Investigation 8: Designing a Cold Pack
Hypothesis: The optimum ratio of solute to solvent should be 4:6 ( 4 parts
solvent and 4 parts solution), as going over that would mean that there wouldn’t
be enough water to dissolve the solvent.
Method:
1. Using a measuring cylinder, measure 9 ml of distilled water and add to a
clean dry test-tube. Measure and record the initial temperature of the
water using a thermometer.
2. Using an electronic balance, measure 1 gram of ammonium nitrate and
add to the above mentioned test-tube.
3. Gently shake the test-tube and measure the temperature of the solution
with a thermometer, and record this temperature.
4. Before using the thermometer again, wash it using distilled water to avoid
contamination and assure accuracy of results.
5. Repeat the last 4 steps with 2, 3, and 4 grams of ammonium chloride and
8,7,6 ml of water, making sure to always keep the total amount of solution
to 5 ml.
Data: ( We shared results with another group so that we could increase the
reliability of our results)
Initial Temperature (°C)
Final
Temperature
(°C)
Initial
Temperature (°C)
(other group)
18
18
18
18
13
12
11
9
19
19
19
19
Water(ml)
Ammonium
Nitrate (g)
9
8
7
6
1
2
3
4
Concentration
Of Ammonium
Nitrate
(moles/litre)
1.17
2.63
4.51
7.01
Difference in
Temperature
from another
group. (°C)
5
10
11
7
Final
Temperature
(°C)
(other group)
14
9
8
12
Average in Temp.
Difference
(°C)
Solute to
solvent ratio
5
8
8.5
8
1-9
2-8
3-7
4-6
Difference in Temperature (degrees
Celcius)
Change in Temperature as amount of
NH4NO3 Changes
10
9
8
7
6
5
4
3
2
1
0
0
1
2
3
4
5
NH4NO3 Used
Difference in Temperature (degrees
Celcius)
Change in Temperature as amount of
NH4NO3 Changes
10
8
6
4
2
0
0
1
2
3
NH4NO3 Used(g)
4
5
The first graph shows only the results obtained by our own group, and the 2nd
graph shows the average of the results of our group as well as another group,
which was using the same method as us.
Data Analysis :
The graph 1st graph indicates that the optimum ratio seems to be 4-6, with four
parts ammonium nitrate and 6 parts water. However, the second graph shows us
that the optimum ratio is in fact 3-7. However, the data acquired from the 2nd
group seems to be inconsistent, as the difference in temperature should be
increasing linearly, or even exponentially, but shouldn’t be decreasing.
Conclusion: