Homogenous and Heterogenous Mixtures

Homogeneous Mixture

Learning Objectives

 

  • Define mixture.
  • Define homogeneous mixture.
  • Give examples of homogeneous mixtures.


How do you like your coffee?

A cup of coffee is a homogenous mixture

How do you like your coffee?

Many people enjoy a cup of coffee at some point during the day. Some may drink it black, while others may put cream (or some dairy substitute) and sugar in their coffee. You can buy high-end coffee drinks at espresso stands (either sit-down or drive-through). Whatever your preference, you want the coffee to be the same at the beginning and the end of your drink. You don’t want the components to separate out, but you want your drink to be uniform from top to bottom.

 

Mixtures

Ordinary table salt is called sodium chloride. It is considered a substance because it has a uniform and definite composition. All samples of sodium chloride are chemically identical. Water is also a pure substance. Salt easily dissolves in water, but salt water cannot be classified as a substance because its composition can vary. You may dissolve a small amount of salt or a large amount into a given amount of water. A mixture is a physical blend of two or more components, each of which retains its own identity and properties in the mixture . Only the form of the salt is changed when it is dissolved into water. It retains its composition and properties.

Homogeneous Mixtures

A homogeneous mixture is a mixture in which the composition is uniform throughout the mixture. The salt water described above is homogeneous because the dissolved salt is evenly distributed throughout the entire salt water sample. Often it is easy to confuse a homogeneous mixture with a pure substance because they are both uniform.  The difference is that the composition of the substance is always the same. The amount of salt in the salt water can vary from one sample to another. All solutions would be considered homogeneous because the dissolved material is present in the same amount throughout the solution.

One characteristic of mixtures is that they can be separated into their components. Since each part of the mixture has not reacted with another part of the mixture, the identities of the different materials is unchanged.

Summary

  • A homogeneous mixture is a mixture in which the composition is uniform throughout the mixture.
  • All solutions would be considered homogeneous.


 

Practice

Questions

Use the link below to answer the following questions:

http://www.buzzle.com/articles/homogeneous-mixture-examples.html

  1. What is the composition of gunpowder?
  2. Why would vinegar be considered a homogeneous mixture?
  3. Name three alloys and list what they are composed of.


 

Review

Questions

  1. What is a mixture?
  2. What is a homogeneous mixture?
  3. Are all solutions homogeneous mixtures?
  4. Can homogeneous mixtures be separated into their components?


 

Glossary

  • homogeneous: A mixture in which the composition is uniform throughout the mixture.
  • mixture: consists of multiple substances put together.
  • substance: It has a uniform and definite composition.


Heterogeneous Mixtures

Learning Objectives

  • Define heterogeneous mixture.
  • Define phase.
  • Give examples of heterogeneous mixtures.


What's the best way to eat a bag of jelly beans?

Handful of jelly beans

What's the best way to eat a bag of jelly beans?

Many people open the bag and eat all the candy, no matter what flavor each piece is. Others pick through the collection. They might say “I don’t like the orange ones.” Or maybe they just care for the lemon ones. There are different kinds of jelly beans in the mixture and people will eat what they want and get rid of the rest.

 

Heterogeneous Mixtures

A heterogeneous mixture is a mixture in which the composition is not uniform throughout the mixture. Vegetable soup is a heterogeneous mixture. Any given spoonful of soup will contain varying amounts of the different vegetables and other components of the soup.

A phase is any part of a sample that has a uniform composition and properties. By definition, a pure substance or a homogeneous mixture consists of a single phase. A heterogeneous mixture consists of two or more phases.  When oil and water are combined, they do not mix evenly, but instead form two separate layers. Each of the layers is called a phase.

Oil and water form a heterogeneous mixture

Figure 2.9

Oil and water do not mix, instead forming two distinct layers called phases. The oil phase is less dense than the water phase and so the oil floats on top of the water.

In the vegetable soup example, one phase would be the liquid soup itself. This phase has vitamins, minerals, and other components dissolved in the water. This phase would be homogeneous. The carrots, peas, corn, or other vegetables represent other phases of the soup. The various vegetables are not mixed evenly mixed in the soup, but are spread around at random.

There are a large number of heterogeneous mixtures around us. Soil is composed of a variety of substances and is often of different composition depending on the sample taken. One shovel may come up with dirt and grass while the next shovel could contain an earthworm.

Smog is another example of a heterogeneous mixture. This murky collection of pollutants can be a mixture of water and contaminants from burning gasoline or plastics mixed with nitric oxide derivatives and ozone. You can see that the smog distribution in the air illustrate below is not evenly spread out, but varies from one part of the atmosphere to another.

Smog is a heterogeneous mixture

Figure 2.10

Smog in New York City.

Summary

  • A heterogeneous mixture is a mixture in which the composition is not uniform throughout the mixture.
  • A phase is a separate layer in a heterogeneous mixture.


 

Practice

Questions

Use the link below to answer the following questions:

http://antoine.frostburg.edu/chem/senese/101/matter/faq/what-is-heterogeneous.shtml

  1. Why is a mixture of sand and sugar a heterogeneous mixture?
  2. What are the phases in a glass of iced tea?
  3. How is blood a heterogeneous mixture?


 

Review

Questions

  1. Define a heterogeneous mixture.
  2. Why is vegetable soup a heterogeneous mixture?
  3. How many phases are in a heterogeneous mixture?


 

Glossary

  • heterogeneous mixture: A mixture in which the composition is not uniform throughout the mixture.
  • phase: A separate layer in a heterogeneous mixture.