Mixtures and Solutions - LESSON 2 Fourth-Fifth Grade
I N T E N D E D C U R R I C U L U M
BIG IDEA: (display in class during the lesson)
Elements and their combinations account for all the varied types of matter around us.
Idaho Standard(s) addressed:
4.S.2.1.2 Describe the physical properties of solids, liquids, and gases. (590.01.b)
5.S.2.1.1 Describe the differences among elements, compounds, and mixtures.
LESSON CONTENT GOALS
1) A solution is a mixture of two or more different substances where one material dissolves in another.
2) Salt can be separated from the water in a salt solution by evaporation. ii
3) Salt (NaCl) is an example of a pure compound.
GUIDINGQUESTIONS
1) What is a solution?
2) How can salt be separated from water in a salt solution?
3) What is a pure compound?
TESLA Mixtures and Solutions Lesson 2 – Separating a Salt Solution DRAFT 07/26/13 1

I M P L E M E N T E D C U R R I C U L U M
Teacher’s Notes:
Useful science concepts to know:
In this lesson, we will focus on mixtures that have components uniformly mixed together, called solutions . To make a solution, one material is dissolved , or incorporated, into another, like salt or sugar dissolved in water. In solutions, the compounds interact with one another. For example, sugar molecules form attractive forces with water molecules in a sugar solution and salt ions form attractive forces with water molecules in a salt solution.
Pure substances (LE2 and LE3)
Solutions (LE2)
Mixtures (LE1)
The salt that we separate from water in this lesson is an example of a pure substance . Water is another example of a pure substance.
To understand the idea of a pure substance, it is helpful to know a bit about atoms. A simple model of an atom is shown to the right. It contains a dense positively charged center surrounded by a much less dense “cloud” of negatively charged electrons. The figure to the right is misleading as far as size of atoms go. About 1 million atoms could be placed side by side and they would equal about the radius of the period at the end of this sentence.
So, even a small sample of a material has a lot of atoms in it. Also, the nucleus is much smaller compared to the electron cloud than suggested by the model. It is more like a golf ball in the middle of a stadium.
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There are about 115 types of atoms, differing by the number of protons in their nucleus. Each type of atom is referred to as an element , and it is possible to have a pure sample of one of these, such as carbon or copper. The Periodic Table lists the elements organized in ways that help chemists make predictions about how an atom of the element will react. For more information about the differences between elements, see http://phet.colorado.edu/en/simulation/build-an-atom .
Atoms combine to make compounds such as water, DNA, aspirin and the table salt used in this lesson, which is composed of sodium and chloride
(NaCl). Pure table salt is easily identifiable because it forms a crystal with an
“x” through it, as shown to the right. This is what students will look for to indicate that they have pure table salt. The definitions of atoms, elements and
A salt crystal
“x” compounds are the subject of Lesson 3.
Over the course of this Lesson and the next, you will tell your students about the existence of atoms, elements and pure compounds, but you do not need to go into further detail.
The big idea of this unit is that all of the variety of materials around us comes from just a few elements. Basically, this means that all matter, from my pillow to the river to people, is composed of elements like carbon, hydrogen, oxygen and nitrogen. The elements combine to form molecules that are specific to each thing, and most of the matter that we encounter on a daily basis is actually a mixture of many different types of molecules. The taste of a real strawberry, for example, is a mixture of over 200 different types molecules!
To prepare before the class
An example of a salt solution: Stir 1 spoonful of salt into 25 mL water to show students before they write their focus questions. If you are short on time, you can just put 25 mL of water in a cup and tell the students it is a salt solution. Also have one filter set up from the last experiment to show as a demonstration.
Materials for groups of 4 students
1 spoon kosher salt
Hand lenses
1 small cup
Syringe, 50 ml
Evaporating dish
Water
Craft stick
TESLA Mixtures and Solutions Lesson 2 – Separating a Salt Solution DRAFT 07/26/13 3

LESSON OVERVIEW
Brief planning:

Read engaging scenario.

Discuss the problem based on the engaging scenario.

Show students an example of a salt solution and that it is not separable by filtration.

Discuss how to solve the problem then write the prediction.

Plan how to separate a solution of salt and water.

