mixtures

what is a mixture

A mixture is a combination of two or more substances in any proportion. This is different from a compound, which consists of substances in fixed proportions. The substances in a mixture also do not combine chemically to form a new substance, as they do in a compound. Instead, they just intermingle and keep their original properties. The lemonade pictured above is a mixture because it doesnt have fixed proportions of ingredients. It could have more or less lemon juice, for example, or more or less sugar, and it would still be lemonade. Q: What are some other examples of mixtures? A: Other examples of liquid mixtures include salt water and salad dressing. Air is a mixture of gases, mainly nitrogen and oxygen. The rock pictured in the Figure 1.1 is a solid mixture. This rock is a mixture of smaller rocks and minerals.

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types of mixtures

Mixtures have different properties depending on the size of their particles. Three types of mixtures based on particle size are solutions, suspensions, and colloids, all of which are described in Table 1.1. Click image to the left or use the URL below. URL: Click image to the left or use the URL below. URL: Type of Mixture Solutions Description A solution is a homogeneous mixture with tiny parti- cles. The particles are too small to see and also too small to settle or be filtered out of the mixture. When the salt is thoroughly mixed into the water in this glass, it will form a solution. The salt will no longer be visible in the water, and it wont settle to the bottom of the glass. Colloids A colloid is a homogeneous mixture with medium- sized particles. The particles are large enough to see but not large enough to settle or be filtered out of the mixture. The gelatin in this dish is a colloid. It looks red because you can see the red gelatin particles in the mixture. However, the particles are too small to settle to the bottom of the dish. A suspension is a heterogeneous mixture with large particles. The particles are large enough to see and also to settle or be filtered out of the mixture. The salad dressing in this bottle is a suspension. It contains oil, vinegar, herbs, and spices. If the bottle sits undisturbed for very long, the mixture will separate into its component parts. Thats why you should shake it before you use it. Suspensions Q: If you buy a can of paint at a paint store, a store employee may put the can on a shaker machine to mix up the paint in the can. What type of mixture is the paint? A: The paint is a suspension. Some of the components of the paint settle out of the mixture when it sits undisturbed for a long time. This explains why you need to shake (or stir) the paint before you use it. Q: The milk you buy in the supermarket has gone through a process called homogenization. This process breaks up the cream in the milk into smaller particles. As a result, the cream doesnt separate out of the milk no matter how long it sits on the shelf. Which type of mixture is homogenized milk? A: Homogenized milk is a colloid. The particles in the milk are large enough to seethats why milk is white instead of clear like water, which is the main component of milk. However, the particles are not large enough to settle out of the mixture.

homogeneous or heterogeneous

The lemonade in the opening picture is an example of a homogeneous mixture. A homogeneous mixture has the same composition throughout. Another example of a homogeneous mixture is salt water. If you analyzed samples of ocean water in different places, you would find that the proportion of salt in each sample is the same: 3.5 percent. The rock in Figure 1.1 is an example of a heterogeneous mixture. A heterogeneous mixture varies in its composition. The black nuggets, for example, are not distributed evenly throughout the rock.

separating mixtures

The components of a mixture keep their own identity when they combine, so they retain their physical properties. Examples of physical properties include boiling point, ability to dissolve, and particle size. When components of mixtures vary in physical properties such as these, processes such as boiling, dissolving, or filtering can be used to separate them. Look at the Figure 1.2 of the Great Salt Lake in Utah. The water in the lake is a solution of salt and water. Do you see the white salt deposits near the shore? How did the salt separate from the salt water? Water has a lower boiling point than salt, and it evaporates in the heat of the sun. With its higher boiling point, the salt doesnt get hot enough to evaporate, so it is left behind. Q: Suppose you have a mixture of salt and pepper. What properties of the salt and pepper might allow you to separate them? A: Salt dissolves in water but pepper does not. If you mix salt and pepper with water, only the salt will dissolve, leaving the pepper floating in the water. You can separate the pepper from the water by pouring the mixture through a filter, such as a coffee filter. Q: After you separate the pepper from the salt water, how could you separate the salt from the water? A: You could heat the water until it boils and evaporates. The salt would be left behind.

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instructional diagrams

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questions

examples of mixtures include

a) lemonade.

b) salad dressing.

c) salt water.

-->  d) all of the above

a homogeneous mixture with particles too small to see or settle out is a

a) colloid.

-->  b) solution.

c) suspension.

d) compound.

an example of a colloid is

a) salt water.

b) salad dressing.

-->  c) homogenized milk.

d) none of the above

you can filter the particles out of

-->  a) suspensions.

b) colloids.

c) solutions.

d) all of the above

a colloid is a heterogeneous mixture.

a. true

-->  b. false

the components of a mixture keep their physical properties when they combine.

-->  a. true

b. false

components of mixtures can be separated by physical processes.

-->  a. true

b. false

diagram questions

No diagram questions associated with this lesson