Illustrated Guide to Home Chemistry Experiments

Chapter 15 Laboratory: Thermochemistry and Calorimetry 275

5.epeat the preceding step with another 100 mL of heated R

water from the large beaker. After 30 seconds, dump the

water into the sink.

6. While you are preheating the graduated cylinder, use the
   strainer to separate solid ice from the ice-water slush
   mixture and fill the calorimeter about half full with ice.
   Replace the cover on the calorimeter to prevent the ice
   from absorbing heat from the room air.


7. Using the beaker tongs, add about 25 mL of the heated
   water to the graduated cylinder. Measure the volume of
   the water to 0.1 mL and record the volume on line A of
   Table 15-2.


8. Measure the temperature of the water in the graduated
   cylinder to 0.1 °C and record that temperature on line B
   of Table 15-2.


9. Carefully pour off any water that has accumulated in
   the calorimeter, and add the 25 mL of warm water from
   the graduated cylinder to the calorimeter. Replace the
   calorimeter cover and stir the ice-water mixture. (Some
   ice must remain in the calorimeter at the conclusion of

10.

11.

12.

this step. If all of the ice melts, remove the calorimeter

cover and quickly add more ice.)

Measure the temperature of the ice-water mixture, and

record the value to within 0.1°C on line C of Table 15-2.

(Ideally, that temperature should closely approach 0°C,

but under experimental conditions, a temperature of 2°C

to 3°C is acceptable. Simply watch the temperature until

it stabilizes at its lowest value and record it.)

Pour the contents of the calorimeter through the

strainer and into the graduated cylinder. Try to make

sure that all of the water in the calorimeter is transferred

to the graduated cylinder without spillage and that none

of the remaining ice is transferred to the graduated

cylinder. Measure the volume of the water in the

graduated cylinder and record that value to 0.1 mL on

line D of Table 15-2.

Repeat steps 1 through 10 at least once, and record the

observed values in Table 15-2. If your results are poor

(that is, they vary widely), run additional trials with the

same steps and record the observed values in Table 15-2.

TABLE 15-2: Heat of fusion of ice—observed and calculated data

Item Trial #1 Trial #2 Trial #3Trial #4 Trial #5

A. Volume, initial ____.__ mL____.__ mL____.__ mL____.__ mL____.__ mL

B. Temperature, initial ____.__ °C____.__ °C____.__ °C____.__ °C____.__ °C

C. Temperature, final ____.__ °C____.__ °C____.__ °C____.__ °C____.__ °C

D. Volume, final ____.__ mL____.__ mL____.__ mL____.__ mL____.__ mL

E. Temperature change (B – C)____.__ °C____.__ °C____.__ °C____.__ °C____.__ °C

F. Volume change (D – A) ____.__ mL____.__ mL____.__ mL____.__ mL____.__ mL

G. Heat of fusion of ice ______.___ cal/g______.___ cal/g______.___ cal/g______.___ cal/g______.___ cal/g

RQEWEvI UESTIOnS

q 1 : Using your experimental data for each of the first two trials, calculate the heat of fusion of ice in cal/g and record your calculated
values on line G of Table 15-2. The actual value for the heat of fusion of ice is 79.72 cal/g. If the value you obtained experimentally
differs significantly, propose possible reasons for this variation.