Lab 3: Separation of Mixtures

Print Friendly

In this lab we are going to investigate different ways to separate mixtures of substances by taking advantage of their physical properties. It will be inquiry-based, and you and your group will get to decide which techniques you want to use to separate a heterogeneous mixture of sand, poppy seeds, beans, salt and iron fillings.

Experimental Title: Lab 3 Separation of Mixtures

Date of laboratory:  June 17, 2014

Purpose: The purpose of this laboratory is to learn procedures and techniques used to separate mixtures of substances based on their physical properties.

Introduction:

A mixture is a combination of two or more substances in varying proportions. Scientists often need to separate mixtures into their components for analysis or to use in an experiment. It is possible to exploit differences in physical properties to separate substances from a mixture.

Special safety concerns for Lab 3:

  • If anything spills, please clean it up immediately with a paper towel and let your instructor know.
  • If glass breaks, do not pick it up with your bare hands. Notify your instructor immediately.
  • Be sure to wash your hands when you are finished with this lab

Materials:

    • A heterogeneous mixture of beans, sand, salt, poppy seeds, and iron fillings
    • Forceps
    • Magnet
    • Plastic bag with tie
    • Beakers
    • Water
    • Graduated cylinders
    • Filter paper
    • Transfer pipette
    • Soda bottle filter
    • Soda bottle distillation apparatus (soda bottle cut in half, with lid)
    • Ice
    • Newspapers
    • Aluminum foil
    • Containers to hold separated substances
    • Plastic spoons

Procedures:

For this laboratory you and your group will decide which of the following procedures you will use to separate the mixture you receive. Keep in mind that you may need to repeat some procedures at different stages of the process. Go ahead and write the procedures below in your notebook now and you can refer to them by number as you use them. For example, “We added 25 mL of water, and then used procedure 4 to filter the mixture.” Be sure to write down the actual steps you use on lab day as well.

Procedure 1. Sorting or Manual Separation

Substances may differ in this size, shape and color. If the differences are large enough, it may be reasonable to simply pick out one of the substances with a pair of forceps and place it in a separate container.

candy-pick-out

For example, it would be relatively easy to pick the white jellybeans out of this mixture.

Procedure 2. Use a magnet to remove certain metals

Some substances (certain metals) are attracted to magnets and others are not. You can use this difference in magnetic properties to separate some mixtures.

If the metal fragments are small, place the magnet in a plastic bag and tie it shut. 

magnet-sand-setup

The baggie covering will make the metal fragments easier to remove from the magnet.

magnet-sand-results

Drag the magnet over the mixture to attract magnetic metals. Brush the attracted metals off the plastic bag into a separate container.

Side note:  Have you ever tried this at the beach? Sand naturally contains iron fragments. In some places you might even be able to find small meteorites.

The following procedures require the addition of water to the mixture. Remember that if you add water, you might be dissolving some of the substances in the mixture. For example, salt or sugar dissolve into water making a solution.

Procedure 3. Decanting

It is possible to separate some substances based on differences in density. For example, oil floats on top of water. Add water, allow the substances to separate based on density, and then pour the upper layer with the less dense materials into a separate container.

If you have never done it, this video shows the standard way to decant in chemistry (direct link).

Procedure 4. Filtration

Filtration takes advantage of differences in particle size to separate mixtures. Generally filtration in chemistry involves special glassware, such as shown in figure 3.14 on page 65 in the textbook.

In this lab, we will use a large soda bottle cut in two, with the top inverted into the bottom.

soda-bottle-filter

Place the filter paper into the top of the soda bottle filter. Pour the liquid to be filtered through the filter. Larger particles will be trapped in the filter, and the liquid and smaller particles will pass through into the catchment container. Remove the filter and invert into a dish. Scrape off the solids with a spoon, if necessary.

Procedure 5. Evaporation

Both evaporation and its cousin, distillation, depend on differences in boiling points to separate materials. For example, with a solution of salt and water, the water has a lower boiling point. When heat is applied, the water boils away and the salt is left behind.

It is also possible to leave the solution in the sun for several days. The heat from the sun evaporates the water, again leaving the salt behind.

Evaporation involves applying energy to a solution in the form of heat, usually to remove water from a solution.

We will probably not be using evaporation today.

Procedure 6. Distillation

Distillation also takes advantage of differences in boiling point. In this case, the gas/vapor is captured again via condensation, rather than being allowed to escape into the air. A typical laboratory setup for distillation is shown in figure 3.13 on page 65 in the textbook.

n-distillation-apparatus

We will set up a distillation apparatus from a soda bottle that has been cut in half.

Place the homogeneous solution in the bottom of the soda bottle. Place an empty glass in the center. Then invert the top of the soda bottle (with the cap left on) into the bottom half. Press down so it fits tightly and doesn’t allow gases to escape. Fill the top of the soda bottle with ice. Cover with newspaper (insulation) and then aluminum foil. Set in the sun.

The water should evaporate from the bottom, condense on the top and then run into the cup.

__________________

Many other separation procedures are possible in chemistry. For example, in a future lab we will be using chromatography to separate pigments in ink.

Conclusions:

Once you have completed the separation, sit down and write a sentence or two to explain the results.

Discussion:

Record any thoughts you have about the experiments, including:

  • Possible improvements to the procedures or how to tweak techniques
  • How the results differed from your expectations
  • Suggestions for other experiments
  • What key concepts you learned about separating mixtures

We’ll go over the key concepts together at the end of lab.

If you would like to learn more, check this online chemistry lab from Phoenix College.

Please leave a comment or send an e-mail if you have any questions before our meeting.

Leave a Reply

Your email address will not be published. Required fields are marked *