PI 2
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CHEM 101
Subject
Geology
Date
Dec 6, 2023
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Practical Investigation 2.1
Boiling Stones
“You can't always get what you want, but if you try, sometimes, you might find you get what you need.”-
Rolling Stones
Can rocks change the temperature of water?
Background:
When in survival situations it can be important to boil water before
drinking to kill off bacteria. Unfortunately, if you find yourself lost in
the wilderness you are not likely to have a pot in your backpack.
Adventurists and others who practice bushcraft will heat rocks in a
fire and place them in water to heat it. Your challenge today is to
test the effectiveness of this method and estimate how many rocks
it would take to bring water to a boil.
Materials:
●
Boiling water and room temperature water
●
2x Mugs or Styrofoam cups
●
Collection of small pebbles and metal washers (
Alternatively:
Marbles and coins could substitute)
●
2x thermometers (
Alternatively:
One thermometer which you move back and forth would be less
accurate but could provide enough information if needed)
●
Tongs or chopsticks
Procedure
1.
Work in your
group
for the
entire practical investigation
. However, record all observations in your
own
Practical Investigation eBook worksheets for PI2.1
.
2.
Fill one cup with boiling water and the other with cold water. For this investigation the cup of boiling
water will represent our “fire”. To keep the “fire” hot it may be necessary to replace the boiling water
several times throughout the investigation.
3.
Collect your rocks (or marble alternatives) and place them in your “fire.” Use thermometers to
measure the heat of both cups. (The temperature of your hot water will act as an estimate for the
temperature of the rocks)
4.
Use the tongs to carefully transfer one rock from the “fire” to the room temperature water.
Remember that the rock will be quite hot and can burn you (> 60
o
C),
do not touch the rock with
your hand.
Record the temperatures of the room temperature water before and after the addition of
the rock in the table below.
©2020 Chadron M. Friesen, Ph.D., Christy Peters & Shane Durbach, PhD
Procedure (Cont.)
Table 1. Temperature observations
Rocks
Heat of rock
Water temp before
Water temp after
Change in temperature
1
91.3
°
C
26.7
°
C
28.5
°
C
1.8
°
C
2
85.8
°
C
27.3
°
C
27.6
°
C
0.3
°
C
3
75.2
°
C
27.9
°
C
28.1
°
C
0.2
°
C
4
71.5
°
C
27.9
°
C
28.8
°
C
0.9
°
C
5
69.1
°
C
27.9
°
C
28.7
°
C
0.8
°
C
5.
Based on the temperature change from the addition of one rock how many rocks do you think it will
take to bring the water to a boil (100°C)? Do you think this estimate is accurate? Why or why not?
Technically, it would take 39 more rocks to increase the temperature by 71.5
°
C to reach boiling at 100
°
C.
However, I don’t think this is accurate because the water is continually cooling as we are testing and
boiling the tocks, and the water we have is a very small amount compared to what you would need for
sufficient drinking water in the wild. A larger amount of water would take longer to boil, need more
rocks to boil it, and it would take longer to cool. There are many different factors.
6.
Add more rocks and continue to monitor the temperature changes in Table 1
7.
Did the heat of the water increase in consistent increments? Why do you think this is?
The heat of the water didn’t increase in equal increments. This is because the water we have is in a very
small amount and cools very quickly. Also because using one thermometer from hot to lukewarm and
then back to hot is going to give a less accurate reading.
8.
Many wilderness guides suggest taking the rocks out of the water when replacing them with new
rocks. Can you suggest at least two reasons why this would help the water boil?
My best guess would be that as the rocks cool off in the water, that they contribute to the temperature
of the water. When the water warms up from the new, hot rocks, the cooled down rocks are already
working against it in temperature because they are actively sitting there, cold. The cool rocks will be
consistently fighting with the hot rocks to change the water temperature.
9.
What if you used washers or different types of rocks (granite versus limestone) to heat water?
Which material would be faster in heating water for the same amount of mass? Provide reasoning
for your choice.
If you have time, try a washer or a coin and check it out!
©2020 Chadron M. Friesen, Ph.D., Christy Peters & Shane Durbach, PhD
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