A report written following a practical investigation into heat loss through calorimetry. Includes calibration of thermometers, cooling curves of stearic acid, paraffin wax and boiling water with cold copper metal. Received distinction for this assignment and should be used as a guide to reach the h...
Keeping Up the Standards
1. Introduction to Calorimetry
What is calorimetry? Calorimetry is an experimental technique used to measure the amount
of heat lost or absorbed during a chemical reaction. By measuring the temperature changes
through equipment, such as thermometers, a cooling curve can be produced, and a clearer
indication of state changes can be observed by the lack of temperature change (the graph will
level out during state changes). Additionally, this graph can allow us to determine the cooling
rate by calculating the gradient of the graph at different points using the equation
∆y
Gradient= . Multiple gradients can be calculated showing how the cooling rate changes
∆x
throughout the reaction.
Calibration of Thermometers
Thermometers are devices used to determine the surrounding temperature and need to be
highly accurate, especially in a scientific or industrial setting. The thermometers can be
subcategorised into liquid filled or digital thermometers, used relevant to the practical being
investigated. Our two thermometers of choice were a liquid mercury thermometer and a
digital thermometer. By using known temperatures and figures both liquid and digital
thermometers can be calibrated, and their accuracy checked. The two knowns in the
calibration of thermometers are that the point at which water has solidified (become ice) the
temperature should be approximately 0° and that boiling water has a temperature of 100°.
Therefore, when the thermometers are fully submerged into a container of ice or boiling
water their temperature should be that of what is expected (taking into account margin of ±
0.1-0.2°). To calibrate the thermometers for 0° a beaker with crushed ice and tap water is
used and the thermometer submerged inside (ensuing that the entire bottom of the
thermometer is sufficiently covered). Take the temperature reading
after 30 seconds of submersion in the ice. Re-heat the thermometer
back up to above 0°, repeat 4 times and then calculate an average. The
same goes for the boiling water calibration/100°. Using a kettle, pour
boiling water directly into a beaker then place the thermometer inside.
Take a temperature reading after 30 seconds, cool the thermometer
down to bellow 100°, repeat the heating process 4 more times and then
calculate an average. The closer to 0° and 100° the more accurate the
thermometers are and sufficient to use within the practical. The set-up
of a digital thermometer’s calibration can be seen in figure 1.1. Here are Figure 1.1 – Calibration
set-up
the results from the calibration of the liquid mercury seen in figure 1.2
and the calibration of the digital thermometer seen in figure 1.3. The
average readings for the thermometers were accurate enough, taking into consideration the
external temperature of during the calibration, for them to be used within our investigation.
Calibration results in (°C) Calibration results in (°C)
0° 100° 0° 100°
st
1 Test 5 85.7 1st Test 0.9 84
2nd Test 5.5 90 2nd Test 1.1 80
3rd Test 5.8 90 3rd Test 1.1 75
4th Test 6 95 4th Test 1.2 72
Averag 5.575 89.05 Averag 1.075 77.75
e Figure 1.2 – Calibration e Figure 1.3 – Calibration
results of liquid mercury results of digital
thermometer thermometer
, Cooling curves
The way in which we can display the data we collect from calorimetry investigations are
through plotting cooling or heating curves. Cooling curves are line graphs that are used to
show a rate of cooling and any phase changes throughout practical investigations. In the case
of our three investigations, all of the graphs with be cooling curves as we are measuring the
heat loss throughout practical’s, not a heat gain. Phase changes are seen to be a flattening of
the graph where no there is no heat loss for a period of time. Additionally, the steeper the
decline in heat loss the greater the rate of cooling will be. The rate of cooling is a numerical
value given to how quickly heat has been lost in a certain amount of time. To calculate to rate
of cooling a tangent needs to be drawn against a downward slope on the graph. From this
∆y
point tangent a gradient can be calculated. The equation used for this is Gradient= .
∆x
Additionally, multiple tangents can be drawn, and gradients calculated to show how the rate
of cooling changes throughout. In our investigation we calculated three gradients for each
graph to show how the heat loss changes in different stages of the practical.
2. Calorimetry of Boiling Water and Cold Copper
For this practical our aim was to measure the heat lost when a cold metal was added to a hot
liquid. To create this scenario, we used cooled copper pieces and boiling water from a kettle.
The apparatus used to conduct this investigation included 100g of copper at 10°C; 100ml of
boiling water; a kettle; a Styrofoam cup; a liquid mercury thermometer; a clamp and clamp
stand; a set of scales; and a stopwatch.
To set up and record the data for this practical use the following method:
Set the Styrofoam cup onto the work bench with the thermometer clamped in the clam
stand above the Styrofoam cup ensuring that the bulb is relatively near the bottom of
the cup
Using the scales, weigh out approximately 100g of the cold copper (at roughly -10°C)
Simultaneously, turn the kettle on and leave to boil
Place the copper pieces into the Styrofoam cup
Measure out 100ml of the boiling water and immediately transfer into the Styrofoam
cup
Put the thermometer directly into the cup and take the
temperature instantly
Record the temperature readings into a table for 30
minutes at 100 second intervals
The set-up for this calorimetry investigation can be seen in
figure 2.1.
The results from the calorimetry practical for boiling water and
cold copper can be seen in figure 2.2 and the subsequent graph
can be seen in figure 2.3.
Figure 2.1 – Set-up for Calorimetry
of Boiling Water and Cold Copper
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