Pre-Lab

Identification of a Solid Purpose: The aluminum received by your company for use in its manufacturing process is suspect. The boss says, "It doesn't look right. Check it out. I think they shipped us zinc or iron, or an alloy." Your boss recommends that your team verify the identity of the metal using physical properties: appearance, density and specific heat. In order to increase confidence in the results, your team has decided that at least 20 measurements of density and 20 measurements of specific heat are needed to have confidence in the results. Pre-Lab 1. You will need to determine the density of a solid using water displacement. Write a detailed procedure (including all necessary steps) in your lab notebook.

2. Review the methods for using triple beam mechanical balances in your lab handbook.(p19) According to the handbook, how should you handle the solid before massing it? Why?

3. Review the methods for measuring liquids in the lab handbook.(Section VIII) If you don't read the volume while holding the meniscus at eye level, you can get incorrect measurements. If you are looking down on the meniscus, will the measured volume be too high or too low?

4. Look up the density and specific heat (heat capacity) of aluminum, zinc and iron. You may need to use the Handbook of Chemistry and Physics (library).

Part 1 Determine the density of the solid

Use your procedure (Pre-lab question 1) to determine the density of the solid three times. Determine your own average and standard deviation. Combine the team data with yours and determine the average and standard deviation. Calculate your %error using the team average as the accepted value.

What does the team average density suggest is the identity of the solid? Calculate the %error between the team average density and the known density of the solid. Does your average agree? Which average is better? Why? Include the answers to this in your discussion of the results.

Part II Determine the specific heat of the solid

The specific heat of a substance is the amount of energy necessary to raise the temperature of 1 g of solid 1 Kelvin. This intensive property can be calculated using the heat transferred by the warm solid to a known quantity of water and measuring the temperature change. The calculation takes advantage of the First Law of Thermodynamics, which can be summarized, for this experiment, as:

heat lost by the solid + heat gained by the water = 0

The basic process involves heating the solid in boiling water until thermal equilibrium is achieved (the temperature of the solid is the temperature of the water). A coffee cup calorimeter with a temperature probe in some water will be standing by. You will obtain a base line temperature (T_initial) for the water in the coffee cup and then add the warm solid to it. The temperature will rise. (It is important to continuously stir the liquid to ensure transfer of heat from the solid to the water.) The temperature will stabilize again and you will record this temperature as (T_f).

The heat transferred in from the solid and gained by the water can be calculated using the equation:

heat = mass x specific heat x (T_final - T_initial)

Information that you need to collect to complete the calculation:

mass of solid
initial temperature of the solid final temperature of the solid
mass of water used in the Styrofoam cups
specific heat of water (4.184 J/gK)
initial temperature of water in the calorimeter before you add the hot solid
final temperature of water in the calorimeter after you add the hot solid

The Calorimeter: 2 Styrofoam cups or a Styrofoam cup in a beaker can be used as a crude calorimeter. A cover with a hole for the temperature probe can be fashioned using Styrofoam or cardboard.

General Procedure for Using the CBL to Collect Temperature Data

1. Begin heating a sufficient amount of water to cover your sample of solid.

2. Mass the solid and place it in the warming water. It should be heated in boiling water for at least 5 minutes. The temperature of the water bath is the initial temperature of the solid.

3. Begin setting up the CBL.

Plug the temperature probe into the adapter cable in Channel 1 of the CBL System.
Use the link cable to connect the CBL System to the TI Graphing Calculator. Firmly press in the cable ends.
Plug in the electrical converter to the CBL and the electrical outlet.
Turn the CBL and the calculator on.

On your TI 83 calculator, select [PRGM]; use the arrow keys to select [CHMBIO] and hit [ENTER]. Continue hitting [ENTER] until you get to the Main Menu.
Select [SET UP PROBES] and hit [ENTER].

{TI-85 or TI-86 Calculators:

Press , press to select < NAMES >, and press a menu key to select < CHEMB > (usually ). Press , then press again to go to the MAIN MENU.}

4. Set up the calculator and CBL for one temperature probe and a temperature calibration. · Select SET UP PROBES from the MAIN MENU. Note: To select an item from TI-82/83/92 menus, use

to highlight the menu item and press

(or simply press the number of the menu item on your calculator). To select an item from a TI-85 menu, press a menu key,

, ...

