Chlorine Chemistry: A Building Block of Matter

This activity is designed to give students an introduction to some of the "building block" elements of the periodic table, especially chlorine, one element they may already be familiar with. Students will observe and record what happens to various chloride compounds during a lab investigation. The students will analyze which chlorides have the most similar physical and chemical properties. Students will also collaborate with lab partners to synthesize the difference between a physical property and chemical property.

Key Concepts: Chlorine is one of the major building blocks of matter (one of a handful of single elements that combine to form most of the matter on the earth). Chlorine likes to combine with other elements and compounds, and scientists have found ways for chlorine to help build or improve things in the world around us, at home and at school.
Vocabulary Words: Element - A substance composed of one type of atom and cannot be chemically separated
Compound - two or more elements bonded together.

The following lesson's demonstration is suitable for grades 1-6. The lab could be modified for grades 6-12. Our science class consists of 31 fourth grade students. This lesson includes a demonstration, large group discussion, and lab activity. It is written to be taught over two 40 minute class periods. The lesson provides a great introduction to one of the elements on the periodic table. However, it could be extended to a more in depth discussion about chlorine and its use in the water purification process our cities use to clean waste water and drinking water. Materials needed are chlorine (or household bleach), iron chloride, calcium chloride, and sodium chloride (these compounds could be obtained by contacting your local high school chemistry teacher. Be sure to make a copy of the MSDS too!)

Day One: Demonstration - 1) Before the students arrive, fill two clear glasses with about 4 ounces of warm tap water. Add one drop of red or yellow food coloring to one of the cups. Add 3-4 droppers full of household bleach to the other. 2) When the class is situated, call their attention to the two glasses in the front of the room. Ask then to observe very closely what they see in the two glasses. Make a list of observations of each cub on the board. 3) Explain that some chemical "magic" will take place. Pour the colored solution into the "water" and set aside. In about 40 seconds the solution will clear! 4) Ask students to explain what they just observed. Record answers on the board. Brainstorm with students what could have taken place. 5) Explain that the cup that looked like water actually had another liquid in it too, chlorine. (The is a good time to contrast observations and inferences with the class). Continue to explain that chlorine is present in many other "compounds" that are a part of our daily lives. 6) Ask the class to pair and share what compounds chlorine may be a part of that they are familiar with. Have each pair record their answers on post it notes and place them on the white board. 7) Watch a streaming video about chlorine found on the following website: http://www.americanchemistry.com 8) Next, revisit the post it notes and make additions or deletions as needed. 9) Explain that chlorine likes to combine with other elements and compounds. Define element and compound as needed. Chlorine is an important "building block," one of several single elements that combine to form most of the matter on earth. The other building block elements are: oxygen (O), silicon (Si), aluminum (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), magnesium (Mg), hydrogen (H), phosphorus (P), chlorine (Cl), and carbon (C ). The elements are referred to as "building blocks" because they make up over 99% of the earth's crust, atmosphere, and oceans, by weight. 10) Tell the students that they will explore several compounds with chlorine in them during tomorrow's lab! 11) Hand out Activity Sheet One. Tell the students to circle anything on that sheet that they see at home as homework. Bring it back the next day.

Day Two: Lab - 1) Review yesterday's lesson and the chlorine compounds we use or see every day with the students (based on the movie and Activity Sheet One). 2) Tell the students they will have a chance to explore some chlorine compounds in class today. 3) Pass out the "Exploring Chlorine Compound" lab instruction sheet (Activity Sheet Two). Discuss the procedure with the class. Review with the class the difference between physical (appearance, color, odor, etc) and chemical properties. Make the materials available to the students. 4) Be sure the students follow the recommended safety precautions when using the materials.

Answers to Questions (taken from the American chemistry website):
1. Which of the chlorides seem to have the most similar physical properties and chemical properties? Sodium and calcium chloride seem to have the most similar properties. Although dissimilar in appearance and in their reaction with water, they are both white, form neutral solutions and do not react with aluminum foil or ammonia. Cupric and iron chloride both form acid solutions in water and react with ammonia and aluminum foil. The least similar physical properties and chemical properties? Answers vary. Cupric chloride has no common properties with either ammonium chloride or calcium chloride. Others may have some common properties.
2. How do you explain the differences in the chemical and physical properties of these chlorides? Student answers should indicate that all the compounds contain chlorine. Therefore any differences in properties must be due to the other chemicals present in the compounds.
3. How do the observations you made in this activity support the idea of chemicals as "building blocks?" (Note that chlorine is a gas at room temperature and has a strong odor.) Each chloride is a solid at room temperature and has no detectable odor. Each chloride has chemical and physical properties that differ from chlorine gas -- and other chlorides. These changes result from the different elements or "building blocks" that combine with chlorine to form each compound. Activity Sheet One (Microsoft Word 52kB Jul24 08) Activity Sheet Two (Microsoft Word 77kB Jul24 08) Extension (Microsoft Word 30kB May26 11)

Day One's Demonstration could be used for grades 2-6. It would be a great introduction to the periodic table of the elements. You could stop at day one's discussion and skip the lab depending on the age of your students. Day Two's lab is intended for older students in grades 6-12; however, it could be modified for students in grades 4-5 too.

Students will hand in both activity sheets one and two for a participation grade. I will also continually monitor their progress during the lab exploration and large group discussions.

Minnesota Academic Science Standards: 4.I.B.3 - evidence and logic are necessary to support scientific understandings, 4.I.A.3 - recognizing the impact of scientific and technological activities on the natural world.