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Unit 1

How do we analyze a system?

Modeling and Measurement

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Lab Session 4

How do we use models to differentiate substances?

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The ChallengeThree volatile solvents have been found in different containers in an illegal drugs lab. Based on prior experiences, you infer the

potential identity of these substances:

Butanone C4H8O

Ethanol C2H6O

Hexane C6H14

How can you determine the identity of the solvent in each container?

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So, what do we need to measure to determine mNA for a gas sample?

How can these properties be measured?

PV

MTRm

AN

Your Ideas

According to the ideal gas model:

Discuss in your groups the actual procedure you propose to follow.

Available resources:

Sample of known substance (acetone, K2);

Balance, thermometer, barometer; Hot and cold baths; Glassware;

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Your Plan

How are you planning to generate the sample of gas?

How are you planning to measure its temperature?

How are you planning to measure its pressure?

How are you planning to measure its mass?

How are you planning to measure its volume?

PV

MTRm

AN

WHY?

Where are the most likely sources of error?

How can you plan to avoid or minimize them?

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Apply your ideas and experimental skills to determine the molar mass of the known

substance provided.

Available resources: Sample of known substance (acetone, K2);

Balance, thermometer, barometer; Hot and cold baths; Glassware;

Make sure to repeat your

measurements at least two

times!

You have 45 minutes

Skill Building Tests

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Present your measurements and calculations to the class.

Decide as a group which data should be shared to facilitate the analysis.

Share Results

Acetone (Tb = 56.5 oC) mNA = 58.08 g/mol C3H6O

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Some ReflectionsAs a group

Discuss the difference, if any, between the average experimental result and the actual molar mass of the gas. How do you explain these differences?

Discuss what the standard deviation tells you about the precision of the average value.

How could you modify your experimental procedure to improve the accuracy and/or the precision of your results?

How could you modify your model to improve its usefulness in identifying unknown substances?

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Beginning QuestionsWhat questions would your group need to

answer to face the challenge?

Discuss with the whole group the best strategy to find the identity of the three unknowns.

Group Question

1

2

3

4

5

6

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Your Real Challenge

Design and implement an experimental procedure that will allow you determine the

identity of the three unknowns.

You have 60 minutes

Available resources: Samples of unknown substances (K1, A1, C1);

Balance, thermometer, barometer; Hot and cold baths; Glassware;

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Claims and Evidence

Based on the results of your experiments, present your major claims and the evidence that you have to support the answer to your question.

Is the group answering their

beginning question?

Are their claims clear?

Is the evidence reliable?

Is the evidence appropriate to support the claims?

How do you explain your results?

Butanone

Ethanol

Hexane

mNA = 72.11 g/mol

mNA = 46.07 g/mol

mNA = 86.17 g/mol

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The Identity

How do you explain the differences?

Butanone (Tb = 80.0 oC) C4H8O mNA = 72.11 g/mol

Ethanol (Tb = 78.4 oC) C2H6O mNA = 46.07 g/mol

Hexane (Tb = 69.0 oC) C6H14mNA = 86.17 g/mol

K1

A1

C1

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What did you learn from doing your experiment?

How would you improve what you did?

How have your ideas changed as a result of this lab?

What do you not completely understand?

What new questions do you have?

Final Reflections

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Beginning questions (2 p): What questions guided your explorations?

Safety Considerations (2 p):What did you do to stay safe in the lab?

Procedures and Tests (2 p):What experiments did you do to answer your

questions?

Data, calculations, and representations (6 p):What observations did you make?What data did you collect?What calculations and representations helped

you make sense of the data?

Your Report

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Claims (2 p): What can you claim to answer your questions?

Evidence and Analysis (6 p):How did you interpret your results to support

your claims?

Reflections and additional questions (10 p):What did you learn?What do you not completely understand? How have your ideas changed as a result of this lab?What new questions do you have?

How would you improve what you did?

Your Report

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Post-Laboratory Questions:

Your Report

1. Discuss what your results indicate about the use of the ideal gas law to determine the molar mass of any gas. Your discussion should include your judgment of the practicality of the technique and the validity of the basic assumptions (ideal gas behavior).

2. Suggest at least one change that you think would produce better results.

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Lab Session 5

What is the relationship between a substance’s color and

the light it absorbs?

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IThe Challenge

A local business produces colored salt solutions for use in baths and spas. Your team of chemists has

been hired to conduct research and provide suggestions for new product colors.

How can you determine how the color depends on the type of light that is absorbed or transmitted?

At this time, the business wants to better understand the

relationship between salt solution color and the absorption or transmission of visible light.