Heterogeneous Mixture - Homogeneous Mixture Worksheet

About heterogeneous mixture - homogeneous mixture worksheet
The heterogeneous mixture – homogeneous mixture worksheet with answer key is below. The worksheet gives common examples of mixtures, in addition to some pure, un-mixed substances. Learn how to classify these examples of mixtures below.
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What is a heterogeneous mixture?

Heterogeneous definition

One heterogeneous mixture definition is when substances are not completely mixed all the way down to the molecular level. To the naked eye, or perhaps with a microscope, you would be able to see patches of one substance dispersed among patches of another substance. Typically, the mixed substances appear as different states, or phases, of matter.

Heterogeneous mixture examples 

An example or a heterogeneous mixture is the atmosphere on a rainy day. The rainy atmosphere is a mixture of the air, which is a gas, with liquid rain droplets. There are patches of dense liquid water falling down through the less dense air. It’s an obviously heterogeneous mixture because there are two states, or phases of matter: liquid and gas.

Importantly, on a rainy day, visibility is limited. We can see through air, because sunlight passes unobstructed through the air. But liquid raindrops bend, scatter, disperse, and block sunlight so that it does not pass through the rainy atmosphere.

The vast majority of substances on planet Earth are heterogeneous mixtures.There are a variety of common heterogeneous mixture examples below.

What is a homogeneous mixture?

Homogeneous definition  
One homogeneous mixture definition is when substances are completely mixed all the way down to the molecular level.  Unfortunately, we cannot see all the way down to the molecular level. Sometimes a mixture appears homogeneous when it is in fact heterogeneous. A key distinction is that a homogeneous mixture can only possibly have one state, or phase, of matter.
 
Homogeneous mixture examples

We have to use our understanding of chemistry to identify a homogeneous mixture. Fortunately, there are really only 3 homogeneous mixture examples. It’s good to know these, and then assume that all other cases would be heterogeneous mixtures.

Here are the 3 homogeneous mixture examples:
1. Dissolving something into a liquid makes a homogenous solution.
2. Gasses always mix homogeneously.
3. Alloys are homogeneous mixtures of metals.

Dissolving

Homogeneous mixture examples include dissolving things like salt, sugar, or food coloring into water. These are called aqueous solutions, denoted (aq), in which water acts as a solvent. When something dissolves, it is broken down completely to the molecular level. Note that we can see through a homogeneous solution. There may be color, such as when dissolving food coloring in water, yet the light will pass because there are no large obstructions to block the light.

Homogeneous solutions don’t have to involve water. Two oils, such as olive oil and coconut oil, would also mix homogeneously.

Gases
Gasses always mix homogeneously no matter what. A good example is the air. It always has about 21% oxygen. Everywhere. This is good, because you don’t have to go to the other end of the room to find some oxygen to breathe. Even at the top of Mount Everest, there is still 21% oxygen content in the air. the problem, though, is that the atmosphere gets “thin” and there’s just not much air way up there in the first place.
 
NITROX is a homogeneous mixture of 21% oxygen and 79% nitrogen that can be stored in a tank. SCUBA divers and mountaineers transport tanks of this breathable gas, which is not exactly air, so they can survive in otherwise unsurvivable conditions. The tank of gas is a homogeneous mixture, meaning that each breath taken from the tank will contain 21% oxygen, just like the air we normally breathe in the atmosphere.
 
In reality, gases dissolve into each other when they are mixed. The gas particles are flying around at rather high speed, so the mixing of gases occurs quite naturally, all the way down to the molecular level. And visibility is maintained, as we can see through gasses.
 
Gases
Gasses always mix homogeneously no matter what. A good example is the air. It always has about 21% oxygen. Everywhere. This is good, because you don’t have to go to the other end of the room to find some oxygen to breathe. Even at the top of Mount Everest, there is still 21% oxygen content in the air. the problem, though, is that the atmosphere gets “thin” and there’s just not much air way up there in the first place.
 
NITROX is a homogeneous mixture of 21% oxygen and 79% nitrogen that can be stored in a tank. SCUBA divers and mountaineers transport tanks of this breathable gas, which is not exactly air, so they can survive in otherwise unsurvivable conditions. The tank of gas is a homogeneous mixture, meaning that each breath taken from the tank will contain 21% oxygen, just like the air we normally breathe in the atmosphere.
 
In reality, gases dissolve into each other when they are mixed. The gas particles are flying around at rather high speed, so the mixing of gases occurs quite naturally, all the way down to the molecular level. And visibility is maintained, as we can see through gasses.
 
Alloys
An alloy is a homogeneous mixture of metals. Examples include bronze, which is a mixture of copper and tin, and also brass, which is a mixture of copper and zinc. Obviously, the metals are first melted at extremely high temperatures. Liquid molten metals flow and dissolve into each other completely down to the molecular level. The molten homogeneous mixture is cast into a mold, cooled, and solidified into an alloy.
 

