Mixtures and Solutions

Students have been reading about mixtures and solutions.

During lab today, students had to separate substances in a mixture.
We examined the mixture, and asked the students, what properties of the substances would help us separate them?  What tools or methods could we use to help us separate these?
We recorded our answers in our notebooks.  Based on this information, I want you to come up with a procedure for how you would separate this mixture into its original four substances.

Before beginning the investigation, remind students that when scientists investigate things, they have a focus question.  We are going to determine how to separate the substances of a mixture based on the properties of the individual substances.

Then, we have to determine the method we will use to separate the mixture.  First we list the properties of the substances.

One way to possibly separate mixtures of solids and liquids is to use a screen.
Another way to separate mixtures of solids and liquids is to use a filter
Which of these three mixtures do you predict we could successfully separate with a screen? Why? Which of these mixtures do you predict we could successfully separate with a filter? Why?
Now that we have written our predictions, we are going to design a procedure to test our predictions. A procedure is a set of steps or actions that you do.

The following items were in the mixture:

pencil shavings
iron filings
sand
aquarium gravel
salt
water

They had the following tools to use:

screen
coffee filter
magnet

    

Many groups first removed the large gravel by using the screen.  They used the magnet to remove the iron filings.  When they had the salt, pencil shavings, and sand, they asked to use water.
They could then use floatation to remove the pencil shavings.  and filter to remove the sand from the salt water.  Finally, they used evaporation to separate the water and salt.

Discussion with class:

What tool worked to separate the gravel?  Why do you think the screen did not work for separating the salt and water?  What property of gravel is different from salt?  What tool worked for separating the salt and sand?  What tool worked to separate the sand and water?  Did the filter work to separate the salt and water?  Why do you thing the filter did not work?

Salt water is a solution.  The ability of salt to dissolve in water is a property of salt.  

What happened when the salt water evaporated?

Student record in journal.  

Scientists look at their data and make claims. 

Based on the evidence from this investigation, what can I claim about the size of particles and how they can be separated? I claim that a mixture of a solid material with large particles and smaller particles can be separated with a screen.

Claims must have evidence to support them. What evidence could I use to support this claim? What did we see from our investigation? 

Learning Target -
Develop, communicate, and justify a procedure to separate simple mixtures based on the physical properties of the substances.