Lesson Plan – Fall 2004
Unit: “In the Household”
Lesson: “What’s in food?”
Planners: David Altman, Alex Tung
Objectives: To look at the different components of different foods, and to understand several ways of identifying or separating different mixtures.
Grade Level: 2-5th
Introduction: How do we separate things that are mixed together?
Today we will talk about different foods and what makes up those different foods. What are some foods you like to eat? What do you think is inside those foods?
Sometimes foods are made up of things that are easy to separate. If we have a bag of trail mix (or different colored M&Ms, etc), how would we separate out one thing from the rest? (by looking and picking them out). If it’s easy to tell by looking, we can just separate them by hand. But sometimes it’s not easy to tell by looking, we have to use other methods.
Today, we’ll look at three different foods and what’s in each of them. We’ll look at the candy coating of M&Ms and see if we can figure out what makes the brown color. We’ll also see if a certain type of compound, starch, is in certain foods. Finally, we’ll look at minerals (especially iron) in
Activity 1: Finding Starch
Brief Description – Students will identify which foods have starch in them by testing them with iodine.
Materials:
- Different starchy and starchless foods – potatoes, apples, carrots, cereal
- Iodine
- Eye droppers, or metal/plastic sticks
- Knife for cutting foods
- Bowl for holding foods
- Cornstarch
- water
Introduction to Activity 1
Many foods have starch in them – starch is one of the basic energy sources for most people. What foods have starch in them? We can try and find out by using iodine. Iodine mixes with starch in foods and turns them a purplish color. If the food does not contain starch, the iodine will remain its reddish color.
First we’ll see what it should look like – put some water in a cup and mix in iodine. Put some cornstarch in a cup with water and add iodine. Compare the two colors.
Procedure:
- Cut up different foods into pieces (we have potatoes, apples, carrots, and cereal)
- Put the foods into a bowl
- Using the eye dropper or sticks, try applying iodine to each food and see what color shows up
- Note down your observations and compare to the cups of water and iodine
Activity 2: Finding Iron
Brief Description – Students will separate out iron from cereal using a magnet.
Materials:
- Cereal (Total or generic equivalent seem to work well)
- Magnets on end of sticks/pencils
- Bowls
- Water
- Plastic bags
- Iron filings
- Tape
- Plastic spoons
- Paper plates
- Towels
Activity 2 Introduction
Lots of foods have vitamins and minerals in them. One of the minerals that is important to us is iron. Iron helps the blood and muscles supply oxygen to the body. This helps us to grow and have enough energy for our daily activities.
Today we’ll look at one way of separating iron from the food we eat. Ask the students if they know about magnets. What sticks to magnets? Metals do, but only certain ones, usually the ones with iron in them. (Show example of steel nail sticking to a magnet vs. a brass nail), we can try to use that fact to find out if there is iron in a certain kind of cereal.
Procedure:
1) Have each student or pair of students place about two small Dixie cups worth of cereal in a resealable plastic bag.
o Point out the cereal to the students and have them make observations about it
o Ask, “Can you tell what’s in this cereal? What does iron look like? Does it look like there’s iron in here?”
2) Have the students mash up the cereal with their hands, and then use the back of a plastic spoon to make the cereal pieces even smaller.
3) Take some of the cereal bits and spread onto a paper plate in a thin layer
4) Have the students move the magnet around under the paper plate and you should see the little bits of cereal bouncing about.
o Why do you think they do this?
o What do you think is in the cereal?
5) Now put the two cups of cereal in a bowl and add enough water so that you can stir it easily (so that it doesn’t clump up)
6) Stir the cereal and water with the magnet on a stick for a couple minutes.
7) After a little while, take the magnet out (if too much cereal sticks to it, try adding more water)
8) Look at the magnet and you should see small dark pieces stuck to it. (if you don’t see anything, keep stirring!)
9) Wipe the magnet off on a piece of white towel. Do you see the iron?
Activity 3: Finding Colors in Candy
Brief Description: Students will separate the colors of brown Reese’s pieces and brown M&M’s using thin-layer liquid chromatography.
Materials
- small Dixie cups
- large red plastic cups
- coffee filters
- plastic spoons
- Reese’s Pieces ad M&M’s
- Yellow and blue food coloring
Introduction – What’s in the candy shell of a brown Reese’s Pieces vs. a brown M&M?
Explain to the students that food and candy can be given a certain color by mixing colors. For example, combine the yellow and blue food coloring to get green. Explain, that what we will do today will be the opposite – we will try to separate colors from their final form to their individual components.
1) Give them each a brown M&M and a brown Reese’s Pieces – make sure they don’t eat them.
- Ask them what they think that the brown comes from different colors…what colors?
- Ask them if they think that the M&M and Reese’s were made from the same original colors.
- The Reese’s is a little lighter, but they look pretty similar.
2) Give them a cup with 4 M&M’s and 4 Reese’s in the bottom. Tell them to put 1 spoonful of water in the cup (have a big plastic cup filled with water that they can dip into). Mix the candies until the color comes off.
3) They should try to stop when they reach the white candy shell. This is every easy for the M&M’s – the color comes off before you start going through the candy shell. This is harder for the Reese’s – the candy shell will probably start showing through to the peanut-stuff by the time sufficient color is removed.
4) Add four more candies to each cup (be sure to keep track of which cup is which – or have them do one at time – the latter will probably work better). Have them mix in these color shells also.
5) ASK them – do you still think the 2 browns come from similar colors?
6) At this point, the 2 viscous liquids look strikingly different. The Reese’s looks paler and slightly purple (which makes sense – since we will see its brown-liquid results in a striking blue band when separated on paper).
7) Have them place a coffee-filter upside-down over the top of a red plastic cup. Try to pull the filter taut, so the flat part of the filter forms a flat surface over the mouth of the cup:
8) Explain to them that you are going to separate the colors that make up the brown-liquids by putting them on the filter paper. Once put on the paper, the water in your liquid will creep across it:
- You can explain that the water will move on the filter like when water moves across a paper towel when you wipe up a spill. Capillary action is a difficult concept – do we want to address it here?
9) Explain: the dyes that make up the candies’ colors stick to both the water and the paper. Different dyes stick with different strengths to the paper and water. So – when the water creeps along the coffee-filter, it will drag the different dyes at different speeds – causing them to separate as the water moves along the paper.
10) Slowly place ~1/3-1/2 of a spoonful of the brown liquid in the center of the filter paper.
11) It will take ~10-15 minutes for the liquid to spread sufficiently. But, before then – you will start seeing a broad red band radiating out from the center of both liquids. A blue band will form at the front of the Reese’s brown-goo. And eventually, you will start seeing yellow and green at the front of the M&M dye-band.
Discussion and Conclusion
What did you observe? Which foods had starch in them? (write on board) Which didn’t? What colors came out of the M&M’s? What about the Reese’s Pieces?