Common heterogeneous mixture examples

Precipitation reactions and suspensions
A precipitation reaction is when a solid suddenly appears in a liquid or solution. It’s called a precipitation reaction because there are patches of more dense solid falling or raining down through the less dense liquid or solution. It’s an obviously heterogeneous mixture because there are two states, or phases of matter: solid and liquid. Notably, visibility is limited, because the solid particles bend, scatter, disperse, and block the light from passing. We call this a suspension, because tiny solid particles are settling very slowly due to gravity and appear to be suspended. 
 
An example of a precipitation reaction to produce a suspension of tiny, concrete like solid particles is shown in the below video. The particles are too tiny to see. Yet, because the solid particles are big enough to block the light, the suspension appears opaque. This is an extremely important piece of information that tells us that it is definitely a heterogeneous mixture. A homogeneous mixture would allow the light to pass, even if it did have some color.
 
A suspension could also result from mixing solids that won’t dissolve into a liquid. For example, muddy water has lots of small small solid particles floating around and suspended. We know for sure it’s a heterogeneous mixture because the light does not pass, and it appears opaque. Given enough time, perhaps some days, the dirt particles would settle to the bottom to produce and obviously solid layer below a liquid water layer.
Oil and water
Oil and water don’t mix. Interestingly, they are both in the liquid state of matter. The less dense oil floats on top of the more dense water. We would say that there are two liquid phases, a watery phase and an oily phase. This makes it obviously heterogeneous.
 
Milk is a less obvious heterogeneous mixture. Milk is opaque, meaning it has to be a heterogeneous mixture. It’s indeed mostly water. Tiny, oily, fat globules are suspended in the water, blocking the light, and causing the opaque appearance. These fat globules are also white, causing the distinct color of milk. We know it’s heterogeneous not because of the color, but rather because it is opaque. 
 
 
Another common example is blood. It appears opaque because tiny solid blood cells block the light from passing. Cells have an oily casing (a lipid bilayer) that keeps them intact, much like milk’s suspended fat globules that won’t dissolve.

heterogeneous mixture because the light does not pass, and it appears opaque. Given enough time, perhaps some days, the dirt particles would settle to the bottom to produce and obviously solid layer below a liquid water layer.

Soap, oil, and water  
Mixing just oil and water results in 2 liquid layers. If we add just a bit of soap, the two clear layers combine into a single, cloudy layer. This must be a heterogeneous mixture because it’s cloudy and the light does not pass. Soap does allow water and oil to mix to some extent, as the oil won’t just float on top of the water in the presence of soap. The soap encapsulates tiny oil droplets and allows them to be suspended in the bulk water, much like the fat globules which are suspended in milk.
 
Solid powders
Solids could never mix all the way down to the molecular level. This is because they are rigid and have surfaces. We can grind solids down to microscopic, or smaller, particles that could not be seen. Various powders or granules could be mixed by stiring them together, such as mixing salt and sand. We could always pick such heterogeneous mixtures apart using tweezers, assuming we have infinite patience. Also, note that there would be tiny air (gas) pockets contained within a mixture of solid powders, making it obviously heterogeneous.
 
Salt and Sand Mixture Separation
Steel
Steel is not an alloy. Strictly speaking. In the real world, lots of people talk about steel alloys; however, it’s a blatant misuse of the word alloy.
 
Steel is made by throwing charcoal powder into molten iron. Tiny flecks and bits of the charcoal, which is pure carbon, remain in the steel after it is cast. It’s obviously heterogeneous, because there are patches of carbon interspersed within the bulk metal. You would have to look at a freshly cut piece of steel under a microscope to see the carbon. Most people have never looked at steel under a microscope. So basically you just have to know this one. Steel is a heterogeneous mixture with 2 solid phases, metal and carbon.
 
 

Pure substances: Compounds and Elements

Most substances on planet Earth are examples of mixtures.  Theoretically, we can extract pure substances from a mixture. It can, however, be difficult, time-consuming, and costly in practice.
 
Most pure substances are chemical compounds. Water, commonly known as H2O, is a compound. The formula indicates that water is two parts hydrogen atoms and one part oxygen atoms. The hydrogen and oxygen are not mixed, but are rather combined chemically. We could not extract the hydrogen or oxygen from water directly. However, it is totally possible to have a chemical reaction which chemically transforms the water into its constituent hydrogen and oxygen parts. This is chemical transformation, not un-mixing, because the water vanishes. This happens readily whenever electricity passes through water.
 
Hydrogen and oxygen are elements, not compounds. This means that they are the most basic and fundamental particles that make up matter. elements, like hydrogen and oxygen, cannot be broken down further by chemical or any other means.
 
Elements appear on the periodic table. Pure compounds are made from these elements. Mixtures involve combining pure compounds and possibly elements according to the heterogeneous definition and homogeneous definition as described above.
 
 

Exercise 1.

Describe the following as an element, a compound, a homogenous mixture, or a heterogeneous mixture: