Properties of Metals
Grade level(s):Grade 5, Grade 6, Grade 7, Grade 8, Grade 9, Grade 10, Grade 11, Grade 12
Topic:Magnetism and Flame tests
Different elements have different physical properties.
element, physical properties, metal, nonmetal, metalloid, magnetic
What you need:
General: Poster of the Periodic Table - (SEP has several different kinds, including a table with a picture of each of the elements (C239), and a class set of these (C471, C472) particularly effective at illustrating the great number of metal elements), Student Worksheets (see attached, as well as the websites for additional possibilities)
Station 1: Iron in cereal: magnets (SEP, K109) iron filings (SEP, EC018), a variety of other magnetic and non-magnetic metals scraps, 4 petri dishes, clear plastic cups (1 per student), Popsicle sticks or plastic straws for stirring (1 per student), 2 kinds of breakfast cereal (Total and another that is not iron-fortified - i.e. Corn Pops), blender, water.
Station 2: Flame tests: safety goggles (SEP, E452 or E457), propane or butane torch, test tube rack, glass test tubes, wire loops, 1.5-ml eppendorf tubes, 5M solution of hydrochloric acid, 0.5 M solutions of: barium chloride, lithium chloride, potassium chloride, sodium chloride salts.
After the brief introduction to the day's lesson, the class will be divided into 2 groups. Half the class will go to Station 1 first, the other half to Station 2. When time is called, they will switch stations.
1 hr 15 min total:
5-10 min introduction
~30 min at Station 1
~30 min at Station 2
5-10 min wrap-up
Students will be able to see the iron filings in breakfast cereal fortified with iron and qualitatively compare the iron content between 2 different cereals. They will also see that as part of a salt solution, some elements give off characteristic colors when placed in a flame.
Students should have been introduced to the periodic table and be familiar with some of its elements. They should know that most of the elements in the table are metals.
At the end of the lesson, students should:
1) Be able to list several physical properties that differ between elements,
2) Know that some metals are magnetic while others are not,
3) Know that some metals produce characteristic colors in a flame test.
Iron in cereal background
Iron, cobalt and nickel (found next to each other on the periodic table) are the three magnetic elements. Generally, iron is found in our food as an iron compound which does not show visible attraction to a magnet. However, some of our breakfast cereal (Total) is fortified with "raw" elemental iron. When Total is blended with water, a magnet can pull out the added iron filings.
Flame test background:
When some elements are heated in a salt solution, the electrons are excited. Then as these electrons fall back from one energy level to another, they will emit photons of light. The light will have different colors depending on the element and its discrete energy levels. That is, different wavelengths of light (colors) will be emitted when the electrons of different elements go down the step(s) between their energy level(s). Each element will have its own set of steps, therefore each will have its own color or set of colors.
General: Make enough copies of the worksheet for the entire class.
Station 1: Iron in cereal: Prepare some iron filings in 2 Petri dishes and some zinc metal in 2 other Petri dishes. Also prepare 2 cereal stocks: blend cereal with water to create a mixture that is watery enough to pour (you will not need the entire box of cereal). Divide evenly into plastic cups so that each student will have one of the 2 cereal mixtures.
Station 2: Flame tests: Label eppendorf tubes as "unknown 1, unknown 2, etc." until you have enough samples for half the class. Measure out apx. 1ml of salt solutions into these labeled tubes, noting which solution is in which tube. Make sure you have enough of the stock solutions to do the initial demo!
Safety considerations: At station 2 the volunteer or teacher must hold the propane/butane torch at all times so that the kids do not get their hands on it. Students should wear safety goggles at all times. From the very start tell the kids that hydrochloric acid is very dangerous so that they must never touch it - only the adult can handle the hydrochloric acid.
Lesson Implementation / Outline
Ask the class what they know about the Periodic Table - depending on their age and background knowledge ask further questions (i.e. What is an element? What are elements composed of? How is the Periodic Table organized?)
Discuss physical properties of the elements. (i.e. color, shininess, state of matter, etc.) Remind them that Metals make up the majority of the elements, whereas nonmetals and metalloids make up a much smaller percentage of the elements in the far right section of the table. Discuss some some of the properties of metals (i.e. luster, conductivity of electricity, magnetism etc.). Explain that in today's lesson, the class will focus on two properties of metals:
- Magnetism, and they will use this property to pull out the iron in breakfast cereal.
- Metal solutions will glow different colors when heated in a flame! We will explore this property today using flame tests.
