Specific Heat of a Metal Lab

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Objective

Student will be able to identify an unknown metal through performing an experiment to gather necessary specific heat data.

Big Idea

The specific heat of a substance is unique and allows scientists to determine the substance's identity.

Introduction

In this lesson students design a lab to determine the identity of an unknown metal through using specific heat calculations.  This lesson builds on the previous lessons in the unit where students have already learned about specific heat capacity and have performed several calorimetry experiments including finding the heat of fusion of ice, the calories in a Cheeto, the calories of food (virtually), and the heat capacity of various substances (virtually).

  • This lesson aligns with the Next Generation Performance Expectation of  HS-PS 3-1 Create a computation model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known.  It does so because students use the specific heat equation to calculate the specific heat of an unknown metal.
  • This lesson aligns with the Next Generation Crosscutting Concept 5: Energy and matter.  It does so because students are thinking about specific heat and how energy is transferred between systems.
  • This lesson aligns with the NGSS Science and Engineering Practice 3: Planning and Carrying Out Investigations: It does so because students come up with their own procedures for planning the lab and then carrying out the lab to gather the necessary data.

For this lesson various resources are needed for each lab group including:

  • 250 mL beakers
  • A way to heat the metal (either Bunsen Burner with wire gauze, ring stand and iron ring OR hot plate)
  • Styrofoam cups
  • metal shots (I give a different metal to each group from the metal shot kit from Flinn including copper, brass, aluminum, or steel)
  • thermometers (glass and/or temperature probes)

Explain

10 minutes

I begin the lesson by having students take several minutes to read over the specific heat of a metal lab paper to themselves. 

After several minutes I get students' attention and review the lab with them.

  • I ask students what the goal of the lab is and call on a student to share out.
  • I then show students examples of the metals and tell them that this is similar to what they did in Unit 1 where they identified an unknown metal using density (see my lesson Density Part II and Review), but this time they will be using specific heat.
  • I explain to students that they will be using calorimetry similar to the labs that they previously did in the unit to come up with their own procedures to perform this lab.
  • I then point out the equations that students will be using to find specific heat capacity.
  • I tell students that they will be coming up with their own procedures and to make sure that they are written so that somebody else could read through them and perform the lab.
  • I point out that the five measurements indicated on the paper should be able to be found when following their written procedures. 
  • I then go over all of the lab equipment available to students which I have laid out on the front bench.  While doing this I tell students that there are multiple ways to heat up water, so they will choose their materials based on their desired method.
  • Many students get confused with the different waters used in the lesson (one for heating the metal, one for use in the calorimeter).  I go over this in detail by demonstrating this to students as can be seen in this video.  I tell students to make sure to use enough water to cover the metal in both the the beaker and the calorimeter (should be at least 50mL). 

Elaborate

70 minutes

As students perform the lab I walk around to make sure that students are on task, help with questions, and review several parts of the lab that confuse students.

  • I have each group choose an unknown metal from a Ziploc bag of metals which includes metal shot samples.
  • In order to help the groups with confusion over the two types of water (one for heating the metal, one for the calorimeter) I spoke to each group on their own:
    • I gave each group a 250 mL beaker and told them to use this to heat up the water with the metal and that whatever temperature the water is will be used as the initial temperature of the metal.
    • I also gave each group a Styrofoam cup and a beaker and told them that they will be putting cold water from the sink into the Styrofoam cup.  I told them that this water must be measured and the temperature of this water will be the initial temperature of the water.
  • As students finish their procedures I make sure to check them before they go ahead with the lab.  As I check the procedures I make sure that they allow for the collection of the five necessary measurements indicated on the lab paper.  If students do not have the procedures written well I point out the steps where they are missing information or which measurements they are missing and tell them that I will come and check again in a few minutes.
  • This movie shows how I check students lab procedures.
  • As students complete their labs I tell them to look at the Metal specific heats list to determine which type of metal they had.

Evaluate

After students have competed their labs I grade them using the Specific Heat of a Metal Lab Rubric.

Here are some examples of graded labs:

  1. In this first example (Student Example #1) the student earned all of his points.  You will notice that in his procedures there are changes made from when I checked the work of his group and pointed out that they were not giving enough detail.  I like how this student simply crossed off parts and added in changes because I try to stress to students that making mistakes are okay and that science is messy.  This student's data was not in a table but was still easy to read so I have full credit.  Finally he had a good analysis and conclusion regarding the sample being tin.
  2. In this second example (Student Example #2) the student missed points on her procedure, analysis and conclusion.  You will see that in her procedure she is missing some specifics in terms of how to measure the water, set up the Bunsen burner, and how to heat the metal.  This student did have a good data table, but she missed the analysis and conclusion.  She did not show her work as to how she determined the sample is tin (I assume she was copying from one of her partners) and did not show any of her work for the analysis.
  3. In this third example (Student Example #3 ) the student did a great job with her procedures and almost earned all of her points, but she was missing some of her work and units in the analysis section. 

From grading the labs I found that the hardest struggle for students was being complete with writing their procedures and correctly plugging in their values for the analysis section.