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Catchy Title: The Chemistry of Lead
Theme/Topic of Lesson: chemistry, lead, lead poisoning
Time Commitment: 2 class periods (45-60 minutes each)
Subject Area(s):
Health - Disease
Science - Chemistry
Grade Level(s): 11,12
Standards Alignment:
Class Challenge Question: What are the characteristics of the element lead, what are some reactions with other substances, and how is it harmful to the human body?
Overview:
In this introductory chemistry lesson, students will develop a basic understanding of the physical and chemical properties of the element lead, as well as its historical and modern day uses, and how and why it is toxic to the human body. Through lecture and discussion, students will learn about basic reactions of the element and how it interacts with absorption of other important metals into human body systems.
This lesson was designed to be completed during National Childhood Lead Poisoning Prevention Week in October of each year, to raise awareness about lead poisoning, but can be done at anytime throughout the school year. The later in the school year the lesson is done, the more in-depth a chemistry teacher can go with some of the more complex chemistry concepts.
In 2006, National Childhood Lead Poisoning Prevention Week is October 22-28.
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Learning Objectives:
The Students will:
- Students will learn:
- basic physical and chemical properties of the element lead
- how lead is toxic to the human body
- the health effects of lead poisoning
- the most common sources of lead and how lead enters the body
- how lead poisoning is treated and prevented
Assessment
Grade the student worksheet for completion and accuracy.
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Resources
Materials
Per class-
Optional: cosmetics, can of paint, toy jewelry, old pipe, hair dye, children's toys, etc.
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- clear container that holds approx. 2 1/2 gallons ( 10 liters) of water
- clear container that holds approx. one quart
- red food coloring
- chemistry-lead-godwin-presentation
Optional National Institute of Health presentation to use on Day2;
chemist Godwin investigates how lead disrupts protein function
(View) - chemistry-lead-standards (View)
- chemistry-lead-teacheranswerkey.doc (View)
- chemistry-lead-day2.ppt
PowerPoint presentation to use as a discussion guide on Day 2; be
sure to access the "Notes" section directly in the presentation to help
guide the discussion. (View)
Per Student- chemistry-lead-studentworksheet.doc
(View) - leadawareness-SHmoreinfo.doc (View)
Vocabulary
- Pb - chemical symbol for the element of lead; derived from the latin word Plumbum; plumber=leadsmith
- chemical reaction - process in which one or more substances are converted into a new substance with different physical and chemical properties
- single replacement reaction - one element displaces another (optional)
- double replacement reaction - exchange of elements to form new compounds (optional)
- ore - A mineral or an aggregate of minerals from which a valuable constituent, especially a metal, can be profitably mined or extracted
- galena - an ore that contanis lead; sulfide ore (PbS)
- lead - Lead is a heavy, bluish-gray metal that has a low melting point. It occurs naturally in the Earth's crust, but it is not a particularly abundant element. It is rarely found naturally as a metal, but rather in its divalent (2+) oxidative state in ore deposits widely distributed throughout the world.
- lead-based paint - paint or other surface coatings that contain more than 0.50% (1/2 percent) lead by weight or more than 0.7 milligram per square centimeter as measured by the x-ray flourescence method
- person at risk (of lead poisoning) - child under the age of six years or a pregnant woman; both are particularly vulnerable to lead-based paint hazards.
- blood lead level - a measure of lead in the blood; > 10 mcg/dl is considered a level of concern by the CDC
Procedures
This lesson format is written as a lecture and discussion, however, you could modify it by printing copies of the web resources referenced, even if computers are available for students, and having students work in small groups to complete the worksheet on Day 1.
There are optional modifications and additions to the activities throughout the lesson, as noted in the Teacher Background section below, and provided directly in the activities.
On Day 1 The first activity provides an introduction to the element lead, including history, uses and chemical and physical properties. The second optional activity goes into more detail about the types of reactions. On Day 2, the activities focus on the health effects of lead, and lead poisoning. There is also an optional activity that goes into some bio-chemistry about how lead disrupts protein functions.
Since some of the activities are optional based on student knowledge level, there is no formal assessment for this lesson. You may choose to give a quiz based on topics covered.
Teacher Background and Student Prerequisites:
Familiarize yourself with the content covered in the lesson, in order to best decide how in-depth to go with each topic. Specifically, access and review all the web resources provided. How much you will cover will depend upon your students' existing knowledge level, as well as where you are in the school year relative to how much has already been covered about general chemistry.
Since this lesson is written for chemistry teachers, there is assumed knowledge of how to balance chemical equations, and how elements react and/or bond with one another.
The optional sections of the lesson (as noted in specific activities) assume students have a solid understanding of basic chemistry, such as chemical reactions and how elements bond together. Therefore, if you haven't covered these concepts you do not need to teach these optional sessions in order for the lesson to be of value in a chemistry class.
If your school has access to United Streaming, you may want to first show some introductory and interesting video segments about chemistry, compounds and reactions.
A few recommendations:
1. The Elements
2. Introduction to the Elements (full video)
• Modern Elemental Theory (segment)
There is another video entitled Chemistry Connections: Primary Cells Secondary Cells and Fuel Cells. The video illustrations show the rechargeable aspect of secondary cells, and this is explained using a lead storage battery.
Day 1: Introduction to Lead
Daily Challenge Question: What are the basic physical and chemical properties of the element lead and how does it react with other elements and compounds?
one class period
Set-up Directions:
- Make enough copies of chemistry-lead-studentworksheet.doc for each student.
- You will need a computer with Internet access and LCD projector.
- You may also use a computer lab or computers available in the classroom for Activity #1, and have students complete the worksheet on their own, using the Internet resources provided. After the students complete the worksheet, you would then discuss as a class their findings.
- If you've brought in some products that contain lead, display them in the front of the room
Teacher Presentation & Motivation:
Begin by asking students what they know about lead. Responses may include:
- discovery
- historical and modern day uses
- why it's dangerous
- properties, element # or symbol
Take notes on the board about their collective responses.
Show some of the products you have brought in (if you have done so) and ask students which ones they think might contain lead.
Tell students that in this lesson they will learn about the basic properties of lead, some of it's reactions with other elements and compounds, and why it's a dangerous element.
Modification
If you have access to United Streaming, a great introductory video segment can be used entitled, Modern Elemental Theory.
The video explains that the modern understanding of elements began hundreds of years ago when alchemists tried to discover a method to turn lead into gold; they thought there were only a few major substances that could be altered and turned into one another; the work of alchemists lead to what is now known as modern chemistry.
Activity 1 - Lead: History, Uses, Characteristics
This activity can be done either as a class (teacher displays websites at front of the room and guides discussion) or students complete the worksheet in pairs as they navigate through the websites.
Guide a class discussion as students complete the worksheet. Answers can be found on the chemistry-lead-teacheranswerkey.doc.
(1) Bring up the following site: http://www.chemsoc.org/viselements/pages/pertable_fla.htm. This is the visual elements periodic table. Ask students if they know which visual element is the symbol for lead.
(2) Click on the lead symbol -- this will bring up the following page: http://www.chemsoc.org/viselements/pages/lead.html- When was lead discovered?
- What is the origin of lead's symbol Pb?
- Optional: What is the significance of alchemical symbols, relative to lead?
- What were some historical uses of lead?
(3) Bring up the table of periodic elements http://www.webelements.com
(or refer to the classroom poster). Ask students what they know or can tell you about lead from the table:
- atomic number
- atomic weight
- lead is a metal (how do you know)
(4) Guide a discussion, using the board to illustrate the chemical equations. Reference the teacher answer key for details.
- Where do we get some of our metals?
- What is an ore?
- Has anyone heard of galena (what is it?)
- How is lead extracted from Galena?
- Chemical equations
(5) Bring up the following site: http://www.atsdr.cdc.gov/cabs/lead/leadcabs_use.html
- What are the forms of lead?
- Refer to list brainstormed at beginning of lesson (uses of lead). How has lead been used in the past? What are some of it's uses today?
- Note on the site that many uses were reduced or banned...Ask, why might this be? Explain to students that on Day 2 of the lesson they will further explore the toxic effects of lead.
Optional Enrichment
You could spend some time going into the organic use of lead -- tetraethyl and tetramethyl -- primarily used for "anti-knocking" and improving octane rating (see http:///www.chm.bris.ac.uk/motm/leadtet/leadh.htm)
Activity 2 - Lead's Use Today / Reactions (Optional)
This activity is optional and should only be completed if students have a basic understanding of chemical reactions.
