This was the first Investigation of the LabLearner CELL Properties of Compounds. In it, students examined several compounds’ qualitative and quantitative properties.

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A. Begin this part of the Investigation by reviewing the experiments students performed in the lab.  Ask the following questions to promote discussion of the experiments:

1. Ask students: What was the theme or focus of the investigation? Students investigated some of the qualitative and quantitative properties of seven compounds, as well as the role of elemental composition in determining the properties of compounds.

2. Ask students: Think about Trial 1. What questions did you answer when performing Trial 1? How did you answer these questions? Students investigated the questions:  What are some of the qualitative properties of compounds?  Do these properties alone distinguish one compound from another?  To answer these questions, they investigated seven different compounds by observing their state of matter and color.  Students then compared the properties of each of the seven compounds.

3. Ask students: What questions were Trial 2 designed to answer?  How did you answer these questions? Trial 2 was designed to answer the question:  Are volume and mass qualitative or quantitative properties of compounds?  How can volume and mass be measured?  Do volume and mass alone distinguish one compound from another?  To answer these questions, they investigated seven different compounds and measured the volume and mass of each. Students then compared the properties of each of the seven compounds

4. Ask students: What were the two focus questions for the entire experiment?  How did you answer them? The two focus questions for the entire experiment were:  Do compounds with similar elements have similar properties?  Do compounds that have different elements have different properties? To answer the questions, students reviewed the elements found in each of the seven compounds, reviewed the qualitative and quantitative properties, and compared the properties of compounds with the same and different elements.

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B. Begin analysis of Trials 1 and 2 by examining the qualitative and quantitative nature of the properties of compounds that were explored in the lab.

1. Ask students:  Which properties of compounds did you find to be qualitative?  How did you know? Students should indicate that the state of matter and color were qualitative. They are qualitative because they could only be observed; they cannot be measured.

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2. Ask students:  Which properties of compounds did you find to be quantitative? How did you know? Students should indicate that volume and mass were quantitative because they could be measured using scientific tools, and a specific value could be assigned.

It should be noted that the information about mass is only useful for distinguishing compounds when the volume of the compounds is the same. If the volumes are different or if students are asked to obtain a certain mass of each compound, such as 5 grams, the mass measurement ceases to be useful in distinguishing one compound from another.

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3. Ask students:  Which qualitative or quantitative property would allow you to distinguish one compound from another? Students should indicate that the qualitative properties they investigated for the seven compounds were not unique to the compound; they did not distinguish one compound from the other six.  Students should recognize that volume was not a defining property of the compounds because the instructor determined its value.  In this case, the mass could be used as a defining property for all seven compounds because each 40 ml compound sample had a different mass.  If the volumes of the samples were different, then mass could not be used as a defining property.

4. Ask students: Think about the sugar, salt, vinegar, and rubbing alcohol you tested in the lab.  Are there any other qualitative properties that you could have observed to help you distinguish between the compounds? Students may indicate that they could have tasted the salt and the sugar or smelled the vinegar and rubbing alcohol to help distinguish them from the others.

5. Ask students: Why do you think we did not test the properties of smell and taste in the lab? Student answers may vary.  Encourage students to realize it is unsafe to touch, smell, or taste any items in the lab.  Students should realize that they cannot always tell the identity of a substance by simply looking at it.

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C. Continue the analysis of Trials 1 and 2.

Ask students: Were these substances elements or compounds?  How do you know? Student answers may vary. Students should indicate that the seven substances were compounds because each was composed of elements. The elements found in each compound were listed in the data tables students used to record their results in the lab.

1. Explain to students that all seven substances examined in the lab were compounds. Each of the examined compounds comprises a different combination of elements.

Ask students: Where can you find information about elements? Students should indicate that the Periodic Table of the Elements contains information about elements.

2. Ask students: Which elements (atoms) were found in more than one compound?  Which elements were unique to one compound? Students should indicate that hydrogen, carbon, and oxygen atoms were found in five compounds, and sodium atoms were found in two compounds. Chloride atoms and potassium atoms were unique to one compound.

3. Ask students: Think about the elements in rubbing alcohol, vinegar, and sugar. How are the compounds similar? Students should indicate that each of these compounds is made up of carbon, hydrogen, and oxygen atoms.

4. Ask students: Each of these compounds (rubbing alcohol, vinegar, and sugar) has the same elements, yet scientists would say they are different compounds.  How can that be? Student answers may vary.  Encourage students to realize that although each of the three compounds contains identical atoms, those atoms are present in different amounts. It is this difference that makes each compound unique.

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5. Direct students to locate the table in Problem 4 in their Student Data Record.  Explain to students that they will look at the chemical structure of each of the seven compounds from the lab. Students will use the Periodic Table of Elements to help them complete the table.

6. Tell students that each compound has a unique chemical structure in addition to a unique set of properties. The chemical structure of a compound not only indicates which elements make up that compound, but more importantly, it indicates the number of atoms of each element.

7. Inspect the chemical formula for baking soda on this slide: NaHCO₃ (sodium bicarbonate). Encourage students to copy the formula in the appropriate box in the table in Problem 4 of their Student Data Record.

8. Analyze this chemical formula as follows:

a. Explain to students that the compound of baking soda contains four different elements:  Na (sodium), H (hydrogen), C (carbon), and O (oxygen).