Students will prepare and then pour a salt solution into evaporating dishes, label and set into FOSS trays to evaporate.

Observe solids and record data in charts.

Making Meaning Conference: guided discussion on writing claims based on evidence obtained and defining a pure compound.

Conclusion: write a response to the construction company.

Reflection: write an investigable question that will allow further investigation.
DAY ONE
ENGAGING SCENARIO
Clearwater Construction is very happy with your work in determining how to separate gravel and diatomaceous powder from water. They are anxious for you to help them again. It turns out that much of their water on their construction site is a solution of salt and water. They would like to know if it is possible to isolate the pure salt, which is a crystal with an “X” through it, because they would like to sell the pure salt. They would like a report in two weeks. What is the problem here?
Word Wall
Pure substance: a single type of matter.
Word Wall: A solution: a mixture of two or more different substances where one substance dissolves in another.
FOCUS QUESTION (discuss by groups, display, record in notebooks)
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Students are to think what problem(s) they need to solve for this next investigation. Solicit ideas for the focus questions from the class and display on the board.

Make a selection of the one that will best solve the problems in the scenario.

Students write CLASS FOCUS QUESTION in their notebooks, if it is different from theirs.

Check notebooks and provide feedback when necessary.
SUGGESTED CLASS FOCUS QUESTIONS
How can we separate pure salt from a solution of salt and water?
PREDICTION (discuss in groups, record in notebooks)

Teacher’s Notes:
Word Wall- Solvent: The major component(s) of a solution.
Word Wall- Solute: the minor component(s) of a solution.
Show students the example of a salt solution that you have made up already.
Teacher says
, “
When you mix water and salt a solution forms. What characteristics do you
observe in a salt solution? The salt dissolves in the water meaning you cannot see the salt
mixed in the water. How is this solution different from a mixture of gravel and water?”You cannot see the salt, but you can see the gravel. The salt dissolved in the water, the gravel did not.

Pour salt through a filter set up. Teacher says,
“
Solutions are composed of solutes and solvents. Is it possible to separate the solute (salt) from the solvent (water) by filtration?”
No
Students write predictions on how to separate pure salt from water using the sentence stem below.
Remind students that they have to include the word “because” in order to justify their prediction.
Example of a Prediction:
I think that pure salt can be separated from water by _________________ ______________ because__________________.
For example: I think that pure salt can be separated from water by evaporating the water because I
5

DAY TWO: PLANNING

Remind students of the FOCUS QUESTION.

Have a premade salt solution available to show students again as a reminder.

Lead a discussion on how to separate the salt from the water, asking for ideas. Once the idea of evaporation has come up, guide students in sketching the process.
Word Wall- Evaporation:
Change of state from liquid to gas.
Teacher says,
“We will draw a chart showing how we plan to separate the salt from the water. In our charts, we will include a description of the physical properties of the salt water solution and also leave a place to sketch the appearance of the salt after it is separated from the water.”
Word Wall
A crystal is a solid material with a specific and repeating pattern of atoms
Suggested CHART SHOWING THE PROCESS OF SEPARATING A SALT SOLUTION
Time: Before evaporation During evaporation After evaporation
Sketch:
Water evaporating
Leave blank until crystals form and students look at them
Physical appearance:
Solution of salt and water looks like plain water. It is clear.
Heat source
Salt crystals
Salt crystals begin to form Leave blank until crystals form and students look at them
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DAY THREE: EXPERIMENT
Teacher’s notes:
Instruct each group of students to:
 gather salt, water, a cups, a stirring stick and an evaporating dish from the materials table.
 mix 1 spoonful of salt with 25 ml of water.
 mix until the salt is no longer visible and the solution is clear. There may be a few grains of salt on the bottom of the cup, but most will dissolve although it may take a minute or two of stirring.

Label the evaporating dish with the group name.

Pour the solution into an evaporating dishes labeled with the group name. Leave any undissolved grains in the cup (if a few go in, it is not the end of the world).

Place the dish in a sunny windowsill out of the way of class activities. Crystals will not form well if the dishes are jostled or moved.

