LAB: What Metal is This? Using Student-Engineered Calorimeters in Lab

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Objective

SWBAT use their small group designed and tested calorimeters during a specific heat capacity investigation in which students determine the identify of an unknown metal through determining its specific heat capacity.

Big Idea

Determining the amount of heat lost by hot metal to cool water can be used to determine the specific heat capacity of that unique metal, thereby helping us identify what metal it might be.

Why This Lesson?

During this lesson, students will use a calorimeter that they have designed, tested, and modified in a previous four lesson series (links are provided below).  Students will determine the specific heat capacity of their unknown metal and then determine that metal's possible identity based on that information.  

Through this particular investigation, students are exposed to several Crosscutting Concepts: XC-EM-HS-1: The total amount of energy in a closed system remains constant, XC-EM-HS-2: Changes of energy in a system can be described in terms of energy flows into, out of, and within that system, and XC-EM-HS-3: Energy cannot be created or destroyed, only moves between one place and another place, between objects or systems.  

Students need to understand that when they take their heated sample of metal and place it in a room temperature sample of water, the metal will transfer heat to the water until both are the same temperature.  In order to be successful, students will meet Performance Expectation HS-PS3-1: Create a computational model to calculate the change in energy of one component in the system when the change in energy of the other component(s) and energy flows in and out of the system are known.  Here, the calorimeter (if well-made) should contain the energy within and students can measure temperature changes in the water inside in order to determine energy flows from the metal.  One assumption that students will make is that when the water has reached its maximum temperature, the metal has lost the equivalent heat needed to cause the water's temperature change.  This engages them in HS-PS3-4: Plan and conduct an investigation to provide evidence that the transfer of thermal energy when two components of different temperature are combined within a closed system results in a more uniform energy distribution among the components of the system.

 

Lesson Series to Design the Calorimeter:

Day 1 of 4--Engineering a Calorimeter: What is a Prototype?

Day 2 of 4--Engineering a Calorimeter: Designing and Testing a First Prototype

Day 3 of 4--Engineering a Calorimeter: Testing and Re-designing 

Day 4 of 4--Engineering a Calorimeter: Modifying and Re-testing a Prototype to Inform Final Product Build

 

 

Warm-Up

5 minutes

While I take attendance, students usually do a warm-up activity in their composition Warm-Up/Reflection books.  I use warm-ups to either probe for students' prior knowledge about the day's upcoming lesson or to have them bring to mind and review what they should have learned previously.  (To read more about Warm Up and Reflection Books,  please see the attached resource.)

Today, however, I have students answer pre-lab questions on their lab handout instead of using their Warm-Up/Reflection books.

First, I pass out the LAB - Specific Heat Capacity of a Metal activity handout to my students.  Then, I tell my students that their warm-up today is to answer the Pre-Lab question at the top of the handout:

What is specific heat capacity and why is it unique for different substances?

Some students may need to look up the answers on their phones, which I allow and encourage.

Pre-Lab

10 minutes

Once students have had enough time to answer their Warm-Up question (I allow the full 5 minutes because they will need to look up their answers.), I explain that today students will be using their calorimeters or heat containers that they engineered during this lab investigation.

I direct students to the Lab Masters, set up on 6 different lab stations and ready to go.  I explain that there should be two student groups per Lab Master and that they should use regular thermometers for measuring their temperatures.  The Lab Masters will only be used for quickly creating hot water baths in order to heat the metal samples.  I explain that each group will get a small test tube with a metal sample inside.  I tell students to heat the metal sample INSIDE of the small test tube--to put the entire test tube with metal inside in the hot water bath.  Once the test tube (with metal inside) has been heated for about 5 minutes (allowing the metal sample to reach about boiling temperature), then students can pour the sample from the tube into the water inside their calorimeters.

Student Investigation

30 minutes

Students will work with a Lab Master, two groups per set up.  The Lab Masters should just be used as hot water baths for heating the metal samples.  Once the test tube with metal has been in the boiling water bath for about 5 minutes, the sample should be ready.

As samples are heating, students should be measuring 50 mL of tap water into their calorimeters.  They should record an initial temperature for the water.

Once the metal sample is ready, students should dump the hot metal into the water in the calorimeter.  Students should watch the temperature of the water increase until it reaches a maximum.  That maximum temperature then should be recorded as the final temperatures of both the metal and the water.  Students will need to understand that the heat that the water gains is equal to the heat that the metal loses.  That data can then be used in the q=mc (delta)T equation.

As students finish collecting their data, I help them to complete their calculations.  I use one group's data to walk through the calculation steps on the whiteboard so that students see where their data fits into calculating the specific heat capacity for their samples.

 

Sample student work:

Student #1

Student #2

Student #3

Most of my students had difficulty articulating the difference between heat flow and temperature change.  As demonstrated by students #1 and #3, students reported temperature changes as heat gained and/or lost.  Although temperature changes are caused by heat flow, they are not the same thing.  I need to be more clear about this subtle but big difference.

Student #1 identified her unknown metal as iron, which it was.  Her calculations yielded a specific heat capacity of 0.46 for her metal, only 0.02 away from iron's actual specific heat capacity.

Student #2 describes heat flow very well.  She seems to have a strong conceptual understanding of heat flow and what is going on during this investigation, but her calculations yield a specific heat capacity much higher than expected.  

Student #3 calculated his unknown to be iron as well (which it was).  He is a usually quiet student who had been absent for almost the entire calorimeter engineering 4 lesson sequence that led up to this particular lesson.  I put him with a pair of high achieving students who worked with him really well.  As a result, student #3 was able to understand the investigation and even says in his lab report that he "liked working with people that know what they are doing, and I learned from them."  How exciting!

Student Reflection

5 minutes

Because today’s investigation takes the entire class period, there is not enough time to have students bring out their Warm-Up/Reflection Books to complete a Student Reflection.  I have, however, included questions in the lab handout that address the same information I would have included as a Student Reflection.  The key learning that I want students to focus on as I wind the lesson down is included in the Conclusion section of the handout (desired student responses in italics):

What did you learn about heat transfer?  Heat flows from higher temperature to lower temperature; Heat gains come from something else's heat loss.

What did you learn about specific heat capacity?  Metal has a low specific heat capacity and water has a high specific heat capacity; specific heat capacity tells us how much heat is needed to increase the temperature of a specific substance and is dependent on how much substance there is; specific heat capacity is unique for each substance type.

Which metal do you think you have based on the following specific heat capacity values?  Unknown samples given to students were either iron or zinc, but students should choose whichever metal from the list is closest to what their data and calculations indicate.

And as a way to have students thinking about the investigation on a positive note, I usually end lab handouts with the question, “What did you like about this lab?”

 

Samples of student work: