Expt 007 -- Iron in Cereal--Separation

Many breakfast cereals boast that they contain iron, an essential part of our daily diet. A slurry of cereal is stirred with a strong magnet held to the outside of a transparent container. A spot of iron particles appears and is moved with the magnet.

Chemical Concepts

1. Physical properties are maintained by the individual components in a mixture.
2. This conservation of properties may often be taken advantage of to separate out components in a mixture.
3. A homogeneous mixture is one in which the components are evenly distributed. A heterogeneous mixture has uneven distribution of its components. Breakfast cereals serve as good examples of heterogeneous mixtures.
4. Iron in elemental form is strongly attracted to magnets. Compounds of iron are not as strongly attracted to magnets.

Safety

• Use ordinary laboratory safety procedures.
• Use goggles for the acid variation.

Procedure

Do this step in advance to soften the cereal.

1. Place approximately one cup water and one cup of cereal in the blender, let sit for a few minutes until the cereal is soft, then blend to make a smooth, shake-like slurry.

!!!Click here to See Movie. Click |> or <| to step the slides forward or back.

Variation A--Strong magnet and blender available.

Hold the magnet to the outside of the blender while it is whirling. Stop the blender.

!!!Click here to See Movie.

Variation B -- Weaker magnets

Pour the cereal slurry into the clear plastic cup. Hold one pole of the bar magnet against the outside of the cup about mid-way up, and use the plastic spoon to gently stir the slurry for 20-30 seconds.

!!!Click here to See Movie. Click |> or <| to step the slides forward or back.

To close with either variation:

Pull the spot about with the magnet. Move the magnet a cm to one side.

!!!Click here to See Movie.

To accentuate the spot and to keep it from dispersing too quickly, press the back of the plastic spoon up against the spot from behind and then lift the magnet aside. If one wishes to remove the iron, re-position the magnet and then slowly lift it up (while stirring) to bring the spot up to the surface of the slurry. Then scoop the iron spot out with the tip of the spoon.

To "reset" the slurry for the next class, simply stir the iron back into the cereal -- with no magnet applied. The same slurry may be used all day.

Additional test

Add 10 mL of 1.0 M HCl to 100 mL of the cereal slurry to simulate stomach acid. Place the cup in a beaker of hot water to warm it. Stir, then come back to check later. Use the magnet and spoon in the same way that you collected iron from the cereal earlier. This solution can then be tested for the presence of iron ions with the addition of a few mLs of 1.0 M NaSCN solution.

Questions

1. Is the iron in cereal already part of a compound like iron chloride, or is this iron the same kind of elemental iron that is used to make hammers and nails?
2. If it is elemental iron in the cereal, why do we not see it or at least feel it when we bite into the cereal?
3. Can our cereal rust if it's left out long enough?
4. Will the iron travel through the intestinal tract as coins and nails do? Explain.

Handout Makeup

Name ___________________________ Class _______

Teacher __________________________

BeckerDemos 007 Iron in Cereal--Separation

Watch the movies.

1. Describe the iron in the cereal.
2. Answer the questions.

Curriculum-

This activity works well early in the semester when discussing chemical and physical separations or heterogeneous mixtures. This activity also ties in well with units on magnetism and foods and dietary requirements.

Activity-

Demonstration - Student or Teacher

• This activity works well as a demonstration, although it could be modified into a hands-on lab activity.
• As a lab activity, grind the cereal in the blender and dispense portions in plastic cups.

Safety-

Use ordinary laboratory safety procedures.

Time-

Teacher Preparation: 10 minutes

Class Time: 5 minutes

Materials-

• some high-iron cereal (such as Total^®)
• water
• a blender
• a clear plastic cup
• a strong bar magnet (such as a cow magnet)
• a white plastic spoon

Optional:

• 10 mL of 1 M HCl (1 liter -- Add 83 mL of 12 M HCl, hydrochloric acid solution to approximately 550 mL of water. After the solution equilibrates, dilute to 1000 mL with water.)

Disposal-

Dispose of the slurry at the sink with running water.

Lab Hints-

If your lab is not equipped with a blender, you may wish to slurry the cereal at home with a blender, mixer, or food processor. Bring the slurry to the lab in a jar and use variation B.

Observations-

• On the inside surface of the cup, just behind where the magnet was positioned, one should be able to observe a dark concentrated spot easily visible even from several meters away.
• As it turns out, at least some of the iron with which our breakfast cereals are fortified is in the form of "raw," elemental iron. [Although iron in its elemental form (not combined and not charged) is strongly attracted by a magnetic field, iron in compounds does not show this same degree off attraction.] It is the small pieces of elemental iron then, that are attracted to the magnet along side the cup and which gather there to form a dark spot. The longer the slurry is stirred, the darker the spot. With the magnetic field removed, the spot gradually falls and disperses back into the slurry.
• After the addition of HCl, the spot no longer forms, because the acid oxidizes the elemental iron to iron(III) ions, which are not as attracted to a magnetic field as the iron atoms were. The addition of NaSCN solution should turn the slurry red, confirming the presence of these iron ions.

Answers-

Q1. Is the iron in cereal already part of a compound like iron chloride, or is this iron the same kind of elemental iron that is used to make hammers and nails?

A1. At least some of the iron with which our breakfast cereals are fortified is in the form of "raw," elemental iron. Although iron in its elemental form (not combined and not charged) is strongly attracted by a magnetic field, iron in compounds does not show this same degree off attraction.

Q2. If it is elemental iron in the cereal, why do we not see it or at least feel it when we bite into the cereal?

A2. The pieces are very small.

Q3. Can our cereal rust if it's left out long enough?

A3. Yes, the cereal can rust, but both iron and rust dissolve in stomach acid, forming the same iron compounds.

Q4. Will the iron travel through the intestinal tract as coins and nails do? Explain.

A4. No. Since the iron dissolves in the "stomach" acid, it does not simply travel through unchanged. Small particles dissolve faster than a large nail. However, we have not done any tests to see if it is actually transported through the membranes.

Reference-

Acknowledgement: This is a variation on a demonstration shown to me by Richard Piotrzkowski, Stamford, CT. In the original activity, the slurry is placed in a large beaker and a magnetic stirrer is used to collect the iron. The iron gets spread out rather thinly on the stir bar, however, and it is not quite as easy to see.

Key Words 1-

separation, heterogeneous mixture, mixture, magnet