Station 1: Iron in breakfast cereal
1) Give each student a worksheet and a magnet.
2) Ask the students to determine whether or not iron, zinc (and any other metal scraps you obtained) are magnetic and to record the answers on their worksheets. (Only iron. nickel and cobalt are magnetic, zinc and all other metals are not.)
3) Now that they know that iron is magnetic, they can use this property to fish out the iron in cereal. Introduce the two cereal types, (i.e. Total and Corn Pops). Have the kids predict which will contain more iron and record their prediction.
4) Pair up the kids and give each student in the pair a different blended cereal mixture. Have each student record which kind of cereal they have on their worksheet.
5) Demonstrate how to find the iron: stir the mixture while holding your magnet up to the side of the cup (ask a student volunteer to help hold the cup on the table while you stir). You will see some black iron particles collect near the magnet. When you move the magnet, they dissipate.
6) Pass out stirrers to the kids and tell them to find the iron in their cereal. They should work with their partner, where one person holds the cup while the other one stirs. (Alternately, you can use a ziplog bag to mix the cereal in water and then wait 15min. as shown in the instructive video attached).
7) Have the pairs compare whose cereal yielded more iron, then see if all the groups agree. (Total should have more iron than another cereal that is not iron-fortified). Record the group consensus on the worksheet.
8) If time permits, you might discuss why iron filings can be pulled out of total and some of the merits and drawbacks of iron-fortified cereal:
Generally, the iron in our food is found in a compound and cannot be detected by a magnet. However, Total is fortified with actual elemental "raw" iron (or iron filings). The flakes are so small that they can be dissolved and digested by your stomach acids.
Iron is an essential element required by our red blood cells to carry oxygen from the lungs to the muscles and other organs, thereby giving you energy. Iron-deficiency can cause fatigue, irritability and headaches. However, too much iron may cause kidney damage. Since total has 100% of the daily recommended iron, if you eat it daily, you shouldn't take iron supplements or seek out lots of other iron-rich foods.
(for more, see: http://home.nycap.rr.com/useless/total_cereal/index.html)
9) When the students move to their second station, remind them to take their worksheets with them.
Station 2: Flame tests
1) Make sure each student has their worksheet from the last station.
2) Tell the kids that there will be some dangerous chemicals and flames at this station so they must not touch anything unless an adult gives them permission (otherwise they won't be able to do the really cool experiment). Also, at all times, only the adult will be working the propane torch.
3) Show the students the 4 solutions of barium, lithium, potassium, and sodium, each of which gives off a characteristic color in a flame. Take a wire loop and dip it into the barium solution.
4) Turn on the propane torch and put the loop into the blue part of the flame - the flame will turn green.
5) Have the students record the flame color in the chart on the worksheet.
6) Clean the wire loop: dip it into the hydrochloric acid, then place it in the flame as before. Do this 1-2 times.
7) Repeat steps 3-6 for the other 3 salt solutions. (Lithium turns red, potassium turns lilac/purple, sodium turns orange). Note: it is hard to cleanse the wire loop of sodium, so you should either have a separate wire loop for sodium only, or simply have 4 total - one for each solution. Otherwise the sodium contamination may confuse the students.
8) Once you have finished with the known samples, give each student an eppendorf tube containing one unknown solution.
9) Repeat the above procedure, allowing each student to carefully dip the wire loop into their salt solution and place it in the flame. The adult should still handle the hydrochloric acid.
10) Have each student record which unknown tube they received and identify their element based on the flame test.
The students should complete the worksheet as they go. At Station 1, ask the students to name some other metals that may or may not be magnetic. You can also discuss why Total has more iron than the other cereal (Total chose to fortify their cereal with the element iron.). At Station 2, ask the students how the flame test may be useful in science - you can use it to identify elements when you have an unknown sample. Some kids may wonder what happens if you mix 2 solutions together - have them make a prediction, then test it out! (You will see both characteristic colors appear.)
Gather the class together at the end and ask them what they learned today. Also go over the summary questions on the worksheet, which should be a review of the introduction.
Extensions and Reflections
At Station 1, keep the lids on the Petri dishes during the lesson to avoid creating a mess with iron filings. It may be a good idea to tape the edges with Scotch tape. Also, be prepared - the kids may ask to eat the leftover cereal, in particular the Corn Pops! At Station 2, the kids will behave themselves if you emphasize from the very start that hydrochloric acid is dangerous and can burn the skin.
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