Point to the formula for baking soda on this slide:

b. Encourage students to record these four elements in the appropriate boxes on the table.  It should be explained to students that the symbol for each element in a chemical formula starts with a capital letter.

c. Ask students:  What element does “Na” stand for? Where can you find this information? Student answers may vary. Students should indicate they can use their Periodic Table to find the answer.  “Na” is the symbol for the element sodium. Encourage students to record this information on the table.

d. Direct students to use their Periodic Table to determine what the remaining three letters (H, C, and O) stand for. Encourage students to record this information on the table.

e. Ask students: How many atoms of each element make up baking soda? Student answers may vary. Encourage students to realize that the chemical formula also shows how many atoms of each element make up a compound. Students can either look at the number that follows an element or count the number of times an element appears in the formula for the compound.

f. Encourage students to record this information on the table.

g. Refer to the chemical formulas for the remaining six compounds on the slide. Direct students to copy these formulas into their tables.

h. Divide students into groups of three. Direct student groups to complete the table in problem 4 and answer Problems 5a-5c on their Student Data Record.

i. When students have completed Problems 4 and 5, allow several groups to share their answers with the class.

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Instruct students to think about Trials 1 and 2. Ask students to verbally Summarize what they did in the lab and why they did it. After students have outlined their experiments, ask the following questions to organize their recall of what was done:

1. Ask students: How are elements different from compounds? Students should indicate that an element is a substance that cannot be broken down into another substance by ordinary chemical reactions. In this sense, it is one of Earth’s smallest types of matter. Elements are atoms that combine to make compounds. A compound is a substance that is made up of one or more elements. Encourage students to record their answers in Problem 6a of their Student Data Record.

2. Ask students: Do compounds composed of similar elements have the same properties? Different properties? Support your answer with data from the lab. Students should indicate that compounds made of similar elements can have similar and very dissimilar properties. For example, vinegar and rubbing alcohol are both made of carbon, hydrogen, and oxygen. They are both colorless liquids. However, 40 ml of vinegar has a different mass than 40 ml of rubbing alcohol. In addition, vinegar, rubbing alcohol, and sugar are made of the same elements, yet vinegar and rubbing alcohol are clear liquids, while sugar is a white solid.

3. Ask students: Do compounds made of different elements have different properties? Similar properties? Support your answer with data from the lab. Students should indicate that compounds that are made of different elements can have similar and dissimilar properties. For example, salt is made of sodium and chloride, while sugar is made of carbon, hydrogen, and oxygen. Students determined that 40 ml of salt has a different mass than 40 ml of sugar. However, they are both white solids.

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D. Summarize Trials 1 and 2 by leading students in the following discussion:

1. Ask students: Why do you think that compounds made of the same elements can have different properties? Students should indicate that although two compounds may share similar or even the exact same elements, each compound contains a different number of atoms of those elements. This difference in the number of atoms of elements is one of the reasons that compounds contain a unique set of properties. For example, sugar and rubbing alcohol are both composed of atoms of the elements of carbon, hydrogen, and oxygen. The difference in the number of those atoms of elements gives them their unique set of properties.

Encourage students to record their answers in Problem 6b of their Student Data Record.

2. Ask students: Think about a roll of aluminum foil and a metal spoon. Do you know which item is a compound and which is an element? Student answers may vary. Encourage students to realize that aluminum foil is made of atoms of the single element aluminum (Al), while a metal spoon is a compound that is made up of different types of metal elements.

3. Ask students: How could you determine that aluminum foil is an element and that a metal spoon is a compound? Student answers may vary. Explain to students that, in most cases, it is impossible to tell the difference between elements and compounds by simple observations. The items would have to be tested for specific qualitative and quantitative properties to determine whether or not they are elements or compounds.

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E. Encourage students to apply the knowledge they have gained from this Investigation to daily situations by engaging them in the following activity:

1. Tell students they will read a short story aloud. Instruct students to find the story in Problem 7 of their Student Data Record. Ask them to follow along as the story is read.

2. Ask student volunteers to read the following story aloud:

READ:

“Mrs. Sark is preparing to set up the science lab for an experiment. She asks Tanya to help her gather the materials for the lab. Mrs. Sark gives Tanya a list that describes which materials are needed for the experiment. The list reads:

• 5 400 ml beakers

• 10 test tubes

• 5 test tube racks

• 5 lab scoops

• 100 ml of salt

“Tanya begins to collect the materials. She finds the beakers, test tubes, test tube racks, and lab scoops in the cabinet. Tanya still needs to find the salt. She opens another cabinet and sees two jars that have the labels shown on this slide:

“Tanya tells Mrs. Sark that two jars in the cabinet contain 40 ml of a white solid. Mrs. Sark explains that one jar contains sugar, and one contains salt. What other information could be included on the labels to help Tanya determine which jar was contains salt?”

3. Divide the students into groups of three. Direct students to answer Problem 8 of their Student Data Record. Allow sufficient time to complete this activity.

4. Ask students: What information did you add to your labels? Student answers may vary. Student answers may include the mass of 40 ml of sample and/or chemical formula.

5. Ask students: Which properties are unique to salt? Which properties are unique to sugar? Students should indicate that 40 ml of salt and 40 ml of sugar each have a different mass. Salt and sugar also have unique chemical formulas.

6. Ask students: Are you more likely to determine an unknown substance by looking at a single property or a set of properties? Why? Students should indicate that they would be more likely to determine an unknown substance’s identity if they had a set of properties. Since many different compounds can share many of the same properties, knowing only one property will not always allow a person to identify a specific compound.

Encourage students to record their answers in Problem 9 of their Student Data Record.