Thermochemistry!
Read the following pages before class:
Day 1 Activity: In your reading, you learned about specific heat. The specific heat of a substance (the
value) is an accepted value that the scientific community has agreed upon after many calorimetry
experiments on that substance. Today, we are going to experiment with finding the specific heat values
of unknown metals and how the number of trials affects how we decide what the unknown metal is.
Please answer the pre-lab questions and then work through experimental procedure. Collect (neatly)
ALL data from your experiment. Please think deeply about the post lab questions and answer them to
the best of your ability.
Dot Plot: Draw a number line. Place an X above the number line for each data point. If more than one
data point exists for a specific value (say you have 2 data points that are 0.5), stack the X’s. Please ask
your teacher for specifics if you do not know how to draw one of these.
Go to the following website to see MORE examples of how to calculate the specific heat of an unknown
substance. http://www.chemteam.info/Thermochem/Determine-Specific-Heat.html
Example:
After placing 10.38g of unknown metal at 99.6 C° into 60.50g of water at 22.1°C, the entire system
reaches a uniform temperature at 27.6 °C. Calculate the specific heat of the metal.
q water  qmetal
mwater cwater T final  Tinitial   (1)mmetal cmetal T final  Tinitial 
60.50 g  4.18
J 
27.6C  22.1C   (1)10.38 g cmetal 27.6C  99.6C 
g C 
cmetal   1.861
J
g C

1390.895 J  (1) 747.36 g C cmetal 
Pre-lab Questions – to be done before the lab
1. A blacksmith heats up metal so that s/ he can bend and shape it. After s/he has in the shape s/he
wants it to be, it is plunged into water.
a. Why is the metal plunged into water?
b. What happens to the metal when it is put in the water?
c. What happens to the water when the metal is put in it?
2. If the blacksmith puts 100g of hot metal into 100g of cool water, which will change in temperature
the most, the water or the metal? Explain why you think this is the case.
3. What if you compared putting 100g of hot iron versus 100g of hot copper into 100g of cool water,
would you expect to get the same results? Explain why or why not.
4. Heat refers to the transfer of energy between two bodies of different temperatures. Which of the
following would you use to warm up a cold bath, 1 cup (250 mL) of 100C water or a bucket (10 L) of
50C water? Why?
b. Based on your answer to part a, which has the ability to transfer more heat, 1 cup (250 mL) of
100C water or a bucket (10 L) of 50C water?
c. Does transfer of heat depend only on temperature? If not, what else does it depend on?
5. When heat is transferred, what happens to the particles of the substance that absorbs heat? That
loses heat?
b. From your answer to part a, how is heat transferred from one substance to another?
Problem
What is the specific heat of an unknown substance?
Materials
Hot plate
Deionized water
400 mL Beaker
Styrofoam cup
Thermometer
Balance (±0.01g)
600 mL Beaker
tongs
Metal pieces of unknown metals 1 and 2
DAY 1
Case 1 – Unknown Metal 1
In your group will be three to four people. As a group, perform the experiment once (2 people
performing the experiment and 2 people calculating specific heat). After that first experiment, read post
lab question 1 and answer it with your group. Continue to run the experiment 18 more times (same 2
people performing the experiment and same 2 people calculating specific heat). Answer the rest of the
post questions.
Procedure
1) Obtain a 600 mL beaker, fill with about 500 mL of deionized water and place on hot plate.
2) Allow water to boil
3) Obtain a sample of unknown metal 1 and weigh the sample to 2 decimal places. Record this
information.
4) Place a piece of unknown metal 1 into the boiling water. Allow the metal to come to
equilibrium with the boiling water (same temperature – about 2 or 3 min).
5) In the 100 mL graduated cylinder, add approximately 40 mL of deionized water and record the
WEIGHT of the water in grams.
6) Put 40 mL of water into empty Styrofoam cup.
7) Put the thermometer into the Styrofoam cup and measure the temperature of the water in the
cup in degree Celsius. (Leave the thermometer in the Styrofoam cup.)
8) Remove the unknown metal piece from the boiling water with tongs and QUICKLY and efficiently
transfer the metal to the Styrofoam cup and place into water.
9) Swirl the water in the cup to ensure even heat transfer.
10) Allow metal to come to equilibrium with the water (Water temp will increase)
11) When temperature of water stabilizes, record the temperature of the water. This will be the
final temperature of the water and of the metal. (change in temperature will not be much so
pay attention)
12) Place metal piece back into the boiling water and dump used water in Styrofoam cup down the
drain.
13) After completing first trial, answer the following question:
Based on running one trial, predict which metal is the unknown metal by comparing the
specific heat values.
