Hot Pack Cold Pack.docx-Hot Pack/Cold Pa...
Hot_Pack_Cold_Pack.docx-Hot Pack/Cold Pack Intro : Hot
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Hot_Pack_Cold_Pack.docx-Hot Pack/Cold Pack Intro : Hot
##### Page 4
Table 4: Mass and Cost of Salts Used in 500 mL Cold and Hot Pack
MgSO
4
CaCl
2
LiCl
LiBr
KNO
3
NH
4
NO
3
KCl
NaC
2
H
3
O
2
q
water
(kJ)
102.5
102.5
102.5
102.5
-48.1
-48.1
-48.1
102.5
q
salt
(kJ)
-102.5
-102.5
-102.5
-102.5
48.1
48.1
48.1
-102.5
Moles
salt
1.33
6.03
3.20
2.36
1.57
2.10
3.40
7.43
Mass
salt
(g)
160
669
136
205
159
168
253
609
Total
Cost (\$)
16.00
46.83
17.68
26.65
11.13
8.40
15.18
42.63
Using
q
water
for both the hot and cold experiments, the mass of salt that is necessary to change the
temperature of the water to the target point can found be found as well as the total price of salt. A
sample calculaon using CaCl
2
is given as follows:
q
water
=−
q
CaC l
2
,q
CaC l
2
=−
102.5
kJ
∆H
soln
=
q
CaC l
2
n
,
17
kJ
mol
=
102.5
kJ
n
,n
=
6.03
mol
m
CaC l
2
=
n × MW , m
CaC l
2
=
6.03
mol ×
110.98
g
mol
,m
CaC l
2
=
669
g
(
5)
TotalCost
=
m
CaC l
2
×
Cost
m
CaC l
2
,Total Cost
=
669
\$
0.07
g
,TotalCost
=
\$
46.83
(
6
)
Discussion
:
The purpose of this experiment was to design a hot and cold pack using the dissoluon process
that common salts undergo in water. In choosing the salt that would provide for the best opon in
creang a commercially viable hot pack, magnesium sulfate appears to be the best opon because it is
not at all toxic as indicated by its unavailable LD
50
, is the cheapest “hot” salt, and provides the second
lowest mass to reach the target temperature when dissolved in 500 mL of water. The salt that appears
to oﬀer the most commercially viable cold pack is potassium nitrate. Potassium nitrate is desirable due
to its comparavely low toxicity, low cost, and in providing the least amount of mass to aain the target
temperature of all “cold” salts in 500 mL of water. If these salts were to actually be used in a hot or cold
pack, the magnesium sulfate hot pack would only need to be labeled with precauonary advice
acknowledging the possibility of skin or eye irritaon. The potassium nitrate cold pack would need to be

##### Page 5
labeled with precauonary advice indicang that ingesng large amounts of potassium nitrate can be
harmful as well as the risk of explosion that is presented by igning or extensively heang the salt.
Although seemingly minimal, there are a few signiﬁcant sources of error provided in this
experiment. The most prevalent source of error is the imperfect nature of the calorimeter. Since it is
impossible to contain all heat within the Styrofoam cup, the ﬁnal temperature readings are lower than
expected for the “hot” salts and more than expected for the “cold” salts. Even though the technique of
extrapolaon was applied to the temperature graphs in aempt to make up for the amount of heat
gained from and lost to the surroundings, the temperature values are sll not exact and erroneous.
Error is also included in the actual mass of salt that was placed in soluon with the water because some
salt remained on the watch glass aﬅer the rest was inside the coﬀee cup. This is an issue because the
mass of the salt was measured prior to being placed in soluon. Aempts to overcome these sources of
error include using a more insulated calorimeter that would prevent the exchange of heat from the
system and surroundings, as well as applying a more precise method of introducing the salt into
soluon.
Aﬅer doing research about real world cold and hot packs and how they are made in industry, it
became apparent that magnesium sulfate and potassium nitrate were not the only commercially viable
salts used in hot and cold packs that were tested in this experiment. In reality, the use of calcium
chloride salt is also used in hot packs and as an ice melt ingredient. The other viable “cold” salt that is
widely used -maybe the most prevalent in the industry- is ammonium nitrate. Although the health
eﬀects of this salt are widely recognized, it is sll a popular and eﬀecve salt to use in instant cold packs.
Since the only consideraons that were taken into account in judging a hot/cold pack were the
temperature change of the water as an indicator of eﬀecveness, toxicity, and cost, other possible
scenarios exist that may limit the usefulness of a parcular salt. These scenarios include the eﬀects a salt
has on the environment over long periods of me, possible changes to the speciﬁc heat of the heated or
cooled soluon that limits the length of use, and the reacvity a salt has.

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