Guide a discussion using the outline below.
The major use of lead today is in Lead Storage Batteries to start our cars. A 12-volt battery is made of 6 rechargeable voltaic cells connected together. Each cell has 2 electrodes. The anode is made of Lead (Pb) and the other, the cathode is made of Lead dioxide or lead (IV) Oxide. The electrodes are immersed in Sulfuric Acid. The chemical reactions that occur in the battery when it supplies power to the car (to start the engine or power the lights) involve the transfer of electrons between the chemical species. These reactions are called oxidation-reduction reactions (or redox reactions). Oxidation reaction is the loss of electrons and Reduction is the gain of electrons. (A mnemonic device to remember this is OIL RIG: oxidation is loss of electrons and reduction is gain of electrons. Both reactions occur at the same time. One cannot occur without the other.
These two half reactions occur when the battery is discharging (supplying power to car):
- Pb(s) + SO42- (aq) --> PbSO4(s) + 2e- (oxidation)
- PbO2(s) + 4H+(aq) + SO42- (aq) + 2e- --> PbSO4(s) + 2H2O(l) (reduction)
The sum of these two half reactions gives us the overall spontaneous reaction:
- Pb(s) + PbO2(s) + 2H2SO4(aq) --> 2 PbSO4(s) + 2H2O(l)
What is happening inside the battery?
The PbSO4 (lead sulfate) slowly builds up on the electrodes and the concentration of the sulfuric acid decreases. The battery is recharged when the car is running. The reverse reaction occurs and the lead and lead dioxide form again on the electrodes. The reaction is nonspontaneous and requires the input of energy (direct current from the car).
It sounds like lead storage batteries should last forever. Do they? No!
Why not? Small amounts of lead sulfate fall off the electrodes. Eventually there is not enough lead sulfate for the recharging reaction to occur.
Hands-On Enrichment:
Check your chemistry textbook for an example of a hands-on activity that has students create a battery.
Wrap Up:
Considering the three main forms of lead (metallic lead, lead and lead compounds, and organic lead), have students think about why and how these forms are toxic to the human body. How might humans be exposed to these various forms? What might be the pathways to exposure?
Tell students to come prepared to discuss their ideas on Day 2 of the lesson.
Day 2: The Effect of Lead on the Human Body
Daily Challenge Question: How is lead toxic to the human body?
45-60 minute class period
Set-up Directions:
You will need the following materials:
- Computer with Internet access (optional) connected to an LCD projector
- Day 2 Lead Poisoning Awareness PowerPoint presentation loaded onto the computer (chemistry-lead-day2.ppt); be sure to access the teacher notes directly in the presentation to help guide the discussion
- Getting the Lead Out PowerPoint presentation (chemistry-lead-godwin-presentation.ppt) (Optional)
- Any posters or brochures you have ordered, set up around the room (see list of recommended resources in the Resource section)
- Clear containers: one should hold about 2 1/2 gallons (10 liters) of water; the other should hold about a quart.
- Red food coloring
- Enough copies of the Lead Awareness Student Handout (leadawareness-SHmoreinfo.doc)
Teacher Presentation & Motivation:
Review concepts covered on Day 1. Ask students why they think lead might be harmful to the human body, and how it gets into the body systems.
Tell students that lead poisoning is very dangerous and unfortunately common in certain groups of people. Segue into presentation.
Activity 1 - Lead Poisoning: What Everyone Needs to Know
Using the notes provided directly in the PowerPoint presentation (chemistry-lead-day2.ppt) guide students through the presentation and facilitate a conversation. Make the lesson as interactive as possible, discussing with students the topics and issues to ensure understanding. Ask probing questions throughout the presentation, and direct students to complete the worksheet as the class collectively discusses the answers.
When showing slide #6 (how lead affects children and adults differently), and to illustrate what >10mcg/dl means, do the following with the clear containers:
- Explain that the large clear container represents approximately the amount of blood in an adult who weighs 160 pounds. Measure 10 mg of red food coloring and drop it into the water (this is 10 mcg/dl). Note that the water turns pink
- Next drop the same amount of food coloring into the smaller container and explain that the quart represents the approximate amount of blood in a small child (around age 2). Note that the water is darker, illustrating how the same amount of lead is more harmful to a young child because they have less blood; the concentration of lead is greater.