The length of time that it takes for crystals to form can be as short as a few hours, depending on the temperature, humidity and surface area of the solution. You should get crystals by the next day.
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DAY FOUR: MAKING MEANING CONFERENCE (Teacher directed)
Give students an opportunity to observe the evaporated salt solutions, and to record their observations in their charts. If only a few crystals have clear “x”s, let students look at those crystals (a magnifying lens can help). Reserve at least a few of biggest crystals with the best “x”s for the next lesson.
1) Share and display findings.
Remember, this is the conferencing stage. It is preferable that students contribute with their ideas..
Ask students to share the information they have written on their chart and drawings. Replicate the chart on the board or an overhead to analyze data. If students need to check the information they wrote on their charts, this is the right time to do it.
2) Looking for patterns from the data charts:
Guide students to analyze the data by asking the following questions (suggested answers in the chart below):

How can we tell that we made a solution?

How can we tell that the solute dissolved in the solvent?
 Why couldn’t we filter the solution to separate the solute from the solvent?

How can we tell that the water evaporated?

How can we tell whether the salt is a pure compound?
Guide students in writing CLAIMS from the evidence on the data chart. As they share information, assistance will be given to students in making associations with the claims and evidence.
.
Examples
CLAIMS EVIDENCE
I claim that ….. I claim this because…..
I know that….. I know this because…..
1. Salt and water make a solution
2. Salt dissolves in water
1. I was not able to see the particles of
salt in the water.
2. I was not able to see the particles of
salt in the water after mixing.
3. Salt and water can be separated by
evaporation
4. Salt is a pure compound
3. after we left the solution, the water
evaporated and the salt crystals appeared.
4.Our salt crystals had “x”s on them.
Teacher decides to list as many claims and evidence needed for students to understand process and concept. Once finished teacher states, “Based on our claims let’s REVISIT THE GUIDING
QUESTIONS and discuss the answers based on our evidence.” Teacher then goes over the guiding questions and makes sure students are able to respond to them.
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CLAIMS AND EVIDENCE (record in notebook)
Teacher says
“
You are now going to write 3 claims and evidence statements. I want you to look at the guiding questions and answer them with a claim based on the evidence. Revisit the class data chart in order to write your claims. Record them on your notebook.”
Teacher will go with students individually as they write their claims and evidence based on the guiding questions.
Exampl e s entence struct ures:
I cl aim t hat ____________________ I cl ai m this because __________________.
I know that __________________. I know this b ecause _________.
Share and dis cus s cl aims and evi dence with the cl ass
Check and provide feedback
DAY FIVE: CONCLUSION AND REFLECTION
CONCLUSION (record in notebooks)
Ask your students to write a 1-2 paragraph report or business letter to the Clearwater Construction
Company telling them how to solve the problem presented in the engaging scenario.
Check and provide feedback
REFLECTION ( record in notebooks )
Students will revisit the “Big Idea” and their results. They write a new investigable question
I wonder if……. What about if………What would happen if……….. that is related to the topic covered and “big idea”.
Check and provide feedback
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A C H I E V E D C U R R I C U L U M
PROFICENCY FEEDBACK:
This guide is:
 to be posted on the board/butcher paper so students know what is expected in their notebooks
 to be an evaluation tool for teachers as students work in their notebooks
 to be converted into questions as a student self assessment piece
SUGGESTED PROFICIENCY FEEDBACK GUIDE
MIXTURES AND SOLUTONS
LE 2
S T
Focus Question

Question written clearly

Related to the scenario
Prediction
Two

Predicts the process for separating the parts of a salt water solution
 uses “because”
Us
Data
1 chart
 complete and accurate
 labeled with titles
Claims & Evidence

3 complete sentences showing
understanding of guided questions
Conclusion

Grammatically correct

Describes results
Reflection
 writes one question for further investigation
TESLA Mixtures and Solutions Lesson 2 – Separating a Salt Solution DRAFT 07/26/13 10

TESLA Mixtures and Solutions Lesson 2 – Separating a Salt Solution DRAFT 07/26/13 11

CHART SHOWING THE PROCESS OF SEPARATING A SALT SOLUTION
Time:
Sketch:
Physical appearance:
Before evaporation During evaporation After evaporation
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