Unit 1: Properties of Materials and Mixtures

Differentiating Scientific ClassificationSC020105

Lesson 5: Solutions and Mixtures

Big Ideas of the Lesson

A mixture is something that is made of two or more things that are mixed together.
A sieve is a tool with holes that is used to separate mixtures.
A filter is something that is used to separate a liquid from a solid.
A solution is a liquid that is made when something dissolves in water
Evaporation is when a liquid turns into a gas.
Mixtures and solutions can be separated with a sieve, a filter, or with evaporation.

Abstract

In this lesson children learn how to separate various combinations of materials using tools such as a sieve and filter paper. They try several separations in small groups, and write about why the method they used to separate the mixture worked. Children also learn about dissolving – that a substance added to water that seems to “disappear” is really still in the water, and can be separated out of the water again by evaporation.

Grade Level Context Expectation(s)

Children will:

describe objects and substances according to their properties (e.g., color, size, shape, texture, hardness, liquid or solid, sinking or floating) (P.PM.02.12).
recognize that some objects are composed of a single substance (water, sugar, salt) and others are composed of more than one substance (salt and pepper, mixed dry beans) (P.PM.02.41).
generate questions based on observations of various objects (S.IP.02.12).
recognize that when a science investigation is done the way it was done before, similar results are expected (S.RS.02.13).

Key Concept(s)

attribute

material

mixture

property

Instructional Resources

Equipment/Manipulative

Aquarium gravel (1 bag multicolored)

Aquarium rocks (1 bag, approx. 1 cm larger than the gravel)

China marker or pencil

Clear plastic Petri dish or clear glass pan

Dry beans

Filter paper

Measuring cups (1/2 cup and ¼ cup)

Plastic bowls (1 per group)

Plastic spoons (1 per group)

Salt

Samples of white beans, pepper, short-grain rice

Sieve (1 per group, strainer with holes large enough to let aquarium gravel and short-grain rice to pass through)

Water

Student Resource

Gabrys, Jennifer, and Claudia B. Douglass. Supplemental Materials (SC02010501.doc). Teacher-made material. Waterford, MI: Oakland Schools, 2008.

Oxlade, Chris. Mixing and Separating. New York: Crabtree Publishing, 2008.

Teacher Resource

Texley, Juliana, and Claudia B. Douglass. Second Grade Unit 1 Teacher Background (SC020100TB.doc). Teacher-made material. Waterford, MI: Oakland Schools, 2008.

Sequence of Activities

Advance Preparation: Have materials prepared in sets for each group: two empty plastic cups, plastic bowl, sieve, filter paper, plastic spoon, and plastic funnel.

1. To start the lesson, tell the children that over the next several days they are going to investigate mixtures, and use their knowledge about magnets, too. Ask them to name some things they mix together. Have them think about preparing food, or other things they do around the house. Examples may include mixing vegetables in a salad, salt and pepper on a plate, dry lemonade and water, rocks and sand in a fish tank, etc. Give the children some examples to get them started, if needed.

2. Rocks and gravel. Mix together aquarium rocks with aquarium gravel in front of the class. Ask the children to suggest ways of separating the rocks from the gravel. Distribute 1/2 cup of the gravel/rock mixture to each group in a plastic cup. Have groups use their sieve to separate the rocks from the gravel, catching the gravel in the plastic bowl. Have each group write an explanation of how they separated their mixture, and why their separation method worked. [The sieve can separate gravel from rocks because the gravel is small enough to go through the sieve holes but the rocks are not.]

3. Gravel and water. Have each group put their gravel into a plastic cup, then pour 1/4 cup water into their gravel, then ask them if it is possible to separate the gravel and water with the sieve. [No, both the gravel and water go through the sieve.] Ask them to think of another way that they could get the gravel out of the water. Some might suggest pouring off the water; some might suggest using a spoon. If so, let them try either or both ways.

Ask them if they were able to separate all of the water from the gravel? If not, ask them to suggest what else they might do. Some might suggest using a hair dryer to dry the gravel. This would work, although the explanation of how the water is separated from the gravel should wait until later in this lesson, after the evaporation experiment.

If no one suggests using the filter paper (most children at this age do not have experience using filter paper), show them how to set up their funnel and filter paper and demonstrate pouring water through it into a plastic cup. Then have each group set up their own funnel and filter paper and pour their gravel/water mixture through the filter.

4. Using their Student Pages, have the children think about additional mixtures and how they might be separated. Ask each child to consider each mixture, choose the best method for separating the mixture, and explain how the separation would work. Allow enough time to complete this, then discuss as a class.

Beans and rice: The sieve would work because the rice grains are small enough to pass through, but not the beans.

Rice and pepper: Some sieves might work, if the holes were small enough to let the pepper through but not the rice.

Beans and water: A spoon might work, although the sieve would be best. Filter paper could be used, too, although it takes more work than the sieve and is probably slower letting water through.

Pepper and water: The sieve will not work because the holes are too large to stop the pepper. Filter paper must be used. After you have talked about this example, ask the children what they think might happen if they mix salt and water. Some may know that it dissolves in the water so that it is invisible, which would mean that a filter could not remove it from the water. The next activity is about dissolving.

5. Salt and water. Mix about a tablespoon of salt in water in front of the class, so they see it dissolve. They should notice that the salt is no longer visible. Ask them how they know the salt is still in the water. [It tastes salty.] Tell them this is a mixture of salt and water, but it has a special name: a solution. Whenever something dissolves in water, it is a solution.

Ask the children if they think it is possible to separate the salt from the water after it has been mixed together. Ask if they could use the spoon, the sieve, or the filter paper? If they need to examine the solution up closely, let them do this.

6. Pour some of the solution, not more than 1/2”, into the two clear plastic petri dishes. Mark the level of the water on the side of each dish with a china marker or pencil. Explain that you are going to leave them out over night and check them tomorrow. Ask the children to predict what might happen. Some will have had experience with water evaporating from puddles on the sidewalk or from an aquarium. Ask them what they think they might see in the morning.

Leave the dishes in a warm spot, by a heater or in a window where they will get strong sunlight, to speed up evaporation.

7. Check the dishes each day over the next several days. Let the children observe each day, noting how far the water has gone down from the original mark, and writing their observations on their Student Pages.

Continue to mark the side of the container each day. In a day or two all of the water will evaporate and there will be salt on the sides and bottom of the dishes. Help the children conclude that the water evaporated but the salt did not, making evaporation a good way to separate a substance that has been dissolved in water.

Ask the children to talk about what has happened to the water in the solution. Many will say that it has “dried up.” You can tell them that it actually goes into the air in extremely tiny pieces (molecules) that they cannot see because they are so small. There are water molecules in the air all around them, all the time.

Note: This is not an easy concept for 2nd graders, as research has shown many times. The idea of molecules is a middle school benchmark, so you do not need to spend much time trying to convince children about water molecules in the air.

8. Review the different methods used to separate mixtures and solutions.

Assessment

Use the completed Student Pages as a formal assessment. Use the class experimentation as an informal assessment.

Application Beyond School

Children can explore their environment for mixtures and solutions. (Both mixtures and solutions can be found in a salt-water fish tank. Sand and gravel are a mixture and the salt and water is a solution.)

Connections

Social Studies

Children can compare the concept of a physical mixture to the analogy of diversity in society as a social mixture.

The Oakland Schools Curriculum Page 1 of 4

scope.oakland.k12.mi.usJune 24, 2009