Prediction: ______________________
14) Repeat steps 5 through 12 19 times.
Results
Case 1:
1) Using the data collected, (all 20 trials) calculate the specific heats of unknown metal 1 (this
should have been taking place while each trial was being run).
2) Create a table for your data.
3) Put the specific heat data into a dot plot
4) Label the axis appropriately as you will be turning in this dot plot.
Substance
Specific Heat
in J/g°C
Magnesium
Aluminum
Iron
Nickel
Zinc
Copper
1.900
1.650
1.220
1.200
0.825
0.790
Follow-up Critical Thinking Questions – Please deeply think about these questions and answer them in
complete sentences!
Case 1
1) Based on all 20 data points you collected, identify the unknown metal.
2) How sure are you that the unknown metal actually is the metal you identified? Use the data
(the variability of the data and your dot plot) to support your answer.
3) Was the prediction you made after the first trial and your prediction after 20 trials the
same?
a. If the same, how did adding trials increase your confidence that the metal truly was
what you identified.
b. If different, what did adding more trials do to the data and your ability to predict.
4) Compare and contrast how confident you were in your identifications after 1 trial and after
20 trials.
 If your confidence is different, what aspect of the data creates the difference and
why is it important?
5) If identifying metal 1 was a life or death decision, which procedure would you rather
follow? 1 trials or 20 trials? Why?
6) What does your analysis tell you about how the number of trials affects variation and the
confidence in your results?
DAY 2
Day 2 Activity: Today, we are going to experiment with finding the specific heat value of unknown metal
2. Please work through the experimental procedure below. Collect (neatly) ALL data from your
experiment. Please think deeply about the post lab questions and answer them to the best of your
ability.
Case 2 – Unknown metal 2
In the same group you will perform the experiment again, but with unknown metal 2. The group of 2
calculating the specific heat will now perform the experiment and the other 2 will calculate. There are
some minor changes. They are listed below:


Work with unknown metal 2 instead of unknown metal 1.
Use 60 mL of Deionized water instead of 40 mL of deionized water.
Results
Case 2:
1) Using the data collected, calculate the specific heat of unknown metal 2. (This should have
been taking place while each trial was being run).
2) Create a table of specific heats.
3) Put your data into a dot plot.
4) Label the dot plot appropriately – you will turn this in.
Substance
Specific Heat
in J/g°C
Magnesium
Aluminum
Iron
Nickel
Zinc
Copper
1.900
1.650
1.220
1.200
0.825
0.790
Follow-up Critical Thinking Questions– Please deeply think about these questions and answer them in
complete sentences!
Case 2
1) Based on all 20 data points you collected, identify the unknown metal.
2) How sure are you that the unknown metal actually is the metal you identified? Use the data
(the variability of the data and your dot plot) to support your answer.
3) Was the prediction you made after the first trial and your prediction after 20 trials the
same?
a. If the same, how did adding trials increase your confidence that the metal truly was
what you identified.
b. If different, what did adding more trials do to the data and your ability to predict.
4) Compare and contrast how confident you were in your identifications after 1 trial and after
20 trials.
 If your confidence is different, what aspect of the data creates the difference and
why is it important?
5) If identifying metal 1 was a life or death decision, which procedure would you rather
follow? 1 trials or 20 trials? Why?
6) What does your analysis tell you about how the number of trials affects variation and the
confidence in your results?
7) Describe how number of trials can either increase or decrease the variability in data.
8) Why would it be important in a scientific exploration to decrease the variability of your data
as much as possible?
9) Where does variability in lab collected data come from? Can we make all variability go
away? What can we do to increase our confidence in our results and decrease the
variability in our data?
YOUR LAB REPORT – Results (raw data, calculated data and dot plots)
Answer to questions from Day 1 and Day 2 – hand written or typed
MUST BE IN COMPLETE SENTENCES!!!
Potential Data collection sheet:
DAY 1 DATA: Unknown Metal 1
Water Cwater
(g)
(J/g°C)
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
Dot plot:
Tfinal water
(°C)
Tinitial water
(°C)
Unknown
metal 1
(g)
Tfinal Metal °C
Tinitial metal
°C
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
C unknown metal 1
(calculated) J/g°C
DAY 2 DATA
Water Cwater
(g)
(J/g°C)
Tfinal water
(°C)
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
4.18
Dot Plot: _______________
Tinitial water
(°C)
Unknown
metal 2
(g)
Tfinal Metal °C
Tinitial metal
°C
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
97.3
C unknown metal 2
(calculated) J/g°C