solute. In these solutions, the physical properties, such as density or the freezing point of the solvent, vary. For example, a solution of salt water has a freezing point below that of pure water, which freezes at 0°C.

Concentration of a Solution

If you mix water with salt, you can choose to add a lot or very little salt. When we compare, we can say that the solution to which we added more salt is more concentrated than the second. We can also say that the second, to which we have added less salt, is more diluted than the first. But what happens when we continue to add salt? A moment will be reached when the solvent (water) cannot support more salt. Then the excess salt will be deposited at the bottom of the container. The solution is saturated.

Calculating the Concentration of a Solution

The concentration of a solution is equal to the amount of solute that is dissolved in a certain amount of solution. The general formula is:

There are two ways to apply this formula because the concentration of a solution can be expressed as a percentage by weight or in grams/liter:

For example, if we have a solution of 20 grams of alcohol in 500 cm³ of water, what is the concentration in % by weight and in grams/liter? (It should be remembered that a cm³ of water equals one gram of water).

Separating Homogeneous Mixtures

In nature, it is very difficult to find pure substances, as both inorganic and organic matter are very mixed. However, industry needs to work with pure substances. For this, the components that form a mixture must be separated. Depending on the components of a homogeneous mixture that we want to separate, there are different techniques:

• Separating Solids from Liquids

  The goal is for one component to change state while the other stays the same. The technique used is crystallization. The reverse step is to dissolve a solid in a solvent. The solvent is allowed to evaporate to leave only the solute. This technique separates salt from saltwater: water is evaporated, leaving large pools, and then the salt that has crystallized is collected.

• Distillation

  With this technique, the components of a solution are separated based on each component having a different boiling point. The solution is heated, and the first component that evaporates passes to a condenser where it cools and returns to a liquid state, ready to be collected in a container. This technique is used to separate the components of oil (kerosene, gasoline, tar, etc.).