Another way to illustrate the idea of how much 10 mcg/dl is:
- tell students to imagine pouring 5000 2-liter soda bottles of water into a small square swimming pool measuring 3.16 meters on each side, and 1 meter deep (approx. 10.5 ft x 3 ft deep), filling it to the brim.
- Dissolve ten 100-milligram aspirin tablets into the water. The water in the pool now contains 10 mcg/dl of aspirin. The water represents the blood in the body and the aspirin represents the lead.
- Imagine a bathtub which is almost full (~1000 liters). One 100 milligram asprin tablet will be about 10 mcg/dl.
Activity 2 - The Chemistry of Lead Poisoning (Optional)
How is lead toxic to kids?
This activity/ lecture would most likely be taught towards the end of
the school year after students have had most of the key concepts of
chemistry. They need to have a basic understanding of
bonding, rates of reactions and metals vs. nonmetals to be able to
follow the PowerPoint presentation. Students also need to have
some biology experience, including an understanding of proteins,
enzymes, DNA.
Discuss the PowerPoint presentation, Getting the Lead Out, by Chemist
Hilary Godwin (chemistry-lead-godwin-presentation.ppt), who
investigates how lead disrupts protein function in the human
body. You might want to expand upon the last few slides and
discuss how lead interferes with calcium and iron absorption.
Some additional notes to go along with the presentation, if you choose to use it:
Lead poisoning results from the interaction of the metal with
biological electron-donor groups, such as the sulfhydryl groups, which
interferes with a multitude of enzymatic processes. Sulfhydryl groups
are present on various amino acids, which make up all the proteins in
the body. These proteins then regulate and determine the enzymatic
processes. Lead also interacts with essential cations, particularly
calcium, iron, and zinc; it interferes with the
sodium-potassium-adenosine triphosphate (Na+/K+-ATP) pump; and it
alters cellular and mitochondrial membranes, which causes the cell to
be more fragile.
What is this sodium potassium pump? In order to maintain the cell
potential, cells must keep a low concentration of sodium ions and high
levels of potassium ions within the cell. Outside cells there are high
concentrations of sodium and low concentrations of potassium, so
diffusion occurs through ion channels in the plasma membrane. In order
to keep the appropriate concentrations, the sodium-potassium pump pumps
sodium out and potassium in through active transport.
Wrap Up:
Wrap up the lesson by distributing the Lead Awareness student handout
(leadawareness-SHmoreinfo.doc). Tell students that if they live
in an older home, especially if they have younger siblings that they
should discuss with their parents what they learned in class, including
visiting some of the websites listed on their handouts and ordering the
free brochures.
Ask students why lead poisoning should be of concern to them (see
second-to-last slide in PowerPoint presentation). Guide a
discussion to get them to give some of the following responses:
- they may have younger siblings or someday have children
- they may currently live in, or eventually rent an apartment or buy a home has lead based paint or old lead pipes
- they have rights as tenants to ensure their safety and the safety of their families
- after graduation, they may have jobs (i.e., construction) where they are exposed to higher amounts of lead
If time, take students through a scenario:
After graduation, you rent your first apartment in an older
building. What do you look for to make sure that you are not in
danger of lead poisoning?
Enrichment Options
Parent-Home Connection
Order enough posters and/or brochures for every student in the class
so that they can take them home to discuss with their parents.
Field Experiences
Visit a local hospital, health facility or community forum on lead to learn more about lead poisoning.
Cross-Curricular Extensions
Hands-On Activity:
Consult your chemistry text book; many have examples of how to conduct a hands-on activity constructing a lead battery
English Language Arts: Have students investigate tetaethyl lead and tetramethyl lead and write a research paper on why leaded gasonline was banned.
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As a reflective
practitioner, note how this lesson could be adjusted after its initial
implementation. How successful were the students in demonstrating their
knowledge about the subject matter? What did the assessment demonstrate
about the students' learning? What skills do the students need to
revisit? What instructional strategies worked and what made them
successful? What will you change the next time you use this lesson? Why?
Author: D. Schnupp, K. Petterson, A. Reynolds, M. Dudley
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