, that corresponds to the menu item (to select SET UP PROBES, press

· Enter "1" as the number of probes. Note: To enter a value, type the number on your calculator, then press .

· Select TEMPERATURE from the SELECT PROBE menu.

· Enter "1" as the Channel Number.

· Select USE STORED from the CALIBRATION menu. (This choice may not appear. Continue.)

5. Set up the calculator and CBL for data collection. · Select COLLECT DATA from the MAIN MENU.

· Select TIME GRAPH from the DATA COLLECTION menu.

· Enter "6" as the time between samples, in seconds.

· Enter "70" as the number of samples (the CBL will collect data for 7 minutes).

· Press . Select USE TIME SETUP to continue. If you want to change the sample time or sample number, select MODIFY SETUP.

· Enter "19" as the minimum temperature (Ymin).

· Enter "30" as the maximum temperature (Ymax).

· Enter "5" as the temperature increment (Yscl).

6. When everything is ready, press

on the calculator to begin data collection. After about 1 minute has elapsed, add the solid to the water in the calorimeter. A real-time graph of temperature vs. time will be displayed on the TI calculator screen during data collection. Temperature readings (in °C) can also be monitored on the CBL screen. When data collection stops after 7 minutes, "SAMPLING" will change to "DONE" on the CBL screen. A message will be displayed on the calculator telling the data lists in which the time and temperature data are stored.

7. Press to display a graph of temperature vs. time on the calculator screen. Examine the data points along the displayed curve:

TI-82 or TI-83 Calculators:

Use or to examine the data points along the curve. As you move the cursor right or left, the time (X) and temperature (Y) values of each data point are displayed below the graph. Determine the initial temperature, T_initial, and final (or maximum) temperature, T_final. Record the temperature values in your lab notebook’s data table (rounded to the nearest 0.01°C).

TI-85 or TI-86 Calculators:

Use , , , or to examine the data points along the curve. As you move the cursor, the time (X) and temperature (Y) values of each pixel on the calculator screen are displayed below the graph. If you position the cursor on a data point along the curve, its time and temperature values are displayed. Using this method, Determine the initial temperature, T_initial, and final (or maximum) temperature, T_final. Record the temperature values in your data table (round to the nearest 0.01°C). Note: Since these values are pixel coordinates, they represent only approximate data values.

8. Use the TI-Graph Link cable and program to transfer the graph of temperature vs. time to a IBM-compatible computer. Print a copy of the graph. Paste or tape one graph into your lab notebook. Don't print again when you repeat the experiment. Your goal is to have one "picture of the graph" in the notebook.

9. Repeat the experiment two more times. Determine your own average and standard deviation. Combine the team data with yours and determine the average and standard deviation. Calculate your %error using the team average as the accepted value.

What does the team average specific heat suggest is the identity of the solid? Calculate the %error between the team average specific heat and the known specific heat of the solid. Does your average agree? Which average is better? Why? Include the answers to this in your discussion of the results.

Post lab questions

1. Describe the effect that bubbles on the solid surface would have on the measured density of the solid.

2. If you used more water in your calorimeter, would the observed temperature change upon the addition of the hot solid be larger or smaller than the temperature change you observed.

3. Your boss handed you a 1-L sample of a liquid and asked you to determine it's specific heat. How would you determine the specific heat using the equipment in this lab?

4. It is difficult to keep the calorimeter covered and to stir the liquid conntinuously. How did you accomplish this? What effect would not covering the liquid have had on the change in temperature on the water?

5. Would you expect the class experimental data for specific heat to be above the accepted value for the solid, below the accepted value, or evenly distributed around the accepted value. As you think about this question, examine the effects of the various errors you observed on the final specific heat.

6. What if the element sodium had a density and specific heat very close to your unknown. Could the solid be sodium? Why or why not?

Prepare a formal lab report following the format in your Lab Procedures or syllabus. Include the answers to the post lab questions at the end of the report.