Ice Calorimeter

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This report is a description of an experimental determination of the enthalpy of reaction of sulfuric acid in a reaction with magnesium to produce magnesium sulfate. Through the use of an ice calorimeter, the rxn H° D for this reaction is determined to be 1 360kJ mol − − × . Introduction:

This report details an experiment in thermochemistry. Included are the methods, results, and interpretation of results of an experimental determination of an enthalpy of reaction. The reaction being studied is between sulfuric acid, and magnesium metal.

( ) ( H2SO4 aq +Mg s)®H2 ( g )+MgSO4 (s)
This reaction is run as an isothermal reaction, where the enthalpy change is measured by the change in volume of melting ice. Published values for the density of water, and ice, as well as the heat of fusion of water will be used to determine the amount of heat energy that is released by the reaction. The relationship between the changing volume of the calorimeter, and the amount of ice that is melted by the reaction can be expressed mathematically by the following expression.

uantity of ice melted uantity of ice melted
olume before rxn olume after rxn
ensity of ice ensity of water
− = −
In order to account for the natural melting of ice at room
temperature, the data will be plotted on a coordinate system. A leastsquares linear regression will then be used to identify the equations of two lines, one representing the rate of ice melting prior to the addition of the sulfuric acid, and one representing the rate of ice melting after the reaction has reached completion. These equations will enable the determination of the volume change due to the heat produced by the reaction by use of basic analytic geometry.

An ice calorimeter is used to determine the change in volume of the water and ice. This consists of a beaker with a modified stopper. The stopper has holes in which a test tube, a graduated pipette stem, and a fill tube with petcock are firmly seated. The beaker is packed full of ice and water, the stopper is securely installed, and the entire assembly is packed in a bucket of ice. At this time 5 mL of chilled 1.00 M sulfuric acid is measured using a 5.00 mL pipet, and placed into the test tube installed in the calorimeter lid. Once theses preparations have been made, the 3

assembly is observed for a couple of minutes to ensure there are no apparent leaks. Once satisfied that the assembly is water tight, the stopwatch is started, and the initial pipet reading is recorded. Throughout the run, the pipet reading is recorded every 30 seconds. The volume is observed for 3 minutes to establish the normal melting rate of the ice. At this time, 0.209 g Mg(s) is added to the calorimeter in the form of solid ribbon cut into very small pieces. The reaction is allowed to run to completion while recording the pipet reading every 30 seconds. Once the change in volume over several consecutive time intervals is changing at the same rate as during the initial 3 minutes of monitoring, the reaction is assumed to be complete.

Table 1. Change in calorimeter
volume over time
time(s) pipette reading(mL)
0 0.750
30 0.735
60 0.730
90 0.715
120 0.710
150 0.700
180 0.690
210 0.685
240 0.675
270 0.670
300 0.615
330 0.525
360 0.450
390 0.385
420 0.325
450 0.270
480 0.230
510 0.185
540 0.150
570 0.125
600 0.100
630 0.080
660 0.060
690 0.045
720 0.035
750 0.020
780 0.010
810 0.000
Figure 1. change in calorimeter volume over time
0 100 200 300 400 500 600 700 800 900
time (s)
pipet reading (mL)
Figure 2. Projection of normal volume change
y = -0.0003x + 0.7463
R2 = 0.9901
y = -0.0004x + 0.3095
R2 = 0.9944
0 100 200 300 400 500 600 700 800 900
pipet reading(mL)
The heat of the reaction in the test tube caused some of the...
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