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Chemistry, Matter and Interactions
Investigation 2 – PostLab
ASK WHY
There are five major branches of chemistry today – organic chemistry, analytic chemistry, physical chemistry, inorganic chemistry, and biochemistry. Organic chemistry is a brank of chemistry that focuses upon molecules and compounds that contain the carbon atom. Since living organisms contain many thousands of types of carbon-containing molecules, organic chemistry is sometimes associated with compounds derived from living organisms.
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According to the American Chemical Society, Analytical chemistry is the science of obtaining, processing, and communicating information about the composition and structure of matter. An analytical chemist may conduct basic laboratory research, perform process and product development, design instruments used in the analytical analysis, teach, or work in marketing and law. Analytical chemists perform both qualitative and quantitative analyses.
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SLIDE VCHEM2-post-1
Begin this part of the lnvestigation by reviewing the experiments students performed in the lab.
Ask students: What did you do in the lab? Student answers will vary but should include the tasks accomplished in the lab, such as finding the masses of the wood block and the metal cube when using a weigh dish, finding the mass of baking soda and water, and finding the mass of different amounts of baking soda and water.
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SLIDE VCHEM2-post-2
Direct students to turn to Trials 1-3 in their Student Data Record. Pose the following questions to students in order to discuss the procedure of using a container when determining mass:
Was the mass indicated on the triple beam balance different when you used a weigh dish or beaker to hold the samples? Students should indicate that there was a difference in the mass indicated on the triple beam balance when a container was used to hold the samples.
Why? The container also has mass. When both the container and sample were on the platform, the mass indicated on the triple beam was that of both the container and the sample.
Were you able to determine the mass of the sample even when using a container to hold it? How? Students should indicate that they were able to determine the mass of the sample even when using a container to hold it by obtaining the mass of the container alone and obtaining the combined mass of the container and sample, then subtracting the mass of the container.
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SLIDE VCHEM2-post-3
Help students analyze their observations of Trials 2 and 3 and compare their results to the predictions made from their experiments with the pan balance in Investigation 1.
- Direct students to refer to Problem 2c in Investigation One of their Student Data Record. Remind students that they used the pan balance to compare the amount of matter between the five samples including the baking soda and water.
Ask students: Based on your results from the pan balance, which sample did you predict would have a greater mass? (Remind students of the predictions they made in the Pre-Lab section of this Investigation). Students should have predicted the water sample would have more mass because when using the pan balance, it was the heavier sample.
How did your results from Trials 2 and 3 compare to your prediction? What was the difference in mass between the two samples? Students should indicate that the results of Trials 2 and 3 proved their prediction that the sample of water had a greater mass than the sample of baking soda, as the sample of water was approximately 10 g heavier than the sample of baking soda.
What was the mass of the baking soda? Student answers will vary. Students should indicate that the mass of the baking soda was approximately 34 g.
What was the mass of the water? Student answers will vary. Students should indicate that the mass of the water was approximately 45 g.
Do both solids and liquids have mass? What evidence from your experiments supports your conclusions? Students should indicate that both solids and liquids have mass because they were able to determine the mass of solid objects, baking soda, and water during the course of their experiments.
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SLIDE VCHEM2-post-4
Encourage students to complete the Table containing the properties of all five samples now that they determined the mass of the baking soda and water. The table has been reproduced in Problem 5 of their Student Data Record.
1. After the students complete the table, ask them how they could explain what they have learned about the properties of matter thus far.
2. Pose the following questions to assist students in answering the question:
Did all of the samples have the same properties? Students should indicate that all samples did not have the same properties.
Which properties were different? Students should indicate that the samples each had different colors, shapes, and textures and that there were two different states of matter.
What do we call the properties that can be described but not measured? Students should indicate that these are qualitative properties.
What kind of properties use measurements to describe matter? Students should indicate that quantitative properties use measurements to describe matter.
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SLIDE VCHEM2-post-5
Conclude the analysis of the laboratory experiments by directing students’ attention to the results of Trial 4. Remind students that in Trial 4 they measured different amounts of baking soda and water. Ask students the following questions to help them draw conclusions from their results:
Did you use more or less baking soda than the original sample in Trial 4? Student answers will vary based on the choice made by their group.
How did changing the amount of baking soda affect the mass of the sample? Student answers will vary. Students should indicate that increasing the amount of baking soda increased its mass, and decreasing the amount of baking soda decreased its mass.
How did changing the amount of water affect the mass of the water? Student answers will vary. Students should indicate that increasing the amount of water increased its mass, and decreasing the amount of water decreased its mass.
Did any of the qualitative properties of the baking soda or water change when the amounts of either sample change? Students should indicate that none of the qualitative properties changed when the amount of either baking soda or water was changed.
What conclusion can you draw about how changing the amount of matter affects the qualitative and quantitative properties of a sample? Student answers will vary. Students should indicate that changing the amount of matter can affect quantitative properties such as mass, but does not change the qualitative properties of the sample.
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SLIDE VCHEM2-post-6
Conclude the Investigation with this slide.
Ask Students: How would you summarize what you discovered about the types of properties liquids and solids have and how the amount of matter affects qualitative and quantitative properties? Students should indicate that the solids and liquids tested in their experiments had both qualitative and quantitative properties. In addition, students should indicate that changing the amount of matter in both solid and liquid samples affected the quantitative property of mass, but did not change the qualitative properties of the sample.
Direct students to record their answer in Problem 6 of their Student Data Record.
KEYS: POSTLAB
